NL8101498A - REMOTE SYSTEM USEFUL WHEN BRINE WELL COMPLETING. - Google Patents

Description

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Spacing system "useful in completing wells with brine.

The invention relates to the completion of wells and in particular to a method of introducing a completion fluid into the borehole under conditions such that contamination of the completion fluid by downhole fluids is reduced.

Boreholes are drilled deep into the earth when detecting oil and gas. These boreholes are lined with a casing which is usually of heavy steel pipe and cement is forced down through the casing and up through the annular space between the outer wall of the casing and the wall of the borehole. The cement is pushed to the bottom of the liner using a displacement fluid, in particular drilling fluid. The cement and drilling fluid are usually separated by a fixed plug. After this cementing procedure and prior to putting the well into production, the casing should be cleaned with respect to this fluid and production equipment should be set up.

Actions for cleaning the upholstery are known. Typically, the technique involves lowering a tubing string into the casing, injecting a completion fluid down through the annular space between the casing and tubing string to move the drilling mud out of the annular space and drilling mud and to carry the waste through the tubing string to the surface. Contact between the displacing completion fluid and the displaced drilling fluid results in a two-bottle mixture. At the earth's surface, the drilling fluid is separated from the completion fluid. Usually the completion fluid contains between 1 and U vol. # Of rinse after the first circulation. After contamination with this concentration of drilling mud, the completion fluid is not useful for completion operations.

Usually, the filtering of the completion exists

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- 2 - brine from filtration through a 50 micron filter followed by a 10 micron filter. Ideally, the final filtrate should be passed through a 2 micron filter prior to recirculation into a wellbore. However, the high concentration of drilling mud (1 to U vol.%) Added to the muds commonly used in cementing causes the 2 micron filter to clog along with the 10 micron filter and become impermeable. If filtration becomes impossible, disposing of this type of brine creates problems from environmental pollution. Therefore, it is necessary to limit the filtration requirements and to reuse the completion brine.

The known completion techniques include the use of brine or clean water as a buffer between the drilling fluid 15 and the completion fluid. However, this practice is not satisfactory since the annular space is not completely cleaned of rinse with the result that the brine of completion is contaminated and there is a related risk that due to reduction of the hydrostatic pressure on the brine or freshwater buffer, a breakthrough production fluid can occur which is hazardous to personnel and equipment on the surface of the earth. To control such a breakthrough, packers are arranged in the annular space between the tubing string and the liner. However, breakthroughs can provide sufficient pressure, making these packers insufficient.

Known buffer fluid techniques are disclosed in U.S. Patent No. 108,779 which relates to an aqueous hydrocarbon emulsion with solid granular additives dispersed herein for use as an oil well fluid. More specifically, this emulsion is used as a buffer or packer fluid to clean the annular space between the casing of the well and the wall of the well. The fluid displaces and cleans the annular space with respect to drilling mud and is displaced by cement. This fluid is injected between a drilling mud and cement and is not usable as a buffer between mud and a completion fluid.

The invention relates to a buffer system and a method of using it, the system being useful for effectively separating different types of completion fluid and drilling mud during well completion, and comprising a buffer fluid having a viscosity of about 5 to 100 centipoise and additionally a scrubbing fluid and a repelling fluid. The system can be designed for use with a water-based flush or an oil-based flush.

In a method of completing a wellbore reaching into an underground formation, wherein a completion fluid is pumped into the annular space between the tubing string and the casing extending into the wellbore to displace the mud from the well, the invention provides punching a buffer system in the liner to displace the flush and then pumping the completion fluid into the liner to displace both the buffer system and the flush. The drilling mud, completion fluid, buffer system and mixtures thereof are collected at the surface of the earth. The drilling mud and buffer system are discarded and the completion fluid plus mixtures of fluid containing completion fluid are collected, filtered and recirculated into the tubing string and annulus until the annulus in well bore is sufficiently cleaned to start production.

