in master of science

A LABORATORY ANALYSIS OF PERMEABILITY

OF TYPICAL CEMENT MIXTURES USED IN THE PERMIAN BASIN

by

VIRAJ V .DESHMUKH, B.E.

A THESIS

IN

PETROLEUM ENGINEERING

Submitted to the Graduate Faculty Of Texas Tech University in

Partial Fulfillment of The Requirements for

The Degree of

MASTER OF SCIENCE

IN

PETROLEUM ENGINEERING

Approved

Shameem Siddiqui Chairperson of the Committee

Lloyd Heinze

Co-Chair of the Committee

Malgorzata Ziaja

Accepted

John Borrelli Dean of the Graduate School

August, 2007

Texas Tech University, Viraj Deshmukh, August 2007

ii

ACKNOWLEDGEMENTS

My journey at Texas Tech has been a long and enjoyable one. This thesis in

association with BJ Services is the icing on the cake of my Masters program here.

Firstly I want to thank Dr. Lloyd Heinze who was instrumental in sending me

to the BJ Services lab in Odessa, which was the starting point for this thesis.

A special thanks also to Mr. Henry Lopez and Mr. Dean Olsen of BJ Services,

who treated me great during my training, gave me ideas for this project, and also helped

me immensely in conducting the whole research.

Also this thesis would not be possible without the help of Dr. Shameem

Siddiqui, the instructor of the Core Lab at Texas Tech who guided me during this period.

I also want to give credit to Abiodun Amao, Joe Mcinerney & James from the Geology

Department.

Last but not the least, my family has played an important role in me coming to

Texas Tech, and without their unconditional support I would not be here today.


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TABLE OF CONTENTS ACKNOWLEDGEMENTS…………………………………………………………….…ii ABSTRACT……………………………………………………………………………….v LIST OF TABLES………………………………………………………………………..vi LIST OF FIGURES……………………………………………………………………...vii LIST OF ABBREVIATIONS…………………………………………………………….ix CHAPTER I. INTRODUCTION…………………………………………………………………...12 1.1 Project Objectives……………………………………………………………….12 II. LITERATURE REVIEW…………………………………………………………….14 2.1 Cement Permeability Measurement: A Background…………………………….14 2.1.1 The Humble Oil Study…………………………………………………….14

2.1.2 Halliburton Study………………………………………………………….17

2.1.3 Other related studies…………………………………...……….....……....18

2.2 The Traditional Sulfate Problem on Cement…………………….….…………...19 2.2.1 The process of sulfate attack………………………………………………20 2.3 Cements Used in the Permian Basin……………………………….………....….22 III. EXPERIMENTS & METHODOLOGY…………………………….….…….……..25 3.1 Equipment Selection…………………………………………….…...…….……25 3.2 Testing Principles………………………………….……………....…….………31 3.2.1 Darcy’s Law……………………………………………………………….31 3.2.2 Klinkenberg Effect………………………………………………………...32


iv

3.3 Experiment Details………………………………….……………..……………34 IV. EXPERIMENTAL RESULTS……………………………………………………...37 4.1 Test Results…………………………………………………………….…….....37 V. ANALYSIS AND COMPARISON OF RESULTS…………....………...................72 5.1 Comparing Neat Vs Pozzolan Cement Permeability………………….….……..73 5.2 Influence of Sulfate Percentage in Mixing Water on Cement Permeability.........80 VI. CONCLUSIONS ……………………………….…………………………..………84 VII. RECOMMENDATIONS………………………….….……………………………85 BIBLIOGRAPHY………………………………..………………………………………86 APPENDIX………………………………………………………………………………88 A Cement Slurry Mixing Sheets……………..……………….………………………89


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ABSTRACT

In the Petroleum Industry today, downhole cement plays an important role

during drilling & production operations. It is responsible for lending strength to the

casing for future production, it helps in preventing collapse of the formation, as well as

restricts fluid movement between permeable zones.

This downhole cement however, has different problems in the field from

inadequate compressive strength, early setting of slurry etc. But of all these problems,

sulfate attack on downhole cement is probably the biggest one facing the industry today.

Another problem in using different cement slurries has been the traditional lack of

research for cement permeability, which has the biggest influence on the degree of this

sulfate attack.

Thus Texas Tech University and BJ Services have thus carried out a new study

in my thesis, where we have studied and analyzed how sulfates in water react with the

dry cement initially by measuring this initial permeability. Thus a study has also been

carried out in measuring cement permeability of typical cement slurries used in the

Permian Basin, something not yet documented and recorded officially before. This will

give us a better understanding of cement properties for future reference.


vi

LIST OF TABLES 4.1 Observations and Results for Sample No 27861…………………………………….38 4.2 Observations and Results for Sample No 27862…………………………………….40 4.3 Observations and Results for Sample No 27865…………………………………….42 4.4 Observations and Results for Sample No 27866…………………………………….44 4.5 Observations and Results for Sample No 27877…………………………………….46 4.6 Observations and Results for Sample No 27878…………………………………….48 4.7 Observations and Results for Sample No 27884…………………………………….50 4.8 Observations and Results for Sample No 27885…………………………………….52 4.9 Observations and Results for Sample No 27907…………………………………….54 4.10 Observations and Results for Sample No 27908…………………………………...56 4.11 Observations and Results for Sample No 27939…………………………………...58 4.12 Observations and Results for Sample No 27940…………………………………...60 4.13 Observations and Results for Sample No 27950…………………………………...62 4.14 Observations and Results for Sample No 27951…………………………………...64 4.15 Observations and Results for Sample No 27953…………………………………...66 4.16 Observations and Results for Sample No 27952…………………………………...68 5.1 Summary of Cement Permeability for all the samples………………………………72


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LIST OF FIGURES 2.1 Permeameter Setup for B.E. Morgan Study on Cements…………………………….16 3.1 Gas Permeameter Set-up in the Core Lab at Texas Tech……………………………26 3.2 Nitrogen Cylinders used in the Experiment………………………………………….27 3.3 Ziploc Bags used to Ship the Cement Plugs…………………………………………28 3.4 Oven Used to Heat Cement Plugs……………………………………………………28 3.5 Set of Cement Plugs numbered before Experiment………………………………….29 3.6 Schematic for Gas Permeameter……………………………………………………..30 3.7 Typical Klinkenberg Correction Graph for a Normal Core………………………….33 4.1 Klinkenberg Correction Graph for Sample No 27861……………………………….39 4.2 Klinkenberg Correction Graph for Sample No 27862……………………………….41 4.3 Klinkenberg Correction Graph for Sample No 27865……………………………….43 4.4 Klinkenberg Correction Graph for Sample No 27866……………………………….45 4.5 Klinkenberg Correction Graph for Sample No 27877……………………………….47 4.6 Klinkenberg Correction Graph for Sample No 27878……………………………….49 4.7 Klinkenberg Correction Graph for Sample No 27884……………………………….51 4.8 Klinkenberg Correction Graph for Sample No 27885……………………………….53 4.9 Klinkenberg Correction Graph for Sample No 27907……………………………….55 4.10 Klinkenberg Correction Graph for Sample No 27908……………………………...57 4.11 Klinkenberg Correction Graph for Sample No 27939……………………………...59 4.12 Klinkenberg Correction Graph for Sample No 27940……………………………...61 4.13 Klinkenberg Correction Graph for Sample No 27950………………….…………..63


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4.14 Klinkenberg Correction Graph for Sample No 27951……….……………………..65 4.15 Klinkenberg Correction Graph for Sample No 27953……………..……………….67 4.16 Klinkenberg Correction Graph for Sample No 27952………...………..…….…….69 5.1 Graph of Neat vs. Pozzolan Mixed Cement Permeability…………….……………..73 5.2 Graph of Cemex Distilled Neat vs. Pozzolan Cement………………….……………75 5.3 Graph of Lehigh Distilled Neat vs. Pozzolan Cement…………………….…………75 5.4 Graph of Cemex 1000mg/l Neat vs. Pozzolan Cement……………………..……….76 5.5 Graph of Lehigh 1000mg/l Neat vs. Pozzolan Cement……………………..……….76 5.6 Graph of Cemex 2000 mg/l Neat vs. Pozzolan Cement…………………….……….77 5.7 Graph of Lehigh 2000 mg/l Neat vs. Pozzolan Cement…………………….……….77 5.8 Graph of Lehigh 4000 mg/l Neat vs. Pozzolan Cement…………………….……….78 5.9 Graph of Cemex 4000 mg/l Neat vs. Pozzolan Cement……………………….…….78 5.10 Graph Comparing Cement Perm for Cemex Neat with Diff Mix Waters…….……81 5.11 Graph Comparing Cement Perm for Lehigh Neat with Diff Mix Waters……….…81 5.12 Graph Comparing Cement Perm for Cemex 50:50:10 with Diff Mix Waters..….…82 5.13 Graph Comparing Cement Perm for Lehigh 50:50:10 with Diff Mix Waters…...…82 5.14 Overall Graph for the 4 Cement Types with Different Mixing Waters………...…..83


ix

LIST OF ABBREVIATIONS

API- American Petroleum Institute

ASTM- American Society for Testing Materials

atm- Atmosphere

C- Centigrade

C3A- Calcium Trialuminate

CaO- Calcium Oxide

cc/s- Cubic centimeter per second

cm- centimeter

cm2 –Square Centimeter

cP- centipoise

Diam- Diameter

dP- Pressure difference

F- Fahrenheit

ft- Feet


x

Hg- Mercury

Kl - Liquid Permeability

Kg- Gas Permeability

Leng- Length

m- Meter

mD- millidarcy

mg/l- milligram/Liter

MgO- Magnesium Oxide

N2- Nitrogen

Pavg-Average Pressure

Pdown- Pressure Downstream

Pres- Pressure

psi- Pound per Square Inch

Pup- Pressure Upstream


xi

q- Flow rate

t- Time

Temp- Temperature

Visc- Viscosity

vs. – versus


12

CHAPTER I

INTRODUCTION

Sulfates are a big form of contaminant for downhole cements in the oil

industry today. These sulfates, usually present in water in the form on Calcium or Sodium

sulfate compounds, are notorious in reacting with the cement through a process of

reactions to form ettringite, which is known to cause expansion and cracking of the

cement. The remedy for this is often an expensive process of squeeze cementing. Thus

the object of this thesis is to probe the possible negative effects of the ettringite formed in

the cement. However, it must be noted that ettringite is of two types: primary and

secondary. In this thesis we will only investigate possible effects of primary ettringite

formation on the cement performance.

