GB2552198A

GB2552198A - Fluids

Info

Publication number: GB2552198A
Application number: GB1612188.1A
Authority: GB
Inventors: GODØY Rune; Kaarigstad Håvard
Original assignee: Statoil Petroleum ASA
Current assignee: Equinor Energy AS
Priority date: 2016-07-13
Filing date: 2016-07-13
Publication date: 2018-01-17
Also published as: GB201612188D0

Abstract

Use of a composition as, or as a component of, a drilling, completion or workover fluid. The composition comprises an organic liquid selected from an alcohol, glycol and glycol ether having dissolved and/or suspended therein at least one Group I or Group II metal salt. The metal salt may be an inorganic salt. The metal salt may be a halide, carboxylate or carbonate salt of a Group I or Group II metal such as sodium chloride, sodium bromide, potassium chloride, potassium bromide, magnesium chloride, calcium bromide and mixtures thereof. The metal salt may be a blend of two or more Group I and/or Group II metal salts such as sodium chloride / sodium bromide, caesium formate / potassium formate or caesium formate / sodium formate. For example the composition may comprise monoethylene glycol, in combination with calcium chloride and/or calcium bromide. The composition may be used as a weighting agent in a drilling, completion or workover fluid. Methods of drilling, completing or workover of a well, which may be a hydrocarbon well, are carried out in the presence of the composition.

Description

(71) Applicant(s):

Statoil Petroleum AS (Incorporated in Norway)

Forusbeen 50, 4035 Stavanger, Norway (72) Inventor(s):

Rune Godoy Havard Kaarigstad

1612188.1 ₍₅₁) |_NTCL:

C09K8/48 (2006.01)

13.07.2016

C09K8/32 (2006.01) (56) Documents Cited:

WO 2016/091384 A1 WO 2003/016426 A1 US 6489270 B1

WO 2003/089540 A1 WO 1986/001253 A1 US 20070213233 A1 (58) Field of Search:

INT CL C09K Other: WPI, EPODOC (74) Agent and/or Address for Service:

Dehns

St. Bride's House, 10 Salisbury Square, LONDON, EC4Y 8JD, United Kingdom (54) Title of the Invention: Fluids

Abstract Title: Downhole composition comprising Group I or Group II metal salt (57) Use of a composition as, or as a component of, a drilling, completion or workover fluid. The composition comprises an organic liquid selected from an alcohol, glycol and glycol ether having dissolved and/or suspended therein at least one Group I or Group II metal salt. The metal salt may be an inorganic salt. The metal salt may be a halide, carboxylate or carbonate salt of a Group I or Group II meta, such as sodium chloride, sodium bromide, potassium chloride, potassium bromide, magnesium chloride, calcium bromide and mixtures thereof. The meta, salt may be a blend of two or more Group I and/or Group II metal salts such as sodium chloride I sodium bromide, caesium formate / potassium formate or caesium formate I sodium formate. For example the composition may comprise monoethylene glycol, in combination with calcium chloride and/or calcium bromide. The composition may be used as a weighting agent in a drilling, completion or workover fluid. Methods of drilling, completing or workover of a well, which may be a hydrocarbon well, are carried out in the presence of the composition.

Fluids

Field of the invention

The present invention relates to fluids for use in the drilling of wells for the recovery of hydrocarbons such as oil and/or gas. In particular, it relates to fluids for use during drilling, completion and workover operations.

Background of the invention

In drilling operations, for example in drilling of oil and gas wells, drilling fluids (also known as drilling muds) are used. Generally these are either oil-based muds (OBMs) or water-based muds (WBMs), although emulsions containing both oil and water may also be used.

Drilling fluids perform several functions. In addition to cooling and lubrication of the drill bit, and carrying out cuttings (i.e. particles of crushed or cut formation or rock produced by drilling) to the surface, an important function of a drilling fluid is to provide the necessary hydrostatic pressure within the well to prevent formation fluids from entering the well bore. Traditionally this has been achieved using solid (i.e. particulate) weighting materials, such as clays (e.g. bentonite), which confer sufficient density to the drilling fluid that this is able to produce a pressure greater than the surrounding pressure in the well bore. When pumped, such fluids are typically freeflowing, but when pumping stops the static fluid forms a gel-like structure that resists flow and serves to provide the required pressure within the well bore.