The invented buffer system should be compatible with water-based rinses, including substances such as lignosulfonate and polymers, and oil-based rinses. The term "compatible" as used hereinafter means that the adjacent fluid does not cause degradation or alteration of the properties such as rheology, etc., of the other fluid.

The invented buffer systems should also be compatible with the types of completion fluid commonly used in the completion of oil wells and serve the viscosity 8101498 *

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- not noticeably disadvantage the completion fluid. Conventional completion fluids include solutions of salts that are highly water-soluble and stable, have a high specific gravity and do not react with other dissolved constituents of the formation. The high specific gravity of the fluid is used to control the differential pressure in the annular space and the tubing string during production. Useful salts are; calcium chloride, potassium chloride, sodium bromide, sodium chloride, mixtures of calcium chloride and calcium bromide, and mixtures of zinc bromide, calcium bromide and calcium chloride.

The buffer system includes a buffer fluid and preferably a buffer fluid preceded by a scrubbing fluid and followed by a dislodging fluid. The buffer fluid 15 is composed of a solvent and a viscous maker. The solvent can be an aqueous or hydrocarbon solvent. The term "aqueous solvent" includes, but is not limited to, freshwater, saltwater, and seawater and may include a saturated calcium chloride solution. The term "hydrocarbon hydrogen solvent" includes, but is not limited to, kerosene and diesel oil. If a water-based rinse is to be displaced, an aqueous solvent is preferred as the solvent. If an oil-based rinse is to be displaced a hydrocarbon solvent is preferred.

Preferably, the buffer fluid contains sufficient amount of the viscous maker to have a sufficiently high viscosity that the buffer fluid exists in a laminar or uniform flow during normal circulation rates, but the viscosity should be within such a limit that the buffer fluid is pumpable, the viscosity generally being between about 5 and 1 * 00 centipoise. The term "viscous maker" includes any agent that increases the viscosity of the solvent and provides a buffer fluid that is compatible with the rinse and the completion fluid. Agents useful according to the invention include, but are not limited to "limited, colloidal agents such as clays," certain polymers, emulsifiers, diatomaceous earth, and rigid seis. Useful clays include kaolin overnight materials (kaolinite, halloysite, dickite, nacrite, and endellite), bentonites (mont-5 morillonite, beidellite, nontronite, hotorite, and saponite), aqueous micas (bravaisite or illite), attapulgite, sepiolite, and the like. Useful polymers include carboxyl methylellulose, hydroxyl methylellulose and the like which are useful with aqueous solvents. When choosing a viscous maker, consideration should be given to the viscosity to be added, the chemical compatibility of the buffer fluid with both the rinse and the completion fluid, and the ease of filtration to remove solid particles from the buffer fluid. Preferably, the viscous maker is easily floatable in the brine of completion and easily filterable from the brine. More specifically, the viscous maker for an aqueous solution should be clay. Preferably, the viscous maker for an aqueous solution is an atta-pulgite clay.

The buffer fluid should be stable in the environment encountered in the coating where the temperature may be higher than 80 ° C and the pressure higher than 35 atmospheres. The fluid, including the viscous maker, is intended to transport all debris and sand present in the coating. The buffer fluid should have a very high fluid loss so that the fluid can be easily filtered to remove the flush. In addition, the clay used as a viscous maker should be easily flocculated from the buffer fluid.

An ideal buffer fluid is a thixotropic, colloidal fluid with a gel strength, ie a fluid which, when agitated or circulated (for example by pumping or otherwise), has a measurable relatively low viscosity and is free-flowing (non-plastic), especially at high temperature; but when such agitation or circulation Ssrf 35 is terminated, the fluid regains its gel strength. The degree of gel- 8101498 _ r..f, "......______". "... TT, ..... ..." ll ,, 5_ ......... - 4 * ·· - · ----- r. * .. aw ^ .. · - -......... '--1 - -' - · · - »·· - 6 - post-agitation formation is reduced so that the mud and debris contained in the fluid are only allowed to fall a short distance before the gel structure is sufficiently strong to support the mud and debris.