Thus it would be interesting to see if the cement permeability corresponds

directly to the amount of sulfate present in its mixing water, since primary ettringite may

be responsible for causing reactions that expand the cement and increase its permeability.

That apart, cement permeability as such has rarely ever been studied or

recorded. The simple reason for this is most often, the absence of the different equipment

necessary in measuring this permeability, due to the very low permeability values that

cement exhibits. Hence this thesis utilizes the infrastructure present in the Petroleum

Engineering department at Texas Tech University to try to measure and record the

cement permeability of different cement slurries used in the Permian Basin mixed with

different waters.

1.1 Project Objectives

1] To collect a set of typical cement slurry samples used in the Permian Basin by BJ

Services and measure the cement permeability for all these samples.


13

2] To carry this out by setting up a modified Digital Gas Permeameter having a high

pressure rating, so as to be able to measure very low cement permeability by the use of

high pressure differentials across the cement samples.

3] To analyze the results of these test samples for their cement permeability and analyze

if there exists a relation of the cement permeability to-

a) sulfate content in the mixing water.

b) cement slurry type.

4] On the basis of the analysis, suggest to BJ Services the appropriate cement slurry

mixture to be used depending on the type of formation water existing for the particular

well.

5] To put on record the permeability of the typical cement slurries used by BJ Services in

the Permian Basin for their future use and reference.

6] To also set into place a study which can be continued in the future for analyzing the

effect of sulfates during the later part of the cement i.e. six months from the set date. This

will be done by placing the cement plugs used in this study in sulfate water over the six

month period. These plugs can then be tested for permeability at the end of the six

months, and then compared to the present permeability as recorded in my thesis, to note

if a change in permeability takes place over that time.

7] To give a better understanding for future research on the complex nature of cement.

The method to go about investigating the above problem seen in industry will

be conducted over a period of two months. It would involve testing various typical

cement slurries used in the Permian Basin by BJ Services

However the key to investigating the variation in cement permeability of the

different slurries will be the use of four different kinds of mixing water to prepare the

different cements. Thus this study utilizes distilled water and three other samples

containing different strengths of sulfate from 1000 mg/l up to 4000 mg/l for mixing of the

cements.


14

CHAPTER II

LITERATURE REVIEW

2.1 Cement Permeability Measurement: A Background

Cement by nature is extremely tight. Thus conventionally the measurement of

such tight cement permeability has not been widely documented or carried out. The

cement permeability however is not constant, and is variable on the composition of the

cement slurry. Thus in today’s industry a number of different combinations for cement

slurries are used. They include pozzolan, cement with expansion additives etc. BJ

Services typically uses a fixed set of cement slurries in the Permian Basin depending on

variations of depth and temperatures in the well.

However amongst a few of the studies carried out relating to cement

permeability measurement were carried out by B.E Morgan of Humble Oil Company as

far back as 1952 as well as by John Goode of Halliburton. However these studies merely

mentioned procedures on measuring cement permeability, without really documenting the

data for a particular set of cement slurries.

2.1.1 The Humble Oil Study

In The BE Morgan study, several variations in test procedure were tried. In

some cases the mold was greased with light grease, while in other cases no grease was

used. Permeability tests were run directly on the set cement in the mold. The cement

sample was then removed with a hydraulic punch. It was then placed in a rubber cylinder

which was tightly fitted in a steel cylinder. The permeability of the cement sample as then

once again measured. Several set cement plugs were dried at 105°C for 24 hours. Their

permeability to air was then measured.


15

Typically same values for water permeability were obtained with the cement

specimen for the ungreased mold as with the cement plug in the rubber holder. These

results indicated that permeability values obtained by casting cement specimens in

ungreased molds were reproducible, that was no leakage of water around the cement

specimen under the conditions used, and that the result represented he true wet

permeability of the set cement.

Higher and inconsistent values were obtained when the mold was greased.

Values obtained for air permeability were much higher than water permeability as

expected, due to the alteration of the set cement by drying.7

The setup for this study was as seen below in Figure 2.1:


Figure 2.1 Permeameter Setup for B.E. Morgan Study on Cements7

Thus the Humble Oil study did conclude that air permeability is higher than

water permeability for the cement, but a detailed record for all the cement specimens was

not done in this study.

16


17

2.1.2 Halliburton Study

The Halliburton study is summarized as follows:

Procedure

The two instruments used for obtaining permeability data were the air

permeameter and the liquid permeameter. Both instruments used a Hassler sleeve-type

arrangement, with a liquid such as water providing pressure on the outside of the rubber

sleeve to seal the specimen in the cell, and gas or liquid inside of the sleeve to achieve a

pressure differential across the specimen for measurement of flow rates, The principal

difference in these instruments was the amount of pressure for which they were designed,

the air instrument utilizing much higher pressures than the liquid apparatus,

Gas permeability tests were made on eight different cementing compositions

cured at atmospheric pressure and temperatures of 80°, 100°, 120° and 140°F for periods

of 7 and 28 days. Water permeability was determined on 10 different cementing

compositions cured at temperatures of 80°, 100°, 120° and 140°F for periods of 1, 7 and

28 days. These tests were conducted at a pressure of 60 psi.

The conclusions for this study were summarized as follows:

1. Water permeability determinations on oilwell cementing compositions were more

reliable than gas permeability, due to the difficulty in obtaining good representative

samples for gas flow measurements,

2. The permeability of cementing compositions decreased with age and temperature, with

the exception of the compositions containing moderate amounts of bentonite.

3. In most of the cements tested, the permeability were so low after seven days’ curing

that there was little to choose among them.4


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Thus this study felt that in choosing a cementing composition for gas-storage

wells, permeability did not appear to be a major factor at low temperatures. This is

because most cementing compositions have no measurable permeability after reasonable

periods of time. The study believed that consideration should more satisfactorily be given

to other properties of cements, particularly the fluid properties such as low fluid flow,

flow characteristics and slurry weight, and to the employment of good cementing

practices in achieving a successful completion.

2.1.3 Other related studies

Another view on cement permeability was also revealed during this thesis

through personal communication with Scott Jennings and Jack Lynn of Saudi Aramco

Company. They have been following for many years a method of testing undried cement,

using the curing water itself to measure the cement permeability. Thus they measured the

wet permeability of the cement samples, unlike the dry permeability measured in this

study.

The test procedure for this wet permeability was summarized by Saudi

Aramco as follows-

“The pump was run in "constant pressure" mode. In this operating mode the pump will

maintain a constant set pressure against a sample face to +/- 0.5% of total span. At the

operating pressure of the test (2500 psig) this is equivalent to +/- 12.5 psig. The test oven

set at 250 °F. The original test specifications called for the temperature to be 290 °F, but

the rubber boots used for confining stress were found to be unstable at this temperature.

The confining stress for the test was 5000 psig, and the pore pressure (back pressure)

was set at 500 psig. Net pressure delivered by the pump was set at 2500 psig, making

the effective differential pressure (dP) 2000 psig. For some selected samples dP was set

to 4000 psig due to low permeability. A burette was attached to the down stream line of

the back pressure regulator to accurately measure the expected low flow volumes. The


19

accuracy of the burette was +/- .001 cc. The times were kept by digital timer and were

accurate to .01 minutes / 24 hours.

Once the test was complete, the samples were removed from the core holder and placed

under their mixing fluid. The measurements were divided into two parts. The first is

termed the "initial perm" which is the permeability measured after the first 6 hours of

flow. The "final perm" is measured at the stabilization point, which varied from 2 to 6

days for the samples”5

Thus this study was very interesting from the point of view of wet permeability measured

for the cement, and the equipment modifications that were done for this.

