Method and composition for consolidating incompetent oil-containing formations

3,389,751

Patented June 25, 1968

United States Patent Office

389 751

METHOD AND COMPOSITION FOR CONSOLIDATING INCOMPETENT OIL-CONTAINING FORMATIONS

Bobby G. Harnsberger, Houston, Tex., assignor to Texaco Inc., New York, N.Y., a corporation of Delaware

No Drawing. Filed Nov. 29, 1966, Ser. No. 597,556 10 Claims. (Cl. 166—12)

The present invention relates to the treatment of permeable underground formations. More particularly, the present invention relates to a method of treating permeable underground oil and/or gas containing formations to stabilize the sandy portion thereof and to a treating composition useful in the stabilization of incompetent sand containing underground formations.

The recovery of fluids such as gas and/or oil from underground formations has been troublesome in areas wherein the underground formation is composed of one or more incompetent said containing layers or zones. The sand particles in the incompetent zone and/or layer tend to move or migrate to the well bore during recovery of the formation fluids from the particular zone and/or layer and frequently the moving sand particles block the passageways leading to the well bore. Plugging or materially impairing the flow of the formation fluids toward the bore hole may result in a loss of these fluids to the producer or so decrease the rate of oil recovery from the well as to cause the well to be shut down because it is economically unattractive to continue to produce therefrom. An additional adverse factor resulting from the movement of the sand particles toward the well bore is that they are often carried along with the formation fluids to the well bore and passed through the pipes, pumps, etc. being used to recover the formation fluids to the surface with resulting damage to the moving parts thereof as the said particles are very abrasive.

Many attempts have been made heretofore to prevent or decrease the flow of undesirable sand particles in the formation and/or in the production tubing and associated equipment, such as by the placement of sand screens, filters, liners, and so forth. These prior attempts have been unsuccessful for a number of reasans among which is that these mechanical devices fail to prevent completely the flow of the formation particles into the production equipment. In addition these devices interfere with various types of completion and workover operations. In recent years the industry has attempted to avoid the difficulties encountered in the use of mechanical devices by employing various chemical compositions to effect consolidation of the underground incompetent formations. These methods have generally consisted of injecting into the underground formation polymerizable resinous materials which when subsequently polymerized consolidate the formation sand to form permeable barriers in the formation to prevent the sand particles from movement therethrough. However, this technique of sand consolidation has not met with widespread acceptance because of the inherent difficulties of effecting polymerization and even distribution of the resinous materials in the formation to a degree sufficient to consolidate these underground formations and yet permitting the unobstructed flow of the desirable formation fluids therethrough. Further, the cost associated with these resin coating methods has been relatively high in comparison with the prior mechanical methods.

By the method of the present invention one is able to treat effectively the underground formation to be stabilized in a rapid and efficient manner while avoiding the disadvantages of these prior art methods both mechanical and chemical.

One object of the present invention is to provide an

CO improved method of treating underground sand containing formations to stabilize the incompetent formation. An additional object is to provide a flud permeable barrier between the formation sand and the well bore to prevent or to minimize the flow of unconsolidated sand particles therethrough while maximizing the flow of desired fluids and particularly petroleum hydrocarbons therethrough. A still further object is to provide a novel treating composition for use in stabilizing incompetent sand formations and to a method of placing same to form a permeable cement filter against the incompetent formation.

How these and other objects of the invention are accomplished will become apparent with reference to the accompanying disclosure. In at least one embodiment of the method of this invention at least one of the foregoing objects will be obtained.

It has now been discovered that an improved method of treating an incompetent sand containing underground formation comprises introucing against said formation a particular treating composition consisting essentially of a water-wet admixture of sand and cement dispersed or suspended in a thickened petroleum oil in an amount sufficient to stabilize the formation adjacent to the well bore and to exert sufficient pressure on the introduced slurry to pack the sand-cement mixture against the formation and to effect removal of excess water and excess oil therefrom. The resultant formed permeable barrier serves to prevent or to materially reduce the flow of the unconsolidated sandy particles therethrough while permitting the flow of desirable formation fluids through the permeable barrier at a substantially unimpaired rate.

In carrying out the method of the present invention the slurry of the water-wet sand-cement admixture suspended in the thickened hydrocarbon oil medium is pumped down the well bore and sufficient pressure is applied thereto to force the water wetted sand-cement admixture suspended in the thickened hydrocarbon oil against the unconsolidated formation. After the slurry is placed against the formation to be consolidated a positive pressure greater than the formation pressure is exerted thereon to force the thickened hydrocarbon oil carrier medium into the formation and deposit the water wetted sand-cement admixture in the form of a filter cake against the formation sand. The deposited admixture sets up and there results a permeable cement barrier to the flow of formation sand therethrough while permitting the flow of formation fluids therethrough. When the sand-cement admixture has hardened (i.e. the cement has set) the pressure is released. The flow of formation fluids through the cement during the hardening period will adversely effect the permeability of the barrier to the formation sands. This back flow of fluids can be prevented by closing in the well until the cement hardens. Hardening of the cement can be accelerated by the use of known cement accelerators. Thereafter the well can be equipped for production and the formation fluids can be recovered by passage through the resulting formed permeable cement barrier into the well bore and recovery therefrom without the formation fluids being contaminated by the presence therein of unconsolidated sand particles.