When such a buffer fluid of the correct viscosity, the correct gel formation rate and the correct gel strength is circulated through a coating, it has a sufficiently high viscosity to carry the mud and debris from the bottom of the borehole to the earth's surface and it has a gel strength such that the rinse and debris can settle in a sump. When quenched, it develops enough gel strength to avoid sagging and debris in the coating when it becomes necessary not to continue circulation for a significant period of time.

If desired, a weight-increasing material is added in an amount effective to impart a specific gravity to the buffer fluid such that it has a useful hydrostatic pressure to maintain the buffer fluid between the drilling fluid and the completion fluid. A variety of conventional weight-enhancing materials such as barium sulfate, calcium carbonate, iron oxide, lead oxide, and cement solids for selectively adjusting the specific gravity of the buffer over a wide range can be used.

The buffer fluid should be pumped down the liner in quantities and at flow rates such that uniform or laminar flow prevails in the annular space between the tubing column and the liner and that the two mixed parts, ie the pre-mixing between the spool -30 and the buffer fluid and the subsequent mixing between the completion fluid and the buffer buffer fluid.

The preferred flow rate decreases the pre- and post-mixing and is such that uniform flow occurs in the annular space between the tubing string and the casing.

8101498 * - 7 -

The scrubbing fluid portion of the buffer system contains a low viscosity solvent. Preferably, the scrubbing fluid has a sufficiently low viscosity so that turbulent flow can be achieved during normal circulation rates of the completion fluid, the viscosity generally being less than 10 centipoise. The scrubbing fluid should be compatible with the fluid to be displaced and with the subsequent buffer fluid.

Preferably, the low viscosity solvent 10 is selected from the group consisting of an aqueous solvent and a hydrocarbon solvent. The terms "aqueous solvent" and "hydrocarbon solvent" have been indicated above for buffers fluid solvents. If a water-based rinse is to be displaced, fresh water, sea water, or brine are preferred as the low viscous solvent. If an oil-based rinse is to be displaced, a hydrocarbon solvent is preferred as a low-viscous solvent.

Preferably, the invented scrubbing fluid additionally contains a scrubbing agent for scouring the walls of the annular space. Useful scrubbing agents include abrasive materials such as sand and surfactants such as detergents. Preferably, the scrubbing agent is good quality sand such as broken sand, which is clean and relatively free of fines, and having a mesh size between about 12 and 60. An scrubbing fluid of about 1 to 10 vol. scrubbing agent is preferred.

Most desirably, the scrubbing fluid contains about 5 vol. Of scrubbing agent. The scrubbing fluid can be composed of a combination of different low viscous solvents and scrubbing agents which are used as a mixture or sequentially.

The scrubbing fluid should be punched down into the liner at such flow rates that turbulent flow prevails in the annular space between the tubing string and 1 8101498

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3 - 8 - the coating and in amounts such that the mixed parts of the adjacent fluids are not mixed.

The dislodging portion of the buffer system assists the operator of the well in determining the end of the buffer system, giving the ability to switch the flow of circulating fluids from a buffer fluid collection point to a buffer fluid collection point. the completion fluid. The buffer system is discarded and the completion fluid is filtered through conventional filter devices and recirculated into the wellbore until the wellbore is sufficiently cleaned. The dislodging fluid should be compatible with both the buffer fluid that precedes it and the completion fluid that replaces the dislodging fluid. The repelling fluid preferably consists of one of the following 15 substances; an aqueous calcium chloride solution, sea water or fresh water.

The repelling fluid serves to be low-pumped into the coating at such flow rates that turbulent flow prevails in the annular space between the tubing string and the coating and in such amounts that the mixed parts of the adjacent fluids are not mixed.

