Improving the Understanding of Matrix Acidizing and Acidizing Design

This report delves into the critical aspects of matrix acidizing in petroleum engineering, focusing on enhancing hydrocarbon production through improved well stimulation techniques. It begins with an introduction to hydrocarbon extraction and the challenges of declining production rates due to formation damage. The study outlines the objectives of understanding matrix acidizing and identifying suitable acid formulations to enhance permeability. A comprehensive literature review covers well stimulation methods, matrix acidizing processes, sandstone acidizing practices, and experimental studies involving various acids like mud acid, fluoroboric acid, chelating agents, and organic acids. The report details the design of a matrix acidizing setup, including system requirements, components, and experimental parameters, followed by a methodology section explaining core flooding procedures and laboratory measurements. Ultimately, the study aims to provide insights into optimizing acidizing treatments for maximum recovery in carbonate and sandstone reservoirs, addressing the limitations and constraints encountered during research.

PETROLEUM ENGINEERING
[Author Name(s), First M. Last, Omit Titles and Degrees]
[Institutional Affiliation(s)]

Contents
INTRODUCTION...........................................................................................................................................3
1.0 Background........................................................................................................................................3
1.1 Problem Statement............................................................................................................................5
1.2 Objectives and Scope of Study...........................................................................................................6
1.3 Research Structure............................................................................................................................7
LITERATURE REVIEW....................................................................................................................................9
2.1 Introduction.......................................................................................................................................9
2.2 Well Stimulation................................................................................................................................9
2.3 Matrix acidizing................................................................................................................................11
2.4 Sandstone Matrix acidizing..............................................................................................................12
2.4. 1 Mineralogy of Sandstone.........................................................................................................12
2.5 Sandstone Matrix Acidizing Practice................................................................................................14
2.6 Treatment Design of Matrix Acidizing..............................................................................................15
2.7 Additives in Matrix Acidizing............................................................................................................16
2.8 Wormholing or channelling of sandstone........................................................................................16
2.9 Literature Reviews on Experimental Studies Conducted.................................................................19
2.9.1 Mud acid (hydrofluoric-hydrochloric acids)..............................................................................19
2.9.2 Fluoroboric acid........................................................................................................................22
2.9.3 Chelating agents.......................................................................................................................24
2.9.4 Organic Acids and Retarded Acids............................................................................................28
2.10 Review Summary...........................................................................................................................32
DESIGN OF A MATRIX ACIDIZING SETUP....................................................................................................34
System requirements............................................................................................................................35
Components of system..........................................................................................................................35
Experiment Parameters.........................................................................................................................39
METHODOLOGY.........................................................................................................................................41
Setup of Core flooding...........................................................................................................................41
Core flood experiment...........................................................................................................................42
Laboratory Procedures/Measurements................................................................................................42
Results.......................................................................................................................................................49
Conclusion.................................................................................................................................................56
References.................................................................................................................................................57

IMPROVING THE UNDERSTANDING OF MATRIX ACIDIZING AND ACIDIZING
DESIGN IN A PETROLEUM WELL
INTRODUCTION
1.0 Background
Hydrocarbons which are mainly oil and gas are extracted from numerous miles beneath the
ground. They are collected within a rock formation which has proper permeability and porosity.
They flow via the channels in between various pores from the rock pores all the way to the
production tubing and end up at the surface level finally. In the ancient production years, the
rates of flow of such hydrocarbons generated were promising owing to the naturally high
permeability and porosity of reservoirs (Akanni & Nasr-El-Din, 2015). Another reason for the
promising production during the early years was attributed to the high pressure difference
between the pressure of reservoir and the pressure of bottom hole.
Nonetheless, there has been a reduction in the production over time owing to numerous causes
including formation damage near the wellbore, declines in the pressure of reservoir as well as
swelling or migration of clays which then lead to clotting of pore spaces.
Acidizing treatment of one of most widely used and recommended techniques in the
enhancement of production of hydrocarbon after some time of production and has been use for
numerous years. A graph of Nigerian oil well upon treatment of mud acid and hydrofluoric acid
is shown in figure 1 (Akanni & Nasr-El-Din, 2016). The figure demonstrates that there are not
some much increments with mud acid with regard to the rate of production even though on other
hand, hydrofluoric acid treatment offers significant recovery in the field. This fact offers proof

that the appropriate acid combination for a given field would enhance production of
hydrocarbons.
Figure 1: Production improvement after treatment with hydrofluoric acid
Various types of acidizing treatments have been developed including matrix acidizing, acid
washing and fracture acidizing among other treatment types. The purpose in acid washing is
basically tubular and wellbore cleaning. There is no consideration to the treatment of formation
that is generated. Acid washing is mostly performed in cleaning out scale among other materials
which inhibit flow within the well.
For the case of fracture acidizing, an acid is introduced into a fracture that has been created by
acid itself or through a viscous fluid that is used in the generation of fracture. The acid reacts
with the fracture walls as it progresses leading to dissolution etching (Ali & Nasr-El-Din, 2018).
Matrix acidizing which is the main focus of this dissertation refers to a process where an acid is
introduced into formation at pressures that are lower than the fracturing pressure of formation
thereby there is no formation of fractures. The injected fluid undergoes a reaction with the

formation and some of present materials dissolved and thus removal of formation damage and/or
enhancement of permeability in the near-wellbore area. The acidizing process result in maximum
recovery of carbonate as well as sandstone reservoirs alongside enhancing economic reserves.
1.1 Problem Statement
There is a decrease in the production of hydrocarbons over time. This scenario may take place
owing to the few reasons among them presence of dissolved minerals in the pore spaces,
formation damage near well bore and enhanced skin factor among other possible explanations.
All the stated reasons would reduce the initial permeability and porosity of formation which
would in turn lead to a decline in the production of formation.
Matrix acidizing stand out to the first method that has been recommended in fixing the challenge.
Yet the acidizing process is unique for every formation and may not be generalized. Among the
factors influence the condition include formation history i.e. how it has been shaped, acidizing
history i.e. if there has been an acidizing treatment that has been used into formation as well as
location of formation n i.e. dome, anticline among others.
More damage would occur to the formation should the acid used be incompatible with each of
them or with the formation fluids of formation. By examining the sample of core extracted from
the wellbore (evaluation of features including solubility, formation lithography, mineralogy
among others) is then only way that a method may be chose for optimization of production.
This project is associated with a few constraints that are met in the course of conducting research
(Babaei & Sedighi, 2018). Equipment and material unavailability in the lab tend to be a limiting
factor as it confines the experiment to be similar to the ones that have so far been carried out in
the industry. a few of such constraints including the sample not being extracted from real

formation, unavailability of gas for SEM machine to be used in the identification of arious cores
as well as unavailability of equipment to be used in the injection of acids. Nonetheless, the
experiment would still proceed since the main objective is to establish the most appropriate and
effective acid formation that would result in an increase in the rock properties especially with
regard to permeability as well as porosity.
1.2 Objectives and Scope of Study
The main objective of this study is to gain a better understanding of matrix acidizing and come
up with the most suitable acid formulation which enhance the mineral properties the most,
specifically permeability. An increase in the permeability results in an increase in the ease of
flow via the connected pores ad thereby an increase in the rate of production in real formation
through the production tubing up to surface level. A few prior concerns that have been taken into
consideration include:
 Finding out the most appropriate acid formulation which would enhance the performance
of core the most, specifically permeability
 Examine the initial features of core (Badri & Taherian, 2018)
 Performing an experiment to test the impacts of different acid formulations on production
of formation
The scope of study is inclusive of:
 Carrying out research, calculations, experiments as well simulation with regard to matrix
acidizing
 Use of conventional acid systems including HCO, HF or even a combination of two
alongside boric acid only

