RHEOLOGICAL PROPERTIES OF HIGH-TEMPERATURE A THESIS …

RHEOLOGICAL PROPERTIES OF HIGH-TEMPERATURE

DRILLING FLUIDS

by

RONALD P. BERNHARD, B.S.

A THESIS

IN

GEOSCIENCES

Submitted to the Graduate Faculty of Texas Tech University in Partial Fulfillment of the Requirements for

the Degree of

MASTER OF SCIENCE

Approved

Accepted

December, 1981

30^" • / ^

l 9 ^ l ^- ACKNOWLEDGEMENTS

The writer acknowledges with gratitude the guidance and assis

tance given by Dr. Necip Guven. His sincere interest, criticisms,

and helpful suggestions are in a large measure responsible for the

successful completion of this study. Appreciation is also extended

to Mr. Leroy Carney for his assistance with the analysis of the rheo-

grams and the interpretation of the Theological data gathered.

The writer is indebted to Mr. Robert E. Chumley for his patient

instructive guidance in the operation of technical equipment. I am

also grateful to Dr. A.D. Jacka for his advising comments.

Thanks must also be extended to the many fellow students,

including Fateh Malekahmadi and Li-Jein Lee, who shared my interests

in this subject and rendered invaluable assistance in the work.

The project was financially supported by Sandia National Labora

tories (contract 13-5104), Albuquerque, New Mexico, and by the Center

for Energy Research of Texas Tech University.

11

TABLE OF CONTENTS

Page

ACKNOWLEDGEMENTS ii

LIST OF TABLES iv

LIST OF FIGURES vi

CHAPTER

I. INTRODUCTION 1

II. REVIEW OF PREVIOUS WORK 3

III. MATERIAL AND METHODS OF INVESTIGATIONS 5

IV. ATTAPULGITE BASED MUDS 14

V. SEPIOLITE BASED MUDS 17

VI. FORMULATED HIGH TEMPERATURE MUDS 21

VII. ANALYSIS OF CORE SAMPLES 24

VIII. CONCLUSIONS 27

LIST OF REFERENCES 29

APPENDIX A: TABLES 30

APPENDIX B: FIGURES 46

111

LIST OF TABLES

Table Page

1. Partical size of sepiolite powder 31

2. Partical size of attapulgite powder 31

3. Attapulgite/HÔ rheological data 32

4. Attapulgite/MgClo/HÔ rheological data , 32

5. Attapulgite/CaCl2/H„0 rheological data 33

6. Attapulgite/KCl/H20 rheological data 33

7. Attapulgite/NaCl/HÔ rheological data 34

8. Attapulgite/CaCl^/HÔ rheological data 35

9. Attapulgite/NaCl/H 0 rheological data . 35

10. Attapulgite/MgCl^/HÔ rheological data 36

11. Attapulgite/KCl/HÔ rheological data 36

12. Attapulgite/Mg(0H)2/H20 rheological data 37

13. Attapulgite/Ca(0H)2/H20 rheological data 37

14. Attapulgite/NaOH/H20 rheological data 38

15. Attapulgite/K0H/H20 rheological data , 38

16. Sepiolite/HÔ rheological data 39

17. Sepiolite/MgCl^/HÔ rheological data 39

18. Sepiolite/CaCl2/H20 rheological data 40

19. Sepiolite/NaCl/H 0 rheological data '̂O

20. Sepiolite/KCl/H20 rheological data 41

21. Sepiolite/Mg(0H)2/H20 rheological data 42

22. Sepiolite/Ca(0H)2/H 0 rheological data 42

IV

Table Page

23. Sepiolite/Na0H/H20 rheological data ^^

24. Sepiolite/K0H/H20 rheological data

25. Bulk X-ray analysis of cores

43

44

26. Clay X-ray analysis of cores 45

LIST OF FIGURES

Figure Page

1. Schematic of viscometer 48

2. Consistency curve of Bingham plastic . . 50

3. Interpretation of plastic viscosity, apparent viscosity

and yield point 52

4. Attapulgite/HÔ rheograms 54

5. Attapulgite/HÔ rheograms .'54

6. Attapulgite/MgCl^/HjO rheograms 56

7. Attapulgite/MgCl2/H^0 rheograms 56

8. Attapulgite/NaCl/HÔ rheograms . . . 58

9. Attapulgite/NaCl/H20 rheograms 58

10. Attapulgite/KCl/H20 rheograms 60

11. Attapulgite/KCl/H20 rheograms 60

12. Attapulgite/CaCl2/H20 rheograms . 62

13. Attapulgite/CaCl2/H„0 rheograms 62

14. Attapulgite/Mg(0H)2/H20 rheograms 64

15. Attapulgite/Ca(0H)2/H20 rheograms 64

16. Attapulgite/NaOH/HÔ rheograms 66

17. Attapulgite/K0H/H2D rheograms 66

18. Sepiolite/HÔ rheograms . 68

19. Sepiolite/HÔ rheograms 68

20. Sepiolite/MgCl2/H20 rheograms 70

21. Sepiolite/MgCl2/H20 rheograms 70

VI

Figure Page

22. Sepiolite/CaCl2/H20 rheograms 72

23. 5epiolite/CaCl2/H20 rheograms ,72

24. Sepiolite/KCl/H20 rheograms 74

25. Sepiolite/NaCl/H20 rheograms 74

26. Sepiolite/Mg(OH)2/H2O rheograms 76

27. Sepiolite/NaOH/H20 rheograms 76

28. 5epiolite/Ca(0H)2/H20 rheograms . . . .78

29. Sepiolite/K0H/H20 rheograms 78

30. ITEM 'J' rheogram 80

31. ITEM-'I' rheogram . . . " .82

32. HTM-1 rheogram 84

33. Permeability ratio vs. stagnation 86

34. Low magnification SEM of grains in virgin 1-64 core of

East Mesa 88

35. Flaky illite/smectite mixed layer clays on sand grains . . .88

36. Chlorite rosettes on sand grains 90

37. High magnification clays in 1-64 90

38. Chlorite rosettes and quartz crystals . . . , 92

39. High magnification of chlorite rosette 92

40. Illite/smectite mixed layer 54

41. 2-76 illite/smectite mixed layer ^4

42. Chlorites in pore throats ^^

43. High magnification chlorites 5'6

44. Massive clay covering in pores .98

45. Clays bridging pore gaps - . . . . 98

VI1

CHAPTER I

INTRODUCTION

The behavior of the drilling fluids under high temperature and

high pressure is extremely important for drilling geothermal wells

and for drilling deep wells. Drilling fluids based on fibrous mag

nesium clays (attapulgite and sepiolite) have been found by Guven and

Carney (1979) to remain stable under high temperature and high pres

sures. A systematic examination of rheological properties (viscosity,

fluid loss, gel strength, pH, yield point and cake thickness) of these

fluids is the main subject of this thesis. For this purpose 4 to 5?o

suspensions of these clays were prepared and autoclaved in the tem

perature range 300-800°F (149-427°C) for 9 to 24 hours under pressures

up to 20,000 psi. The rheological parameters of these fluids were

then measured with a FANN 50C high temperature viscometer and with a

FANN 35A room temperature viscometer. Chlorides and hydroxides of the

salts of Na, K, Ca and Mg were also added systematically to these

systems in order to evaluate their effects on the rheology of these

fluids.

Rheological changes in drilling fluids have many effects on the

degree of efficiency with which a fluid performs its primary functions.

With this in mind, the effects of formation damage were also considered

in this thesis. Formation damage occurs when drilling mud invades the

formation and causes a reduction of permeability at the well bore/

formation interface. During drilling, mud invasion and damage occur

with all fluids when the mud column pressure is greater than the for

mation pressure, and it is important that efforts by made to minimize

2 these detrimental effects. In geothermal wells permeability impairment

can be much greater than in most oil or gas wells because of high tem

peratures and complex chemistry of the formation waters. Cores from a

well-known sandstone geothermal reservoir from East Mesa, Imperial

Valley were examined with respect to the pore mineral components in

order to evaluate the effects of drilling fluid invasion. For this

purpose the East Mesa cores were subjected to tests in Terra Tech

Laboratories (University Research Park, Salt Lake City, Utah). The

cores were tested under simulated geothermal conditions of overburden

stress, pore fluid pressures, temperatures, pore fluid chemistry,

and drilling fluid compositions. Permeability impairment of these

cores was then evaluated as a function of drilling mud, temperature,

and stagnation time. The same cores (before and after the tests)

were sent to Texas Tech University for examination of bulk mineralogy,

and pore fill minerals. These examinations were done by x-ray dif

fraction, SEM/EDAX and Transmission Electron Microscopy. The results

are expected to explain the nature and the behavior of pore fill

minerals (especially the clays) during drilling operations and the

invasion of drilling muds into formations.