After drilling a well to the desired depth, the drilling fluid is typically replaced with a completion fluid which is pumped downhole. This is generally a solids-free and thus non-damaging composition which minimises any reduction in permeability of the production zone. The density of the completion fluid is generally selected to match that of the drilling fluid in order to maintain the hydrostatic pressure of the column of drilling fluid which is replaced.

During servicing or repair of a well there is also a need to contain the formation pressure by employing a column of high density fluid in the well bore. Typically this will be a column of fluid which exerts a hydrostatic pressure which exceeds the formation pressure. Workover fluids are used for this purpose and may, for example, be used during operations such as squeezing operations, perforation operations, well shut-ins, fracturing and gravel packing. Workover fluids are thus used once the well has been put into production I injection and in cases where mechanical and/or hydraulic intervention work is required.

Materials which have been used as completion and workover fluids include drilling muds. However, the solids contained in these have a tendency to penetrate the interstices of the formation and to seal off the formation or reduce its permeability, thereby reducing its production capability. Unlike drilling fluids, completion and workover fluids are therefore typically free from solids in order to avoid formation damage. However, these fluids still need to be of a sufficiently high density to control the formation pressures downhole. To control well pressures without the use of any solid weighting agents, such fluids are typically composed of substances that are highly water soluble in order to increase fluid densities. These substances should also be compatible for use downhole, i.e. non-reactive.

Brines and brine blends containing chloride and/or bromide salts of sodium, potassium, calcium or zinc have been proposed for use as drilling, completion and workover fluids and have the advantage that these tend to be free from particles. Their properties can be adjusted by varying the concentration and compositions of the salts in solution. For example, increasing the concentration of CaBr₂ (which is more soluble than CaCI₂) and decreasing the concentration of CaCI₂ produces a brine with a lower crystallisation temperature. The use of combinations of dry and liquid salts also allows for a degree of optimisation of their properties. Nevertheless, these fluids still have limitations in terms of their densities and/or crystallisation temperatures due, at least in part, to their solubility at relevant temperatures. For example, commercially available blends of CaCI₂ and CaBr₂ having a density of 1.80 g.cm'³ have high crystallisation temperatures, e.g. about 10°C. Below the crystallisation temperature, salt precipitates from the solution giving rise to undesirable solids. This restricts their use. For example, crystallisation temperatures as low as -2°C for winter time use and +7°C for summer time use are typically required.

The use of brines and brine blends in the treatment of deeper, high-pressure wells where higher densities are required is thus still limited. The need for a high density can result in a higher crystallisation temperature which further restricts their practical use to certain times of the year in order to prevent salt precipitation.

High pressure wells, in particular, require fluids having higher densities with controlled crystallisation points. Alkali metal formates meet this need and these may be added to drilling, completion and workover fluids, particularly those for use in treating high pressure wells in which a high degree of well control is required. One such material which finds use in the oil and gas industry today is caesium formate.

Aqueous solutions of caesium formate, produced by reaction of caesium hydroxide and formic acid, are used both as oil well drilling and completion fluids. The high density of caesium formate brines (up to 2.3 g.cm'³), together with their low toxicity, makes them particularly suited to this purpose. Caesium formate is generally considered to be environmentally friendly; for example, it is biodegradable. However, its main drawback is the limited access to caesium raw material, thus increasing its cost and the overall cost of oil and gas production.

Thus there exists a need to provide alternative fluids for use in drilling, completion and workover operations of hydrocarbon-producing wells. In particular, there is a need for such fluids which are more cost-effective than caesium formate whilst providing a sufficiently high density in order to effectively control the hydrostatic pressure within the well and which can be used at lower temperatures without crystallisation.

Summary of the invention

We now propose alternative brine-based materials for use in drilling, completion and workover operations of oil and gas wells. These have suitable densities for use in high pressure wells whilst providing a cost-effective alternative to currently available fluids. These also have lower crystallisation temperatures than conventional brines, for example below 10°C.

The materials for use in the invention comprise an organic liquid selected from an alcohol, glycol and glycol ether in which at least one Group I or Group II metal salt is dissolved and/or suspended to impart the desired density and crystallisation temperature. Such materials may be employed as a drilling, completion or workover fluid or, alternatively, may be added directly to such a fluid and provide an alternative to conventional high density fluids such as caesium formate brines.