 The cores are saturated using various acid formulations as there is not equipment in place
for the injection of acid in laboratory
1.3 Research Structure
This dissertation has six chapters as discussed below
Chapter 1: Introduction-The research topic is introduced and a brief background given. The aim
and objectives, research questions as well as significance of study are outlines. The main purpose
if this chapter is to introduce and brief the reader of dissertation on what is contained in other
chapters
Chapter 2: Literature review-Previous journals and works of other authors regarding
understanding of matrix acidizing and acidizing design in a petroleum well. The main purpose of
this chapter is to equip the author and reader with a deep understanding of topic of research.
Chapter 3: Methodology-The chapter discusses approach adopted in data collection as well as
various data collected techniques adopted
Chapter 4: Discussions-The information which was obtained from the literature review is
discussed in details with reference to research aims and objectives. In this chapter, the research
questions are answered.
Chapter 5: Conclusion-This chapter offers study summary of research conducted.
Recommendations and final remarks are included in this chapter
Chapter 6: References-All information sources of data used in the dissertation are noted in this
chapter and such include books, journals, and articles among other sources which contain
relevant information to the research topic.

LITERATURE REVIEW
2.1 Introduction
The demand for energy around the globe has continued to be on increase in the recent past. As
per the prediction, it is anticipated that the demand of energy will be 40% more that the present
by year 2020 and thus the continuous expansion of limit and boundary in the oil and gas sector
with regard to technology and commercial aspects. The development of innovative as well as
feasible technology in stimulating and enhanced oil recovery has turned out to be one of main
focuses in the oil field.
2.2 Well Stimulation
The gas and oil operations including work over, drilling, completion, production alongside long-
time operations led to the deposition of minerals close to the wellbore over time. As a result, this
leads to the depletion in the production owing to the formation of damage which takes place
about the wellbore. Hence, the field engineers have to establish the solution to carry out well
treatment to hence the productivity of wells to ascertain economic returns. One such technique is
labelled well stimulation (Bastami & Pourafshary, 2016).
Well stimulation is a method that is used in the enhancement of production of gas or oil from a
reservoir to the wellbore. It has played an integral role in the oil and gas wells development
ascertaining good economic returns. Numerous creative and innovative approaches are currently
being used in the treatment of wells. Hydraulic fracturing is being used in improving the
production of oil and gas through the creation of fracture in the reservoir via injection of
hydraulic fluid pressure. Hydraulic fracturing still occupies the greatest interest in well
stimulation in the industry.

Nonetheless, acidizing as well plays a significant role in various case studies with the use of
main acid including hydrochloric acid and other acids among them acetic acid, formic acid as
well as hydrofluoric acid is equally important. fracture acidizing, matrix acidizing and hydraulic
fracturing the most commonly used stimulation techniques. Each of methods comes along with
limitations as well as advantages in well stimulation.
For the formations of sandstone, matrix acidizing often have limited depth penetration. Ideally,
matrix acidizing has a shorter depth of penetration of about 0.3M as compared to fracture
acidizing and hydraulic fracturing. It is usually not used for formations having low permeability
since it needed long penetration depth in order to be stimulated successfully. Nonetheless, matrix
acidizing is an effective and viable technique especially in cases where the well is fractured
naturally and is often used in the removal of formation damage close to the well that prevents
flow into well (Bhatnagar & Alam, 2017). Thus, the acid may dissolve the plugging minerals in
production flow path. The various methods for well stimulation have various suitability and
practicality for various formations as shown in the figure below
Figure 1: Various methods for well stimulation

2.3 Matrix acidizing
Matrix acidizing is a widely developed method in well stimulation. Acids are injected to the
bottom hole well using a pressure that is less than the pressure of formation of fracture during
acidizing process. Since the 1960s, sandstone matrix acidizing has remained to gain an avalanche
of applications as well as remaining to play a vital role in the petroleum industry. Various acids
had been invented for use in the stimulation of depleted reservoirs of sandstone after numerous
years of production of oil and gas. Acids have a major role to play when it comes to the
improvement of permeability as well as porosity of a reservoir formation. The acids as well serve
to lower the formation damage besides improving the productivity of well (Duthie, Saeed,
Shaheen, Saiood, Moore & Krueger, 2017).
Mud acid is the most commonly used acid in the treatment of sandstone stimulation. The mud
acid is formed by mixing hydrofluoric acid and hydrochloric acid. This is done due to the fact
that hydrofluoric acid is able to adequately dissolve the minerals that are found in a sandstone
matrix while hydrochloric acid has properties that enable the control of precipitation. However,
high temperature well acidizing tend to be of immense importance. Reservoirs having great
temperature and depth have turned out to be the epicentre of attention in the recent past to oil and
gas exploration reserves.
Wells are generating from deep hot reservoir using a temperature that is greater than 200⁰F and
such reservoirs normally have temperatures that range between 100⁰F and may go to higher than
500⁰F. The use of mud acid has been limited recently in the evolution of matrix acidizing with
focus being on wells having high temperatures. Hence, all the components of acid simulation
including corrosion rate, acid efficiency as well as stability have to be enhanced to ascertain
successful treatment of well.

There are a few significant challenges of adoption of mud acid at temperatures that are above
200⁰F. Mud acid may result in high reaction rates with the contents of minerals in the sandstone
matrix at conditions of high temperature. The resultant is a reduction I the effect of acidizing
process and could even completely fail in the worst case scenario owing to early and rapid
consumption of acid (Frick, 2018). Still, the use of hydrofluoric acid during situation of well was
found to be resulting in significant reduction in the compressive strength formation especially in
regions that are having high content of clay.
As a result, there will be disintegration of formation leading to reduction in permeability and
porosity. Besides, mud acid is associated with highly corrosive features that make it a life hazard
acid which is challenging for safety control as well as health. Hence, the acidizing treatment is
rendered of lower efficiency (Garrouch & Jennings 2017). It can be noticed that the high
temperature sandstone acidizing method is experiencing an upsurge in demand hence has turned
out to be a focus of attention among current researchers.
2.4 Sandstone Matrix acidizing
2.4. 1 Mineralogy of Sandstone
Sandstone, sometimes called arenite is a clastic sedimentary rock that is composed of silica and
numerous silicate minerals. Sandstone matrix is mainly composed of feldspar, quartz and various
forms of clay with the presence of zeolite at times even though in vary low concentrations. The
concentrations of various minerals present in an ideal Berea sandstone core sample that is used in
the industry for the purposes of core flooding test is shown in the table below.

Table 1: Berea sandstone Mineralogy
The figure below shows the mineral components of sandstone rock
Figure 2: Components of Sandstone Rock
The dissolution rate of clays and feldspar is higher than that of quartz when reacting with
hydrofluoric acid owing to the features of quartz that has relatively more stable structure as well
as relatively low specific surface area.

2.5 Sandstone Matrix Acidizing Practice
Matrix acidizing is majorly done to improve the production of a sandstone well as well to reduce
the skin. The technique has been for a very long time been used in the stimulation of formations
of reservoirs through changing the features of rocks that include permeability and porosity. The
acid injection pressure is often lower that the pressure formation fracture during the operation.
Upon the injection of acid, all the minerals in the soluble reservoir rock are dissolved leading to
the creation of more pore spaces hence an increase in the fluid flow rate from the layers of
reservoir formation to the wellbore (Ghommem & Brady, 2016).
In the initial stage, using mud acid in the acidulation of sandstone offers a significant
breakthrough in the region of well stimulation technique. 3% hydrofluoric acid and 12%
hydrochloric acid is the most commonly practiced composition of acid doing the operation. The
table below illustrates the chemical compositions which are available in sandstone as well as
their solubility levels in hydrochloric as well as hydrochloric/hydrofluoric mud acid.
Table 2: Solubility of sandstone minerals
Sandstone matrix acidizing is broken down into three main stages as discussed.