CHAPTER II

REVIEW OF PREVIOUS WORK

The effects of temperature and pressure on flow properties of clay

based drilling fluids have been studied since the hydraulic aspects of

rotary drilling were recognized.

The rheological properties of bentonite have been evaluated exten

sively, first at room temperature and at atmospheric pressure conditions

with a simple concentric rotational viscometer (Hauser and Reed, 1937).

Later, aspects of bore-hole drilling conditions were analyzed by testing

bentonite fluids to high temperatures, as high as 180°F (Srini-Vasan and

Gatin, 1958). Annis (1962) raised temperatures to 300°F and confining

pressures to 1000 psi by means of the FANN 50 viscometer. Likewise,

rheologic testing (Hiller, 1963) evaluated properties of bentonite

based mud at temperatures of 350 F and pressures of 10,000 psi. Sinha

(1969) furnished a new technique to determine the equivalent viscosity

of drilling fluids under high temperature and high pressures. Sinha's

procedure maintained a constant temperature and allowed the pressure

to vary at each desired temperature level. Concepts of evaluating

drilling fluid performance under conditions that simulate those in well

bores have been intensively studied and tested. These tests revealed that

bentonite based muds were the most proficient fluids for improving the

viscosity and controlling the filtrate loss. As drilling commenced in

coastal brines and offshore in salt dome regions bentonites became less

effective, because in salt water bentonite loses its ability to swell,

and additional treatment became necessary.

In Florida, Cross and Cross (1937) found that using attapulgite

would thicken a mud regardless of the salt content. But at high tem

peratures this fluid lacks important rheologic properties. Carney and

Meyer (1976) published results in reference to investigations of sepio

lite as a clay base for drilling fluid. This report evaluated the

rheologic parameters of the sepiolite fluids and introduces them to

the drilling industry for uses in high temperature drilling conditions.

Further investigations (Bannerman and Davis, 1978) supported the fact

that sepiolite based drilling muds remained stable under high pressure

drilling conditions.

CHAPTER III

MATERIALS AND METHODS OF INVESTIGATIONS

Sample Description

Clays used in preparation of drilling fluids in this investigation

are sepiolite and attapulgite. The sepiolite, a product of Industrial

Mineral Ventures Co. is from Aschenbrenner Deposit, Nye County, Nevada.

X-ray diffraction of the clay shows about 2-3% dolomite as an impurity.

Particle size distribution of the powdered sepiolite is given in table 1.

The attapulgite, a product of International Minerals and Chemicals, is

from the attapulgite deposits in Georgia and Florida and is known as

"Floridian Attapulgite 150". Unlike sepiolite, attapulgite contains

large amounts of impurities. X-ray diffraction indicates, 15-20% smec

tites, 5?o illite, 5?o calcite in the clay fractions. In coarser fractions

quartz is seen as predominating impurity. Particle size distribution of

the powdered attapulgite sample used in this study is shown in Table 2.

A 5?o weight-volume clay-distilled water suspension was prepared in

a Hamilton Beach blender for 15 minutes. Five hundred milliliters of the

mud was then transferred to an autoclave cell and was heated to a desired

temperature and pressure. After autoclaving the muds rheologic properties

were tested by means of the FANN 50C high-pressure/high-temperature visco

meter, the FANN 35A viscometer, the Baroid high-pressure/high-temperature

filter press, the Baroid standard filter press, and Baroid 600-20 pH meter.

In addition to the clay suspensions tested, solutions containing

chlorides and hydroxides also were examined by the above technique.

One gram of chloride or hydroxide of Na, Ca, K, or Mg is mixed with 4

grams of clay and added to 100 ml of distilled water to form a 5?o

weight/volume solution. These systems are tested to evaluate the

effects of the chemicals on rheology of the fluids.

Methods of Analysis

High Temperature and High Pressure Autoclave.

The autoclave was designed and manufactured by Autoclave Engineers,

Erie, Penn. The cell itself has a sample capacity of 500 ml and is cap

able of reaching 1000 F and 20,000 psi. The autoclave uses Autoclave

Engineers self-sealing closure metal seals, which seal against high

pressure by the use of unsupported area principle. This principle

enables internal pressures to force the cover against the seal ring,

which presses the seal ring against the body. Slight variation of the

angles between contact surfaces of the body and the seal ring results

in a line contact between the two surfaces. Autoclave's cell was used

for static heating at high temperatures (400-800 F) under the confining

pressures of 10,000 psi. The pressure is initially produced by a

Haskel air driven liquid pump #DHW 300. The temperature is maintained

by an Autoclave Engineers temperature controller which consists of

Barber-Colman, Model 520 analog and digital set point controllers.

Temperature and pressure are monitored and recorded automatically by a

Barber-Colman single pen strip chart recorder, in degrees Fahrenheit

and pounds per square inch. The sample was heated at a rate of 250 F/

hour to the desired temperature and the temperature was maintained for

6 hours, when this was accomplished the autoclave was cooled in air for

14 hours. The sample was then transferred for further testing.

FANN 50C Viscometer

The FANN viscometer model 50C is a concentric-cylinder, rotational

type viscometer. The viscometer is equipped with a standard rotor cup

7 with a sample capacity of 50 ml and a rotor cup speed of 0-600 RPM.

The viscosity is calibrated by shearing a thin film of the liquid be

tween concentric cylinders. The outer cylinder can be rotated at a con

stant rate and the shear stress measured in terms of the deflection of

the inner cylinder (or bob), which is suspended by a torsion spring,

(Fig. 1). The sample can be heated up to 500°F by an oil bath which is

also used for cooling the sample. Pressures in the sample cup reach

1,000 psi. The temperature and viscosity of the mud are automatically

recorded by a Houston Instruments two pen, bichannel strip recorder.

FANN 35A Viscometer

Gel strength, yield point and plastic viscosity are measured at

room temperature and atmospheric pressure with a FANN 35A viscometer; it

is a concentric-cylinder, rotational type viscometer which operates on

the same principle as the FANN 50C. The FANN 35A is operated by a two

speed, 100 volt synchromous motor. The instrument is direct reading and

can function at six rotation speeds.

Baroid Hiqh-Pressure/Hiqh-Temperature Filter Press

The filter press is designed for testing fluids at elevated temper

atures and pressures. Mud is placed into a 250 ml filter cell and is

heated to 300°F. Pressure is increased by 600 psi by pressurized nitro

gen gas. A back pressure receiver is maintained at 100 psi as filtrate

is collected. The filtrate test is run for 30 minutes, or until blow

out, upon which the volume of filtrate is recorded and the filter cake

thickness is measured and reported in thirty seconds of an inch.

Baroid Standard Filter Press

This unit consists of a fluid cup supported by a frame, a filtering

medium, a pressurized nitrogen gas cylinder and regulator. A graduated

cylinder is used to catch and measure the discharged filtrate.

The filter test requires 100 psi pressure for 30 minutes, or until

blowout occurs, upon which the filtrate is measure and recorded. The

filter paper with the mud cake deposited on it is removed from the pres

sure cell and the mud cake thickness is recorded in thirty seconds of an

inch.

Baroid Methylene Blue Test Kit

The cation exchange capacity of a clay suspension has been evaluated

by means of methylene blue adsorption. This method involves the titration

of an aqueous dispersion of clay with methylene blue solution containing

3.74 grams USP grade methylene blue per liter which reacts with the clays

by cation exchange. The Baroid test kit contains all equipment needed

for CEC evaluation. A methylene blue dye (1 ml = 0.1 milliequivalent) is

added to a dilute suspension (0.05 gm/40 ml HÔ). The suspension is aci

dified with 0.5 ml of 5N sulfuric acid, then 3% hydrogen peroxide is

added for the removal of organics. The solution is boiled for ten minutes,

and then cooled before adding the dye. The suspension is titrated syste

matically with increments of 0.5 ml of methylene blue, after which, one

drop of the suspension is removed and placed on a filter paper. An end

point is indicated when excess dye appears as a sky-blue coloration radi

ating from the normally heavily-dyed solids in the center. From this pro

cedure the cation exchange capacity of the clays in the drilling fluids

may be expressed as milliequivalents of methylene blue dye solution per

100 grams of clay used (0.5 grams) in suspension.

Testing Drilling Fluids

Specific physical properties of a drilling fluid must be maintained

if the mud is to sufficiently perform its functions. Standard tests are

used to evaluate the fluid and determine the condition of the mud. Tests

used in this work are described below.