In one aspect the invention thus provides the use of a composition as, or as a component of, a drilling, completion or workover fluid, said composition comprising an organic liquid selected from an alcohol, glycol and glycol ether having dissolved and/or suspended therein at least one Group I or Group II metal salt.

In another aspect the invention provides a drilling, completion or workover fluid comprising an organic liquid selected from an alcohol, glycol and glycol ether having dissolved and/or suspended therein at least one Group I or Group II metal salt. Such fluids will typically also comprise at least one additional material conventionally used in such fluids, such as those herein described.

In a further aspect the invention provides a method of drilling, completion or workover of a well in the presence of a fluid as herein described. Such methods will generally be performed in the context of an operation intended to recover oil and/or gas.

Detailed description of the invention

As used herein, the term “drilling fluid” refers to a fluid used during the operation of drilling of a hydrocarbon-producing well.

As used herein, the term “completion fluid” refers to a fluid pumped downhole to conduct operations after the initial drilling of a hydrocarbon-producing well.

As used herein, the term “workover fluid” refers to a fluid used during remedial operations after a hydrocarbon-producing well has been completed and has produced oil and/or gas.

As used herein, “crystallisation temperature” is the temperature at which a salt solution crystallises. This may also be referred to as the True Crystallisation Temperature, or simply “TCT”. This is an important criterion in selection of suitable materials for use downhole.

The Group I and Group II metal salts which may be employed in the invention include both organic and inorganic salts, although inorganic salts are generally preferred. The salts may be selected from halides, carboxylates, carbonate salts, and mixtures thereof. Particularly preferred are the halide salts and mixtures of halide salts of the Group I or Group II metals.

Suitable halide salts may be selected from the chloride and bromide salts of the Group I and Group II metals. These include, for example, sodium chloride, sodium bromide, potassium chloride, potassium bromide, magnesium chloride, calcium chloride, calcium bromide, and any mixtures thereof.

Suitable carboxylate salts include the metal formates. These include, for example, sodium formate, potassium formate, caesium formate, and any mixtures thereof.

Examples of suitable carbonate salts include sodium carbonate, potassium carbonate and mixtures thereof.

Blends of any of the metal salts herein described may be used. Such blends may comprise two or more of the defined salts, but typically these will be a blend of two salts. Suitable blends include the following: calcium chloride I calcium bromide; sodium chloride I sodium bromide; caesium formate I potassium formate; and caesium formate I sodium formate. A preferred blend is that based on a combination of calcium bromide and calcium chloride. The ratio of salts in a blend may be adjusted to provide the desired density of the fluid in which these are dissolved, for example based on knowledge in the art relating to the use of salt blends in drilling, completion and workover fluids. For a given density, the ratio of salts determines the TCT of the fluid - even small changes in the ratio of different salts can result in significant changes in the TCT. It is within the level of skill in the art to adjust the ratio of salts to produce a fluid having a desired TCT at a defined density.

Some of the salts for use in the invention, such as sodium chloride and potassium chloride, are readily available as dry salts. Dry salts are anhydrous and, as such, typically will contain less than 10 wt.% water, preferably less than 5 wt.% water, e.g. 2 to 5 wt.% water. The use of dry salts may be beneficial to achieve an increase in the density of the fluids.

Other salts, such as sodium bromide, potassium formate, calcium chloride, and calcium bromide are generally manufactured as liquids and are commercially available as stock fluids in defined concentrations. Athough these salts can be provided in dry form this requires processing of the liquids which is energy intensive.

Combinations of dry and liquid salts are particularly suitable for use in the invention and these may be employed in order to adjust (e.g. to increase) the density of the fluids.

Alcohols, glycols and glycol ethers are generally known and used in drilling operations, although not in the context of any of the uses proposed herein. Any alcohol, glycol, glycol ether or combination thereof which is compatible with downhole conditions, and which is compatible with the metal salts herein described may be used in the invention.

The choice of alcohol, glycol or glycol ether for use in the invention will be dependent on various factors and, at least in part, will be dependent on its density and its ability to dissolve any of the metal salts herein described. Those skilled in the art may readily select an alcohol, glycol or glycol ether which meets the required density and which is compatible with the chosen salt or blend of salts.