 A pre-flush stage that dissolves sodium, calcium and potassium ions which will have
reactions with silica leading to the formation of insoluble silicates
 The major flush stage that involves the dissolution of silicate, clay, feldspar and quartz
alongside carbonates after pre-flush
 An after-flush stage which involves the removal of used acid in a bid to maintain
wettability in the original state as well as clean the formation
2.6 Treatment Design of Matrix Acidizing
The success of an acidizing treatment of sandstone majorly relies on development of design of
acid treatment. By far and large, the procedure for the design should be pegged on conventional
steps of treatment. Technical analyses as well as statistical survey were carried out
comprehensive over more than 650 cases of matrix stimulation treatment in nine different
countries and findings of study established that incorrect field procedure turned out to be the
major cause of acidizing failure (Ghommem, Qiu, Brady, Al-Tajar, Crary & Mahjoub, 2016).
Nonetheless, the specific procedure for design should be kept open and may be lowered to
incorporate just the needed steps as per the case by case analysis. Some successful application of
case study done in the field has been illustrated in the Netherlands.
All the information including the history of well, data from laboratory test alongside the past
operation experience are fundamental during an operation of a matrix acidizing for the engineer
to make decision on fluid to be used for acidizing treatment. An elaborate reservoir
characterization workflow approach in needed to achieve a successful treatment of matrix
acidizing and careful consideration must be attached to each detail from the treatment design all
the wall to the execution phase.

2.7 Additives in Matrix Acidizing
Numerous well challenges including generation of precipitants, generation os slue, production of
fine particles as well as corrosion of steel may be caused by matrix acidizing. When temperatures
are high i.e. ranging between 150⁰F and 250⁰F, the sensitivity of fines migration to hydrochloric
acid is enhanced resulting in more severity of porosity reduction mostly at outlet part of core of
sandstone. These common challenges have been addressed using a number of acid additives as
shown in the table below which illustrates the additives against their functions.
Table 3: Matrix acidizing additives and their functions
2.8 Wormholing or channelling of sandstone
Wormholing sequence is common in acidizing of carbonates in while for the case of sandstone
acidizing, a uniform pattern of face dissolution is noticed with no preferential path being
produced. It is very rare to produce wormholes mostly in homogeneous formation of sandstone.
This is owed to the rate of reaction that occurs between the quartz that is the main mineral
present in sandstone and the acid, hydrofluoric acid (Ghommem, Taherian, Dyer & Qiu, 2016).

However, numerous literature and research studies conducted have shown that a pattern of
channelling that is similar to carbonate worming may take place during the process of acidizing
sandstone. In cases where the sandstone is highly heterogeneous, a fine-scale channelling pattern
that has high permeability would be noted. The process of generation of wormholes in Bandera
and Berea cores of sandstone flooding experiment is shown in the figure below.
Figure 3: Wormholes in Bandera sandstone

Figure 4: Wormholes in Berea sandstone
As per the sandstone core flooding test, it is also shown that some sandstone channels or
wormholes were generated upon being treated using 6 and 9 wt.% hydrofluoric acid as indicated
in the figure. The findings of laboratory investigation showed that lower acid injection rate is a
positive factor in the generation of wormholes in sandstone.

Figure 5: Wormholes in sandstone of South America
2.9 Literature Reviews on Experimental Studies Conducted
The feature of reservoir rock alongside the main intention of stimulation determines the choices
of selection of additive and acid. there are numerous reported experiments which conduct
investigations on efficiency of different types of acids that are used in sandstone acidizing. a
critical review of such important studies have report and hence the findings of this study have
ideally offered a conceptual structure for setup as well as planning of numerical alongside
experimental works which are recommended for use in the future (Hanafy, Nasr-El-Din, Rabie,
Ndong, Zhou & Qu, 2016).
2.9.1 Mud acid (hydrofluoric-hydrochloric acids)
Core flooding was performed by Thomas et al. (2001) on samples of Jauf core using acetic acid
and hydrochloric acid in the pre-flush stage at a temperature of 150⁰C. The findings were a
reflection of need of pre-flush acid that was used prior to the mud acid owing to the channels that

were generated. The permeability had been enhanced significantly by channelling effects during
the application of main acid. The impact of concentration ratio of mud acid was also investigated
on changes on permeability on different samples and the findings are as illustrated in the table
below
Table 4: Core floor test results summary
Matrix admixing apparatus had been designed, assembled and tested by Nevito Gomez (2006) on
conventional mud acid and experiment was carried out using Berea sandstone core at room
temperature and at a temperature of 100⁰F. Higher permeability was as a result of high rate of
flow at room temperature while the optimum rate of flow was found to be 30 ml/ml at 100⁰F.
The effect of mud acid concentration ration on variations in the permeability of sandstone core
matrix were investigated by Wang et al. (2013) and Gomaa et al. (2013) whentemperature was
maintained at 180⁰F. For various mixtures of mud acid concentration were tested with the core
sample through application of core flooding method and the findings showed that all the four

ratios of acid mixing have the ability to positively enhance the permeability of core sample. It
was as well observed that as the ratio of hydrofluoric-hydrochloric acid increased, the results of
permeability as well increased. Still, there was noted a reduction in the volume of acid injection
required (Karale & Alam, 2018).
The optimum hydrofluoric acid concentration for formations of high temperature sandstone was
determined by Abdelmoneim and Nasr-El-Din in which high temperature of between 280⁰F and
350⁰F were utilized in carrying out the core flooding tests. Following the findings of experiment,
there relationship between the optimum HF concentration and the mineralogy was found to be
that of inverse proportionality. Retarded acid was proposed for temperatures that went beyond
300⁰F.
Mud acid has proved to be effective and efficient in its performance when it comes to sandstone
acidizing hence quickly gaining popularity. However, reports were made that it resulted in rapid
reaction rate, when temperatures were elevated to 200⁰F. This can be explained to be as result of
quick kinetics of secondary as well as tertiary reactions at such temperatures that are high. This
led to a reduction in the inefficiency of sandstone acidizing due to the undesirable early acid
consumption. This was as well the major reason for the failure of acid treatment in most of cases.
Still, there was formation of disintegration due to the relatively significant reduction in the
compressive strength of high clay content formation upon being treated with hydrofluoric acid.
Hydrochloric acid had a significant role to play in mud acid since it did not leave any insoluble
products from the reaction processes with the minerals. Besides it advantage of being cost
effective, hydrochloric acid has found wide applications in sandstone stimulation. Nonetheless,
hydrochloric acid is very hazardous to the well and highly corrosive especially in cases where