Preferably, the buffer system comprises from about 50 vol. Of scrubbing fluid, from about 25 to about 85 vol. Of buffer fluid and from about 5 to about 50 vol. Of scavenging fluid. The most desired buffer system consists of about 20 to 30 vol. # Of scrubbing fluid, from about Ho to 60 vol. # Of buffer fluid, and from about 20 to 30 vol. # Of repelling fluid.

The filtration of the separated complete pe-boulder can be accomplished by known techniques such as filtration through a coarse filter followed by a fine filter.

Preferably, the coarse filter has a mesh size of about 10 microns and the fine filter has a mesh size of about 2 microns.

The following examples give various embodiments of the invention.

Example I.

A buffer system was achieved consisting of a buffer fluid consisting of a mixture of 5 pounds of attapulgite, 5 390 pounds of barite and 28 gallons of sea water to each form a barrel of buffer fluid, a scrubbing fluid consisting of a mixture of 45 pounds of crushed sand per barrel of fresh water and a repelling fluid consisting of 0.1 gallon DMS surfactant and 0.25 quarts Wellaid 840 corrosion inhibitor per barrel of fresh water. A completion fluid was achieved consisting of 40.4 wt.% Calcium bromide, 14.5 wt.% Calcium chloride, 6.5 wt.% Zinc bromide and 38.6 wt.% Freshwater.

An 8,500 foot-deep well was drilled, clad, and cemented off the coast of Louisiana. The cement was moved into the wellbore by a water-based mud of 16 pounds per gallon. The diameter of the tubing string was 2 7/8 inches and the diameter of the liner was 75/8 inches.

30 barrels of scrubbing fluid was pumped into the 20 jut at 4 bbl / min, followed by 50 barrel buffer fluid at 4 bbl / min, followed by 20 barrel repellent fluid at 4 bbl / min and then followed by 262 barrel completion fluid at a flow rate of 4 bbl / min.

The scrubbing fluid and the buffer fluid were discarded as was part of the dislodging fluid. The final fluid contained 0.5 vol. Of rinse after the first circulation. The final fluid was filtered through a 50 micron filter, then through a 10 micron filter and recirculated. After three complete circulations, the fluid contained less than 0.1 vol. # 30 rinse.

Example II

A buffer system was achieved consisting of a three-part scrubbing fluid; a first part was 30 barrels of diesel oil, the second part was 8 barrels of Wellaid 311 35 (a detergent) and the third part was 30 barrel of fresh water backward - injected one after the other and a buffer fluid consisting of 37 8 wt. Calcium chloride in aqueous solution, dispersed with Polybrine (a viscous maker), the buff yard having a viscosity of 20 to 50 centipoise. A completion fluid 5 was prepared from 37 * 8 wt.% Calcium chloride in aqueous solution.

An 18,922 foot-deep well was drilled in Louisiana lined and cemented. For the cementation procedure, a water based rinse of specific gravity of 12 pounds per gallon was used. The diameter of the coating was 7 5/8 inches decreasing to 7 inches decreasing to 5 inches. The diameter of the tubing string decreased from 2 7/8 inches to 2 3/8 inches.

30 barrels, 8 barrels and 30 barrels of scrubbing fluid were pumped into the annular space between the liner 15 and the tubing column at a flow rate of 5 bbl / min, followed by 50 barrels of buffer fluid at a flow rate of 5 bbl / min and then followed by 700 bar of completion fluid at a flow rate of 5 bbl / min.

The buffer system was discarded. The completion fluid contained 0.1% rinse after the first circulation. The priming fluid was filtered through a 10 micron filter and then through a 2 micron filter and then recirculated in the bore. After three complete circulations in the bore and filtrations, the fluid was clear with no noticeable solids.

The results of the examples show that the buffer system preserves the completion fluid by significantly reducing the concentration of wash in the completion system. The concentration in a typical brine to complete a well at the end of the first circulation is between 1 and 1% by volume. In both of the above examples, the concentration was 0.1 to 0.5% by volume rinse, making it possible to recirculate the completion fluid again.

