Modification of bentonite properties for drilling fluids

Abstract

A method and composition for modifying bentonite to allow the bentonite to be useful in drilling mud applications. The method includes the steps of: preparing bentonite local to Saudi Arabia using raw water to remove contaminants from the bentonite; grinding the bentonite to a fine powder; sieving the fine powder to be between about 50 m and about 150 m in particle size to produce a sieved fine powder; mixing the sieved fine powder with polyanionic cellulose polymer to produce a modified bentonite composition; adding the modified bentonite composition to water until a homogeneous solution of modified bentonite in water is formed; and allowing the homogeneous solution of modified bentonite in water to rest for about 16 hours to form a composition useful in drilling mud applications.

Claims

1. A modified bentonite composition useful in drilling mud applications, the composition comprising: a powdery mixture composition comprising: bentonite local to the Khulais area of Saudi Arabia, the bentonite having been ground to a fine powder, the ground fine powder between about 50 m and about 150 m in particle size, a first polymer comprising polyanionic cellulose polymer with carboxymethylcellulose sodium salt, the first polymer present at about at least 3% by weight of the powdery mixture composition, the first polymer having a first viscosity in water, and a second polymer comprising carboxymethylcellulose, the second polymer having a second viscosity in water, where the second viscosity is lesser than the first viscosity; and water, where a ratio of yield point to plastic viscosity for the modified bentonite composition after static aging for at least 16 hours is between about at least 0.73 and about 1.10, with a pH between about 8.14 and about 8.93, the pH controlled in part by an amount of soda ash between about 1% by weight and about 2.5% by weight of the powdery mixture composition, and is sufficient for cuttings transport and suspension in the drilling mud applications, the modified bentonite composition not being modified by sodium hydroxide.

2. The composition according to claim 1, wherein crystalline mineral phases of the powdery mixture composition comprise by weight percent about 71% sodium montmorillonite, about 5% feldspar, about 15% SiO.sub.2, about 6% kaolinite, about 0% halite, and about 1% illite.

3. The composition according to claim 1, wherein the modified bentonite composition substantially meets the API's requirements for drilling mud.

4. The composition according to claim 1, wherein the powdery mixture composition comprises between about 4% and about 10% of the first polymer by weight.

5. The composition according to claim 1, wherein the powdery mixture composition comprises between about 4% and about 9% of the first polymer by weight.

6. The composition according to claim 1, wherein the powdery mixture composition comprises between about 5% and about 8% of the first polymer by weight.

7. The composition according to claim 1, wherein the powdery mixture composition comprises about 8.5% of the first polymer by weight.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) These and other features, aspects, and advantages of the present disclosure will become better understood with regard to the following descriptions, claims, and accompanying drawings. It is to be noted, however, that the drawings illustrate only several embodiments of the disclosure and are therefore not to be considered limiting of the disclosure's scope as it can admit to other equally effective embodiments.

(2) FIG. 1 shows a process diagram for one embodiment of a method to modify non-American Petroleum Institute (API) bentonite into a composition suitable for a drilling mud according to API standards.

(3) FIG. 2 shows a diffractogram comparing the compositions of a sample of API bentonite, a sample of non-API bentonite (Untreated Bentonite), and a sample of modified non-API bentonite (Treated Bentonite).

DETAILED DESCRIPTION

(4) So that the manner in which the features and advantages of the embodiments of compositions of and methods for making modified non-API bentonite, as well as others, which will become apparent, may be understood in more detail, a more particular description of the embodiments of the present disclosure briefly summarized previously may be had by reference to the embodiments thereof, which are illustrated in the appended drawings, which form a part of this specification. It is to be noted, however, that the drawings illustrate only various embodiments of the disclosure and are therefore not to be considered limiting of the present disclosure's scope, as it may include other effective embodiments as well.