Viscosity - Yield Point

Determination of viscosity in the samples tested is evaluated by

concentric rotary viscometer. When testing a drilling mud the outer

sample cup is rotated, which in turn shears the mud. As the mud shears

around the "bob", it is caused to rotate (except for slight slippage)

until the torque in the spring develops a shear stress at the contact of

the mud sample and the "bob". This shear stress is more than the shear

strength of the fluid, laminar flow begins at the surface of the "bob"

and, with a constant rotation maintained, the flow proceeds away from the

"bob" until the complete sample is in laminar flow. With continuous

rotation at a constant speed, the torque increases in a linear way after

the critical torque is achieved, as shown in Figure 2. The critical

torque and the slope of the laminar flow line is dependant on the rheo

logical characteristics of the drilling mud. The viscometer used (FANN

35A) follows the designs of Savins and Roper (1954), which is a direct-

reading viscometer that enables the plastic viscosity and yield point to

be calculated very simply from two dial readings, one at 600 RPM and the

other at 300 RPM. By theory, Savins and Roper (1954), calculated the

plastic viscosity to be the dial reading at 600 RPM minus the dial

reading at 300 RPM. The yield point may be calculated by subtracting

the plastic viscosity from the 300 RPM. The equations below give plastic

viscosity in centipoise and yield point in pounds per 100 square feet:

The apparent viscosity (shear stress divided by shear rate) may

also be calculated when the following information is known:

2 1 dial unit = 5.11 dynes/cm (shear stress)

1 RPM = 1.7033 reciprocal seconds (shear rate)

with 300 centipoise per unit per RPM

so:

300 X Units read RPM . apparent viscosity =

RPM

the standard method of measuring apparent viscosity is with rotation of

600 RPM so the equation is simplified to:

units read 600 RPM apparent viscosity = -

A graphic translation of the calculations for yield point, plastic vis

cosity and apparent viscosity is shown in Figure 3.

Rheology tests are used as a method of evaluating drillings so

that proper treatments may be in order. Plastic viscosity is the resis

tance of flow caused by mechanical friction between the particles in a

drilling fluid and by shearing of the liquid phase of the mud. So in

general, plastic viscosity depends on the concentration of the solids

put into the mud. The yield point is dependant on the electro-chemical

charges in the mud under flowing conditions. Particles may be charged

so that they attract each other giving way to a high yield point, or

particles may repel one another making the yield point lesser. In

either case a yield point may be regulated by the use of chemical

additives. If parameters are maintained for the yield point and the

plastic viscosity, proper treatments can be derived, and the apparent

viscosity may be easily regulated.

Gel Strength

Gel strength is the measuring of thixotropic properties of a drilling

fluid under non-flow conditions, while the yield point measures these

properties under flow conditions. However, both the yield point and gel

strength deal with the attractive forces between solid particles in the

mud.

Generally, gel strengths are of two types, a weak-fragile gel strength

or a strong-progressive gel strength. A weak gel strength seems to be

associated with a thin mud and initially has a high gel strength which

is very easily broken and will increase only slightly with increase of

stagnation time. A strong gel strength is associated with thicker muds

and on initial rotation is hard to break. The longer the stagnation

time the greater the gel strength becomes.

Both yield point and gel strength result from flocculation forces

and are related to thixotropic properties, so as the yield point decreases

the gel strength generally decreases. Gel strengths are determined by

the FANN 35A viscometer at 3 RPM. Mud is allowed to stagnate for 10

seconds, then the outer cup is rotated at 3 RPM - by observing the dial

on the viscometer the maximum deflection (before the gel breaks), is

recorded. The same procedure is repeated after allowing the mud to

stand for 10 minutes, the gel strengths are reported in pounds per

100 square feet.

Filtration

The filtration properties of drilling muds are a measure of the ability

of the solid phase of a fluid to form a thin, low-permeability cake of

filtered solids. The less permeability the cake has, the thinner the

cake will form. This property is dependant on the size, type and volume

12 of colloidal material in the fluid. The loss of fluid from the mud is

dependent on permeability of the filter cake, permeability of the for

mation being drilled and pressures at the bore hole-formation contact.

When minimum water loss is maintained, a thinner filter cake forms and

drilling problems are minimized. If a thick filter cake develops then

the effective size of the bore hole is reduced and various problems are

created, such as an increase of torque on the rotating pipe, excessive

drag when the pipe is pulled and adherence of the pipe to the wall.

Also formation damage may occur due to filtrate and filter cake inva

sion. In the evaluation of filtrate properties both the low temperature/

low pressure test and the high temperature/high pressure tests are used,

because in deep drilling low pressure/low temperature tests are misleading.

Hydrogen Ion Concentration

The hydrogen ion concentration is the reciprocal of the hydrogen ion-

concentration in grams mols per liter. To measure pH a glass electrode

meter was used. The meter consists of: 1) a glass electrode made of

a thin-walled bulb of special glass; 2) a reference electrode consisting

of a saturated calonel cell; 3) an amplifier, for amplifying the poten

tial difference between the mud sample and the glass electrode; 4) a

meter reading in pH units; and 5) a standard buffer solution for in

strument calibration. The effect of pH on muds is influential on clay

dispersion because of its effects on base exchange equilibrium, but

the electro-chemical conditions in a system vary from fluid to fluid,

so the effect of changing pH also will vary. Systems with high pH

filtrate may dissolve formation cements such as amorphous silica,

releasing fine particles which may block pores, eventually causing

impermeability.

13

Cation Exchange Capacity

The total amount of cations adsorbed, expressed in milliequivalents

per 100 grams, is called the cation exchange capacity, (C.E.C.). The

value of the C.E.C. varies slightly even within a single clay mineral

group. The C.E.C. of a clay and the species of cation exchanged are

indicators of the colloidal activities of clays. Montmorillonites

have a high C.E.C. (70-130 meq/100 gms) because this clay swells and

suspensions thicken with even low concentrations of this clay, and the

interlayer cations are easily exchanged with saturating cations in the

solution. On the other hand, kaolinite is very passive and adsorption

of cations is relatively low, because adsorption occurs mainly at the

surface areas.

There are generally three causes for C.E.C. of clay minerals;

first substitutions within the atomic lattice structures, as in the

smectites. Secondly, broken bonds around edges, which give rise to

unbalanced charges to such edges. Thirdly, hydroxyIs or hydrogen is

exchanged with a saturating cation which is introduced to the solution

(Grim, 1968).

14 CHAPTER IV

ATTAPULGITE BASED MUDS

Effects of Chlorides on Attaoulqite Based Muds

Muds in this system after high temperature treatments (400 -600 F)

have been tested with respect to their rheologies with the FANN 50C

viscometer from ambient temperatures to 500 F. These tests reveal vis

cosity changes with respect to temperature whether it be related to aging

in the autoclave, or produced during shearing in the FANN 50C viscometer.

The rheogram of the original attapulgite fluid (7gms attapulgite/

100 ml H2O) with no pretreatment is seen in Figure 4 (curve A). This

shows a viscosity "hump", with a maximum viscosity of 4.8 centipoise,

and a minimum viscosity at 500 F of 2.0 centipoise. Similarly, the

sample autoclaved to 400°F reveals a viscosity "hump", but the maximum

viscosity reached is only 4.0 centipoise. Notice that rheograms of

samples prepared at above 500°F express very low viscosities.

In reference to plastic viscosity, yield point, gel strength and

filtrate tests. Table 3 summerizes data collected from the pure atta

pulgite sample. The API fluid loss is measured to be 182 ml for the

attapulgite prepared at 70°F. In contrast, the sample autoclaved to

600°F has a filtrate loss of 304 ml, much too high for use as a drilling

fluid. In the attapulgite/MgCl2 systems the rheological properties

improved slightly, the yield point for all muds increased (Table 4),

and fluid loss shows better control at high temperatures. The rheograms

in Figure 7 show higher viscosities, as the scale in centipoise has

a maximum of 15- The viscosity humps displayed by the rheograms are

thought to be caused by changes in mineralogy and morphology due to

hydrothermal reactions in the system (Guven and Carney, 1979). The

15 remaining systems with NaCl, KCl, and CaCl2 influence attapulgite in

similar ways. In Tables 5-11 the plastic viscosities remain fairly low,

as does the yield point. At elevated temperature API filtrate volumes

become very high and are unacceptable for use in high temperature dril

ling muds. In Figures 8-13 the rheograms exhibit low and straight line

viscosity and are much lower than what is to be observed in the sepiolite

systems.

Effects of Hydroxides on Attapulgite Based Muds

The behavior of attapulgite upon the addition of hydroxides differs

greatly from that of an attapulgite/chloride system. The evidence of

the viscosity hump is much more prominent (Figure 14) in the attapulgite/

Mg(OH)« system, than in the previous systems. Even at elevated tempera

tures of 600°F (curve D) the viscosity hump is still a predominant feature

on the rheogram. Table 12 fluid loss data reveals significant control

compared to that of the attapulgite/chloride systems. At 600 F the

sample maintains a plastic viscosity of 14.0 centipoise.