Some other related work has also been done over the years on both cement

permeability measurement as well as study of sulfates on concrete, but these studies are

more related to the civil engineering field. However as part of the literature review it

would be worth mentioning some of the tests carried out by the American Society for

Testing Materials or ASTM include the following-

ASTM C1202 Rapid Chloride Permeability Test for Electrical Conductivity ASTM C1012-04- Standard Test method for Length change of Hydraulic Cement

Mortars Exposed to a Sulfate Solution

2.2 The Traditional Sulfate Problem on Cement

Ettringite is a crystalline mineral. It is basically formed due to the reaction

between sulfates, calcium aluminates and water. The aluminates are in the form of

calcium trialuminate (C3A). This calcium trialuminate is one of the four primary

compounds that make up Portland cement. Sulfates are present in the gypsum. This

gypsum is added to the clinker during the grinding process, to slow the hydration of


20

aluminates and to prevent the cement from sudden setting. Sulfates may also be present

in the clinker from the raw materials which are used to make the clinker. The formation

of the primary ettringite occurs just after water has been added to the cement, but before

the concrete reaches the initial set.

External sulfate attack, however, results from the chemical reactions which

take place when cement is exposed to penetrating external sulfate ions present in the

downhole water. Thus sulfate attack is primarily caused by two chemical reactions:

1) the formation of gypsum by the combination of sulfate and calcium ions, and

2) the formation of ettringite through the combination of sulfate ions and hydrated

calcium aluminate.

In both the cases, the formation of the reaction product causes an increase in volume due

to expansion.

Thus sulfate attack is a degradation mechanism of cement. Since it is capable

of such a negative impact on the cement like cracking, lots of research and studies have

taken place to analyze this process, especially in the Civil Engineering field.

Thus based on all the above, API has come up with a classification for oil well

cements that is similar to the one by ASTM and other European codes. Thus API

differentiates oil well cements into three groups, ordinary, moderate and high sulfate

resistance, depending on their chemical composition.

2.2.1 The process of sulfate attack

Ettringite is the common name for hydrated calcium trisulfoaluminate

(C3S.C3A.H32). This is a crystalline meta-stable hydration product of Portland cement

which occurs during the first 24 hours of hydration of the cement. The tricalcium

aluminate (3CaO.Al2O3), also referred as C3A, reacts with gypsum (Ca S04.2H2O), to

form primary ettringite. The reaction for this is as follows-


21

3CaO.Al2O3 + 3 (CaSO4.2H2O) ---------> Ca 6[Al (OH) 6]2. (SO4)3.26H2O

As cement gets more and more hydrated the amount of gypsum decreases and

part of the ettringite is transformed into calcium monosulfo-aluminate hydrate. This

reaction is as follows:

Ca 6[Al (OH) 6]2(SO4)3.26H2O + 2 (CaO.Al2O3) + 4H2O ---------->

3 (3CaO.Al2O3.CaSO4.12H2O)

This reaction also depends on factors such as the pore solution alkalinity, the

water to cement ratio (w/c) and the environment temperature. It also of course is hugely

dependant on the amount of calcium trialuminate present in the cement. Thus the amount

of calcium trialuminate varies based on the grade or the brand of the cement.

Further as the hydrated cement is placed in an environment containing high

sulfate concentrations, as is true in certain formations, the calcium monosulfo-aluminate

hydrate and the calcium hydroxide present in the cement paste react with the sulfate ions

coming from the environment to form the secondary or delayed ettringite

3CaO.Al2O3.CaSO4.12H2O + 2(CaSO4.2H2O) + 16H2O ----------->

3CaO.Al2O3.3CaSO4.32H2O

The ettringite formed from the above equation is a big molecule containing 32

water molecules. Therefore, the formation of ettringite involves considerable expansion

and weight growth. As the reaction takes place, the expansive product (mainly ettringite)

will start filling the cement paste pores and once these are complete, will start building up


22

internal pressure that causes cement cracking and strength loss. This phenomenon is

known as sulfate attack.6

2.3 Cements Used in the Permian Basin

In oilwell cements different classes of cement are used from Class A to Class J depending

on the depth & downhole temperature.

This can be summarized as follows-

Classes of cement Nine API classes: Class A

• Depth surface – 6000 ft (1830 m)

• No special properties

• Similar to ASTM C 150, Type I

Class B


• Moderate to high sulfate resistance

• Similar to ASTM C 150 Types II

Class C


• High early strength


• Similar to ASTM C 150 Types III


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Class D

• Depth from 6000 ft – 10,000 ft (1830 m - 3050 m)

• Moderate and high sulfate resistance

• Moderately high pressure and temperature

Class E

• Depth from 10,000 ft – 14,000 ft (3050 m - 4270 m)

• Moderate and high sulfate resistance

• High pressure and temperature

Class F

• Depth from 10,000 ft – 16,000 ft (3050 m - 4270 m)


• Extremely high pressure and temperature

Class G

• Depth surface – 8000 ft (2440 m), as basic cement, fine

• Can be used with accelerators and retarders for other specifications


• No addition other than calcium sulfate or water

Class H

• Depth surface – 8000 ft (2440 m), as basic cement, course




Class J

• Depth 12,000 – 16,000 ft (3660 m - 4880 m)

• Extremely high pressure and temperature


24




Of all these cement classes, BJ Services most widely uses the Class C & Class

H cements in their wells in the Permian Basin. Of these two, we have studied their Class

H cement for different slurry types.

Also we have used two different Class H companies, Cemex & Lehigh. While

Cemex H cement contains 3% calcium trialuminate, Lehigh H cement contains 0%

calcium trialuminate. Two other additives to the cement slurries often used are bentonite

and pozzolan.

Pozzolana is the chemical used to prepare pozzolan. It is also known as

pozzolanic ash and it is a fine volcanic ash. Thus pozzolan is a vitreous siliceous

material. This pozzolan goes on to react with calcium hydroxide and this forms calcium

silicates. Other cementitious compounds are also formed from the reaction of pozzolan

with the calcium hydroxide depending on the exact type of pozzolan used.

The pozzolan used in the industry today, is prepared by mixing either natural

or industrial pozzolan with Portland Cement. The pozzolanic reaction may be slower than

the rest of the reactions which occur during cement hydration, and thus the short-term

strength of concrete made with pozzolans may not be as high as concrete made with

purely cementitious materials.

The advantages of pozzolan are that in addition to underwater use, the

pozzolana's high alkalinity makes it especially resistant to common forms of corrosion

from sulfates. Once it fully hardens the Pozzolan mixed cement may be stronger than

Portland cement. This is because it has a lower porosity making it more resistant to water

absorption and also to spalling. Pozzolan is also added to Portland cement to increase its

long term strength and other material properties of Portland cement.3


25

CHAPTER III

EXPERIMENTS & METHODOLOGY

3.1 Equipment Selection

The setting up of the modified permeameter was one of the essential

highlights of this thesis. It is well seen from the literature review, especially on

permeability measurements of permeability of cores, even normal cores can sometimes

be difficult to measure.

This is true in cases of tight cores, like limestones which can have a

permeability value as low as 1mD.

In the case of cement this is even more significant. Cement is basically very

tight, & hence has extremely low permeability. Thus we need to use certain modifications

from the certain conventional setup for measuring permeability of sandstone of limestone

in the measurement of cement.

As far as the equipment is concerned the Advanced Core lab at Texas Tech University’s

Petroleum Engineering department has the following-

1] Ruska Permeameter

2] Texaco Permeameter

3] Klinkenberg Permeameter

Of these the Klinkenberg Permeameter has a Hassler core Holder of rating of

2000 psi. Thus since large pressures were expected in this experiment it was preferred

over the Texaco Permeameter which has a lower pressure rating of 1000 psi.


The nylon piping used in the gas permeameter equipment also has a pressure

rating upto 1000 psi. The regulator used could operate in a range from 40-100psi.

Also the gas flow was provided by use of nitrogen cylinders for the

experiments. Helium was an option, but was not considered necessary as nitrogen was

able to necessitate flow through all the cores tested in this thesis. The major modification

here was setting up of the appropriate pressure gauge for conducting all of the above

tests. Hence for the normal setup the pressure differentials achieved during the tests are

usually from 2 to 10 psi. However cement being so tight a pressure gauge with much

higher pressure rating was utilized. This gauge had a maximum pressure reading of 200

psi with increments of 10 psi. Most of the readings were carried out between 40 to 100

psi, & thus this pressure gauge with maximum pressure rating of 200 psi was sufficient.

Attached below in Figure 3.1 and 3.2 are some of the pictures of the Digital

Permeameter set-up in the Advanced Core laboratory.

Figure 3.1 Gas Permeameter Set-up in the Core Lab at Texas Tech

26


Figure 3.2 Nitrogen Cylinders used in the Experiment

During the study the cores were dispatched from BJ Services in zip lock bags and then

dried in the oven as shown below in Figure 3.3, 3.4 and 3.5.

27


Figure 3.3 Ziploc Bags used to Ship the Cement Plugs

Fig 3.4 Oven Used to Heat Cement Plugs

28


Figure 3.5 Set of Cement Plugs numbered before Experiment

29


A basic schematic for the Permeameter setup is as follows in Figure 3.6:

Figure 3.6 Schematic for Gas Permeameter

As mentioned above, the permeability of cement tends to be extremely low.

Thus for flowing a fluid through this tight cement we need to apply very high pressure,

both at the inlet & the overburden as well. The overburden pressure used consistently for

all the tests remained at 250 psi.