(5) Bentonite is an absorbent aluminum phyllosilicate, essentially impure clay consisting mostly of montmorillonite. Montmorillonite is the most abundant of the smectite clay minerals. A good quality bentonite contains mainly smectites (montmorillonite) and secondary minerals such as quartz, calcite, and micas. Bentonites come about in numerous forms on the market. In industry, montmorillonites are generally classified as sodium (Na), or calcium (Ca) types, depending on which exchangeable ion is dominant. Bentonite has certain characteristics such as negative electric charge, fine size, and very high specific surface area, and high sensitivity to hydration. Bentonite's functions in drilling mud include the control of the flow properties and the filtration rate of drilling fluids in drilling operations, which are important aspects of drilling fluid technology.

(6) Desirable rheological properties include a high shear thinning viscosity. In other words, the higher the shear rate, the lower the viscosity, and there is a relatively high gel strength with a high ratio of yield point to plastic viscosity for cuttings transport and suspension.

(7) Referring now to FIG. 1, a process diagram is shown for one embodiment of a method to modify non-American Petroleum Institute (API) bentonite into a composition suitable for a drilling mud according to API standards. In process 100, unmodified bentonite, local to Saudi Arabia and not meeting API standards for use in drilling mud, was cleaned and rinsed with raw water to remove contaminants at step 102. At step 104, the cleaned and rinsed unmodified bentonite was ground to a very fine powder using a Mortar Grinder RM 200 by Retsch. At step 106, the ground unmodified bentonite was sieved to about 75 m (200 mesh) particle size using an electronic sieve shaker column. At step 108, the sieved unmodified bentonite was mixed with polyanionic cellulose polymer (PAC-R) at a weight ratio of about 91.5% by weight unmodified bentonite to about 8.5% by weight PAC-R polymer.

(8) Bentonite ore is normally accompanied by other mineral materials which vary in amount and composition according to the location at which the bentonite is mined or quarried. Some common impurities in bentonite, to be removed by water, are clay-sized silica, gypsum, illite, and non-crystalline compounds.

(9) PAC-R polymer is a product of Halliburton and is a modified natural polyanionic cellulosic polymer that is a white, free-flowing powder. PAC-R polymer is composed largely of carboxymethylcellulose sodium salt. While the specification and examples discuss the use of PAC-R polymer, one of ordinary skill in the art would understand other suitable polymers could be used in the embodiments of the present disclosure, either in addition to or alternative to PAC-R polymer. At step 110, the mixture of sieved unmodified bentonite and PAC-R polymer (the mixture also being referred to as modified bentonite throughout) was added to distilled water and mixed until the solution became homogeneous, after about 20 minutes. At step 112, the modified bentonite in water (an example drilling solution) was covered and stored overnight for about 16 hours.

(10) At step 114, the modified bentonite was analyzed according to API specifications for bentonite drilling mud. The analysis shows that the modified bentonite is similar to the commercially available bentonite.

(11) Table 1 compares certain properties of bentonite that meets the American Petroleum Institute's standards for making drilling mud with modified local bentonite or bentonite local to Saudi Arabia that has been modified with PAC-R polymer. In some embodiments of the present disclosure, because bentonite local to Saudi Arabia is a sodium-type bentonite, no sodium hydroxide is used or required for modifying the bentonite.

(12) TABLE-US-00001 TABLE 1 Physical properties of modified bentonite local to Saudi Arabia versus commercially available bentonite. API Bentonite VS. Modified Local Bentonite Viscosity Yield dispersed centipoise Plastic Point (YP) Plastic (cp) Viscosity (lbs./100 b ratio Viscosity 600 300 pH (PV) (cp) ft..sup.2) YP:PV (cp) API 71 43.5 7.6 27.5 16 0.58 25 benton- ite Local 68.5 44 8.4 24.5 19.5 0.79 25 benton- ite

(13) Table 2 provides x-ray powder diffraction (XRD) data comparing the compositions of unmodified bentonite local to Saudi Arabia and modified bentonite (using PAC-R polymer) local to Saudi Arabia. XRD is an analysis technique used for clay minerals identification. For the unmodified sample, after the preliminary removal of sand, clay was separated from silt by using a centrifugation technique. XRD patterns were obtained for air-dried samples and for samples treated with ethylene glycol vapor or heated to 350 C. and 550 C. Diffraction patterns were compared with standards for identification of minerals.