the environment is of high temperature and high pressure. Hence in the future research, the
limitations of mud acid have to be considered carefully (Karimi, Shirazi & Ayatollahi, 2018).
2.9.2 Fluoroboric acid
The application of fluoroboric acid in various case studies has been demonstrated. Fluoroboric
acid produces hydrofluoric acid at a slower rate and hence proving more time for the
penetration of acid into sandstone. Fluoroboric acid hydrolyses in aqueous solution resulting in
the formation of hydrofluoric acid until it gets to a limit extent as demonstrated in the equations
below
HBF4+H2O HBF3OH+HF (slow)
HBF3OH+H2O HBF2 (OH) 2+HF (quick)
HBF2 (OH) 2+H2O HBF (OH) 3+HF (quick)
HBF (OH) 3+H2O H3BO3+HF (rapid)
Fluoroboric acid is as well important in the removal formation damage alongside stabilization
of clay among other fines. Nonetheless, fluoroboric acid retardation tends to be of less
significance when temperature is increased to 150⁰F. The rate of hydrolysis of fluoroboric acid
resulting in the formation of water was established to increase when temperature is increased.
Ayorinde et al. (1992) demonstrated the benefit of fluoroboric acid in the treatment of Nigerian
oil well which was facing numerous issues related to server fines migration generation by
conventional mud acid. the generation of oil well was found to be about 850 barrels per day after
acidizing using mud acid (Livescu, Sturgeon & Watkins, 2017). Nonetheless, owing to the fines
migration, there was a decline in the production to almost zero. The production improved to

about 2500 barrels per day after successfully treating the well with fluoroboric acid and a
production rate of 220 barrels per day was maintained even after the lapse of a year.
The scanning electron microscope resulting of clay which filled the pores as well as post
treatment using conventional mud and fluoroboric acid is shown in the figure below. From the
figure, it is vivid that there was dissolution of clay as well as partial fusion of kaolinite platelets.
This has aided in the prevention of issue of migration.
The use of fluoroboric acid in sandstone acidizing through the use of organic acid was further
developed by Jaramillo et al. (2010) and the formation of a new system of acid from fluoroboric
acid known as organic clay acid. Numerous wells have been stimulated using the organic clay
acid and the treatment done in reservoirs that are at low temperatures that are less than 140⁰F.
The effectiveness and efficiency of organic clay acid in clay stabilization and fines control was
proved by field results. Compared with the initial increase in production of wells that were
treated using organic mud acid, it was noted that increase in higher initial production took place
on wells that were stimulated using organic clay acid, an indication that the acid had successfully
resolved the issue of fines migrations resulting from organic mud acid (Lou, Auzerais, Borisova
& Moscato, 2017).
Besides, an investigation was carried out by Feng et al. (2011) on high-temperature deep
penetrating acid in which salts of a mature of organo-phosphate was developed to be used as a
new corrosion inhibitor. It would produce hydrofluoric acid and hence making the high-
temperature deep penetrating acid being compatible at formations that occur at high
temperatures. High-temperature deep penetrating acid was found to be having a relatively higher
solubility as compared to mud acid for quartz mineral and would also cut back the levels of

precipitation. High-temperature deep penetrating acid is as well a better permeability enhancer as
compared to fluoroboric acid.
The chemistry of fluoroboric acid was investigated by Pituckchon (2014) in a bid to gain better
comprehension of its application in stimulation in the real field. The acid spent during core
flooding tests over time intervals is analyzed using 11B and 19Fhigh field nuclear magnetic
resonance solution state. The temperatures of conducting the core flooding tests were 75⁰F and
200⁰F in the determination of impact of temperature on rate of compatibility of fluoroboric acid.
The findings demonstrated a reduction in the permeability of core when temperature was at
200⁰F owing to amorphous silica precipitation.
Core flooding experiments were as well conducted by Zhou et al. (2016) using 12% fluoroboric
acid that is combined with 12% Hydrochloric acid and temperatures of 25⁰C and 65⁰C and the
findings of experiment compared against the conventional 3% hydrofluoric acid and 12%
hydrochloric acid. Still, the permeability increase was found to be higher when temperature was
at 65⁰C compared to 25⁰C (Medina, Sierra, Garcia, Gleaves & Mendez, 2015). This experiment
only made a comparison between 65⁰C and 25⁰C temperatures with no optimization work being
carried out and thus the optimum range of temperature for a recommended utilization of
fluoroboric acid is still not determined. Besides, the core sample that was used was
heterogeneous sandstone that had 9% of composition as clay and calcite.
2.9.3 Chelating agents
Chelant was developed based on hydroethylaminocarboxylic acid and evaluated on Berea
sandstone by Frenier et al. (2004). The findings of test demonstrated that the
hydroethylaminocarboxylic acid chelant may be used in sandstone reservoir that has high
temperatures. Among the benefits of chelant were among them reduced rate of corrosion,

reduced rate of reaction as well as a pH value that is close to neutral. Hydroethylaminocarboxylic
acid serves to inhibit corrosion leading to the formation of insoluble surface chelates. Still, the
substance is found to be featuring low rate of reaction with dolomite. The near neutral pH value
of hydroethylaminocarboxylic acid will do away with the need of treating the fluid before it is
disposed hence the chelant is concluded to be having advantages taking into consideration the
various aspects of environmental, health as well as safety owing to reduced HSE footprint.
The effect of sodium hydroxyethlethylenediaminetriacetic acid which is a solution with low pH
was investigated in the stimulation of high temperature formation. The findings established that
the efficiency of chelating fluid is evident in enhancing the permeability of a high-temperature
well (Migahed, Zaki & Shaban, 2016).
The reaction between glutamic acid N,N-diacetic acid and calcites within the rocks was
instigated and a comparison made between glutamic acid N,N-diacetic acid and numerous other
chelant including nitrilotruacetic acid, ethylenediaminetetraacetic acid, ethanol diglycine acid
and hydroxyethylenediaminetriacetic acid. The efficiency of glutamic acid N, N-diacetic acid
was found to be the same as that of hydroxyethylenediaminetriacetic acid but it was not as
corrosive as hydrochloric acid.
Mahmoud et al. (2011) also used glutamic acid N, N-diacetic acid in the study of its impact on
formations of sandstone. The main focus of research was on numerous parameters among them
volume, rate of injection, temperature as well as the initial pH of glutamic acid N, N-diacetic
acid. The findings of experiment precisely demonstrated the superior ability of glutamic acid N,
N-diacetic acid to chelate magnesium, iron and calcium. Still, glutamic acid N, N-diacetic acid
was established to be able to chelate even very small amounts of ions of aluminium found in the

sandstone cores. Besides, the concentration of glutamic acid N, N-diacetic acid was found to be
almost similar before and after the core flooding test. Glutamic acid N, N-diacetic acid illustrated
a high thermal stability at a temperature of 300⁰F as well as relatively low corrosion properties.
These findings were further grounded by Nasr-El-Din (2013) who found that the core
permeability in increased to 84% at 300⁰F from 21% at 200⁰F by glutamic acid N,N-diacetic
acid respectively while on contrary, HCl led to the precipitation of iron hydroxide resulting in a
42% reduction in the permeability (Pourabdollah, 2017).
A low 2.5 pH glutamic acid N, N-diacetic acid chelant was used in experimentally investigating
the stimulation on sandstone matrix of high quartz clean as well as high clay heterogeneous
sandstones matrix. The findings indicated a decrease in the permeability by 20%for the clean
sandstone even though an increase by 30% in the permeability for the case of heterogeneous
sandstone. This was an illustration that the glutamic acid N, N-diacetic acid-hydrofluoric chelant
could be suitable for use with sandstone that has clay content but not clean sandstone.
Rignol et al. (2015) tested another chelant-based fluid system in the stimulation of sandstone
core at a temperature of 375⁰F that was an ultrahigh-temperature condition. The acid system was
composed of low pH chelant and fluoroboric acid. Flow test was used in the experimenting of
core plugs as well as some chemical analyses. Following the sequential dissolution analyses
conducted, the findings demonstrated the chelant based fluid did not result in silica precipitation
since hydrochloric acid was missing. Still, it had resulted in effective increase in the permeability
of core. The benefits of aminopolycarboxylic acid fluid which was composed of 1.5% HF were
revealed. The fluid system is established to be better than the conventional mud acid which is not
efficient in the stimulation of high temperature sandstone condition beyond 300⁰F owing to the
precipitation of potassium and sodium ions. The use of APCA/HF blend in various fluid systems