30


3.2 Testing Principles

3.2.1 Darcy’s Law The basic law for this thesis revolves around the very important yet basic law

in the petroleum industry, Darcy’s Law. Darcy’s Law is the basic law relating the flow of

a fluid through a permeable medium in terms of flow rate.

Darcy's Law was brought about by Henry Darcy, who derived an equation to

relate flow of a fluid through a medium as a function of :

length

cross sectional area

pressure difference

viscosity of fluid

permeability of medium

The equation for this is as follows:

PALqk g Δ

=μ

Where,

Q- flow rate in cc/sec

μ- viscosity in cP

L- length in cm

A- area in cm2

∆P- pressure difference in atm

All of the above gives us the gas permeability value in Darcy.

Thus to measure the gas permeability for this study, the above equation was used.

31


However we need to measure the absolute permeability, not merely the gas

permeability, for which we use the Klinkenberg Effect principle.3

3.2.2 Klinkenberg Effect

Permeability is the ability for a fluid to flow through a given medium. It thus

predicts fluid flow downhole at different depths depending on the formation.

Permeability of rocks can have a wide range widely from for various rock type and depth

condition.

Some sedimentary rocks show high permeability, while limestones show

lower permeability. Permeability is also influenced by cracks and fractures in the

formation. It is however difficult to predict permeability from other physical properties,

such as porosity.

Permeability does not depend on pore fluid, therefore permeability measured

by gas should be the same with that measure by water. However, it was found that

permeability to gas was higher than that to water. These problems were related to the

pore pressure dependence on gas permeability

of Klinkenberg effect (Klinkenberg, 1941).

Thus in 1941 Klinkenberg discovered that permeability to gas is relatively

higher than that to water, and he interpreted this phenomena as “slip flow” between gas

molecules and solid walls. He stated that gas molecules collide each other and to pore-

walls during traveling through the pore medium. Therefore this additional flux due to the

gas flow at the wall surface, which is called “slip flow”, causes an increased flow rate.

Permeability to nitrogen gas is plotted against the inverse of the average pore

pressure to confirm Klinkenberg effect. This average pore pressure is given as-

2downup

avg

PPP

+=

For most cases, permeability to gas increases linearly with an increase of 1/Pav. Absolute

permeability is estimated from this.3 This absolute permeability can be expressed as:

32


)/1/( pbkk gl +=

An example for the Klinkenberg Effect can be seen from the plot in Figure 3.7 for a

normal core:

Kg

0.014

0.012

0.010

0.008

0.006

0.004

0.002

0.000

y = 0.007x + 0.007 R2 = 0.9272

0 0.1 0.3 0.4 0.5 0.6 0.7 0.8 0.2

1/Pavg

Figure 3.7 Typical Klinkenberg Correction Graph for a Normal Core

33


34

3.3 Experiment Details

The object of this thesis is to measure the cement permeability of different

cement plugs sent by BJ Services to Texas Tech. The experiments conducted for the

purpose of this thesis were carried out over a period of a month & a half.

The starting point of the procedure involved preparing the cement different

slurries decided upon BJ & Texas Tech. Thus a summary of the different samples tested

were in the following order:

SET 1:

Cemex H Neat with distilled water

Lehigh H Neat with distilled water

Cemex 50 + Pozzolan 50 + Bentonite 10 + 5% Salt with distilled water

Lehigh 50 + Pozzolan 50 + Bentonite 10 + 5% Salt with distilled water

SET 2:

Cemex H Neat with 1000mg/l sulfates

Lehigh H Neat with 1000mg/ l sulfates

Cemex 50 + Pozzolan 50 + Bentonite 10 + 5% Salt with 1000mg/ l sulfates

Lehigh 50 + Pozzolan 50 + Bentonite 10 + 5% Salt with 1000mg/ l sulfates

SET 3:

Cemex H Neat with 2000mg/ l sulfates





35

SET 4-

Cemex H Neat with 4000mg/ l sulfates




Thus 16 cement samples were tested as is seen from above. The selection of the 16

cement mixtures was based on the following parameters-

1] Two types of H Cements used:

Cemex & Lehigh are just two different classes of H

cement. Of these Cemex has a known presence of calcium trialuminate known to react

with sulfates of 3%. Lehigh cement on the other hand has a total absence of calcium

trialuminate. Thus it would be interesting to see how these two classes compare as far as

cement permeability is concerned for the different mixing waters.

2] Two types of cement slurries used:

In the Permian Basin very often two basic cement

combinations are most commonly used. The first one is prepared by mixing the cement

neat. The other method included adding pozzolan to the cement with a ratio of 50:50:10

for the cement, pozzolan and bentonite respectively. A description of pozzolan and it’s

properties has been done in the literature review section.

3] Four types of mixing waters used:

Since this study wanted to also investigate how sulfates

in mixing water may influence cement permeability for the above cement combinations,

four different mixing waters were used. This started with distilled water upto a maximum


36

of 4000 mg/l sulfate presence in the water. In the field however, the average strength of

sulfates in downhole waters is seen to be around 2000 mg/l.

Thus these different samples were prepared by BJ Services under the guidance

of Mr. Dean Olsen at the regional BJ services lab at Odessa. The UVA was used to cure

the cement & the cement consistometer was used to measure thickening time. The work

sheets for this are provided in the Appendix of this thesis. Once prepared & tested at the

BJ Lab, these samples were sent to Texas Tech, where they were drilled & chipped off to

an appropriate plug size.

The method for drying the cement neat plugs was consistently kept at a period

of heating in the oven for 24 hours and at a temperature of 45°C. However it must be

noted, that for the pozzolan mixed cement plugs drying the plugs in the oven had to be

replaced by merely drying the plugs under atmospheric conditions for a period of 12

hours instead. The reason for this was that the pozzolan mixed plugs tended to crack

easily when they were dried in the oven.

Finally the samples were then inserted in the Hassler Core Holder of the

Digital Gas Permeameter & the tests were then run on it to calculate cement permeability.

The Core laboratory was consistently kept at a temperature of 23°C.


37

CHAPTER IV

EXPERIMENTAL RESULTS

The experimental observations and results of gas permeability for all the

sixteen cement samples can be seen below from Table 4.1 to Table 4.16. The absolute

permeability values are then obtained from the Klinkenberg Correction plots from Figure

4.1 to Figure 4.16 for the samples.

4.1 Test Results


For Cemex H- Neat with distilled water: Table 4.1 Observations and Results for Sample No 27861

Measurement of Cement Permeabilty BJ Services & TTU

Cement Type - 27861- Cemex Neat Distilled

Length 3.22 cmDiameter 3.77 cm uL/A 0.0052Area 11.1571265 cm2

Pressure 679 mm HgTemperature 23 °CViscosity 0.018

Pressure psi Pressure atm V[cc] t1[sec] t2[s] t3[sec] q1[cc/s]q2[cc/s] q3[cc/s] qavg[cc/s]Kg[mD]

50 3.4 2 20.25 20.31 20.2 0.0988 0.0985 0.0990099 0.09875 0.1508860 4.08 2 18.15 18.05 18.06 0.1102 0.1108 0.11074197 0.110579 0.14079670 4.76 2 15.91 15.91 15.91 0.1257 0.1257 0.1257071 0.125707 0.13719280 5.44 2 14 14.2 13.9 0.1429 0.1408 0.14388489 0.142529 0.13610790 6.12 2 12.5 12.5 12.5 0.16 0.16 0.16 0.16 0.135814

P psi P atm Kg[mD] Pavg 1/Pavg

50 3.4 0.1509 2.2 0.454560 4.08 0.1408 2.54 0.393770 4.76 0.1372 2.88 0.347280 5.44 0.1361 3.22 0.310690 6.12 0.1358 3.56 0.2809

38


Cemex Neat Distilled y = 0.0035x + 0.1297R2 = 0.7604

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.28 0.31 0.35 0.39 0.451/Pavg

Gas

Per

mea

bilit

y

Figure 4.1 Klinkenberg Correction Graph for Sample No 27861 Absolute Permeability of Cemex Neat Cement with Distilled Water = 0.1297 mD

39


For Lehigh H- Neat with distilled water: Table 4.2 Observations and Results for Sample No 27862


Cement Type - 27862- Lehigh Neat Distilled


Pressure 680 mm HgTemperature 23 °CViscosity 0.018

Pressure psi Pressure atm V[cc] t1[s] t2[s] t3[s] q1[cc/s] q2[cc/s] q3[cc/s] qavg[cc/s]Kg[mD]

50 3.4 2 19.8 19.7 19.7 0.100908 0.1014199 0.10147133 0.101266 0.18064260 4.08 2 17.3 17.5 17.5 0.115407 0.1142204 0.11415525 0.114594 0.17034770 4.76 2 15.6 15.6 15.6 0.128205 0.1282051 0.12820513 0.128205 0.16335580 5.44 2 13.9 13.9 13.7 0.1443 0.1443001 0.1459854 0.144862 0.16150690 6.12 2 12.3 12.3 12.3 0.162602 0.1626016 0.16260163 0.162602 0.161141

P psiP atmKg[mD] Pavg 1/Pavg

50 3.4 0.180642 2.2 0.4545454560 4.08 0.170347 2.54 0.3937007970 4.76 0.163355 2.88 0.3472222280 5.44 0.161506 3.22 0.3105590190 6.12 0.161141 3.56 0.28089888