After a limited number of recirculation (2 to 3), the completion fluid was clean enough (less than 0.1% solids or less) to allow the completion of the completion operations. Using the known methods, up to 2 days (30 to c0 circulations) of circulation can be used without "achieving the purity of the fluid" as achieved by practicing the invention.

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Claims (20)

A method of completing a wellbore in which a completion fluid is pumped into a wellbore to displace drilling fluid from the wellbore, characterized by pumping a buffer system into the wellbore to displace the drilling fluid before the completion fluid is pumped into the wellbore, the buffer system consisting of a buffer fluid having a viscosity such that the buffer fluid flows laminarly or evenly during pumping. \ A method of displacing mud from a wellbore during the completion of the wellbore, characterized by pumping a buffer system into the wellbore to displace the mud from the wellbore and pumping a completion fluid into the wellbore around the buffer system and the displacement mud from the wellbore, the buffer system consisting of a buffer fluid of such viscosity that the buffer fluid flows laminarly or evenly during pumping. Method according to claim 1 or 2, characterized in that the buffer fluid has a viscosity of 5 to 00 centipoise. 1) ·. A method according to claim 2, characterized in that the buffer system further comprises a scrubbing fluid with a viscosity such that the scrubbing fluid flows turbulently during normal circulating pumping, the scrubbing fluid being pumped into the coating prior to the buffer fluid. A method according to claim k, characterized in that the method further comprises a repelling fluid with a viscosity such that the repelling fluid flows turbulently during normal circulating pumping, the repelling fluid being pumped into the coating after. the buffer fluid. A method according to claim U, characterized in that the scrubbing fluid consists of a low viscosity solvent selected from the group consisting of an aqueous solvent and a hydrocarbon solvent. m \ 8101498 - 13 - Method according to claim 6, characterized in that the scrubbing fluid additionally comprises a scrubbing agent which is broken sand. A method according to claim 1 or 2, characterized in that the buffer fluid consists of a solvent and a viscous agent. Method according to claim 8, characterized in that the viscous agent is clay. 10. A method according to claim 9, characterized by-10 that the viscous agent is attapulgite. A method according to claim 5, characterized in that the repelling fluid is selected from the group consisting of an aqueous calcium chloride solution, sea water or fresh water. 12. A method according to claim 1 or 2, characterized in that the buffer fluid is pumped down through the coating at such a flow rate that uniform flow prevails in the annular space between the tubing string and the coating. Method according to claim 4, characterized in that the scrubbing fluid is pooped down through the coating at such a flow rate that turbulent flow prevails in the annular space between the tubing string and the coating. Ih-. Buffer system for separating different types of completion fluid and drilling mud during well completion, characterized by a buffer fluid with a viscosity of about 5 to 100 centipoise. Buffer system according to claim 1, characterized in that the buffer system additionally comprises a scrubbing fluid with a viscosity less than about 10 centipoise, the scrubbing fluid being pumped down into the coating prior to the buffer fluid. Buffer system according to claim 15, characterized in that the method further comprises a dislodging fluid with a viscosity less than about 10 centipoise, the dislodging fluid being pumped into the coating after the buffer fluid (8101498). Buffer system according to claim 15, characterized in that the scrubbing fluid is provided with a low viscous solvent selected from the group consisting of fresh water, salt water and hydrocarbon distillate. Buffer system according to claim 17, characterized in that the scrubbing fluid is additionally provided with a scrubbing agent, which is sand. Buffer system according to claim 1U, characterized in that the buffer fluid consists of a solvent and in a viscous agent. A buffer system according to claim 19, characterized in that the viscous agent is a clay. Buffer system according to claim 20, characterized in that the viscous agent is attapulgite. Buffer system according to claim 16, characterized in that the repelling fluid is selected from the group consisting of aqueous calcium chloride solution, sea water or fresh water. * 8101498