in the offshore reservoirs was successful leading to between 30% and 50% improvement in
barrel oil per day production for a period that exceeds 12 months.
A two-step injection process was proposed using chelating agents in the treatment of high
temperature wells. The researcher proposed injection of low-volume even though high
concentration of APC thereafter followed by injection of high volume but low concentration of
APC for example glutamic acid N, N-diacetic acid. The compatibility of removal of carbonate of
glutamic acid N, N-diacetic acid, HEDTA as well as 15 wt. % hydrochloric acid with illicitic
sandstone core at relatively high temperatures of about 300⁰F was examined (Schwalbert, Zhu &
Hill, 2017). The results of core flooding experiment demonstrated that hydrochloric acid is not
compatible in the removal of carbonates from illicitic sandstone even though leads to lowered
permeability and porosity that damaged the sandstone matrix. On another note, glutamic acid N,
N-diacetic acid and HEDTA illustrated high efficiency in the removal of carbon and minerals.
Following previous literature review, numerous experiments were carried out and reported by
previous researcher using chelating agents. Such chelant would be applied in the stimulation of
high temperature wall. The contributions of such previous studies, concentrating on effectiveness
of chelant when working under conditions of high temperature were really acknowledged. It was
established that such acid systems were reliable and suitable in gaining comprehensively wide
applications in real-life practice. Nevertheless, alert should be made that chelating agents tend to
be less suitable for cleaning of homogenous sandstones due to the precipitation of silica during
acidizing process. Hence, they tend to be more suitable for use with heterogeneous carbonates as
well as sandstones that are rich in clay. Another perspective which should be noted is chelant
tend to be very costly products in comparison with mud acid, organic acids as well as retarded
acids. Even though chelating agents may lower the corrosion inhibitor cost that is applied, it is

still of importance in the optimization of budget between the corrosion inhibitor and the
expensive chelant.
2.9.4 Organic Acids and Retarded Acids
The problem linked with the clay minerals and the acids reactions was also studied through the
addition of retarding agent into conventional mud acid. In one of such investigations by Ji et al.
(2014) and Ji et al. (2016), there was addition of aluminium chloride into conventional mud acid
resulting in the formation retarded mud acid. It was also termed as fines control acid that was
composed of 1.5% HF, 15% HCl and 5%AlCl3.6H2O. The experiment was conducted on
samples of Berea core that were at temperatures of 75⁰F and 200⁰F. Aluminium fluoride
precipitate was not detected at either temperature based on result of solubility test. Core flooding
tests were also done and comparison made with using retarded mud acid using aluminium
chloride and the findings indicated that there was a reduction in the reaction rate by retarded mud
acid enabling deeper penetration of acid as well as removal of damage (Shafiq & Mahmud,
2017).
In the preceding years, organic acids including formic acid and acetic acids as well as powdered
acids among them chloroacetic acid and sulfamic acid were created by researchers. A new
approach was for example created by Templeton et al. (1975) for the retardation of rate of
consumption of hydrofluoric acid to generate formic acid using methyl formate. Then, the
production of hydrofluoric acid is a regulated rate through the addition of ammonium fluoride,
NH4F. Generally, methyl formate undergoes a very slow process of hydrolysis to produce HF
acid as shown in the reaction equations below:
HCOOCH3+H2O HCOOH+CH3OH

HCOOH+NH4F NH4++HCOO-+HF
Still, the use of two organic acids was applied that included acetic acid and formic acid in the
stimulation of high temperature high pressure wells. The two acids have suitable characteristic in
sandstone acidizing, slower reaction as well as weak ionization. Hence the acids result in less
corrosion of equipment of well and enable longer periods of reaction. The blend of acid had been
use in Arum limestone formation that was carried out in Indonesia with temperatures ranging
about 350⁰F. The response of well as well as the corrosion response demonstrated positively the
economic alongside technical efficiencies of blend of acid used (Shirley & Hill, 2019).
Core flooding was carried out by Roger et al. (1998) on sandstones using various acid formations
excluding 1.5% HF and 10% HCl. It had been established that such a conventional combination
of acid resulted in formation of damage as shown by a reduction in the permeability by 74%. The
improvement in production from 7400 to 16000 barrels of oil per day was noted in five
production wells stimulated using optimum combination of acid.
Such organic acids are undergoing further development as indicated in most of recent
publications. For example, Al-Harbi et al. (2012) carried out experimental investigations using
different mixtures of organic-HF system of acid in the stimulation of sandstone cores. The
combination of acid was composed of acetic acid, citric acid as well as formic acid. The
precipitation that took place during the reaction between the acid and the rocks is studies along
the factors that affect such precipitations. Following the findings, the type of precipitation as well
as the amount is mainly pegged on pH of solution, initial free fluoride concentration and the type
of organic-HF combination. Other than that, the ration of F/A1 was established to be the major

parameter which was associated with aluminium fluoride precipitation. Aluminium fluoride
precipitation took place at a specific point over the critical ratio.
The use of citric acid as a chelating agent was investigated by Andotra (2014) and a comparison
of results made with those of conventional mud acid which was in the ration of 9:1. Addition of
1 wt. % citric acid into mud acid produced the optimum results. Nonetheless, the researcher also
brought forth the issue of much higher cost that was introduced by addition of citric acid in
comparison with HCl and HF. Still, tests were done of Berea and Bandera cores of L-glutamic
acid N, N-diacetic acid, Na-GLDA which was combined with HF and the findings were a
positive reflection of the chelation of calcium, iron as well as magnesium even though not of
aluminosilicates (Shirley & Hill, 2019). The benefits of such chelating agents in comparison with
HCl were given including lower corrosion, tolerance of very high temperatures that are beyond
200⁰F, sensitivity to minerals as well as being biodegradable.
Another experiment was carried out using a HF-organic acids blend as opposed to mud acid in
the migration of problems linked with mud acid. The kinetic as well as the products of reaction
were analyzed and the findings demonstrated that the kind of minerals available in the core plugs
has implications on reactions. Studies were conducted on efficiency of single stage combination
of sandstone and acid which is a blend of phosphonic acid and HF acid during stimulation of
sandstone acid at a temperature of 300⁰F high-temperature formation. The researchers as well
investigated the working of multiple-acid system in the removal of carbonate minerals form plug
of sandstone core that was inclusive of a low pH 3.8 GLDA, HEDTA as well as formic acid. The
permeability of sample of Berea core was found to increase in permeability as a result of all the
acid systems. Nonetheless, HCOOH was established to be still superior to GLDA and HEDTA in