40


Lehigh Neat Distilled y = 0.0048x + 0.153R2 = 0.8344

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0.2

0.454545 0.393701 0.347222 0.310559 0.2808991/Pavg

Gas

Per

mea

bilit

y

Figure 4.2 Klinkenberg Correction Graph for Sample No 27862 Absolute Permeability of Lehigh Neat Cement with Distilled Water = 0.153 mD

41


For Cemex 50 + Pozzalan 50 + Bentonite 10 + 5% Salt with distilled water: Table 4.3 Observations and Results for Sample No 27865

Measurement of Cement Permeability BJ Services & TTU

Cement Type - 27865- Cemex 50:50:10 Distilled


Pressure 690 mm HgTemp 23 °CViscosity 0.018

Pressure psi Pressure atm V[cc] t1[sec] t2[sec] t3[sec] q1[cc/s] q2[cc/s] q3[cc/s] qavg[cc/s]Kg[mD]

50 3.4 0.1 1.9 1.9 1.86 0.05263 0.052632 0.05376344 0.053009 0.10436860 4.08 0.1 1.76 1.76 1.81 0.05682 0.056818 0.05524862 0.056295 0.09236570 4.76 0.1 1.61 1.61 1.61 0.06211 0.062112 0.0621118 0.062112 0.08735180 5.44 0.1 1.48 1.48 1.46 0.06757 0.067568 0.06849315 0.067876 0.08352590 6.12 0.1 1.32 1.32 1.32 0.07576 0.075758 0.07575758 0.075758 0.082865


50 3.4 0.1044 2.2 0.45454560 4.08 0.0924 2.54 0.39370170 4.76 0.0874 2.88 0.34722280 5.44 0.0835 3.22 0.31055990 6.12 0.0829 3.56 0.280899

42


Cemex 50:50:10 Distilledy = 0.0052x + 0.0745

R2 = 0.862

0

0.02

0.04

0.06

0.08

0.1

0.12

0.28 0.31 0.35 0.39 0.451/Pavg

Gas

Per

mea

bilit

y

Figure 4.3 Klinkenberg Correction Graph for Sample No 27865 Absolute Permeability of Cemex 50:50:10 Cement with Distilled Water = 0.0745 mD

43


For Lehigh 50 + Pozzalan 50 + Bentonite 10 + 5% Salt with distilled water: Table 4.4 Observations and Results for Sample No 27866


Cement Type - 27866- Lehigh 50:50:10 Distilled

Leng 3.75 cmDiam 3.7 cm uL/A 0.00628Area 10.74665 cm2

Pres 680 mm HgTemp 23.1 °CVisc 0.018

Pressure psi Pressure atm V[cc] t1[sec] t2[sec] t3[sec] q1[cc/s] q2[cc/s] q3[cc/s] qavg[cc/s] Kg[mD]

50 3.4 0.1 2.14 2.14 2.14 0.04673 0.04673 0.0467 0.04672897 0.08632560 4.08 0.1 1.92 1.92 1.9 0.05208 0.05208 0.0526 0.05226608 0.08046270 4.76 0.1 1.76 1.76 1.76 0.05682 0.05682 0.0568 0.05681818 0.07497480 5.44 0.1 1.63 1.63 1.64 0.06135 0.06135 0.061 0.061225 0.0706990 6.12 0.1 1.51 1.49 1.49 0.06623 0.06711 0.0671 0.06681778 0.068576

P psi P atm Kg[mD]Pavg 1/Pavg

50 3.4 0.086 2.2 0.4545560 4.08 0.08 2.54 0.393770 4.76 0.075 2.88 0.3472280 5.44 0.071 3.22 0.3105690 6.12 0.069 3.56 0.2809

44


Lehigh 50:50:10 Distilled y = 0.0045x + 0.0626R2 = 0.9728

0

0.02

0.04

0.06

0.08

0.1

0.28 0.31 0.35 0.39 0.45

1/Pavg

Gas

Per

mea

bilit

y

Figure 4.4 Klinkenberg Correction Graph for Sample No 27866 Absolute Permeability of Lehigh 50:50:10 Cement with Distilled Water = 0.0626 mD

45


For Cemex H- Neat with 1000mg/l sulfates: Table 4.5 Observations and Results for Sample No 27877


Cement Type - 27877- Cemex Neat 1000mg/L




50 3.4 2 20 20.22 19.5 0.1 0.09891 0.1025641 0.100492 0.20778860 4.08 2 16.3 17.2 17.1 0.122699 0.11628 0.11695906 0.118646 0.20443770 4.76 2 14.5 14.75 14.5 0.137931 0.13559 0.13793103 0.137152 0.20256480 5.44 2 12.9 12.8 12.7 0.155039 0.15625 0.15748031 0.156256 0.20193390 6.12 2 11.4 11.5 11.3 0.175439 0.17391 0.17699115 0.175448 0.201541


50 3.4 0.208 2.2 0.4545560 4.08 0.204 2.54 0.393770 4.76 0.203 2.88 0.3472280 5.44 0.202 3.22 0.3105690 6.12 0.202 3.56 0.2809

46


Cemex Neat 1000 mg/l y = 0.0015x + 0.1992R2 = 0.8547

0

0.05

0.1

0.15

0.2

0.25

0.28 0.31 0.35 0.39 0.451/Pavg

Gas

Per

mea

bilit

y

Figure 4.5 Klinkenberg Correction Graph for Sample No 27877 Absolute Permeability of Cemex Neat Cement with 1000mg/l Water = 0.1992 mD

47


For Lehigh H- Neat with 1000mg/l sulfates: Table 4.6 Observations and Results for Sample No 27878


Cement Type - 27878- Lehigh Neat 1000mg/L

Length 4 cmDiameter 3.735 cm uL/A 0.0066Area 10.95092663 cm2


Pressure psi Pressure atm V[cc] t1[sec] t2[sec] t3[sec] q1[cc/s]q2[cc/s] q3[cc/s] qavg[cc/s]Kg[mD]

50 3.4 2 19.4 19.1 19.1 0.1031 0.1047 0.10471204 0.104172 0.20144460 4.08 2 17.6 17.5 17.4 0.1136 0.1143 0.11494253 0.114288 0.18417270 4.76 2 16.5 16.5 16.5 0.1212 0.1212 0.12121212 0.121212 0.16742580 5.44 2 14.5 14.6 14.5 0.1379 0.137 0.13793103 0.137616 0.16632390 6.12 2 13 12.85 13.01 0.1538 0.1556 0.1537279 0.154405 0.165879


50 3.4 0.20144 2.2 0.454560 4.08 0.18417 2.54 0.393770 4.76 0.16743 2.88 0.347280 5.44 0.16632 3.22 0.310690 6.12 0.16588 3.56 0.2809

48


Lehigh Neat 1000mg/l y = 0.0089x + 0.1504

R2 = 0.8093

0

0.05

0.1

0.15

0.2

0.25

0.28 0.31 0.35 0.39 0.45

1/Pavg

Gas

Per

mea

bilit

y

Figure 4.6 Klinkenberg Correction Graph for Sample No 27878 Absolute Permeability of Lehigh Neat with 1000mg/l Water = 0.1504 mD

49


For Cemex 50 + Pozzalan 50 + Bentonite 10 + 5% Salt with 1000mg/l sulfates: Table 4.7 Observations and Results for Sample No 27884


Cement Type - 27884- Cemex 50:50:10 1000mg/L


Pressure 684 mm HgTemp 23 CViscosity 0.018

Pressure psPressureV[cc] t1[sec] t2[sec] t3[sec] q1[cc/s]q2[cc/s] q3[cc/s] qavg[cc/s]Kg[mD]

50 3.4 0.1 1.7 1.7 1.72 0.0588 0.05882 0.05813953 0.058596 0.10131960 4.08 0.1 1.59 1.59 1.59 0.0629 0.06289 0.06289308 0.062893 0.09062570 4.76 0.1 1.39 1.39 1.36 0.0719 0.07194 0.07352941 0.072471 0.08950980 5.44 0.1 1.22 1.22 1.22 0.082 0.08197 0.08196721 0.081967 0.08858290 6.12 0.1 1.09 1.1 1.09 0.0917 0.09091 0.09174312 0.091465 0.087864


50 3.4 0.1013 2.2 0.4545560 4.08 0.0906 2.54 0.393770 4.76 0.0895 2.88 0.3472280 5.44 0.0886 3.22 0.3105690 6.12 0.0879 3.56 0.2809

50


Cemex 50:50:10 1000 mg/ly = 0.0029x + 0.0829

R2 = 0.6824

0

0.02

0.04

0.06

0.08

0.1

0.12

0.28 0.31 0.35 0.39 0.451/Pavg

Gas

Per

mea

bilit

y

Figure 4.7 Klinkenberg Correction Graph for Sample No 27884 Absolute Permeability of Cemex 50:50:10 with 1000 mg/l Water = 0.0829 mD

51


For Lehigh 50 + Pozzalan 50 + Bentonite 10 + 5% Salt with 1000mg/l sulfates: Table 4.8 Observations and Results for Sample No 27885