Examples of suitable alcohols, glycols and glycol ethers include those which are known to be compatible with halogenated compounds and include the following:

alcohols selected from allyl alcohol, amyl alcohol, 1,4-butanediol, butyl alcohol (including iso-, η-, sec- and tert-butyl alcohol), cyclohexyl alcohol, decyl alcohol (including n- and iso-decyl alcohol), diacetone alcohol, dodecanol, ethoxylated dodecanol, ethoxylated pentadecanol, ethoxylated tetradecanol, ethoxylated tridecanol, furfuryl alcohol, ethoxytriglycol, ethyl alcohol, ethyl butanol, 2-ethylbutyl alcohol, 2-ethylhexyl alcohol, heptanol, hexanol, isoamyl alcohol, isooctyl alcohol, methoxytriglycol, methyl alcohol, methylamyl alcohol, nonanol, octanol, pentadecanol, propyl alcohol (including n- and iso-propyl alcohol), tetradecanol, undecanol, and tridecyl alcohol;

glycols selected from butylene glycol, diethylene glycol, dipropylene glycol, monoethylene glycol, hexylene glycol, propylene glycol, tetraethylene glycol, and triethylene glycol;

glycol ethers selected from diethylene glycol dimethyl ether, diethylene glycol monobutyl ether, diethylene glycol monoethyl ether, diethylene glycol monomethyl ether, diisobutyl carbitol, ethylene glycol monobutyl ether, ethylene glycol monoethyl ether, ethylene glycol monomethyl ether, and polypropylene glycol methyl ether.

Preferred for use in the invention are glycols, in particular monoethylene glycol (MEG).

Suitable combinations and amounts of metal salts or metal salt blends, and alcohol, glycol or glycol ether may readily be selected by those skilled in the art depending on the desired density of the composition or fluid and its crystallisation temperature (which may be chosen dependent on factors such as the type of well, drilling conditions, the time of year, etc.).

The overall density of the compositions can be varied in order to provide different density fluids according to need. In one embodiment the density of the fluid may be adjusted to above about 1.80 g.cm'³ with a TCT suitable for use in drilling, completion and/or workover operations. A suitable TCT will typically be at or below +10°C, preferably at or below +8°C, for example in the range from -3°C to +7°C, or in the range from -2°C to +7°C .

The amount of salt (or salts) dissolved in the organic liquid should be sufficient to impart the required density to the composition or fluid without precipitation and can readily be determined by those skilled in the art having in mind the particular salt (or salts) and the chosen organic liquid. Typically, the amount of salt may be in the range of from about 10 to about 50 wt.%, preferably from about 15 to 45 wt.%, more preferably from about 20 to 40 wt.%, e.g. from about 30 to about 40 wt.% (based on the weight of organic liquid).

The materials herein described may be used directly as drilling, completion or workover fluids. However, typically these will be combined with water or other aqueous solutions, optionally together with other materials, to form the desired fluid. It is envisaged that water will generally form the base of the fluid, however, it is possible that an oil-based or oil-emulsion based fluid may be employed. In the case of an oil-emulsion both oil and water are present. Water-based fluids are, however, generally preferred since these are most cost-effective and environmentally friendly. The aqueous component of the fluid may be any water-based fluid that is compatible with the formulation of a drilling, completion or workover fluid and which is compatible with the compositions herein described. For example, the aqueous component may be fresh water or sea water. Preferably it will be fresh water.

The amount of the organic liquid I metal salt composition employed in the drilling, completion or workover fluids herein described is typically that amount which is sufficient to confer the desired density and crystallisation temperature to the final fluid. This may be varied according to its intended use, the conditions downhole, external conditions (e.g. temperature), the nature and amount of other components in the fluid, nature of the base fluid, etc., but may readily be determined by those skilled in the art. Generally the amount may be up to 85 wt.% (based on the total weight of the final fluid), preferably up to 60 wt.%, e.g. about 30 wt.%. The exact amount may be determined by a trial and error method of testing the combination of organic liquid and metal salt and chosen base composition for the drilling, completion or workover fluid to determine the density achieved and the crystallisation temperature.