The attapulgite/Ca(0H)2 samples remain moderately stable with re

spect to temperature change (Figure 15). The curves display more of

a change due to temperature induced thinning, than due to a change in

morphology or mineralogy. Table 13 views the rheological properties of

attapulgite/Ca (OH)2 system. At the temperature of 500°F plastic vis

cosity, gel strength and yield point are improving slightly, but at

600°F the system seems to lose properties needed as a high temperature

drilling fluid.

Attapulgite/NaOH/HÔ has properties much like those of the atta

pulgite/Ca (OH) 2 system. Rheograms in Figure 16 reveal gently sloping

curves, with viscosities of intermediate temperatures in the 8-16

16

centipoise range. Also noticed is the absence of large viscosity

humps without which easy estimation of viscosity values may be

assessed for given temperatures. The rheological data collected on

the attapulgite/NaOH sample is presented in Table 14. The values

of plastic viscosity, yield point, and gel strength are much higher

than any of the other systems. Also at 600 F the fluid loss volume

is high, but chemical or mineral treatment will solve problems of

this kind.

In the remaining attapulgite system, attapulgite/KOH, the

rheological data of intermediate and high temperature tests are very

poor. Although the fluid loss control of these samples is not too

damaging, the plastic viscosity, yield point, and gel strengths are

extremely low, as seen in Table 15. Figure 17 gives the curves

representing changes in viscosity caused by increase of temperature,

B,C, and D are from samples autoclaved at 400 , 500 and 600 F;

the viscosity of muds at viscometer temperatures of 500 F are less

than one centipoise. Curve A, depicts the rheology of the sample

attapulgite/KOH, mixed at room temperature. The curve is comparible

to that of curve A in Figure 16, having very high initial viscosities

and a final viscosity of 8 centipoise at 500 F.

CHAPTER V -̂^

SEPIOLITE BASED MUDS

Effects of Added Chlorides on Sepiolite Based Muds

The representative viscosity curves, graphically describing the

rheological behavior of the sepiolite/chloride based muds, are shown in

Figures 18-25. Major differences in viscosity may be observed from

sample to sample. Pure sepiolite fluids, shown in Figures 18 and 19,

reveal a viscosity "hump" at viscometer temperatures of approximately

300 F, with exception of the muds autoclaved at 700 and 800 F (Figure 18,

curves B and C). This "hump" in the rheograms is seen throughout the

data and is attributed to the mineralogical change of sepiolite during

hydrothermal conditions as described by GCiven and Carney (1979).

In Figure 18, curve A represents the sepiolite mud prepared at

room temperature, and this rheogram exhibits a very large change in

viscosity as compared to the sepiolite/chloride mixtures run under the

same conditions. The sepiolite/NaCl/H20 system (Figure 24, curve A)

prepared at room temperature, does not give the viscosity "hump", but

as samples are autoclaved to elevated temperatures of 400 , 500 and

600°F, the "hump" becomes well developed. Similar results are obtained

by testing sepiolite/KCl/H20 mud system, as shown in Figure 23. These

"humps" become narrow, and the maximum and minimum viscosities are

greater than those of the other sepiolite systems.

In Figures 20-23, the MgCl2 and CaCl2 systems are illustrated.

The rheograms lack the "hump" observed in the previous mixtures, and

overall the viscosities are less than those illustrated in the former

figures.

18 Reactions in the above systems show that major viscosity changes

in sepiolite take place when the temperature is raised to 400°F, and

when the sample is autoclaved at temperatures above 400°F for long

periods of time (16-24 hours) the viscosity changes are increased, as

observed by the FANN 50C. The data obtained by the FANN 35 viscometer

and Baroid filter presses for the sepiolite/chloride muds are given

in tables 16-20. The data on the pure sepiolite mud is summarized

in Table 16. Values for plastic viscosity, yield point, and gel strength

for samples increase in the temperature range from 70° to 500°F. Above

500 F all of these properties begin to decrease showing a thinning in

the sample.

The data in Table 17 illustrates properties of the sepiolite based

mud containing 1% MgCl2. As seen, the addition of MgCl2 effects the

yield point and gel strength of sepiolite in a negative way, keeping

these values much lower than the original sepiolite mud. Also as noted

in Table 17, the gel strength and yield point do not decrease at 600°F

as they did in pure sepiolite (Table 16).

When CaCl2 was added to the mud, the plastic viscosity and C.E.C.

becomes comparible to those of the sepiolite/MgCl^ system. Similarities

are also noticed between these two systems in the rheograms (Figures 20-23)

Table 19 clearly shows a major increase of gel strength in sepiolite/

NaCl/H20 mud at elevated temperatures. Notice the change in ten minute

gel strength between the sample autoclaved at 500 F and the sample which

was autoclaved at 600 F; the increase is almost five fold. Again, such

a change may correlate with a detectable change in the morphology or

structure of the sepiolite as it undergoes hydrothermal transformation

(Guven and Carney, 1979).

19 The effect of temperature is seen in all parameters tested. The

increasing yield point and gel strength with temperature are observed

in all sepiolite/chloride muds. This data in comparison to that obtained

from the attapulgite/chloride muds, shows the sepiolite maintains acceptable

rheological properties for the use of high temperature drilling muds.

Effects of Hydroxides on Sepiolite Based Muds

In order to determine the effects of various hydroxides on rheological

properties of sepiolite muds, four sepiolite/hydroxide systems were formu

lated. Tables 21-24 give fluid loss, gel strength and flow properties

for these systems, while Figures 26-29 illustrate the viscosity changes

which take place during hydrothermal testing. Reactions in the sepiolite/

Mg(0H)2 system differ from those in the sepiolite/MgCl2 system. The pre

sence of Mg(0H)2 instead of MgCl2 seems to be more favorable for the for

mation of the viscosity "hump" as seen in Figure 26. In comparing the two

systems (Figure 7 vs. Figure 26) it is obvious that the Mg(0H)2 has con

tributed to the increase of viscosity. The Mg(0H)2 systems have a range

from 4-35 centipoise, whereas MgCl^ system lies within the 1-10 centi

poise range. An explanation for such a change may be related to the

transformation of sepiolite to smectite (Guven and Carney, 1979).

In sepiolite/Ca(0H)2 systems hydrothermal treatment of 400°F reveals

a viscosity hump at test temperatures between 400 and 450 F (Figure 27,

curve B). This viscosity change probably is caused from an increasing

amount of sepiolite in the mixture altering to smectite. In the system

heated to 500°F, the hump appears less intense (Figure 27, curve C),

but the overall viscosity is greater than that seen in curves A,B, or D.

The rheologic data summarized in Table 22 reveals that a substantial

amount of flocculation takes place in this system. With API filtrate

volumes between 410, and 120 ml, and cake thicknesses up to 3/4 of an

inch, it is evident that chemical treatments would be necessary before

sepiolite/Ca(OH)2 system could be used.

Hydrothermal treatments of sepiolite/NaOH mixtures produced data

which depicts rheological properties that more closely approximate those

required for a high temperature drilling fluid. As seen in Figure 27,

the rheograms are more passive than in previous systems. The initial

viscosities are between 30 and 45 centipoise, and the viscosity of each

sample at temperatures of 500 F is between 8 and 20 centipoise. With

viscosity values as observed and with rheograms lacking the intense

viscosity hump, viscosities for a given temperature may be easily

estimated.

In addition to acceptable rheograms, the sepiolite/NaOH system

possesses low API, and HT-HP filtrate values as seen in Table 23. As

illustrated in Table 23, the yield point and gel strengths remain high,

unlike those listed in Table 24 for the sepiolite/KOH systems. The

plastic viscosity, yield point and gel strength properties drop sharply

at temperatures above 400°F. At 600°F the fluid is extremely thin

and filtration properties in the mud are lost. The rheograms reveal

low viscosities in Figure 29 for muds autoclaved to 500°, and 600 F

(curves C and D). With such low viscosities and poor rheological

values, it is obvious that extensive chemical treatment is necessary to

enhance preferred properties in the system.

CHAPTER VI 21

NEW FORMULATIONS FOR HIGH-TEMPERATURE MUDS

After evaluating the data collected from attapulgite and sepiolite

based muds, new high-temperature mud are formulated by adding polymers.

Rheological measurements on these new drilling fluids are presented in

Figures 30-32. Sample labeled, Fluid "J" is a mud formula consisting

of an attapulgite clay base, with 4#/bbl high mole weight polymer, and

iy//bbl low mole weight polymer added. Figure 30 shows the continuous

change of the viscosity with temperature. The viscosity, at a constant

shear of 1022 sec~ , ranges from a maximum of 25 centipoise at ambient

temperature to a minimum of 3 centipoise when temperatures reach 500 F.

