GB2216574A

GB2216574A - Water base drilling fluid

Info

Publication number: GB2216574A
Application number: GB8905502A
Authority: GB
Inventors: Arthur Herman Hale; George Constantine Blytas; Ashok Kumar Rupkrishen Dewan
Original assignee: Shell Internationale Research Maatschappij BV
Current assignee: Shell Internationale Research Maatschappij BV
Priority date: 1988-03-14
Filing date: 1989-03-10
Publication date: 1989-10-11
Anticipated expiration: 2009-03-10
Also published as: GB2216574B; NO177011C; GB8905502D0; NO891022L; NO177011B; NO891022D0

Abstract

Water base drilling fluid comprising water, clay and a polymer and a polyglycerol.

Description

WATER BASE DRILLING FLUID This invention relates to water base drilling fluids. More particularly, the invention relates to water base drilling fluids having improved characteristics which allow low temperature drilling operations, inhibit formation of gas hydrates which form at low temperatures and high pressures, prevent shale dispersion which results in improved borehole stability, reduce fluid loss, and are environmentally safe.

Water base drilling fluids (or muds) generally comprise water, clays or polymers, and various treating agents which control the physical, chemical and/or rheological properties of drilling fluids in boreholes. The drilling fluid serves to remove chips, cuttings and the like produced by a rotating drill bit from a borehole by circulating the drilling fluid down from the surface of the well, through the drill string, and out through openings in the drill bit such that the drilling fluid is then circulated upwardly in the annulus between the side of the borehole and the rotating drill string.

The selection of a drilling fluid is primarily dependent upon the geological formation being drilled and the problems associated with such formation. Principal concerns in selection of a drilling fluid are low temperature drilling conditions, formation of gas hydrates, shale dispersion, and drilling fluid loss and environmental requirements. Classically, temperature concerns associated with drilling oil/gas wells have been associated with deep hot wells ( > 150 C); however, for deep water and/or Arctic drilling, low temperatures are a concern for two principal reasons: (1) freezing of the mud due to low temperature, especially if the well must be shut in for long durations, and (2) the formation of gas hydrates under low temperature and high pressure conditions after the influx of gas.The present invention provides a drilling fluid additive which overcomes these and other problems in the art as more particularly disclosed hereinafter.

The primary purpose of the present invention is to provide a drilling fluid, and process for the use thereof, which drilling fluid contains additives which depress the freezing point of the fluid to allow low temperature drilling operations, inhibit formation of gas hydrates which form at low temperatures and high pressures, prevent shale dispersion which results in improved borehole stability, reduce drilling fluid loss thereby reducing amounts of other fluid loss additives if any (e.g. gel-bentonite, carboxymethylcellulose, starch), and are environmentally safe.

Accordingly, the present invention is directed to a water base drilling fluid comprising water, clay or polymer and a polyglycerol. The drilling fluid comprises a sufficient amount of polyglycerol and, optionally, glycerol and/or a salt, necessary to reduce the freezing point of the drilling fluid to a predetermined value, inhibit the formation of gas hydrates in the drilling fluid, prevent shale dispersion from the borehole into the drilling fluid, and reduce fluid loss through the wall of the borehole thereby reducing amounts of other fluid loss additives if any (e.g.

gel-bentonite, carboxymethylcellulose, starch).

In addition1 the present invention is directed to a method for drilling a well comprising rotating a drill string to cut a borehole into the earth; circulating a drilling mud through the drill string and through the annulus between the drill string and the wall of the borehole; checking the drilling fluid for evidence of any of the following problems: freezing, gas hydrate formation, shale dispersion and fluid loss; and adding polyglycerol and, optionally, glycerol and/or a salt, to the drilling fluid in an amount sufficient to overcome the above identified problems.

Further, the present invention provides a method for drilling a well comprising determining whether the formation to be drilled will subject the drilling fluid to any of the following problems: freezing1 gas hydrate formation, shale dispersion, and fluid loss; providing a drilling fluid containing a polyglycerol and, optionally, glycerol and/or a salt, in an amount sufficient to overcome the above identified problems; rotating a drill bit to cut a borehole into the earth; and circulating the drilling fluid through a drill string and through an annulus between the drill string and the wall of the borehole.