Cement Type - 27885- Lehigh 50:50:10 1000mg/L




50 3.4 0.1 1.79 1.79 1.78 0.05587 0.0559 0.0562 0.05597054 0.09650560 4.08 0.1 1.54 1.58 1.58 0.06494 0.0633 0.0633 0.06383911 0.09172670 4.76 0.1 1.45 1.44 1.41 0.06897 0.0694 0.0709 0.06977732 0.08593680 5.44 0.1 1.22 1.28 1.28 0.08197 0.0781 0.0781 0.07940574 0.0855790 6.12 0.1 1.16 1.13 1.13 0.08621 0.0885 0.0885 0.08773268 0.084038


50 3.4 0.0965 2.2 0.454560 4.08 0.0917 2.54 0.393770 4.76 0.0859 2.88 0.347280 5.44 0.0856 3.22 0.310690 6.12 0.084 3.56 0.2809

52


Lehigh 50:50:10 1000mg/Ly = 0.0031x + 0.0794

R2 = 0.8849

0

0.02

0.04

0.06

0.08

0.1

0.12

0.28 0.31 0.35 0.39 0.45

1/Pavg

Gas

Per

mea

bilit

y

Figure 4.8 Klinkenberg Correction Graph for Sample No 27885 Absolute Permeability of Lehigh 50:50:10 1000mg/l = 0.0794mD

53








50 3.4 2 26.05 26.05 25.9 0.07678 0.0768 0.0772 0.07692365 0.16010760 4.08 2 23.33 23.33 23.22 0.08573 0.0857 0.0861 0.0858619 0.14892670 4.76 2 22 22 22 0.09091 0.0909 0.0909 0.09090909 0.13515480 5.44 2 19.82 19.82 19.8 0.10091 0.1009 0.101 0.10094215 0.13131290 6.12 2 17.6 17.9 17.9 0.11364 0.1117 0.1117 0.11236668 0.129932


50 3.4 0.1601 2.2 0.454560 4.08 0.1489 2.54 0.393770 4.76 0.1352 2.88 0.347280 5.44 0.1313 3.22 0.310690 6.12 0.1299 3.56 0.2809

54



0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0.28 0.31 0.35 0.39 0.45

1/Pavg

Gas

Per

mea

bilit

y

Figure 4.9 Klinkenberg Correction Graph for Sample No 27907 Absolute Permeability of Cemex Neat Cement with 2000 mg/l Water = 0.1177 mD

55







Pressure psi Pressure atm V[cc] t1[sec] t2[sec] t3[sec] q1[cc/s]q2[cc/s] q3[cc/s] qavg[cc/s] Kg[mD]

50 3.4 2 24.7 24.5 24.5 0.081 0.0816 0.0816 0.08141232 0.13071260 4.08 2 22.04 22.06 22.08 0.0907 0.0907 0.0906 0.09066188 0.12130270 4.76 2 19.63 19.67 19.67 0.1019 0.1017 0.1017 0.10174674 0.11668680 5.44 2 17.45 17.5 17.5 0.1146 0.1143 0.1143 0.11439487 0.11479290 6.12 2 16 15.85 15.87 0.125 0.1262 0.126 0.12573564 0.112153


50 3.4 0.1307 2.2 0.454560 4.08 0.1213 2.54 0.393770 4.76 0.1167 2.88 0.347280 5.44 0.1148 3.22 0.310690 6.12 0.1122 3.56 0.2809

56


Lehigh Neat 2000 mg/l y = 0.0044x + 0.106R2 = 0.8964

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.28 0.31 0.35 0.39 0.451/Pavg

Gas

Per

mea

bilit

y

Figure 4.10 Klinkenberg Correction Graph for Sample No 27908 Absolute Permeability of Lehigh Neat Cement with 2000 mg/l Water = 0.106mD

57





Leng 4.11 cmDiam 3.67 cm uL/A 0.007Area 10.5730865 cm2

Pres 684 mm HgTemp 23 °CVisc 0.018


50 3.4 0.1 1.98 2.05 2.06 0.05051 0.04878 0.0485 0.04927641 0.10140860 4.08 0.1 1.82 1.78 1.76 0.05495 0.05618 0.0568 0.055981 0.09600570 4.76 0.1 1.59 1.59 1.59 0.06289 0.06289 0.0629 0.06289308 0.0924580 5.44 0.1 1.39 1.42 1.43 0.07194 0.07042 0.0699 0.07076502 0.09101990 6.12 0.1 1.27 1.27 1.27 0.07874 0.07874 0.0787 0.07874016 0.090024


50 3.4 0.101 2.2 0.4545560 4.08 0.096 2.54 0.393770 4.76 0.092 2.88 0.3472280 5.44 0.091 3.22 0.3105690 6.12 0.09 3.56 0.2809

58


Cemex 50:50:10 2000 mg/l y = 0.0028x + 0.0859R2 = 0.8974

0

0.02

0.04

0.06

0.08

0.1

0.12

0.28 0.31 0.35 0.39 0.45

1/Pavg

Gas

Per

mea

bilit

y


59




Cement Type - 27940- Lehigh 50:50:10 with 2000 mg/L Water



Pressure pPressureV[cc] t1[sec]t2[sec] t3[sec] q1[cc/s] q2[cc/s] q3[cc/s] qavg[cc/s]Kg[mD]

50 3.4 0.1 2.04 2.05 1.98 0.04902 0.0488 0.0505 0.049435 0.1015527160 4.08 0.1 1.92 1.91 1.9 0.05208 0.0524 0.0526 0.052357 0.0896292770 4.76 0.1 1.77 1.79 1.79 0.0565 0.0559 0.0559 0.056076 0.0822826380 5.44 0.1 1.63 1.63 1.63 0.06135 0.0613 0.0613 0.06135 0.0787678490 6.12 0.1 1.5 1.5 1.5 0.06667 0.0667 0.0667 0.066667 0.0760839


50 3.4 0.1016 2.2 0.454560 4.08 0.0896 2.54 0.393770 4.76 0.0823 2.88 0.347280 5.44 0.0788 3.22 0.310690 6.12 0.0761 3.56 0.2809

60


Lehigh 50:50:10 2000 mg/l y = 0.0062x + 0.0671R2 = 0.9116

0

0.02

0.04

0.06

0.08

0.1

0.12

0.28 0.31 0.35 0.39 0.45

1/Pavg

Gas

Per

mea

bilit

y

Figure 4.12 Klinkenberg Correction Graph for Sample No 27940 Absolute Permeability of Lehigh 50:50:10 with 2000 mg/l Water = 0.0671mD

61








50 3.4 2 25.6 25.6 25.6 0.07813 0.0781 0.0781 0.078125 0.1393710260 4.08 2 22.41 22.41 22.5 0.08925 0.0892 0.0889 0.08912688 0.1324981870 4.76 2 19.6 19.6 19.6 0.10204 0.102 0.102 0.10204082 0.1300254480 5.44 2 17.15 17.17 17.2 0.11662 0.1165 0.1163 0.11645979 0.1298489690 6.12 2 15.52 15.65 15.65 0.12887 0.1278 0.1278 0.12815234 0.12700959


50 3.4 0.1394 2.2 0.454560 4.08 0.1325 2.54 0.393770 4.76 0.13 2.88 0.347280 5.44 0.1298 3.22 0.310690 6.12 0.127 3.56 0.2809

62



0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.28 0.31 0.35 0.39 0.45

1/Pavg

Gas

Per

mea

bilit

y

Figure 4.13 Klinkenberg Correction Graph for Sample No 27950 Absolute Permeability of Cemex Neat Cement with 4000 mg/l Water = 0.1235 mD

63







Pressure psi Pressue atm V[cc] t1[sec] t2[sec] t3[sec] q1[cc/s] q2[cc/s] q3[cc/s] qavg[cc/s]Kg[mD]

50 3.4 2 28.2 28.2 28.2 0.07092 0.0709 0.0709 0.070922 0.1275470660 4.08 2 26.5 26.5 26.6 0.07547 0.0755 0.0752 0.075377 0.1129660370 4.76 2 24.1 23.95 23.94 0.08299 0.0835 0.0835 0.083346 0.1070642980 5.44 2 22 22.1 22.1 0.09091 0.0905 0.0905 0.090635 0.1018743490 6.12 2 19.6 19.9 19.9 0.10204 0.1005 0.1005 0.101015 0.10092625


50 3.4 0.1275 2.2 0.454560 4.08 0.113 2.54 0.393770 4.76 0.1071 2.88 0.347280 5.44 0.1019 3.22 0.310690 6.12 0.1009 3.56 0.2809

64


Lehigh Neat 4000 mg/l y = 0.0064x + 0.0908R2 = 0.8738

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.28 0.31 0.35 0.39 0.45

1/Pavg

Gas

Per

mea

bilit

y

Figure 4.14 Klinkenberg Correction Graph for Sample No 27951 Absolute Permeability of Lehigh Neat Cement with 4000mg/l Water = 0.0908 mD

65








50 3.4 0.1 1.66 1.66 1.67 0.06024 0.0602 0.0599 0.060121 0.11051164160 4.08 0.1 1.56 1.56 1.56 0.0641 0.0641 0.0641 0.064103 0.09819242770 4.76 0.1 1.44 1.42 1.41 0.06944 0.0704 0.0709 0.070263 0.09225340880 5.44 0.1 1.27 1.28 1.22 0.07874 0.0781 0.082 0.079611 0.09146096790 6.12 0.1 1.15 1.14 1.11 0.08696 0.0877 0.0901 0.088255 0.090126425