The results of an API high-pressure/high-temperature filtrate test

give a 42 cc fluid loss and a filter cake thickness of 3/32 of an inch.

The filtrate test was run for 30 minutes at 500 differential psi, and

300°F, no blowout occurred. The plastic viscosity was found to be 23

centipoise at room temperature and atmospheric pressure. The calcu

lated yield point is nine pounds per hundred square feet. The recorded

gel strengths are less, having a ten second gel strength of 2 pounds

per square foot and a ten minute gel strength of 3 pounds per square

foot.

The second sample evaluated as a high-temperature mud was Fluid "I",

this mud consisted of a sepiolite clay base, with 4#/bbl high mole weight

polymer and l#/bbl low mole weight polymer added. Data collected by

the FANN 35 viscometer, and high-pressure/high-temperature filter press

are similar to that of Fluid "J". The plastic viscosity for Fluid "I"

22 is 30 centipoise, the yield point is 16 pounds per square foot and the

gel strengths are 4 pounds per square foot, and 6 pounds per square

foot for ten second, and ten minute tests respectively. Filtrate pro

perties from high-temperature/high-pressure tests give a fluid loss

of 40 ml, and a cake thickness of 3/32 of an inch. The rheogram plot

ted for the sample is shown in Figure 31. A maximum viscosity is seen

at 70 with a value of 38 centipoise. In effect to temperature thinning,

the viscosity decreases to 7 centipoise before the rheogram starts the

viscosity hump. The viscosity hump has a beginning temperature of

400 F, and shows a viscosity maximum of 15 centipoise at about 470 F,

after which the viscosity drops to 8 centipoise.

The third, and last sample tested was a complete formulation, and

is designed to retain critical rheological properties at elevated tem

peratures. The components of this drilling fluid per standard 42 gal

lon barrel is as follows:

Bentonite 5.0 lbs.

Sepiolite 15.0 lbs.

Brown Coal 20.0 lbs.

Sodium Polyacrylate 2.5 lbs.

Sodium Hydroxide 2.0 lbs.

The major difference found in this mixture is the addition of bento

nite clay. The use of bentonite as an additive is effective in main

taining filtration control. The twenty pounds of brown coal (lignite)

is a major component designed especially for geothermal drilling, be

cause it provides a convenient product for improving the filtration

properties in geothermal drilling. Sodium polyacrylate is also used

in controlling the filtrate loss of HTM-1. The sodium hydroxide,

used in water muds for the purpose of raising the pH and to increase

the solubility of lignite (brown coal). The behavior of this sepio- 23

lite/bentonite based mud is qualitatively similar to that of Fluid "I"

of Figure 31. The initial viscosity of HTM-1 is 10 centipoise higher,

displaying a value of 49 centipoise, but the final viscosity at 500°F

is very similar between the two systems Fluid "I", and HTM-1 (Figure

31 vs. Figure 32). The main difference between the two samples is that

the change in viscosity during the hump period is much more for the HTM-

1. The differential hump height in Fluid "I", is 8 centipoise, and in

HTM-1 the change is 15 centipoise. Both formulas show that control

over undesireable properties may be obtained by the addition of chemi

cal, and mineral treatments.

24 CHAPTER VII

ANALYSIS OF CORE SAMPLES

As seen by the previous chapters special drilling fluid formula

tions are required to cope with the high temperatures and circulation

requirements of deep and geothermal wells. The viscosity and rheo

logical properties of such fluids were tested and evaluated under

high-pressure/high-temperature conditions and were found to be suitable

for drilling purposes.

For further testing, samples were prepared from cores, by Terra

Tek, Inc. These cores were taken from a geothermal well in East Mesa,

California, and saturated with a solution representative of the parent

environment. An initial permeability measurement was made on samples

at simulated in place borehole conditions, including overburden pres

sure (5,000 psi), pore fluid pressure (2,165 psi) and temperature

(390°F). All permeability measurements were made in the direction of

backflow. The cores were then subjected to simulated circulation and

stagnation of drilling muds. After tests were completed the cores

were then measured for permeability change due to invasion of drilling

fluids. The results of extended time exposures of a sepiolite/ben-

tonite based drilling mud at both 212°F and 392°F reveal almost a

linear decrease of permeability at a ratio of 1.3?o per hour. Signi

ficant permeability impairment occurs at stagnation times less than

12 hours at 212°F. A plot of permeability vs. stagnation time is

seen in Figure 33. Upon completion of permeability tests, the cores

were then brought to Texas Tech University for mineralogical examina

tion by means of x-ray diffraction and scanning electron microscopy,

(SEM).

The samples consisted of 3 cores, 1-64, 2-64 and 2-76, and each

core is 4 inches long. Samples 2-64 and 2-76 are two inches in dia

meter and sample 1-64 is one inch in diameter. To standardize the

analysis, each core was cut into one inch sections and labeled A, B,

C and D, with A being the core end which was in direct contact with

the mud. The samples were then prepared for bulk powder x-ray dif

fraction, the results are given in Table 25. Evaluation of the less

than 2 micron clay analysis by means of x-ray diffraction is given

in Table 26.

In core 1-64, as seen in the collected data, the mineral content

is homogeneous, with very slight variation in chlorite and feldspar

content. The clay minerals are illite/smectite mixed layers and

chlorites. Relative amounts of these components show a small varia

tion between the four sections 1-64A, 1-64B, 1-64C and 1-64D. The

SEM analysis reveals the morphology of these clays. The micrographs

in Figures 34-37 show the composition of core 1-64. In Figure 34,

individual sand grains (quartz and feldspar) are observed. Most of

these grains are coated with fine materials which are better charac

terized at high magnifications. Figure 35 shows sand grains with

fine illite/smectite mixed layers and hairy illite. Figure 36 illus

trates the covering of chlorite rosettes. An excellent example of

these three clays may be seen in Figure 37, where typical images of

chlorite rosettes, illite laths and flaky illite/smectite mixed layers

grow together. Another view of other chlorite rosettes is presented

in Figure 38 along with secondary quartz. A higher magnification is

seen in Figure 39. These clays are well known for their water-sensi

tivity (i.e. they migrate easily in the pores of the reservior rock

25

26 and plug the pore throats). In fact, core 2-76 with much formation

damage, displays exactly the same clay minerals around the sand grains

and in the pores. Similar observations were made on core 2-64.

As in the virgin core 1-64, the clays in the tested cores 2-64

(tested at 392°F) and the 2-76 core (tested at 212°F) contain illite/

smectite mixed layers and chlorites. The SEM micrographs of cores

2-64 and 2-76, as compared to those of 1-64, show that the clays coating

the sandstone grains are thicker and the morphology is much more mas

sive than that of the flaky-hairy illite/smectite mixed layers in 1-64.

In comparing Figure 40 of core 1-64 to Figure 41 of core 2-76, the clays

in the virgin core are fragile and flaky, while those in the tested

cores are more massive and dense. Figure 42 shows individual sand

grains which are heavily coated with illite/smectite mixed layers and

dense chlorite rosettes. In this figure notice that the clays are

thickest at the pore walls. In Figure 43, a closer look at the clays

shows a less fragile morphology than that of clays in core 1-64.

Close examination of the pore linings shows large amounts of illite/

smectite mixed layers causing formation damage due to their swelling

in the sandstone as can be illustrated by Figures 44 and 45.

This analysis reveals that the clay content in cores 2-64 and 2-76

consists of illite/smectite mixed layers and chlorite rosettes. The

pore spaces and gaps between grain boundaries show large amounts of

parent clays invading the sandstone voids.

It is important to note that these clays are distinctly different

from the clays in the high-pressure/high-temperature formulated dril

ling fluids, in which sepiolite and bentonite are the predominant com

ponents in a ratio of 3 to 1 respectively.

CHAPTER VIII 27

CONCLUSIONS

The flow properties of fibrous clay based drilling muds during

hydrothermal conditions have been tested and evaluated. The rheolo

gical data derived from FANN 50C viscometer and from a combination of

other known techniques allows comparible examination of clays used at

high temperatures. By tracing rheological changes in clays subjected

to hydrothermal treatments, with and without the addition of salts

and hydroxides of sodium, potassium, and calcium and magnesium, condi

tions under which the fluid thickens and thins and the environment in

which the mud completely gels and loses its fluidity may be better

understood.

An overall examination of sepiolite and attapulgite muds reveals

that sepiolite provides more filtration control, a longer lasting vis

cosity at elevated temperatures and gel strengths that do not increase

or drop below operational limits. Furthermore, using sepiolite in

combination with Wyoming bentonite and polymers a drilling fluid can

be formulated, that after heating to temperatures above 600 F, will

maintain very stable viscosity and fluid loss control.