Applicants have found that the addition of a polyglycerol and, optionally, glycerol and/or a salt, in an appropriate amount, to a drilling fluid substantially depresses the freezing point of the drilling fluid to eliminate problems with low temperature drilling operations, inhibits formation of gas hydrates which form at low temperatures and high pressures, prevents shale dispersion which results in improved borehole stability, reduces drilling fluid loss thereby reducing amounts of other fluid loss additives if any (e.g.

gel-bentonite, carboxymethylcellulose (CMC), starch), and is environmentally safe. Thus, according to the Applicants' method, the drill string is rotated to cut a borehole into the earth while circulating a drilling fluid down through the drill string and thence up the annulus between the drill string and the wall of the borehole. While this is occurring, a driller preferably is checking or observing the drilling fluid for evidence of the above noted problems. Alternatively, the formation may be known in advance to present certain problems, and the drilling fluid may be provided with polyglycerol and, optionally, glycerol and/or a salt, in amounts sufficient to overcome these problems.

In most instances, the applicable amount of polyglycerol and, optionally, glycerol and/or a salt, to be added to the drilling fluid will be determined on a well-to-well basis. A concentration of polyglycerol in the drilling fluid of from about 1 to 40, or preferably about 5 to 30 %w (percent by weight based on the total weight of the drilling fluid) and, optionally, glycerol of from about 1 to 60, or preferably about 5 to 35, or salt of from about 1 to 26 tw, or preferably about 5 to 20 %w will reduce the freezing point of the drilling fluid from about 1 to 40 C. A concentration of from about 1 to 40, or preferably about 5 to 30 %w polyglycerol and, optionally, glycerol of from about 1 to 60, or preferably about 5 to 35 Zw and/or from about 1 to 26, or preferably about 5 to 20 Zw salt will inhibit formation of gas hydrates. A concentration of from about 1 to 40, or preferably 1 to 10 %w polyglycerol and, optionally, glycerol of from about 1 to 60, or preferably about 5 to 30 %w and/or from about 1 to 26, or preferably about 5 to 20 %w salt in the drilling fluid will reduce shale dispersion. A concentration of from about 1 to 40, or preferably about 2 to 10 %w polyglycerol in the drilling fluid and, optionally, glycerol of from about 1 to 60, or preferably about 5 to 40 %w and/or salt of from about 1 to 26, or preferably about 1 to 15 %w will reduce fluid loss from the drilling fluid through the wall of the borehole.

Various inorganic salts are suitable for use with the invention, including but not limited to NaCl, NaBr, KC1, Caul2 and NaN03, among which NaCl is preferred. A synergistic effect is experienced when such a salt is used with polyglycerol as a mud additive package, i.e. an effect greater than the sum of the effects from salt and polyglycerol individually. This will be even more apparent from the examples hereinafter.

Polyglycerols are open and cyclic telomers of glycerol. They contain from 6 to 15 carbon atoms in a structure of which the molecular formula is C3x 02x+1 H6x+2 In this class are included: diglycerols, C605H14; triglycerols, C907H20; tetraglycerols, C1209H26; and pentaglycerols, C15 011H32, which are derived by further condensation of tetraglycerols with excess glycerol molecules.

Several of the molecules discussed in this section can undergo further cyclization under extreme conditions of pH and temperature.

This reaction yields polyglycerols containing 5 and 6 membered rings. The cyclized polyglycerols are poorer in oxygen and hydrogen than the straight chain polyglycerol.