terms of efficiency in the dissolution of carbonate minerals in samples of Bandera sandstone
core.
Investigations were carried out in the analysis of combination of hydrochloric acid and acetic
acid in the pre-flush stage after which the authors made a comparison of results with the
conventional use of hydrochloric acid only in the stage. Using an acid combination 2.5% acetic
acid and 7.5% hydrochloric acid led to an increase in the porosity by 18.5%. This provided a
proof that the usability of such a combination tends to be better used as a pre-flush acid as
compared to the conventional 10% HCl that led to just 10.9% change in the porosity. The
research as well noted the significance of pre-flush stage in matrix acidizing as dissolution of
carbonate to inhibit precipitation during the main acid stage that comes after the pre-flush stage.
Various experimentations using different combinations of acids wad carried out by a team of
researchers. The combinations of acids testes by team were among them a mixture of
hydrofluoric acid and orthophosphorus acid, formic acid and hydrofluoric acid and fluorobic acid
and formic acid and the core saturation method was applied in which the sandstone core plugs
were saturated using the mentioned combination of acids. Numerous analyses were conducted to
elaborate on changes in porosity, strength, permeability as well as mineralogy prior to and after
the experiment (Van Hong, Mahmud, Chiat, Foo & Shi, 2018). The combination of acid was 3%
HF: 9% H3PO4 as per the results of investigation. Nonetheless, all the acid combinations were
suitable for application as the main acid during stimulation of sandstone acid.
The acid had a permeability increase of 135.35% indicating that the combination was even more
superior as compared to the standard mud acid that demonstrated lower permeability increase
which was 101.76%. Therefore, a proof was offered that changing the combination of acid would

lead to various outcomes be it in major or minor disparity. Nevertheless, note should be made
that most of these experimental investigations were carried out at room temperature or ambient
temperature conditions only which would not be representative of real-field environment. Thus, a
research gap is left in this investigation which may be reduced through future studies.
A study on phosphonic-based HF acid system was as well conducted as an option to the solution
to mud acid. Numerous parameters influencing the interactions between the clay minerals and
the acid systems were investigated including temperature, time of reaction and concentration of
acid (Zhao, Qiu & Dyer, 2015). As indicated in the results, there was a significant increase in the
permeability as a result of phosphonic-based HF acid systems as compared with mud acid and
which was 177.86% at a temperature of 300⁰F.
2.10 Review Summary
In summarizing the entire review, there are many acids which have need developed in the recent
past that aim at enhancing the results of permeability enhancements even as they prevent
precipitation. Four main groups of acids have identified among them mud acid, retarded and
organic acid, chelating agents as well as fluoroboric acid.
Mud acid is ideal in the stimulation of unconsolidated sandstone at relatively low to moderate
conditions of temperature. It has been widely applied in sandstone acidizing and has managed to
improve the permeability as well as porosity of formations of sandstones with quartz mineral
content successfully. Nevertheless, mud acid is not a recommendation in the use in conditions of
high temperature as a result of rate reaction rate with sandstone mineral leading to early
consumption of acid. Mud acid is as well quite hazardous and corrodes the well equipment.

Fluoroboric acid is on other hand an alternative acid to mud acid and works best under
conditions of moderate temperature. It is as well ideal for unconsolidated sandstone with quartz
mineral. Nevertheless, owing to the slow hydrolysis reaction nature generating hydrofluoric acid,
fluoroboric acid may lead to deeper rate of penetration into sandstone formation. Fluoroboric
acid has been established to be effective in removal of damage, fines control as well as clay
stabilization. However, there is no literature on study of application of fluoroboric acid at
increased conditions of temperature which needs further investigation (Zakaria & Nasr-El-Din,
2016).
Still, chelating agents are majorly effective for sandstone that is rich in clay or heterogeneous
carbonate at conditions of very high temperatures. Chelating agents may prevent precipitation of
iron oxide and has also been found to be less corrosive. Nevertheless, chelating agents are not
recommended for use with homogenous clean sandstone owing to the precipitation of silica that
would reduce the permeability and porosity. Hence, the mineral contents of carbonates or
sandstone would to a great extent influence the suitability of chelating agents. Lastly, retarded
and organic acids are mostly usable for sandstone or carbonates that have high contents of clay.
It is not ideal in the dissolution of quartz content due to lack of fluoride ions.

DESIGN OF A MATRIX ACIDIZING SETUP
In this section, constituents and parameters required to finish the suggested apparatus framework,
which should be efficient to accommodate the research on sizes that vary core illustrations at a
continuous stream and temperatures same to the met field environment will be determined.
Figure 2.1 is the amplified representation of set up.
As shown in the above diagram, brine and acid earlier made and reserved in the accumulators,
are pushed then made hot in accordance with the experimentation and specific position, through
the tubing connection and streams through the fundamental representation. The core
representations are constricted within the core case with a Viton Sleeve by a hydraulic pump.
The used acid is put together and weighed in in the beaker at the completion of experiment. The
exerted pressure given for nitrogen supply through diagram BPR preserves the carbon II
suspension.
In the course of matrix acidizing procedures, the amount and frequency, temperatures, the
pressure exerted inward and outward pressure are set and retained constant. The pressure

differences across the set up during the experimentation is determined by analog pressure
transducers as well as put down by LABVIEW operating system to set up and examine acid
reaction curve. All apparatus left in the laboratory exhaust system to allow the flow of acid
combustion.
System requirements
The following are the essentials requirement for the experiment:
 Pumps with the ability to dispatch at a wide range the amount of liquid at given time and
satisfactorily good to operate with on either continuous flow rate or continuous pressure
rates.
 Core holders, marked alloy set up to hinder acid attrition for a good period of time and
high pressure and temperature repellent
 Accumulators to accumulate the acid combinations needed during the experiments at
varying concentrations
 Heaters and temperature regulators to speed up temperatures up to the best levels and
same to the met field environment
Components of system
Pumps: In matrix acidizing experimentation, an pumping siphoning framework is required
contingent upon particularities of each kind of shake to be dealt with and the ideal
conditions to influence the acidizing procedure. Among these conditions a standout amongst the
most vital is the stream rate at which the liquids are to be dislodged; in most of tests this stream
rate must be steady amid the procedure to precisely decide the weight changes in the stone while
the liquids are going through the center. Subsequent to visiting the labs of two majors
administrations organizations, BJ Services and Schlumberger, we characterized that the best

choice for our application is the Teledyne ISCO 500D. This siphon is a syringe accuracy type
which makes it the perfect gear for a wide scope of synthetic feed applications requiring stream
rates up to 200 ml/min at weights up to 3,750 psig; its 500 ml chamber limit permits conveying
an exact 1 ml/minute for more than 8 hours on a solitary fill.
The ISCO D500 siphon utilizes a "Smart Key" controller that can work any three siphon
modules, either autonomously or together.
Core holder: The core holder is maybe the most essential piece of framework for network
acidizing purposes; these are where the center examples are kept to dislodge the liquids through
them. In view of idea of liquids to be utilized, hydrochloric and hydrofluoric acids at diverse
focus and temperatures, the center holders should be made of extraordinary combination
material. Our center holders were produced by Phoenix Instruments, made of Hastelloy C276, an
erosion safe material and proficient to withstand a working weight of 3000 psi and temperatures
of around 300⁰F.
Each core holder accompanies the ordinary bay and outlet tip with ports 1/8" and the dispersion
example to contact the all-out face zone of center; inside the chamber a unique elastic Viton
sleeve, temperature safe, has been adjusted to limit the center once being used. The center
holders were however to permit the distribution of mud and lead distinctive sort of examinations
on streaming acidizing; hence extra arrangement of tips with spacers were obtained to use in this
specific application in which is fundamental first to make a specific channel mud cake even with
center example.
Accumulators: The collectors were fabricated by Phoenix Instruments and they are type cylinder.
These pieces of set up are where the items to be uprooted through the centers amid the acidizing
experimentation are contained. Three of these aggregators were intended to be consumption safe