As an option to sepiolite, attapulgite clay undergoes changes

during hydrothermal treatments which are less suitable for the use as

a high temperature drilling fluid base. As described by Guven and

Carney (1979), attapulgite converts to a smectite, when subjected to

elevated temperatures (4Q0°-600°F), made of small platelets, rather

than thin flaky films of common smectites. The altered attapulgite

develops muds that display very low terminal viscosities, and the

fluid loss control, after high temperatures, is very low. With the

addition of chlorides and hydroxides, the attapulgite system shows

little versatility for environmental acceptability.

The research that has been conducted provides insight to the

future development of high temperature drilling fluids and displays

progress towards the illumination of detrimental hydrothermal reactions

within mud systems. By the addition of chemical and mineral compo

nents, these problems may be solved. Further testing of such formulas

should increase the efficiency with which a fluid performs its primary

functions, such as: 1) removal of cuttings from the bottom of the

hole, 2) cooling and lubricating the bit and drill string, 3) lining

the borehole with an impermeable cake, 4) controlling subsurface pres

sures and 5) holding cuttings and weight materials in suspension when

circulation is interrupted. It is obvious that the drilling fluid

plays a major role in the search for future energy.

Sandstone cores from a geothermal reservoir were examined with

respect to authigenic pore mineral components in order to evaluate

the effects of drilling fluid invasion and the possibility of mud da

mage to the reservoir. Analyses of the cores revealed that muds,

formulated and tested in the laboratory, performed well under bore

hole conditions. The porosity and permeability damage were probably

caused by swelling of illite/smectites already found in the given

formation.

The above evidence concludes that high temperature muds may be

effectively formulated for use in drilling of geothermal and other

deep wells.

28

29 LIST OF REFERENCES

Annis, M.R., 1967, High-Temperature Flow Properties of Water-Base Drilling Fluids, SPE 1698.

Bannerman, J.K., Davis, N., 1978, Sepiolite Muds Used for Hot Wells, Deep Wells, Oil and Gas Journal, February 27, 1978, pp. 144-150.

Carney, L., Meyer, R., 1976, A New Approach to High Temperature Drilling Fluids, SPE 6025.

Cross, R. , Cross, M.F., 1937, Method of Improving Oil-Well Drilling Muds, U.S. Patent No. 2,094,319 (September 28, 1937).

Gray, G., Darley, H., Rodgers, W., 1980, Composition and Properties of Oil Well Drilling Fluids. Gulf Publishing Co., Houston.

Grim, R.E., 1968, Clay Mineralogy. McGraw Hill Book Co., New York.

Guven, N., Carney, L., 1979, The Hydrothermal Transformation of Sepiolite to Stevensite and the Effect of Added Chlorides and Hydroxides, Clays and Clay Minerals, Vol. 27, No. 4.

Guven, N., Carney, L., 1979, Investigation of Changes in the Structure of the Clays During Hydrothermal Study of Drilling Fluids, SPE 7896.

Hauser, E.A., Reed, C.E., 1937, The Thixotropic Behavior and Structure of Bentonite, J. Phys. Chem., Vol. 41 (1937), pp. 910-934.

Hiller, K.H., 1963, Rheological Measurements of Clay Suspensions at High Temperatures and Pressures, J. Petrol. Technol., (July, 1963), pp. 779-789.

Savins, J.G., Roper, W.F., 1954, A Direct Indication Viscometer for Drilling Fluids, API Drill. Prod. Prac., pp. 7-22.

Sinha, B.K. , 1969, A New Technique to Determine the Equivalent Viscosity of Drilling Fluids Under High Temperatures and Pressures, SPE 2384.

Srini-Vasan, S., Gatlin, C., 1958, The Effect of Temperature on the Flow Properties of Clay-Water Drilling Muds, AIME Tech. Note, No. 2025, pp. 59-60.

30

APPENDIX A

TABLE 1

Size of particles which make up sepiolite powder.

Greater than 420 micron - 4.7%

419 - 250 micron - 12.8%

249 - 177 micron - 16.0%

176 - 149 micron - 5.6%

148 - 125 micron - 6.7

124 - 105 micron - 6.5

104 - 88 micron - 8.3

87 - 74 micron - 4.5

73 - 63 micron - 3.8

Less than 62 micron - 31.1% /O

TABLE 2

Size of particles which make up attapulgite powder.

Greater than 149 micron - 2.2%

148 - 125 micron - 4.6%

31

124 - 105 micron - 6.5

104 - 88 micron - 12.2%

87 - 74 micron - 8.1%

73 - 63 micron - 4.9

Less than 62 micron - 61.5%

TABLE 3

Attapulgite/H20

32

70* 400' 500' 600'

Plastic Viscosity (centipoise)

Yield Point (lb/100 sq ft)

Gel Strength (Ib/lOO sq ft)

pH

API Filtrate (ml/7.5 min.)

HP-HT Filtrate (ml/30 min.)

Cake Thickness (inches)

HP-HT Cake Thickness (inches)

CEC (milliequivalents/lOO gms)

11

7/8

9.5

182

120

7/32

5/32

50

3/9

7.8

320

115

17/32

7/32

30

15

4/5

7.0

182

100

1/2

7.5

304

105

22/32 20/32

17/32 9/32

40 40

TABLE 4

Attapulgite/MgCl2/H20

70' 400' 500' 600'



Gel Strength (lb/100 sq ft)

pH






2

1

2/2

8.3

260

125

5/32

4/32

30

7

11

10/29

6.6

248

115

25/32

10/32

50

11

46

19/31

6.2

120

82

17/32

25/32

30

9

7

7/14

7.6

130

98

15/32

15/32

60

TABLE 5

Attapulgite/CaCl2/H20

33

70 o 400' 500' 600'




pH






0

1/1

8.8

300

120

7/32

4/32

20

10

11/17

7.0

310

105

17/32

8/32

30

8

4/7

6.8

292

95

31/32

16/32

40

7/7

6.8

280

120

21/32

8/32

40

TABLE 6

Attapulgite/KCIAUO

70' 400' 500' 600'




pH






1/1

9.2

346

125

4/15

6.5

274

108

3/9

6.0

216

70

11

9/14

5.9

150

110

3/32

6/32

30

21/32

10/32

40

21/32

9/32

40

19/32

8/32

40

TABLE 7

Attapulgite/NaCl/H20

34

70' 400 500 600




pH






2

1.5

2/2

9.0

280

125

6/32

5/32

30

13

10

12/25

7.0

200

100

24/32

16/32

40

10

14

10/14

6.4

180

102

19/32

15/32

30

7

7

4/8

6.0

210

105

22/32

12/32

40

35

TABLE 3

Attapulgite/CaCl2/H 0




pH





700° 800°

Plastic Viscosity (centipoise) 2 3

Yield Point (lb/100 sq ft) 2 1

Gel Strength (lb/100 sq ft) 1/2 1/2

pH 7.0 4.8

API Filtrate (ml/7.5 min.) 300 260

HP-HT Filtrate (ml/30 min.) lJ-0 i40

Cake Thickness (inches) 6/32 4/32

HP-HT Cake Thickness (inches) ^/^^ 5/32

TABLE 9

Attapulgite/NaCl/H20

700°

2

1

1/2

7.8

192

121

2/32

4/32

800°

3

1

1/2

4.4

270

66

2/32

8/32

36

TABLE 10

Attapulgite/MgCl2/H20

700° 800°




pH 4.1 4.1


HP-HT Filtrate (ml/30 min.) 104 108

Cake Thickness (inches) ^/32 5/32

HP-HT Cake Thickness (inches) ^/^2 17/32

TABLE 11

Attapulgite/KCl/H20

700° 800°




pH 6.5 4.0


HP-HT Filtrate (ml/30 min.) 1̂ ^ 108

Cake Thickness (inches) 10/^2 4/32

HP-HT Cake Thickness (inches) ^^^2 6/32

TABLE 12

Attapulgite/Hg(0H)2/H20

37

70' 400' 500' 600'




pH






4

35

20/20

10.2

80

-

4/32

32/32

30

8

3

4/8

7.7

80

91

17/32

17/32

40

9

2

1/3

7.4

122

105

24/32

19/32

40

14

4

2/5

8.8

40

46

4/32

18/32

40

TABLE 13

Attapulgite/Ca(OH)2/H2O

70' 400 500' 600'