Drilling fluid properties should be such as to promote safe and speedy drilling and completion of the well with the maximum productive capacity. Use of drilling fluids of controlled properties requires expenditure of large sums of money, and to carry out its role properly, the drilling fluid must be protected against the effects of freezing conditions, gas hydrate formation, shale dispersion and fluid loss. The use of polyglycerol and, optionally, glycerol and/or a salt, readily protects the drilling fluid against freezing conditions and gas hydrate formation by lowering the freezing point of the drilling fluid. With respect to shale dispersion and fluid loss, the use of polyglycerol and, optionally, glycerol and/or a salt aids in deposition of an impermeable filter cake, and the filter cake in turn prevents fluid loss and shale dispersion.The filter cake performs its job primarily on the basis of its impermeability to water. If the formation permeability and the fluid-loss properties of the mud are both high, large quantities of fluid will flow through the wall cake and into the permeable formation, leaving a thick wall cake behind. This cake may become so thick as to seriously interfere with movement of the drill pipe when it is withdrawn and may even result in sticking the pipe. If a thick cake is formed over the face of the producing formation, it may not become properly cleaned off during the well completion process and will interfere with the production rate of the well. The fluid which passes into the formation may also exercise an influence.When the drilling fluid is water base and shales and clays which are susceptible to hydration are drilled, the use of high fluid loss drilling fluid may result in swelling and heaving of the shale, slow drilling rates, stuck pipe, fishing jobs and even loss of the hole. If the producing formation contains hydratable clays, the intrusion of water may result in swelling of the clay particles within the sandy formation and permanent loss of permeability with resulting impaired production rates. Polyglycerol and, optionally, glycerol and/or a salt, readily solve such problems by increasing the impermeability of the filter cake to water and thus decreasing the fluid-loss properties of the drilling fluid.

The following examples are illustrative of the application of the process of the present invention and of the drilling fluid composition, and are not to be construed as limiting the scope thereof.

In the below description of the experiments, the word "polyglycerol" is used to refer to a mixture of polyglycerols.

The result for fluid loss was confirmed by examining two simple systems. The fluid loss experiments were carried out as follows. A 5 lb/bbl bentonite-containing gel slurry was mixed with the test solution, hot rolled at 65 "C for 16 hours and tested for fluid loss using the API fluid loss test described in RP 13B (Standard Procedures of Field Testing Drilling Fluid). In the tables the fluid loss is expressed in ml.

One of the systems contained bentonite and water (Tables la and). The second system contained bentonite and a carboxymethylcellulose (CMC) fluid loss additive (Table 2). The results clearly show that the addition of polyglycerol enhanced the effectiveness of these systems to reduce fluid loss.

Table la. Results of fluid loss experiments with glycerol.

Glycerol %v

Bentonitel 0 3 5 10 20 40 lb/bbl 2 56.5 52.6 51.5 48 37.5 29.5 5 1 41.5 40.5 38.5 35 28 23.5 10 1 29 27.5 25.5 23.5 21.5 19 Table lb. Results of fluid loss experiments with polyglycerol.

Polyglycerol %v

Bentonitel 0 3 5 10 20 lb/bbl 2 56 22.5 11.2 8 5.5 5 1 41. 5 17 5.5 4 3 10 1 33.5 17 9 5 3.5 Table 2. Fluid loss experiments with a 5 lb/bbl gel formulation including CMC (column "No polyalc"), the formulation with glycerol and the formulation with polyglycerol.

No Glycerol Polyglycerol

CMC I polyalc 1 5 %v 10 %v 1 5 %v 10 Zv Ib/bbl I I I I 0 1 42 1 38.5 35 1 5.5 4 0.125 1 33.5 1 29.7 27 1 4.5 3.5 0.375 1 24.5 1 19.5 21.5 1 3.5 2.5 0.5 1 20.5 1 15.5 16.5 1 2 1 To determine the cutting dispersion properties of the drilling fluids, cutting dispersion tests were carried out as follows.Sized shale cuttings (6-10 mesh) are rolled in the test fluid for the indicated amount of time at 65 "C. The shale test solution mixture is then sized over 10, 30 and 80 mesh screens. The amount retained on the screens is added and the percent retained is calculated relative to the original starting material (2.5 gm). The results of these tests are shown in Tables 3a, 3b, 4a and 4b.

