Earth boring – well treating – and oil field chemistry – Earth boring – Contains organic component
Reexamination Certificate
2001-07-03
2003-05-13
Tucker, Philip (Department: 1712)
Earth boring, well treating, and oil field chemistry
Earth boring
Contains organic component
C507S209000, C507S211000, C507S925000, C166S282000, C536S020000, C536S055300
Reexamination Certificate
active
06562762
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a novel method of controlling the loss of fluid during well drilling, completion and workover operations to permeable subterranean formations encountered during such operations. More particularly the invention relates to the use of partially hydrated polymer particles in an aqueous liquid to reduce the loss of fluid to permeable subterranean formations contacted by the aqueous liquid.
During the drilling of an oilwell, a usually aqueous fluid is injected into the well through the dill pipe and recirculated to the surface in the annular area between the wellbore wall and the drill string. The functions of the drilling fluid include: lubrication of the drill bit, transportation of cuttings to the surface, overbalancing formation pressure to prevent an influx of oil, gas or water into the well, maintenance of hole stability until casing can be set, suspension of solids when the fluid is not being circulated and minimizing fluid loss into and possible associated damage/instability to the formation through which drilling is taking place.
Proper overbalancing of formation pressure is obtained by establishing fluid density at the desired level usually via the addition of barite. Transportation of cuttings and their suspensions when the fluid is not circulating is related to the fluid viscosity and thixotropy which depend on solids content and/or use of a polymer. Fluid loss control is obtained also by the use of clays and/or added polymers.
Fluid properties are constantly monitored during the drilling operations and tailored to accommodate the nature of the formation stratum being encountered at the time. When drilling reaches the producing formation, special concern is exercised. Preferentially, low solids content fluids are used to minimize possible productivity loss by solids plugging. Proper fluid density for overbalancing formation pressure may be obtained using high salt concentration aqueous brines while viscosity and fluid loss control generally are attempted by polymer addition.
Completion fluids are those fluids used after drilling is complete and during the steps of completing the well. Completion can include cementing the casing in the well, perforating the well, setting the tubing, pump and the like. Completion fluids are generally used to control the well pressure, provide fluid loss control, and to prevent the collapse of tubing from overpressure.
Workover fluids are those fluids used after the well has been producing which has developed problems which need to be remediated.
In the rotary drilling of wells, the drilling operation depends on a continuous circulation of drilling fluid from the earth's surface to the bottom of the wellbore and back to the surface of the earth. As the drilling progresses, various earth formations are encountered and many of these formations have openings in them ranging from small holes and cracks to large fissures and the like. When such openings in the formations are encountered, drilling fluid flows into them and, in many cases, circulation stops, so that it is necessary to seal the opening before the drilling can be continued.
The problem of combating lost circulation in drilling wells is often very difficult to solve. By far the greater number of serious lost circulation zones are found at relatively shallow depths where temperatures are low. Lost circulation is combated in many ways such as by adding granular, flake, or fibrous material of various sizes to the drilling mud. On some occasions such remedial measures are unsuccessful and other approaches are tried. One of the other approaches is to place cement in the wellbore to fill the voids and fissures which caused the lost circulation.
The following U.S. patents disclose various methods of decreasing the loss of fluids during well drilling, completion and/or workover operations: Nguyen et al.—U.S. Pat. No. 5,680,900; Hessert—U.S. Pat. No. 3,818,998; Sandiford et al.—U.S. Pat. No. 4,643,255; Sydansk—U.S. Pat. No. 4,957,166; Fox et al.—U.S. Pat. No. 5,849,674; Walker—U.S. Pat. No. 4,635,726; Weaver et al.—U.S. Pat. No. 5,439,057; Hardy et al.—U.S. Pat. No. 5,762,140; Diggs et al.—U.S. Pat. No. 5,888,943; Cremeans—U.S. Pat. No. 4,217,965; Wagener—U.S. Pat. No. 4,428,844; Burts, Jr.—U.S. Pat. No. 6,016,879; Merrill—U.S. Pat. No. 5,377,760.
Goodhue, Jr. et al. U.S. Pat. No. 5,407,909 discloses aqueous fluids for well drilling having suspended therein partially-dissolved or hydrated or dispersible synthetic, natural, or modified natural polymers, such as polysaccharides, gums, biopolymers, and combinations thereof. The polymers are preferably added in a solid granular, flaked, or agglomerated state with the dry particle ranging in size from 0.01 mm to 50 mm, and currently in a range of 0.01 mm to 10.0 mm, and with the majority by weight of the particles being between 0.10 mm and 2.5 mm. The partially-hydrated or functionable, insoluble particles, referred to as “pearls” or “masses”, are formed upon hydration in a variety of sizes and shapes. The pearls or masses reduce the fluid loss to the formation by being drawn into the formation voids and completely or partially plugging and sealing these voids. The dry particles, flakes, or crystals of materials used to prepare the slurry are of various sizes. They are produced, sorted, and selected in various particle-size sub-ranges to optimize fluid loss control performance in specific types of granular, vugular, or fractured earth formations.
SUMMARY OF THE INVENTION
The invention provides a process or method of reducing the loss of fluid into flow passages of a subterranean formation during well drilling, completion, or workover operations, the fluid being selected from the group consisting of drilling fluids, completion fluids, and workover fluids, the process comprising: (a) stopping injection of the fluid into a wellbore; (b) introducing into the flow passages an effective amount of an aqueous liquid comprising (1) water; (2) a partially hydrated chitosan, the chitosan particles being partially hydrated at an acidic pH less than about 4.5 and (3) a base to raise the pH of the liquid above about 6.5; and (c) allowing the partially hydrated chitosan particles to be deposited within the flow passages thereby reducing the loss of the fluid upon resuming the well drilling, completion, or workover operation.
The invention further provides a process or method of controlling fluid loss in permeable formations penetrated by a wellbore comprising: (a) admixing an aqueous liquid with an acid to provide the aqueous liquid with a pH less than about 4.5 and chitosan under conditions of shear and for a period of time sufficient to partially hydrate the surface of the chitosan particles but insufficient to completely hydrate and disperse the chitosan particles; (b) admixing the chitosan-containing acidic liquid from step (a) with a base to raise the pH of the liquid to at least about 6.5; (c) introducing the chitosan-containing liquid from step (b) into the wellbore and into contact with a face of the permeable formation; and (d) producing a filter cake comprised of particles of the partially hydrated chitosan upon the face of the formation whereby fluid loss to the formation through the filter cake is reduced.
It is an object of the invention to decrease or prevent the loss of fluid to a subterranean formation during well drilling, completion, or workover operations.
It is another object of the invention to prevent lost circulation of the circulating drilling fluid while drilling a well into a subterranean formation.
It is still another object of the invention to provide a lost circulation-controlling fluid or pill comprising an aqueous liquid containing partially-hydrated particles of chitosan therein.
These and other objects of the invention will be obvious to one skilled in the art on reading this specification and the appended claims.
While the invention is susceptible of various modifications and alternative forms, specific embodiments thereof will hereinafter be described in detail
Cowan Jack C.
Kilchrist Michael J.
House Roy F.
Tucker Philip
Venture Chemicals, Inc.
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