that implies they are made of uncommon combination material, Hastelloy C-276, with limits of
1000 ml and 2000 ml the biggest one; there is likewise one collector tempered steel made in light
of fact that is intense to use for brackish water regulation whose limit is 1500 ml. The majority of
collectors have bay and outlet ports 1/8" NPT.
The removal of acid and brackish water is performed by syringe siphons that siphon the pressure
driven oil which thusly follows up on Teflon cylinder pushing either the acid or salt water out at
important weight and stream rate to convey them profoundly by means of pipe arrange until
venturing the center face into center holder. To refill the cylinder collectors with either acid or
saline solution, a PVC compartment is filled first with a pipe and after that air at 100 psi from the
research facility air framework, pushes the items into aggregators to be prepared for
investigations. It is important to vent the oil line over the aggregator to permit either the acids or
saline solution to be gone into gatherers as the oil inside them is evacuated.
Heaters and temperature controller: Temperature is an important factor that influences the
response rates and energy of concoction responses among minerals and acids; on account of HF
with sandstone minerals the energy articulations can be spoken to by:
It is additionally notable that genuine store temperatures are a lot higher than environmental or
room temperature; in this way, temperature turns into a vital perspective to be viewed as while
reenacting distinctive conditions at which the acidizing tests are directed. To make the set up
skilled to imitate genuine conditions on framework acidizing and consider the impact of
temperature on mineral disintegration and wormholing designs two distinct radiators were

considered and introduced on device. This radiator is fit to fold over little width tubing, as little
as 1/8" and for use in either conductive or non-conductive surfaces. Its most extreme permissible
temperature is 900 o F, the wattage is 500 w at 120 volts, and it is 10 feet long. The rope radiator
was introduced wrapping the general stream line between the release of collectors and the bay
valve before entering the center holder.
Back pressure regulator: Back weight is important amid the analyses at the center surge to
reproduce down-opening conditions, as the pore weight does in real strata conditions, to keep
away from the nearness of free CO2 gas bubbles, which can prompt bothersome two-stage
impacts and might expand the fines relocation marvel. The backpressure must be kept steady
what's more, it is wanted to be 300 - 400 psi not exactly the overburden weight. One Mity-Mite
back weight controller show S91-W is introduced on upstream line. The weight in the line
controls the gushing stream and applies the opposition for the reason depicted above, keeping up
consistent weight upstream; the weight is the same as the nitrogen vault weight.
The associations with the stream lines are 1/4" NPT female strings and the association with the
charging line is 1/8" NPT female string. In the front board there is a check to control and watch
the back weight. The weight territory may differ between 100 furthermore, 2000 psi and
temperature - 65⁰F and 200⁰F; the material of body and arch is hardened steel and the stomach is
Teflon. The most extreme Cv is 0.38 and it gauges 4 lbs. The sort of BPR is remotely vault
stacked hence it must be charged from an outside wellspring of gas weight; for our situation arch
weight is provided by a nitrogen bottle with its reporter controllers.
Experiments & Results
A set of fundamental analyses of network acidizing were led on centers of Berea sandstone,
Cream Austin chalk and Indiana limestone to modify the lab set-up and check the limit and

unwavering quality of introduced gear and testing its working go. The trial results were recorded
and for starters investigated. Framework acidizing in Berea sandstone is led to see the impact of
blends of HF/HCl on acid reaction curve, porousness/DP Vs. infused pore volume; while in
carbonates, Cream Chalk and Indiana limestone, the objective was to watch the development of
wormholing designs made by mineral disintegration through exceptionally penetrable pathways
by impact of HCl blends.
Experiment Parameters
Assorted acid blends were set up concurring the detailing already talked about and put away in
the smoke hoods molded for this reason. Centers of Berea sandstone and a few carbonates
(Cream Chalk and Indiana limestone) were first totally vacuum-soaked with ammonium chloride
saline solution. Sandstone centers were acidized at three distinctive stream rates for corrosive
uprooting, 15 ml/min, 30 ml/min, and 45 ml/min. The acid concentration was the customary mud
acid, 12% HCl and 3% HF for the principle acid and the preflush was HCl 15%. Unique
temperatures were utilized at each stream rate; changing the factors, a few relocations were done
at room temperature, 72⁰F, 100⁰F, 150⁰F, and 200⁰F. A specific volume of preflush is required
in all sandstone medications to break down the HCl solvent minerals. In light of response
stoichiometry among HCl and these minerals the idea of dissolving power2 was connected. The
dissolving power communicates, on a mass or volume premise, the measure of mineral that can
be devoured by guaranteed measure of acid. In this way, the gravimetric dissolving power is
characterized as:
Where the terms are the stoichiometric coefficients and MW are the atomic loads; in this
manner, for the response between 100% HCl and CaCO3, b 100 = 1.37 lb CaCO3/lb HCl. The

dissolving intensity of some other fixation is b multiple times the weight portion of acid in the
acid arrangement for an acid 15% HCL, dissolving power b 15 equivalents 0.21. The volumetric
dissolving power X is characterized as the volume of mineral broken down by a given volume of
acid and it is identified with the gravimetric dissolving power by:
A 15% HCl arrangement has a particular gravity of about 1.07 and CaCO3 has a thickness of 169
lbm/ft3. For the response of these species, the volumetric dissolving power is 0.082 ft3
CaCO3/ft3 HCl15%.
Table 4.1 demonstrates the run of mill mineral synthesis of Berea sandstone. As it tends to be
seen HCl solvent minerals are Dolomite and Siderite whose volumetric dissolving power are
0.0628 and 0.0945 individually; in this manner for a center of 6" long and 1" breadth, mass
volume 77 ml, with a porosity of 21%; the volume of HCl to break down the complete dolomite
what's more, siderite was determined as 75 ml, which implies around 5 pore volumes of center.
The porosity of Berea sandstone center examples was estimated at existing lab with the helium
porosimeter as 21.15%.

METHODOLOGY
Setup of Core flooding
Figures 1a and 1b demonstrates core flooding exploratory setup as well as schematic chart
individually, which were utilized for the center flooding of Berea sandstone and Guelph dolomite
center examples with chelates. This center flooding setup is fit for taking care of a weight up to
10,000 psi and a temperature up to 200⁰F. The wetted pieces of the mechanical assembly are
made of consumption resistive material (for example hastelloy), which makes this framework
rust free even at higher convergences of acids. The trial setup comprises of five fundamental
parts which are clarified beneath with nitty gritty capacity.
Center holder is utilized to restrict the center example at wanted weight and temperature. The
material of this center holder is hastelloy. It has two deltas and one outlet. The restricting weight
connected amid the trials is 1000 psi while the temperature is 150⁰F.
The High Performance Liquid Chromatography siphon as appeared in Figure 1a and 1b, is
utilized to infuse the corrosive into the center holder at wanted and controlled rate. It can infuse
fluid at a most extreme rate of 6000 cc/min. The infusion rate for this examination is 1 cc/min.
The less infusion rate is utilized so as to maintain a strategic distance from high back weight
amid the analysis.
The Temperature controller (Figure 1a) with a tape is utilized to warm the center holder at
wanted temperature esteem. The greatest temperature accomplished utilizing this controller is
500⁰F.
The syringe siphon (Figure 1a) is utilized to make a high weight inside the center holder. It
employments crisp water to make a high weight and can make up to 20,000 psi weight.