(14) Samples of API bentonite, non-API bentonite, and modified non-API bentonite were analyzed by XRD. The samples were crushed to fine powder by grinding in a McCrone Micronizing mill. The samples were identified by the three major peaks of individual compounds shown in Table 2 below and in FIG. 2. The quantification of the identified compounds was performed by using the area under each of the major peaks. A sample of bentonite containing known concentration of components was analyzed to calculate the concentration by area of the peaks, because the areas corresponded to actual known values. Then, the non-API bentonite sample and modified non-API bentonite sample were tested. Component concentrations were calculated by area of the peaks. The sodium montmorillonite peak was modified and the area under the peak was increased for the modified non-API bentonite (Treated Bentonite in FIG. 2). The quartz concentration was reduced for the modified non-API bentonite sample. The feldspar concentration was largely unaffected, and clay minerals were also largely unaffected.

(15) TABLE-US-00002 TABLE 2 XRD data comparing the compositions of unmodified bentonite local to Saudi Arabia and modified bentonite (using PAC-R polymer) local to Saudi Arabia. Untreated Modified API non-API (Treated) Bentonite Bentonite Bentonite Phase Identified Weight % Weight % Weight % Na Montmorillonite 74 58 71 Cristoballite - SiO.sub.2 16 n/a n/a Feldspar 8 5 5 Quartz-SiO.sub.2 2 25 15 Kaolinite-Al.sub.2Si.sub.2O.sub.5(OH).sub.4 n/a 8 6 Halite-NaCl n/a 2 0 Illite 2 2 1

(16) The identification of the crystalline mineral phases was achieved using X'Pert HighScore software by PANalytical. Semi-quantification of XRD data was performed by using JADE software by MDI Products based on the area of the peaks. The relative approximate values of the crystalline phases are listed in Table 2.

(17) FIG. 2 shows a diffractogram comparing the compositions of a sample of API bentonite, a sample of non-API bentonite, and a sample of modified non-API bentonite. Table 3 shows a comparison of data for five unmodified bentonite samples, local to Saudi Arabia (collected at different locations and different depths), and their properties. As shown, many of the properties do not meet required specifications, such as yield, dispersed plastic viscosity, dispersed filtrate, the methylene blue test, and the residue on 100 mesh (dry).

(18) There were four main tests that were carried out to determine the rheological properties of the bentonite according to the API specifications. For the yield point:plastic viscosity ratio, the viscosity of samples at 600 rpm and 300 rpm were measured by using the Fan Viscometer device. After measuring the viscosity, the yield point:plastic viscosity ratio was calculated. The pH value of the samples were tested. To test dispersed plastic viscosity, sodium hexametaphosphate (10 wt. %) was prepared and 5 l was added to the modified non-API bentonite. After that, the viscosity at 600 rpm and 300 rpm were measured again. The dispersed plastic viscosity is calculated by taking the difference between the viscosity at 600 rpm and the viscosity at 300 rpm.

(19) To measure dispersed filtrate volume, the sample was pressurized by nitrogen gas to about 100 psi. The filtered water coming out of the pressurized cell was collected after 7.5 minutes of the starting of the nitrogen pressure until 30 minutes had elapsed. Finally, the volume of the water was multiplied by 2 to calculate the filtrate volume.

(20) TABLE-US-00003 TABLE 3 Properties of five unmodified non-API bentonite samples. Internal Required Tests Unit # 1 # 2 # 3 # 4 # 5 Mean Specs. Yield Barrel/ 27.59 37.24 27.59 26.95 27.59 29.39 Minimum Short Ton 90.0 Moisture % by wt. 9.0 8.6 8.6 9.1 8.3 8.72 Maximum Content 13.0 Ratio of Yield 0.50 0.0 0.0 0.0 3.0 0.70 Maximum Point:Plastic 1.50 Viscosity (b) Dispersed Centipoise 1.0 1.0 1.0 1.0 1.0 1.0 Minimum Plastic 10.0 Viscosity Dispersed ml/30 min 46.0 42.0 30.0 54.0 50.0 44.4 Maximum Filtrate 12.50 Cement pH 8.62 8.51 8.89 8.47 8.69 8.636 Maximum Contamination 9 Methylene blue meq/100 g 100 95 100 100 100 99.0 Minimum Test (MTB) 65.0 Residue on 200 % by wt. 0.69 0.64 0.72 0.75 0.65 0.69 Maximum mesh (wet) 2.50 Residue on 100 % by wt. 81.52 87.26 71.33 68.07 65.31 74.69 Maximum mesh (Dry) 2.00