In Tables 3a and 3b data are shown that demonstrate that polyglycerol is an effective inhibitor of cuttings dispersion. On a percentage basis polyglycerol is clearly more effective than glycerol at very low concentrations.

Table 3. Cuttings dispersion test results.

% retained 8 retained Green Canyon shale Pierre shale 15 s 30 s 10.5 hours 18 hours

Test fluid Fresh Water 1 4.8 1.2 1 10.4 7.8 Glycerol 2.5 %v 1 7.6 1.2 1 10.6 8.4 Glycerol 5 %v 1 15.2 3.6 1 11.2 10.6 Glycerol 10 %v 1 18.8 4.4 1 28.4 21.2 Polyglycerol 2.5 %v 1 17.6 2 1 39.6 35.2 Polyglycerol 5 %v 1 31.6 6.8 1 85.2 77.6 Polyglycerol 10 %v 1 56.4 39.2 1 87.2 82 1,2-Propanediol 2.5 %v 1 8 2.2 1 11.2 8.6 1,2-Propanediol 5 %v 1 16.3 4.8 1 12.5 9.6 1,2-Propanediol 10 %v 1 20.2 6.5 1 30.5 25.3 In Tables 4a and 4b data are shown to demonstrate that polyglycerol acts synergistically with NaCl to inhibit cuttings dispersion. This observation was unexpected and provides a means by which improved solids control and borehole stability can be realized. To evaluate the synergistic effects, the percent shale retained in fresh water was subtracted from all of the other test solutions (see column "Corr. results"). The percent retained (minus percent retained in fresh water) in the sodium chloride solution was added to the percent retained (minus percent retained in fresh water) in the polyglycerol fresh water samples. This sum represented the predicted value if the effect of the two reagents was simply additive (see column "Pred. results"). If the experimental values (minus percent retained in fresh water) exceed the predicted then synergy is supported.

Table 4a. Cuttings dispersion test results with Green Canyon shale % retained

Test fluid t Exper. Corr. Pred.

results results results average 0.03 M NaCl 21.1 0.178 %v Polyglycerol/NaCl 1 27.2 15.45 8.8 0.357 %v Polyglycerol/NaCl 1 28.8 17.05 10 0.714 %v Polyglycerol/NaCl 1 29.2 17.45 14.4 1.43 %v Polyglycerol/NaCl 1 32 20.25 18 2.86 %v Polyglycerol/NaCl 1 38.8 27.05 19.6 average fresh water (FW) 1 11.75 0.178 %v Polyglycerol/FW 11.2 0.357 %v Polyglycerol/FW 1 12.4 0.714 %v Polyglycerol/FW 16.8 1.43 %v Polyglycerol/FW 1 20.4 2.86 %v Polyglycerol/PW 1 22 Table 4b. Cuttings dispersion test results with Belridge shale.

% retained

Test fluid Exper. Corr. Pred.

results results results average 0.03 M NaCl 11.2 1.43 %v Polyglycerol/NaCl 25.6 24.2 15.2 2.86 %v Polyglycerol/NaCl 1 40.4 39 19.6 average fresh water (FW) 1.4 1.43 %v Polyglycerol/FW 6.8 2.86 %v Polyglycerol/FW 11.2 In Table 5 data are shown that polyglycerol can be mixed into a polymeric or bentonitic based mud system. The results indicate that properties which are reasonable for field operations can be formulated in the laboratory using polyglycerol.

Resinex is a water-soluble, heat stable synthetic resin used for high temperature fluid loss sold by KI Drilling Fluid Company.

XC polymer is a water soluble polymer including polysaccharides, as sold under the trade name "Kelzan XC" by Kelco Corp. CMC is carboxymethylcellulose. PHPA refers to partially hydrolyzed polyacrylamide.

The drilling fluids were mixed and hot rolled for 16 hours.