pH






17

15

5/8

12.0

194

142

12/32

32/32

30

13

6

3/3

9.0

122

70

16/32

32/32

20

22

15

5/6

9.3

76

78

13/32

24/32

50

14

8

2/2

8.8

92

80

14/32

17/32

50

38

TABLE 14

Attapulgite/NaOH/H20

70°

14

102

kllllx

12.0

116

78

9/32

16/32

400°

26

20

12/16

11.0

80

81

12/32

26/32

500°

11

41

14/15

10.6

90

55

7/32

20/32

600°

31

73

32/33

9.4

110

91

8/32

13/32




pH





CEC (milliequivalents/lOO gms) 40 20 20 20

TABLE 15

Attapulgite/K0H/H20

70° 400° 500° 600°

Plastic Viscosity (centipoise) 3 4 9 2

Yield Point (lb/100 sq ft) 37 3 4 1

Gel Strength (lb/100 sq ft) 9/14 2/2 2/4 1/1

17.6 11.2 9.6 10.0 pH






134 115 100 144

166 130 100 105

3/32 5/32 4/32 8/32

14/32 13/32 12/32 3/32

30 20 30 30

TABLE 16

Pure Sepiolite/H20

39

70' 400' 500' 600'




pH






3

15

14/17

8.7

68

110

3/32

7/32

30

13

17

17/22

7.1

60

80

15/32

34/32

40

26

45

31/41

7.0

57

70

16/32

32/32

50

18

16

4/9

7.5

56

64

33/32

33/32

50

TABLE 17

Sepiolite/MgCl2/H20

70' 400' 500' 600'




pH






2.5

8

5/6

7.7

100

130

3/10

6.4

196

100

11

11

9/13

5.8

100

95

8

13

8/15

6.2

90

85

5/32

5/32

30

27/32

28/32

30

16/32

30/32

50

17/32

32/32

65

TABLE 18

Sepiolite/CaCl2/H20

40

70' 400' 500' 600'




pH






3

6

5/75

8.0

130

120

6/32

4/32

40

8

10

8/26

6.6

145

98

8/32

17/32

30

11

22

26/28

6.8

120

62

12/32

36/32

50

5

15

14/16

6.9

130

70

13/32

32/32

70

TABLE 19

Sepiolite/NaCl/H20

70' 400 o 500' 600'


Yield Point (Ib/IQO sq ft)


pH






3

9

7/13

8.5

106

130

4/32

6/32

30

16

14

14/21

7.0

108

96

17/32

14/32

40

15

25

17/23

7.0

70

70

20/32

34/32

40

17

42

50/106

6.8

48

-

14/32

-

50

41

TABLE 20

Sepiolite/KCl/H20

70° 400° 500° 600°

Plastic Viscosity (centipoise) 2.5 18 12 22

Yield Point (lb/100 sq ft) 8.5 22 24 14


pH 8.7 7.0 7.1 7.0

API Filtrate (ml/7.5 min.) 138 84 70 79

HP-HT Filtrate (ml/30 min.) 110 85 52 72

Cake Thickness (inches) 6/32 22/32 21/32 15/32

HP-HT Cake Thickness (inches) 6/32 35/32 38/32 26/32


42

TABLE 21

Sepiolite/Mg(0H)2/H20




pH






70°

4

36

20/40

8.0

88

85

10/32

10/32

30

TABLE 22

400°

15

43

37/41

7.7

60

75

9/32

29/32

40

500°

14

14

13/26

7.4

100

58

12/32

24/32

40

600°

12

3

2/5

7.0

40

75

13/32

25/32

45

Sepiolite/Ca(0H)2/H20

70° 400° 500° 600°

Plastic Viscosity (centipoise) 5 5 8 2

Yield Point (lb/100 sq ft) 8 1 3 7,5


pH 11.8 9.6 9.3 9.4

API Filtrate (ml/7.5 min.) 410 340 240 120

HP-HT Filtrate (ml/30 min.) 208 214 180 93

Cake Thickness (inches) 19/32 18/32 20/32 10/32

HP-HT Cake Thickness (inches) 9/32 9/32 10/32 24/32


TABLE 23

Sepiolite/NaOH/H20

43

70' 400' 500' 600'




pH

API Filtrate (ml/7,5 min.)





7

32

12/24

11.7

62

92

6/32

15/32

40

29

27

20/27

10.7

64

47

14/32

16/32

30

16

54

23/28

10.4

64

60

17/32

20/32

40

11

104

34/40

10.3

80

70

5/32

33/32

30

TABLE 24 Sepiolite/KOH/H„0

70' 400' 500 o 600'




pH






6

24

4/34

10.4

70

90

9/32

9/32

30

13

26

8/12

10.7

76

82

16/32

22/32

30

5

1

2/2

10.0

118

27

7/32

4/32

40

3

0

.5/1

9.8

134

121

10/32

3/32

40

44

TABLE 25

Bulk X-ray analysis of cores.

1-64A

1-64B

1-64C

1-64D

2-64 A

2-64B

2-64C

2-64D

2-76A

2-76B

2-76C

2-76D

Quartz

60%

80%

60%

60%

75%

75%

70%

75%

60%

60%

75%

50%

Feldspar

30%

10%

20%

30%

15%

25%

25%

20%

25%

25%

10%

20%

Calcite

10%

10%

20%

10%

10%

- 1 %

CO/ J/0

5%

10%

10%

15%

25%

Chlor i te

1%

- 0 -

- 0 -

- 0 -

- 0 -

- 0 -

- 0 -

- 0 -

CO/

CO/ J/a

CO/ JlO

CO/ JfO

TABLE 26

X-ray analysis of clay fraction in cores

45

1-64A

1-64B

1-64C

1-64D

2-64A

2-64B

2-64C

2-64D

2-76A

2-76B

2-76C

2-76D

Illite/Smectite Chlorite Calcite Felds Qtz

40%

40°^ /O

40%

40%

45%

45%

45%

45%

50%

50%

45%

40%

40%

40%

40%

40%

45%

45%

50%

50%

50%

45%

40%

40%

CD/ J/a

CO/ J/Q

CQ/ -?/0

CO/ J/0

•10/ J/0

3%

+1%

+1%

- 0 -

5%

10%

15%

CO/ J/0

CO/ J/0

CO/ J/0

CO/ J/0

-7 0/ J/0

•zo/ J/0

0 0 / Z/0

0 0 / Z/0

1%

- 0 -

CO/ J/0

CO/ J/0

10%

10%

10%

10%

3%

-10/ J/0

0 0/ Z/0

0 0 / Z/0

1%

- 0 -

- 0 -

- 0 -

46

APPENDIX B

47

Figure 1.— Schematic of concentric-cylinder, rotational torsion viscometer. The sample cup rotates, which in turn develops shearing of liquid.

48

Torsion spring

Bob

Sairple cup

— Liquid

Figure 2.— Consistency curve of Bingham plastic in a direct indicating viscometer. The critical torque and the slope of the laminar flow is dependent on the rheologic properties of the fluid.

50

g ^ e

RPM

51

Figure 3-— Graphic interpretation of determination of flow parameters in a two speed direct indicating viscometer. (PV) is plastic viscosity, (AV) is apparent viscosity, (YP) is yield point.

52

(D

CD Q

2

I — I Q

AV (a 600 rpm

1

o o to

I o o

o o tn

0 300

RPM

600

53

Figure 4.— Pure attapulgite based mud: rheograms as measured by a Fann 50C viscometer. Curve (a) is mud prepared at room temperature, (b) autoclaved at 700 F, (c) was autoclaved at 800°F.

Figure 5.— Pure attapulgite based muds: rheograms of muds treated at temperatures of 400°F (a), 500°F (b), and 600°F for curve (c).

54

w CO (—(

o a,

10

8

CO

8 CO

bs.

a b

100 200 300

TEMPERATURE °F

400 500

10

CO

2 8 I — I

CO

o CO > 2.

100 200 300

TBIPERATUPÊ °F

400

55

Figure f).~ Attapulgite/MgCl2/H20: rheograms (a), (b) , and (c) of samples treated at room temperature, 700°F and 800°F respectively.

Figure 7.— Attapulgite/MgCl^/HÔ: rheograms of samples autoclaved at intermediate temperatures of 400°F (a), 500°F (b), and 600°F (c).

56

10,

CO

o ^ 8

8 CO

6 4

4

100 200 300

TEMPERATURE °F

400 500

15 . CO

o &3 12

CO o u CO c

a

9 100 200 300 400 500

TEMPERATURE °F

57

Figure 8.— Attapulgite/\aCl/H20: rheograms illustrating change of viscosity with change of temperature. Curve (a) is mud prepared at room temperature, (b) 700 F, and (c) 800°F.

Figure 9.— Attapulgite/NaCl/H20: rheograms (a), (b), and (c) represent samples autoclaved at 400, 500 and 600 F respectively.

58

TEMPERATURE

TEMPERATURE °E

59

Figure 10.— Attapulgite/KCl/H20: rheograms as measured b\ the Fann 50C viscometer. Curve (a) is mud treated at room temperature, (b) 700 F, and (c) has been autoclaved to 800 F.

Figure 11.— Attapulgite/KCl/HÔ: samples heated to temperatures of 400, 500 and 600 F are represented by rheograms (a), (b) and (c) respectively.