(21) Table 4 shows data comparing five samples of modified non-API bentonite, where the bentonite was modified with low viscosity sodium carboxymethyl cellulose (CMC-LV). During modification, the viscosity at both 300 and 600 rpm, pH value, plastic viscosity (cp), and yield point (lbs./100 ft..sup.2) were modified to meet API specifications.

(22) Table 3 describes yield of unmodified non-API bentonite whereas Table 4 describes the yield point of modified non-API bentonite. Yield is calculated using a yield test, and certain internal minimum specification requirements are 90 barrel/short ton. For yield point, certain internal maximum specification requirements include a maximum ratio of 1.5 yield point:plastic viscosity.

(23) TABLE-US-00004 TABLE 4 Evaluation of five modified bentonite samples. Soda ash PAC-R CMC Sample # Total (g) Bentonite (g) wt. % wt. % wt. % 1 30 27.6 1% 3% 4% 2 30 27.3 1% 3% 5% 3 30 27 1% 3% 6% 4 30 26.7 1% 3% 7% 5 30 26.4 1% 3% 8% plastic Viscosity (cp) viscosity yield point Sample # 600 300 pH (cp) (lbs./100 ft.sup.2) b 1 37.5 22 7.44 15.5 6.5 0.41 2 41 26 8.14 15 11 0.73 3 39.5 23 7.92 16.5 6.5 0.39 4 47.5 28.5 7.9 19 9.5 0.5 5 46 27.5 7.89 18.5 9 0.48

(24) Table 5 shows certain effects of grain size on the modified non-API bentonite performance.

(25) TABLE-US-00005 TABLE 5 Effect of grain size on the modified non-API bentonite. Particle Viscosity Total size PAC CMC (cp) # Mass (g) Bentonite (g) (mesh) wt. % wt. % 600 300 1 30 26.625 1 3.75% 7.50% 30 16 2 30 26.625 50 3.75% 7.50% 38 21 3 30 26.625 100 3.75% 7.50% 43.5 24.5 4 30 26.625 140 3.75% 7.50% 44.5 25.5 5 30 26.625 200 3.75% 7.50% 50 30

(26) Table 6 shows certain effects of soda ash on the modified non-API bentonite performance.

(27) TABLE-US-00006 TABLE 6 Certain effects of soda ash concentration on modified non-API bentonite. Soda ash PAC-R CMC # Total (g) Bentonite (g) wt. % wt. % wt. % 1 30 27.3 1% 3% 5% 2 30 27.15 1.5%.sup. 3% 5% 3 30 27 2% 3% 5% 4 30 26.85 2.5%.sup. 3% 5% 5 30 26.7 3% 3% 5% plastic Viscosity (cp) viscosity yield point 600 300 pH (cp) (lbs./100 ft.sup.2) b 1 41 26 8.14 15 11 0.7333 2 49 31 8.47 18 13 0.7222 3 60.5 41 8.78 19.5 21.5 1.1026 4 55 37 8.93 18 19 1.0556 5 60.5 42.5 9.3 18 24.5 1.3611

(28) Table 7 shows certain effects of PAC-R concentration on modified non-API bentonite.