Additional materials which may be present in the fluids herein described include those conventionally used in drilling, completion and workover fluids. Other materials include bridging agents, filtration control agents, lubricants, de-foamers, fluid loss control agents, pH adjusting agents, shale inhibitors, and anti-bacterial agents. These may be used in conventional amounts known to those skilled in the art or in an amount which could readily be determined by those skilled in the art having in mind factors such as the intended use of the fluid. Additional weighting agents may be present, however, these will generally be in reduced amounts due to the properties of the fluids described herein. Any lowered concentrations of known weighting agents may readily be determined by those skilled in the art.

When used in drilling, the drilling fluid may also contain drilling fines such as shale and sandstone fines.

When used as completion or workover fluids, clarity of the fluid is required to eliminate formation plugging by solids. Such fluids will thus typically be free from solids. By “free from solids” it is intended that the fluids will contain less than 5 wt.%, e.g. less than 1 wt.%, solids (based on the total weight of the fluid).

The drilling, completion and workover fluids can be prepared by mixing all of the components together. In the case of a water-based fluid the continuous water phase will generally comprise about 90% by volume of the fluid.

The density of the fluids can be varied in order to provide different density fluids for use in different situations. For example, drilling depth will impact on the desired density. Typically the density of the fluid may be in the range from 1.70 g.cm'³to 2.05 g.cm'³, more preferably from 1.80 g.cm'³ to 2.05 g.cm'³, e.g. from 2.03 g.cm'³ to 2.05 g.cm'³.

The fluids of the invention can be introduced into the well bore using any conventional technique such as being pumped through the drill pipe. Conventional techniques may also be used to recover the fluids.

During the course of an operation it may be desirable to use the fluid in combination with other agents, e.g. a foam-suppressing agent. Examples of such agents include n-butyl alcohol, 1-butanol propyl carbinol, etc.

Once drilling operations are completed the well is prepared for the completion process, i.e. made ready to be put into production. During the completion process the drilling fluid remaining in the well bore may be displaced by a completion fluid prior to running a production screen into the well. Completion fluids are typically water-based and formulated to have the same density as the mud used for drilling thereby maintaining the hydraulic pressure on the well bore.

The materials according to the invention have been described primarily for use in the drilling, completion or workover of a well for the recovery of hydrocarbons such as oil and/or gas. However, these may be used in other operations where drilling fluids are used, such as in perforation, plug and abandonment operations, slot recovery, killing of wells, etc.

An important advantage of the materials herein described is the ability to adjust the density of the fluid according to need, e.g. according to the conditions in the well, e.g. drilling depth, type of formation, etc. Density can be adjusted by varying the amount of the metal salt (or salts) which is present and/or by selection of a suitable alcohol, glycol or glycol ether.

The fluids according to the invention enable a variety of densities to be achieved, in turn minimising or eliminating the need for any additional weighting material that may be used. Preferably the amount of other weighting materials, such as caesium formate, is less than 5 wt.%, preferably less than 1 wt.%, e.g. about 0 wt.%.

The invention is illustrated by way of the following non-limiting examples.

Example 1

The degree of solubility of dry CaCI₂ in monoethylene glycol (MEG) was determined.

Increasing amounts of dry CaCI₂ were added stepwise to 300 ml (334 g) of monoethylene glycol (MEG) at room temperature (22-23°C) while stirring in a beaker. At up to 30 wt.% (100 g) the salt dissolved well. From 30 to 40 wt% (up to 135 g) the salt still dissolved well. In the range of to 50 wt.% (i.e. up to 170 g) the salt no longer dissolved completely and a precipitate remained at the bottom of the beaker.

Example 2

The degree of solubility of dry CaBr₂ in monoethylene glycol (MEG) was determined.

Increasing amounts of dry CaBr₂ were added stepwise to 300 ml of monoethylene glycol (MEG)) at room temperature (22-23°C) while stirring in a beaker. At up to 40 wt.% the salt dissolved well. Above 40 wt% the salt no longer dissolved completely and a precipitate remained at the bottom of the beaker.

Claims

Claims:

1. Use of a composition as, or as a component of, a drilling, completion or workover fluid, said composition comprising an organic liquid selected from an alcohol, glycol and glycol ether having dissolved and/or suspended therein at least one Group I or Group II metal salt.

2. Use as claimed in claim 1, wherein the metal salt is an inorganic salt.

3. Use as claimed in claim 1, wherein the metal salt is a halide, carboxylate, or carbonate salt of a Group I or Group II metal.