60

w I — (

O

s

10 «

8

CO ^ • o u CO

100 200 300

TEMPERATURE °F

400 500

CO

w u

I — I

t — I

CO

o CJ CO > 2

300

TEMPERATURE °F

Figure 12.— Attapulgite/CaCl2/H20: rheograms of (a) mud treated at room temperature, (b^ mud autoclaved at 700°F, (c) mud heated to 800 F.

Figure 13.— Attapulgite/CaCl^/H„0: rheograms of the muds treated at intermediate temperatures of 400 F (a), 500°F (b), and 600°F (c).

62

10 C/D I — I O a 8

u

CO

o u CO

100 200 300

TENPERATURE °F

400 500

w CO I — I

o

u

O u CO

10

8

2 '

100 • • •

200 300 400

TBIPERATURE °F

500

63

Fiqure 1^-- Attapulgite/Mg(OH)/H2O: rheograms of muds ^ at room temperaturi (1), 400°F (b), 500°F (c)

and autoclaved at 600 F (d).

Figure 15.— Attapulgite/Ca(OH)2/H2O: rheograms illustrate the change in viscosity with respect to change in temperature. Curve (a) is sample prepared at room temperature, (b) autoclaved to 400 F, (c) 500°F, and (d) 600°F.

64

w CO I — I

o W U

10

2: 6

CO 4' o u CO

' \

2'

—T " 100 200 300

TEMPERATURE °F

400 500

w CO \ — 1

o a, 1—1

^

e 2: 1—1

^ 1—1 CO o u CO

20

16

12

8

200 300

TEMPERATURE °F

65

Fiqure lb.— Attapulgite/NaOH/H 0: rheograms (a), (b), (c), and (d) illustrate viscosity changes of samples treated at 70, 400, 500, and 600°F, respectively

Figure 17.— Attapulgite/K0H/H20: rheogram (a) is sample treated at room temperature, (b) at 400 F, (c) at 500°F, and (d) autoclaved to 600°F.

66

w CO I—I

o

I—( CO o u CO

100

TETvIPERATURE °F

CO

o PL,

u

CO o u CO

10 •

8 •

6 .

^ ' • ^ .

- b -c ,d

100 200 I

300 400 500

TB-IPERATURE °F

b7

Figure 18.— Pure sepiolite based mud: rheograms as measured by a Fann 50C viscometer. Curve (a) mud prepared at room temperature, (b) ̂ autoclaved at 700 F, (c) autoclaved at 800 F

Figure 19.— Pure sepiolite based mud: rheograms of muds treated at temperatures of 400°F (a), 500°F (b), and 600°F for curve (c).

68

w CO o a.

u

10

8

CO

o CO

> 2

4 .

100 200 300

TEMPERATURE °F

400 500

10 w CO I—I o OH 8 I—I "

N \

\

H U

CO o u CO

> 2 •

100 200 300

TEMPERATURE

\

op

\

^ \ ^ - b a

400 500

Figure 20.- Sepiolite/MgCl^/H 0: rheograms (a)^ (b), and (ci of samples^treated at 70°F, 700°F and 800 F respectively.

Figure 21.— Sepiolite/MgCl2/H20: rheograms of samples autoclaved at intermediate temperatures of 400 F (a), 500°F (b), and 600°F (c).

70

10

2 8 CO

u I — (

I — I CO

8 CO

> 2 •

V N

4« b' --..

100 200 300

TEMPERATURE °F

400 500

b a

c

10 w CO

2 84

CJ

CO ^ o u CO

5 2^

b̂

c a b

200 •

300 400 100 500

TEMPERATURE °F

71

Figure 22.- Sepiolite/CaCl2/H20: rheograms illustrate change of viscosity with change of temperature. Curve (a) is mud prepared at room temperature, (b) 700 F, (c) 800^F.

Figure 23-— 5epiolite/CaCl2/H20: rheograms (a), (b), and (c) represent samples autoclaved at 400, 500, and 600 F respectively.

20

CO

o 16

72

W TO J

u 12 •

8 CO

o CJ CO

100 200 300

TEMPERATURE °F

400 500

100 200 300

TEMPERATURE °F

7'

Finure 2U.- Sepiolite/KCl/H20: rheograms of (a) mud treated

at room temperature, (b) 400"F, (c) mud autoclaved to 500°F, and (d) 600°F.

Figure 25.— Seoiolite/NaCl/HoO: rheograms of muds treated at 70°F (a), 400°F (b), 500°F (c), and 600°F (d).

74

300

TEMPERATURE °F

500

100 200 300

TEMPERATURE °F

400 500

75

Fiqure 26.- Sepiolite/Mg(0H)2/H20: rheograms of mud treated ^ at joom temperat6re2(a), 400^F (b), 500°F (c), and

600 F (d).

Figure 27.— Sepiolite/NaOH/H20: rheograms illustrate the change in viscosity with respect to the change in temperature. Curve (a) is sample prepared at 70°F, (b) autoclaved to 400°F, (c) 500°F, and (d) 600°F.

76

40

200 300

TEMPERATURE °F

400 500

r b

40 \

300

TEMPERATU'RE °F

Fi gure 28.— Sepiolite/Ca(0H)2/H20: rheograms (a), (b), (c), and (d) illustrate viscosity changes of samples treated at 70, 400, 500, and 600 F.

Figure 29.— Sepiolite/K0H/H20: rheogram (a) is sample treated at room temperature, (b) at 400 F, (c) at 500 F, and (d) autoclaved to 600 F.

78

CO

2 I — I

m

CO O CJ CO

10

8

100 200 300

TBIPERATURE °F

--d

400 500

CO l-H o a,

u

u

CO

10 4

8

6 i

4

2

\ N

• b

c d

100 200 300

TEMPERATURE °F

400 500

7y

Figure 30.— ITEM 'J' Attapulgite: rheogram of high temperature mud formula consisting of attapulgite, 4% high polymer and 1% low polymer

80

w CO l-H

o a,

25 .

^ 20 -f

H U z 15 1

g 10 u CO

5 -

100 200 300

TEMPERATURE °F

400 500

81

Figure 31.— ITEM 'I' Sepiolite: rheogram of high temperature mud consisting of sepiolite, 4% high polymer and 1% low polymer.

82

CO

CO

8 CO

40-

32

24

16

8

•

200 100 300

TEMPERATURE °F

400 500

8''

Figure 32.— HTM-1: rheogram of high temperature mud formulated with the following constituents per standard barrel (42 gallons):

5 lbs Bentonite 15 lbs Sepiolite 20 lbs Brown Coal 2.5 lbs Sodium Polyacrylate 2 lbs Sodium Hydroxide

84

CO l-H

2 >—I

u

50-

40 '

30 '

CO O

u CO

20

10

r \ ' \ f \

100 200 300

TEMPERATURE °F

400 500

85

Figure 33-— A graphical representation of permeability ratio

(K̂ .. ,/K. ... ,) versus stagnation time (0-48 final initial ^

hours) for HTM-1. Curves of 100°C and 200°C runs,

86

1.00

I — I

i

0 0 24 12 18 24 30

STAGNATION TIME, HOURS

36 42 48

87

Figure 34.— A low magnification (200X) SEM image of the 1-64 virgin core of East Mesa, showing the sand grains (quartz and feldspar) coated with clays.

Figure 35.— Sand grains from core 1-64 magnified 300X, shows hairy and flaky illite/smectite mixed layer clays covering quartz and feldspar grains.

88

89

Figure 36.— Extensive coverage of sandgrains in core 1-64 by chlorite rosettes are seen in this SEM image (300X).

Figure 37.— A high magnification (5K) of clays in 1-64 show fragile chlorite rosettes, flaky illite/smectite mixed layer, and hairy illite covering sand grains.

90

VI

Figure 38.— At lOOX chlorite rosettes are seen along with illite/smectite mixed layers and secondary quartz crystals.

Figure 39.— A closer look at the chlorite seen in figure 38 (4K).

92

•̂3

Figure 40.-- This micrograph reveals the flaky illite/ smectite mixed layer and hairy illite of core 1-64 (2K).

Figure 41.— A comparison of clays in core 2-76 to those in core 1-64 (figure 40), the clays in 2-76 are much more massive (2K).

94

'̂5

Figure 42.— In the pore throats of core 2-64 (lOOOX), large amounts of massive chlorite rosettes are seen.

Figure 43.— At 2K clays are observed at grain boundaries decreasing permeability in the sandstone.

96

97

Figure 44.— Massive clay coverings of illite/smectite mixed layer are in the pores of core 2-64 often mud testing (500X).

Figure 45.-- A closer view (3K) of clays bridging pore gaps in core 2-76, a good example of formation damage by migrating clays.

98

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RHEOLOGICAL PROPERTIES OF HIGH-TEMPERATURE A THESIS …