(29) TABLE-US-00007 TABLE 7 Effects of PAC-R concentration on modified non-API bentonite. Soda ash PAC-R CMC # Total (g) Bentonite (g) wt. % wt. % wt. % 1 30 27.9 1% 1% 5% 2 30 27.6 1% 2% 5% 3 30 27.3 1% 3% 5% 4 30 27 1% 4% 5% 5 30 26.7 1% 5% 5% Plastic Viscosity (cp) viscosity yield point # 600 300 pH (cp) (lbs./100 ft.sup.2) b 1 20 11 8.1 9 2 0.2222 2 34 19 8.02 15 4 0.2667 3 41 26 8.14 15 11 0.7333 4 50 31.5 7.46 18.5 13 0.7027 5 68.5 44 8.44 24.5 19.5 0.7959

(30) TABLE-US-00008 TABLE 8 Evaluation for modified non-API bentonite sample (8.5% PAC-R added). Yield Test Internal Requirement Concentration 20 ppb 22.5 ppb 24 ppb Min 90 Barrel/Short Ton Viscosity at 600 rpm 40 53 59 Yield Apparent viscosity 20 cp 26.5 cp 29.5 cp Yield 113.88 Barrel/Short Ton Yield Point/Plastic Viscosity Ratio Test Required Specification Viscosity at 600 rpm 66 Max 1.5 YP/PV Ratio Viscosity at 300 rpm 42 Plastic Viscosity Ratio 22 cp Yield Point 22 lbs./100 sq. ft. YP/PV Ratio 1 Dispersed Plastic Viscosity & Filtrate Test Required Specification Viscosity at 600 rpm 65 Min 10 cp Viscosity at 300 rpm 42 Dispersed Plastic Viscosity 23 cp Dispersed Filtrate 10 ml/30 min Max 12.5 ml/30 min Cement Contamination Test Required Specification pH After Aging 8.6 Max 9 Residue on 100 mesh (dry) Test Required Specification Residue on 100 mesh (dry) 0.15 wt. % Max 2 Moisture Test Required Specification Moisture 10.2 wt. % Max 13 Residue on 200 mesh (wet) Test Required Specification Residue on 200 mesh (wet) 0.12 wt. % Max 2.5 MBT (Active Clay) MBT ( Active Clay ) 122 lb/bbl Peroxide Test RHEOLOGY @ ROOM- Treated Bentonite TEMPERATURE ON Pre-hydrated in: FANN-36 VISCOMETER Water Hydrogen After Static Aging for 70 600 rpm 72 6 Hrs at Room Temperature 300 rpm 46 4 200 rpm 36 3 100 rpm 24 2 6 rpm 4 1 3 rpm 2 1 PV 26 2 VP 20 2

(31) In Table 8, dispersed filtrate is according to API Standard 13A which outlines the test procedure used for drilling fluids. Fluid loss is a measure of bentonite slurry's ability to form a low permeability filter cake. The max internal requirement for testing was 12.5 ml/30 min.

(32) Advantageously in the embodiments of the present disclosure, raw water was used to remove contaminants from unmodified bentonite before its modification by carboxymethylcellulose. Acid was not used to remove contaminants to avoid any negative effect on the chemical properties of bentonite ore. Notably, commercial bentonite was not used in the preparation recipe. PAC-R polymer was used to enhance the viscosity of the bentonite ore in water. In certain embodiments, other additives were not used to enhance the viscosity of the bentonite ore.

(33) The addition of soda ash shows a positive effect in terms of plastic viscosity; however, as the amount of soda ash is increased, the pH of the composition increases as well.

(34) The singular forms a, an, and the include plural referents, unless the context clearly dictates otherwise.

(35) In the drawings and specification, there have been disclosed embodiments of compositions of and methods for making modified bentonite, and although specific terms are employed, the terms are used in a descriptive sense only and not for purposes of limitation. The embodiments of the present disclosure have been described in considerable detail with specific reference to these illustrated embodiments. It will be apparent, however, that various modifications and changes can be made within the spirit and scope of the disclosure as described in the foregoing specification, and such modifications and changes are to be considered equivalents and part of this disclosure.

(36) Where the Specification or the appended Claims provide a range of values, it is understood that the interval encompasses each intervening value between the upper limit and the lower limit as well as the upper limit and the lower limit. The present disclosure encompasses and bounds smaller ranges of the interval subject to any specific exclusion provided. Where the Specification and appended Claims reference a method comprising two or more defined steps, the defined steps can be carried out in any order or simultaneously except where the context excludes that possibility.