4. Use as claimed in claim 3, wherein the metal salt is a chloride or bromide salt of a Group I or Group II metal.

5. Use as claimed in claim 1, wherein the metal salt is selected from the group consisting of sodium chloride, sodium bromide, potassium chloride, potassium bromide, magnesium chloride, calcium chloride, calcium bromide, and mixtures thereof.

6. Use as claimed in any one of the preceding claims, wherein the metal salt is a blend of two or more Group I and/or Group II metal salts.

7. Use as claimed in claim 6, wherein the blend is selected from calcium chloride I calcium bromide; sodium chloride I sodium bromide; caesium formate I potassium formate; and caesium formate I sodium formate.

8. Use as claimed in any one of the preceding claims, wherein the organic liquid is an alcohol, preferably an alcohol selected from allyl alcohol, amyl alcohol, 1,4-butanediol, butyl alcohol (including iso-, η-, sec- and tert-butyl alcohol), cyclohexyl alcohol, decyl alcohol (including n- and iso-decyl alcohol), diacetone alcohol, dodecanol, ethoxylated dodecanol, ethoxylated pentadecanol, ethoxylated tetradecanol, ethoxylated tridecanol, furfuryl alcohol, ethoxytriglycol, ethyl alcohol, ethyl butanol, 2-ethylbutyl alcohol, 2-ethylhexyl alcohol, heptanol, hexanol, isoamyl alcohol, isooctyl alcohol, methoxytriglycol, methyl alcohol, methylamyl alcohol, nonanol, octanol, pentadecanol, propyl alcohol (including n- and iso-propyl alcohol), tetradecanol, undecanol, and tridecyl alcohol.

9. Use as claimed in any one of claims 1 to 7, wherein the organic liquid is a glycol, preferably a glycol selected from butylene glycol, diethylene glycol, dipropylene glycol, monoethylene glycol, hexylene glycol, propylene glycol, tetraethylene glycol, and triethylene glycol.

10. Use as claimed in any one of claims 1 to 7, wherein the organic liquid is a glycol ether, preferably a glycol ether selected from diethylene glycol dimethyl ether, diethylene glycol monobutyl ether, diethylene glycol monoethyl ether, diethylene glycol monomethyl ether, diisobutyl carbitol, ethylene glycol monobutyl ether, ethylene glycol monoethyl ether, ethylene glycol monomethyl ether, and polypropylene glycol methyl ether.

11. Use as claimed in claim 9, wherein the glycol is monoethylene glycol.

12. Use as claimed in claim 1, wherein the composition comprises monoethylene glycol, in combination with calcium chloride and/or calcium bromide.

13. Use as claimed in any one of the preceding claims, wherein the metal salt is present in an amount in the range of from about 10 to about 50 wt.%, preferably from about 15 to 45 wt.%, more preferably from about 20 to 40 wt.%, e.g. from about 30 to about 40 wt.% (based on the weight of organic liquid).

14. Use as claimed in any one of the preceding claims, wherein the composition has a density from 1.70 g.cm'3 to 2.05 g.cm'3, preferably from 1.80 g.cm'3 to 2.05 g.cm'3, e.g. from 2.03 g.cm'3 to 2.05 g.cm'3.

15. Use as claimed in any one of the preceding claims, wherein the composition has a crystallisation temperature at or below +10°C, preferably at or below +8°C, for example in the range from -3°C to +7°C, or in the range from -2°C to +7°C .

16. A drilling, completion or workover fluid comprising a composition as defined in any one of claims 1 to 15, optionally together with at least one additional material conventionally used in a drilling, completion or workover fluid, preferably at least one material selected from bridging agents, filtration control agents, lubricants, de-foamers, fluid loss control agents, pH adjusting agents, shale inhibitors, and anti-bacterial agents.

17. A method of drilling a well in the presence of a drilling fluid as claimed in claim 16.

18. A method of completing a well in the presence of a completion fluid as claimed in claim

16.

19. A method of workover of a well in the presence of a workover fluid as claimed in claim 16.

20. A method as claimed in any one of claims 17 to 19, wherein the well is a hydrocarbonproducing well.

21. Use of a composition as defined in any one of claims 1 to 15 as a weighting agent in a drilling, completion or workover fluid.

Intellectual

Property

Office

Application No: GB1612188.1