50 3.4 0.1105 2.2 0.454560 4.08 0.0982 2.54 0.393770 4.76 0.0923 2.88 0.347280 5.44 0.0915 3.22 0.310690 6.12 0.0901 3.56 0.2809

66


Cemex 50:50:10 4000 mg/l y = 0.0048x + 0.0823R2 = 0.7967

0

0.02

0.04

0.06

0.08

0.1

0.12

0.28 0.31 0.35 0.39 0.451/Pavg

Gas

Per

mea

bilit

y


67




Cement Type - 27952- Lehigh 50:50:10 4000mg/L

Length 4 cmDiameter 3.68 cm uL/A 0.00677Area 10.630784 cm2



50 3.4 0.1 1.69 1.69 1.67 0.05917 0.0592 0.0599 0.059408 0.1183400760 4.08 0.1 1.54 1.54 1.54 0.06494 0.0649 0.0649 0.064935 0.1077919570 4.76 0.1 1.36 1.4 1.36 0.07353 0.0714 0.0735 0.072829 0.103625280 5.44 0.1 1.2 1.2 1.22 0.08333 0.0833 0.082 0.082878 0.1031828190 6.12 0.1 1.08 1.07 1.08 0.09259 0.0935 0.0926 0.092881 0.10278811


50 3.4 0.1183 2.2 0.454560 4.08 0.1078 2.54 0.393770 4.76 0.1036 2.88 0.347280 5.44 0.1032 3.22 0.310690 6.12 0.1028 3.56 0.2809

68


Lehigh 50:50:10 4000 mg/ly = 0.0036x + 0.0964

R2 = 0.738

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.28 0.31 0.35 0.39 0.451/Pavg

Gas

Per

mea

bilit

y

Figure 4.16 Klinkenberg Correction Graph for Sample No 27952 Absolute Permeability of Lehigh 50:50:10 with 4000mg/l Water = 0.0964 mD

69


Error Analysis

During this thesis, the experiments carried out gave fairly consistent results.

However certain human and equipment error must be considered. An example of this is

error in measuring time for fluid to flow t. This error would give an error in the flow rate

since q=V/t and finally in the permeability value since the permeability is a function of

flow rate.

Hence an example of error analysis is shown below for sample no 27861 i.e.

Cemex Neat Distilled at 50 psi.

The general approximation error is given by-

∑=

=Δ

∂∂

=Δni

iZi

ZiGG

1

Thus using this definition, the error to permeability is as follows-

⎥⎦

⎤⎢⎣

⎡ Δ+

ΔΔΔ

+Δ

+Δ

+Δ

=ΔAA

PP

LoLo

oo

qoqokk )(

μμ

Here,

μ= 0.018

∆ μ = 0.005 cP

L= 3.22 cm

∆L= 1 mm

70


71

D = 3.77 cm

∆D= 1 mm, ∆A= 0.295

∆ (∆P) = 0.15 atm

Qο= 0.09875 cc/sec

∆T= 0.2 sec, ∆Q= 0.0097

k= 0.1297 mD [calculated]

Hence the possible error for the experiment setup can be given as-

∆k= 0.0179


CHAPTER V

ANALYSIS AND COMPARISON OF RESULTS

The summary for the cement permeability based on the mixing waters and the slurry

combination is as shown in Table 5.1:

Table 5.1 Summary of Cement Permeability for all the samples

Cement Type Absolute Permeability

Cemex Neat Distilled 0.1297 mD

Cemex Neat 1000 0.1992 mD



Lehigh Neat Distilled 0.153 mD

Lehigh Neat 1000 0.1504 mD



Cemex 50:50:10 Distilled 0.0745 mD

Cemex 50:50:10 1000 0.0829 mD

Cemex 50:50:10 2000 0.0859 mD

Cemex 50:50:10 4000 0.0823 mD

Lehigh 50:50:10 Distilled 0.0626 mD

Lehigh 50:50:10 1000 0.0794 mD

Lehigh 50:50:10 2000 0.0671 mD

Lehigh 50:50:10 4000 0.0964 mD

72


5.1 Comparing Neat Vs Pozzolan Cement Permeability

Figure 5.1 below is a bar diagram representation which basically compares

the permeability for the neat cement versus the permeability for the pozzolan mixed

cement for all the sixteen cement mixtures.

Neat vs 50:50:10

0

0.05

0.1

0.15

0.2

0.25

Cemex

Dist

illed

Cemex

1000

mg/L

Cemex

2000

mg/L

Cemex

4000

mg/L

Lehig

h Dist

illed

Lehig

h 100

0 mg/L

Lehig

h 200

0 mg/L

Lehig

h 400

0 mg/L

Cement Type

Perm

eabi

lity

Neat50:50:10

Figure 5.1 Graph of Neat vs. Pozzolan Mixed Cement Permeability

The important objective of this thesis is to study the influence of the sulfates

in the mixing water to the final cement permeability as well as make an official

73


74

documentation of the different cement permeability of cement mixtures used by BJ

Services in the Permian Basin.

Thus before looking into the influence of sulfates, we first study the influence

of the different components used to prepare the slurry on final permeability of the set

cement.

Hence as mentioned in the Literature Review the two important slurry types

used in the Permian Basin involve the slurries made of the neat cement itself i.e. cement

prepared just by mixing water to the dry cement. The other commonly used slurry type is

the Pozzolan cement. This cement has a proportion of 50:50:10 of the cement, the

chemical pozzolan and bentonite respectively.

What the above chart indicates to us about the basic two slurry types for the

different mixing waters used is that the cement slurry prepared by using pozzolan have a

relatively lower range of permeability than the neat cement samples.

Thus this chart clearly illustrates to us the fact that the pozzolan mixed

cements will always have a lower permeability value for the same mixing water as

compared to their neat counterparts. Thus these pozzolan mixed cements with lower

permeability values will quite understandably show higher resistance to sulfate attack

from downhole waters as compared to the resistance showed by the neat cement slurries.

The above can be confirmed from the fact that the pozzolan mixed cement permeability is

lower for not just one or two, but for all the different mixing waters tested in the

laboratory.

Thus we can once again emphasize this difference between the neat and the

pozzolan mixed cements by seeing the individual charts for cement permeability for all

the different mixing waters as shown from Figure 5.2 to Figure 5.9:


Cemex Distilled

0.1297

0.0745

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

Cemex Neat Distilled Cemex 50:50:10 Distilled

Perm

eabi

lity

Figure 5.2 Graph of Cemex Distilled Neat vs. Pozzolan Cement

Lehigh Distilled

0.153

0.0626

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

Lehigh Neat Distilled Lehigh 50:50:10 Distilled

Perm

eabi

lity

Figure 5.3 Graph of Lehigh Distilled Neat vs. Pozzolan Cement 75


Cemex 1000 mg/l

0.1992

0.0829

0

0.05

0.1

0.15

0.2

0.25

Cemex Neat 1000 mg/l Cemex 50:50:10 1000 mg/l

Perm

eabi

lity

Figure 5.4 Graph of Cemex 1000mg/l Neat vs. Pozzolan Cement

Lehigh 1000 mg/l

0.1504

0.0794

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

Lehigh Neat 1000 mg/l Lehigh 50:50:10 1000 mg/l

Per

mea

bilit

y

Figure 5.5 Graph of Lehigh 1000mg/l Neat vs. Pozzolan Cement 76


Cemex 2000 mg/l

0.1177

0.0859

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14


Perm

eaib

ility

Figure 5.6 Graph of Cemex 2000 mg/l Neat vs. Pozzolan Cement

Lehigh 2000 mg/l

0.106

0.0671

0

0.02

0.04

0.06

0.08

0.1

0.12


Per

mea

bilit

y

Figure 5.7 Graph of Lehigh 2000 mg/l Neat vs. Pozzolan Cement 77


Lehigh 4000 mg/l

0.09080.0964

0

0.02

0.04

0.06

0.08

0.1

0.12


Per

mea

bilit

y

Figure 5.8 Graph of Lehigh 4000 mg/l Neat vs. Pozzolan Cement

Cemex 4000 mg/l

0.1235

0.0823

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14


Perm

eabi

lity

Figure 5.9 Graph of Cemex 4000 mg/l Neat vs. Pozzolan Cement

78


79

Thus based on all of the above findings and results it is clear that as far as

choosing the cement slurry itself is concerned irrespective of the mixing water used, in

cases where there is expected to be high sulfate presence in the downhole water, it would

be far more recommended to use the pozzolan cement slurries instead of the neat cement

slurries. Thus pozzolan gives cement advantages such as making it more light etc, and its

permeability is low, while neat cements have higher permeability and hence should be

avoided in high sulfate water formations, because of the damage that is possible to the

cement and ultimately the casing because of this higher permeability.