The test for fluid loss and the test for the High Pressure High Temperature (HPHT) are described in the API Standard Procedures of Field Testing Drilling Fluid (RP 13B). This document further describes the way in which the shear stress at 600 RPM and at 300 RPM (in lb/100 ft), the plastic viscosity (PV), yield point (YP) and gel strength at 10 seconds and at 10 minutes (in lb/100 ft2) were determined using a Fann 35A viscometer.

Table 5. Laboratory mud formulations, formulations 1, 2 and 3 comprise seawater and bentonite, and formulations 4 and 5 are a polymer mud.

Formulation

1 2 3 4 5 Seawater (ml) 245 221 196 - Water (ml) - - - 284 226 NaCl (gm) - - - 71 56 Polyglycerol %v 1 0 13 26 0 23 Bentonite (gm) 10 10 10 - Drill solids (gm) 1 35 35 35 - Barite (gm) 1 367 360 354 277 264 CLS (gm) 6 6 6 - CMC (gm) 1 1 1 1 0.5 Resinex (gm) 2 2 2 - - XC Polymer (gm) | - 0.5 0.5 Starch (gm) ss - - 4 4 PHPA (gm) t - - 0.25 0.25 Density (lb/gal) 16 16 16 14 14 600 RPM 71 80 85 62 95 300 RPM ss 41 46 50 39 62 PV (cps) 30 34 35 23 33 YP (lb/100 ft2) 11 12 15 16 28 10 s gel 1 3 4 5 4 5 10 min gel 1 13 14 16 11 9 API fluid loss (ml)l 11.5 5.5 2 13.5 2 Cake thickness I (32nd in) 4 2 2 5 2 HPHT (ml) 300 FF 1 26.5 12.5 9.5 22.3 13.5 Cake thickness I (32nd in) 1 20 3 2 8 3 In Table 6 results are shown to indicate that polyglycerol does reduce the freezing point of fresh water or salt water solution (containing 2.5 %w Narc1). This indicates that polyglycerol would be an effective inhibitor of gas hydrates.

Table 6. Freezing point depressions ("C) for polyglycerol solution determined using the ASTM-D1177 method.

Solvent % Polyglycerol Freezing point fresh water 0 0 fresh water 15 -2 fresh water 30 -5 fresh water 60 -6 2.5% NaCl 0 -1 2.5% NaCl 15 -6 2.5% NaCl 30 -14 2.5% NaCl 60 -13 The foregoing description of the invention is merely intended to be explanatory thereof, and various changes in the details of the described method may be made within the scope of the appended claims without departing from the spirit of the invention.

Claims

1. Water base drilling fluid comprising water, clay or polymer and a polyglycerol.

2. Water base drilling fluid comprising water, clay or polymer and a sufficient amount of polyglycerol to reduce the freezing point of the drilling fluid.

3. Water base drilling fluid comprising water, clay or polymer and a sufficient amount of polyglycerol to inhibit formation of gas hydrates in the drilling fluid.

4. Water base drilling fluid comprising water, clay or polymer and a sufficient amount of polyglycerol to prevent shale dispersion in a borehole in which the drilling fluid is employed.

5. Water base drilling fluid comprising water, clay or polymer and a sufficient amount of polyglycerol to reduce drilling fluid loss in a borehple in which the drilling fluid is employed.

6. Water base drilling fluid as claimed in any one of claims 1-5 including glycerol.

7. Water base drilling fluid as claimed in any one of claims 1-6 including salt.

8. Method for drilling a well comprising determining whether the formation to be drilled will subject a drilling fluid to at least one problem of (a) freezing, (b) gas hydrate formation, (c) shale dispersion, and (d) fluid loss; providing the drilling fluid with polyglycerol sufficient to substantially prevent the problem from occurring; rotating the drill string to cut a borehole into the earth; and circulating the drilling fluid through the drill string and through the annulus between the drill string and the wall of the borehole.

9. Method as claimed in claim 8, wherein the drilling fluid is further provided with glycerol.

10. Method as claimed in claim 8 or 9, wherein the drilling fluid is further provided with a salt.

11. Water base drilling fluid as claimed in claim 1 substantially as described in the specification with reference to the examples.