Gathering measuring glass is utilized to gather the responded corrosive example at the
accumulation point as observed in Figure 1a.
Core flood experiment
The core flood was gauged at first and measurements were gotten utilizing Vernier caliper. The
center was put inside the center holder and center flood instrument was setup. The center was
then bound under strain of 1,000 psi utilizing the syringe siphon. The center holder was then
warmed to 150⁰F utilizing the temperature controller and tape. The chelate was infused utilizing
HPLC siphon at a rate of 1 cm3/min where the weight variety was observed at weight
transducers. The steady weight an incentive at HPLC siphon and transducer demonstrates the
consummation of the response. Infusion of corrosive is ended and one hour living arrangement
time was permitted to finish the response of the chelate with the sample of core.
Laboratory Procedures/Measurements
Aside from the center flooding tests, there were assortment of different estimations and readiness
work did too, which notwithstanding:
 Estimating porousness, porosity of the center examples when center flooding tests
 Drying of core samples when each test at 80oC for 24 hours.

 Weight of all dry center examples was estimated when center flooding tests.
 Immersion of core samples utilizing salt water (5% NaCl) for NMR examination utilizing
manual saturator
 Running NMR tests on the salt water soaked examples when each center flooding test.
 The responded corrosive was gathered from the center flood test and was investigated for
different particle utilizing ICP examination.
Table xx: Layers Geostatistical features and main results of radial numerical modelling

Figure xx: Layer 1 Wormholing Pattern (Top) Layer 1 Wormhole length & Skin Evolution
(Bottom)

Figure xx: Layer 2 Wormholing Pattern (Top) Layer 2 Wormhole length & Skin Evolution
(Bottom)

Figure xx: Layer 3 Wormholing Pattern (Top) Layer 3 Wormhole length & Skin Evolution
(Bottom)
Figure xx: Calculating Optimum Acid Coverage depending on volumetric & decord model

Table xx: Calculating maximum injection rate for rc=1200 ft &( kg/ky)0.5=1.5

Table xx: Calculating maximum injection rate for rc=1260 ft &( kg/ky)0.5=2.1
Table xx: Calculating maximum injection rate for rc=1260 ft &( kg/ky)0.5=1.5

Results
The general methodology is followed in all centers recently soaked with brackish water 3%
NH4Cl at vacuum conditions
 Displace the centers with brackish water 3 % NH4Cl until stable enough to gauge
introductory penetrability
 Inject the preflush, 100 to 140 ml of HCl 15%, to expel HCl solvent minerals
 Inject NH4Cl as a spacer, for the most part 170 ml which relates to 10 pore volumes
 Inject the treatment liquid, HF 3% - HCl 15%, at various temperatures and stream rates.
At first was siphoned the most extreme limit accessible, up to 60 pore volumes
 Inject the post flush, 3% NH4Cl brackish water, to decide last penetrability, adequate
sum until achieve this incentive as steady as would be prudent.
Figure above presents acid reaction curve for a regular sandstone acid center flooding. In this
curve, the weight drop and the determined porousness are plotted and the diverse phases of
procedure are itemized; the improvement in penetrability can be watched plainly. The center was
examined when acidizing procedure to see the distinction between the two phases; after the

procedure of acidulation it has all the earmarks of being available some sort of a special stream
channel at the center of center dependent on distinction in thickness.
Amid the preflush arrange, a noteworthy increment in weight drop happened, thus decreasing the
porousness; this might be an aftereffect of either thickness differentiate between the liquids in the
permeable media or the encourages produced when HCl begin responding with the HCL
dissolvable minerals; in any case, after one period proximately equivalent to the volume at first
determined as important to break down these minerals, the weight drop goes down to the
ordinary dimension. In the fundamental acid stage a less serious weight drop increment can be
seen toward the start of stage and it step by step improves until changing to the post flush arrange
when conceivable accelerates and any side-effect are streamed out the center.
The impact of temperature was learned at steady stream rate of 15 ml/min; temperature builds
the response rate between mud minerals and customary mud acid as that utilized in the analyses.
See figure 4.5, in which just the information relating to the principle acid and post flush organize
were plotted to separate from the impact of HCl in preflush to break down carbonates.
Notice that the higher the temperature the greater porousness improvement can be accomplished.
At room temperature could be accomplished a similar outcome in penetrability upgrade as

accomplished at 100⁰F yet being important 40 % of extra acid to be infused as can be seen in
curves 72⁰F (a). In curve 72⁰F can be seen that an expansive volume of acid was important to get
ideal outcomes.
Tests were led at various stream rates to decide first the ability of introduced hardware and see
the impact on framework acidizing process. As it is appeared in figure 4.6, in three center
relocations at room temperature utilizing Regular Mud Acid, the penetrability reaction could be
fundamentally improved when stream rate increments. This might be clarified by reality of
response items are as a rule quickly uprooted.
In any case, it is obviously famous that when utilizing very lower stream rates, as low as 5
ml/min, it appears that the penetrability reaction to the incitement procedure happens gradually
and only an almost no upgrade in penetrability could be gotten. This impact could be because of
absence of dislodging limit of encourages which might be available as results of response among
acid and minerals, driving potentially to cause an extra harm.

The impact of stream rate was other than dictated by dissecting the outcomes from four center
removals utilizing the Regular Strength Mud Acid, which were completed at 100⁰F; were plotted
these diverse curves. It is appeared at lower stream rates the penetrability reaction is still
generally poor contrasted with those acquired at higher ones. In any case, it would appear that
there could be resolved an ideal stream rate, for Berea sandstone centers, in view of outcomes at
30 ml/min, whose porousness reaction looks superior to those accomplished at 15 ml/min and 45
ml/min. At the point when centers tests are acidized at generally high temperatures, more than
100⁰F, and extensive volumes of acid are utilized, in excess of 30 pore volumes, a serious
change in the slant of pattern by and large happens in anyplace amid the principle acid stage
driving to have a progressively fast increment in porousness.

In light of this unwanted impact, an examination was led, infusing as it were 10 pore volume of
acid, whose acid reaction curve, it very well may be seen that very little penetrability
improvement has been come to due maybe to extra movement of fines from deconsolidated
framework.

Lower acid concentration, HF 1% - HCl 9%, were likewise uprooted in Berea sandstone centers;
this concentration is the prescribed by McLeod and Kalfayan for those penetrability more
prominent than 100 mD. Figure below demonstrates the impact of acid focus on acidizing
results. The acid reaction curve for the blend 1% HF-9% HCl does not demonstrate much
accomplishment in the wake of infusing 55 pore volumes; in any case, the pattern in the curve
would permit to extrapolate a superior penetrability improvement by infusing increasingly acid.
The curves for Ordinary Mud Acid, 3% HF – 12% HCl, show comparative conduct and the thing
that matters is expected to the measure of uprooted acid in each examination. Just the
information amid the fundamental acid stage and post flush has been plotted to confine from the
impact on penetrability of HCl in preflush organize dissolving the carbonates.

Method
Simulator will be used in performing an analysis of the main design parameters of matrix
acidizing. The flow chart of the simulation is as shown in the diagram below

Conclusion
Matrix acidizing of the various sandstone reservoirs is a significant step toward ensuring
enhanced production through the elimination of damage or even by introducing new channels.
Numerous studies have been conducted to this extent outlining the significant of acidizing in
formations of sandstones. Numerous scholars came up with various combinations of acids,
utilized various chelating agents to attain the best outcomes in relation to porosity, permeability
as well as precipitation even though are still a few limitations including fast consumption of acid,

corrosion of the various pipelines used as well as low penetration of the acids. There is need for
new combinations of acids that may be used for the aspect of future acidizing as well as further
study is required on the existing technology due to the limitation of the current acid
combinations when used at high temperature besides such limited combinations of various
sandstone formations. Suggested new or used combinations at very high temperatures tend to be
slightly expensive and hence not frequently applied during field operations owing to their
limitations. Still, some of the combinations are not developed to their full potential since their
mechanisms are not yet known and hence suffer poor understanding.
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