80

5.2 Influence of Sulfate Percentage in Mixing Water on Cement Permeability

An important aspect of this thesis was to study the influence of sulfate present

in mixing water on the cement permeability. Thus although it is commonly known that

secondary ettringite which forms in the cement over a long period [over few years] does

damage and crack the cement, the role of primary ettringite [formed as soon as the

cement is set] has not been confirmed to damage the cement like the secondary ettringite

does. Thus we look at the charts for the four different cement mixtures i.e. Cemex Neat,

Cemex 50:50:10, Lehigh Neat, Lehigh 50:50:10 with the different mixing waters used, to

come to a conclusion on the role of the sulfates/primary ettringite on the initial

permeability of the cement, before the secondary ettringite has formed within the cement.

This is represented in Figures 5.10 to Figure 5.13.


Cemex Neat

Cemex Neat

0.1297

0.1992

0.1177

0.153

0

0.05

0.1

0.15

0.2

0.25

Distilled Water 1000 mg/L SulfateWater

2000 mg/L SulfateWater

4000 mg/L SulfateWater

Sulfates in Mixing Water

Perm

eabi

lity

Figure 5.10 Graph Comparing Cement Perm for Cemex Neat with Diff Mix Waters

Lehigh Neat

Lehigh Neat

0.153 0.1504

0.1060.0908

0

0.05

0.1

0.15

0.2

0.25

Lehigh NeatDistilled

Lehigh Neat 1000mg/L

Lehigh Neat 2000mg/l

Lehigh Neat 4000mg/L


Per

mea

bilit

y

Fig 5.11 Graph Comparing Cement Perm for Lehigh Neat with Diff Mix Waters

81


Cemex 50:50:10

Cemex 50:50:10

0.0745 0.0829 0.0859 0.0823

0

0.05

0.1

0.15

0.2

0.25

Cemex 50:50:10Distilled

Cemex 50:50:101000 mg/L

Cemex 50:50:102000 mg/L

Cemex 50:50:104000 mg/L


Perm

eabi

lity

Fig 5.12 Graph Comparing Cement Perm for Cemex 50:50:10 with Diff Mix Waters

Lehigh 50:50:10

Lehigh 50:50:10

0.06260.0794

0.0671

0.0964

0

0.05

0.1

0.15

0.2

0.25

Lehigh 50:50:10Distilled

Lehigh 50:50:101000 mg/l

Lehigh 50:50:102000 mg/L

Lehigh 50:50:104000 mg/L


Per

mea

bilit

y

Fig 5.13 Graph Comparing Cement Perm for Lehigh 50:50:10 with Diff Mix Waters

82


Summary of Results Indicating that Primary Ettringite does not influence Permeability The above four results are summarized below in Figure 5.14:

Permeability vs Mixing water

0

0.05

0.1

0.15

0.2

0.25

Cemex Neat Lehigh Neat Cemex50:50:10

Lehigh50:50:10

Cement Type

Perm

eabi

lity Distilled Watert

1000 mg/L

2000 mg/L

4000 mg/L

Fig 5.14 Overall Graph for the 4 Cement Types with Different Mixing Waters

83


84

CHAPTER VI

CONCLUSIONS

From the above the analysis of results can be summarized as follows:

1] Cement mixed neat shows higher permeability values the cements mixed with

pozzolan.

2] The sulfates present in the mixing water for preparing the cement does not affect the

cement permeability during the initial life of the cement.

Thus based on the above analysis, since one of the objectives of this thesis was

to investigate and make appropriate recommendations for BJ Services for their operations

in the Permian Basin the conclusion for this study can be based as follows:

1] In the Permian Basin BJ Services faces problems in some wells downhole of sulfates

in downhole water attacking and corroding the cement and later on the casing. However

this study shows quite clearly that using mixing water with a lower amount of sulfate in it

will not solve this problem. Thus this also implies on a general level, that initial cement

permeability is not affected by the formation of primary ettringite. However the role of

secondary ettringite which is known to form more than 120 days of cement setting, still

needs to be investigated.

2] The analysis also shows us quite clearly, that neat cement mixtures invariably tend to

show higher permeability than the pozzolan mixed cement mixtures. Thus the

recommendation for BJ Services must be to try and use pozzolan mixed cements,

especially in situations where high sulfate presence in downhole water is expected. Thus

using pozzolan mixed cements in such situations, may lead to higher resistance to sulfate

attack from these downhole waters.


85

CHAPTER VII

RECOMMENDATIONS

Based on the results obtained and the conclusions derived from this study,

certain recommendations for future study have been made. These recommendations are

not limited to just the work done in this thesis, but using this thesis as a base for further

research in other types of study on cement.

1] The role of primary ettringite was found to be insignificant as far as cement

permeability is concerned. However of great interest for future study, would be to test

these same samples around 6 months down the line. I recommend soaking all the cement

plugs tested in this study in sulfate water for this period. Thus it can be expected that the

sulfate in the water would react with the cement and go on to form secondary ettringite

within the cement, a process which is typically known to occur after 120 days of the

original cement setting. Cement Permeability if then measured again after formation of

the secondary ettringite, might then show any existing co relation between cement

permeability to the cement mixture/mixing water, due to formation of secondary

ettringite.

2] Another aspect that can be studied is the role of other cement additives in its

permeability value. Thus since this study limited cement slurry mixtures to only pozzolan

and bentonite mixing, it is recommended to prepare future samples with chemicals such

as expansion additives like MgO or CaO. This would be useful to see whether these

expansion additives also make any significant difference to the cement permeability.

3] Also apart from permeability the above study could also be expanded to measuring

properties such as porosity or expansion of the cement, to give a better understanding of

cement which will help predict downhole cement behavior.


86

BIBLIOGRAPHY

1. Backe, K.R., O.B. Lile, S.K. Lyomov, H. Elvebakk, P. Skalle. “Characterizing Curing

Cement Slurries by Permeability, Tensile Strength and Shrinkage.” In SPE Western

Regional Meeting, 25-27 June 1997, Long Beach, California.

2. Collepardi, M.Civil Engineering Faculty, Leonardo Da Vinci, Polytechnic Milan,

Italy. “A State-of-the-Art-Review on Delayed Ettringite Attack on Concrete.”

www.encosrl.it/enco%20srl%20ITA/servizi/pdf/degrado/67.pdf (accessed May 15,

2007).

3. “Darcy’s Law, Klinkenberg Effect and Pozzolan.” www.Wikepedia.org (accessed June

28, 2007).

4. Goode, John M. Halliburton Co. “Gas and Water Permeability Data for Some

Common Oilwell Cements.” In SPE Production Research Symposium,

April 12-13, 1962, Tulsa, Oklahoma.

5. Lynn Jack, Jennings Scott, Saudi Aramco. Personal Communication. 2007.

6. Morales Marcela, Morris Walter, A. Marcelo, Robles Jorge, Bianchi

Gustavo. "Improving the Sulfate Resistance Performance of API cement Class A upon

Appropriate Slurry Design." Presented at the SPE Latin American and Caribbean

Petroleum Conference, 27-30 April 2003, Port-of-Spain, Trinidad, West Indies.


87

7. Morgan B.E., G.K. Dumbauld, Humble Oil & Refining Co. “Measurement of the

Permeability of Set Cement." Petroleum Transactions AIME, Technical Note 120. Vol

195, 1952.

8. Rabia H. “Oilwell Drilling Engineering: Principles and Practice” Grahman and

Trotman, 1985, London.

9. Roscoe C.Clark Jr., Stanolind Oil and Gas Company. “Influence of Different Types

of Formation Waters on Disintegration of Cements.” Petroleum Transactions,

Technical Note 59. Vol 189, 1950.

10. Sanyal S.K., R.M. Pirnie III, G.O Chen, S.S. Mardsen, Stanford University. “A Novel

Liquid Permeameter for Measuring Very Low Permeability.” In SPE 45th Annual Fall

Meeting, Houston, Texas, Oct 4-7, 1970.

11. Tanikawa W. and Shimamoto T. “Klinkenberg effect for gas permeability and

its comparison to water permeability for porous sedimentary rocks.” Hydrology and

Earth System Sciences Discussions, 3, 1315-1338, 2006.


88

APPENDIX


CEMEX NEAT DISTILLED

89


90


LEHIGH NEAT DISTILLED

91


92


CEMEX 50:50:10 DISTILLED

93


94


LEHIGH 50:50:10 DISTILLED

95


96


CEMEX NEAT 1000

97


98


LEHIGH NEAT 1000

99


100


CEMEX 50:50:10 1000

101


102


LEHIGH 50:50:10 1000

103


104


CEMEX NEAT 2000

105


106


LEHIGH NEAT 2000

107


108


CEMEX 50:50:10 2000

109


110


LEHIGH 50:50:10 2000

111


112


CEMEX NEAT 4000

113


114


LEHIGH NEAT 4000

115


116


CEMEX 50:50:10 4000

117


118


LEHIGH 50:50:10 4000

119


120

PERMISSION TO COPY

In presenting this thesis in partial fulfillment of the requirements for a

master’s degree at Texas Tech University or Texas Tech University Health Sciences

Center, I agree that the Library and my major department shall make it freely available

for research purposes. Permission to copy this thesis for scholarly purposes may be

granted by the Director of the Library or my major professor. It is understood that any

copying or publication of this thesis for financial gain shall not be allowed without my

further written permission and that any user may be liable for copyright infringement.

Agree (Permission is granted.) Viraj Vishwas Deshmukh Student Signature Date 27th July 2007 Disagree (Permission is not granted.) Student Signature Date

in master of science

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