The method of the present invention is adaptable for use in any type of well completion but it is generally used in a well wherein casing has been set and which has perforations therein at the desired intervals behind which the unconsolidated formation sands are located. Packers can be initially set above and below the perforated intervals to prevent the permeable cement slurry in the thickened hydrocarbon oil from passing into the non-isolated portions of the well and also to permit build-up of sufficient pressures on the slurry to force same through the perforations and into the formation without plugging up the

3,389,751 meni ture.

parts provides good wetability and workability. A preferred range is from 0.5 to 0.8 part of water per part of cement.

The hydrocarbon oil component of the slurry should be employed in an amount of from about 0.5 part to about 1.5 parts by weight per part by weight of cement. It is preferred that the oil component be employed in an amount of about 0.7 to about 1.5 parts by weight per part by weight of cement. Use of the oil component in this amount provides sufficient oil to disperse or suspend the sand-cement admixture in the hydrocarbon oil while avoiding a too fluid or too viscous suspension or dispersion.

Suitable hydrocarbon oils include the kerosene, diesel oil and heavier residual fractions of a petroleum crude oil or a refined crude oil and mixture of such oils. A satisfactory petroleum fraction comprises a 100-120 grade aircraft engine oil, i.e., a heavily refined paraffin base residual oil or a blend of such refined residual oil with a heavily refined paraffin base distillate oil,

Typical properties for the heavily refined residual fraction include an API gravity of 26-29, a viscosity at 210° F. of 100-125 cp. and a flash point, COC, of about 520° F. or more.

A necessary component of the petroleum oil fraction of the composition of the present invention is an oil gelling or thickening agent, i.e., a fatty acid soap such as sodium oleate, aluminum stearate, a napthenic acid soap such as sodium naphthenate or a polymeric thickening agent such as a polybutylene of relatively high molecular weight.

The gelling agent is used in an amount of from about 3 to about 7 percent by weight based on the weight of the hydrocarbon oil. A preferred gelling agent is a polybutylene known as and by the trade name Dowell J-105, which is used in an amount of about 5% by volume of the carrier oil. The polybutene is in a petroleum fraction and the product has a Brookfield viscosity at 75° of about 7500 cp., a flash point of about 145' F. and a specific gravity of 0.8, Use of more than about 10% of gelling agent results in decreased permeability to the resulting cement after hardening.

The slurry density of the composition of the present invention may vary from about 12 to about 48 pounds per gallon with a density of 15 pounds being preferred. The solids content of the gelled oil is generally about 10 pounds per gallon, although a range of from about 9 to about 12 pounds per gallon has been found to be satisfactory.

The gelled oil carrier medium containing the water wet sand and cement solids is pumped down the well bore and mto the formation to be stabilized at a rate of from about 0.25 to about 1.5 barrels per minute. Such pumping rates have been found to give the most satisfactory results in the practice of the present invention.

The composition of the present invention requires each of the components, sand, cement, water and gelled oil, to form the permeable cement barrier film. An admixture of sand, cement and water alone will result in a non-porous cement. Omission of the sand will result in an impervious glue. The water component is requited to initiate hydration and hardening of the cement. Omission of the gelling agent would result in reduced permeability and most likely would result in separation of the oil and solids during the pumping stage.

Λ further embodiment of the present invention corn prises incorporating a resinous material in the composition of the present invention. The resinous material serves to further stabilize the permeable cement barrier film to the flo w of formation fluids. In addition the resinous material will reduce the setting time of the cement, i.e., the cement curing time, and permit the more rapid production of tor3 well bore. After the slurry has been forced through the casing perforations and against the formation the well is shut in to permit the cement to set and form the permeable cement barrier.

The slurry composition useful in the method of the present invention must meet certain specific requirements. The sand component in general should be closely sized in the broad range 10-80 mesh, i.e., 12-20, 20-40, 40-60 mesh or intermediate meshes to permit effective relatively high formation fluid permeability cement barriers being formed. In addition, the ratio of the sand component to the cement component should be from about 3 to 4 parts to about 8 or 9 parts by weight of sand per part of cement. It has been found that a frac sand, i.e. a sand customarily used in formation fracturing operations, having a size of between about 20 to 40 mesh is most suitable for use in the cement slurry of the present invention. It is preferred to use a graded sand with the larger grains being not more than about twice the diameter of the smaller grains, i.e., 12-20 mesh, 20-40 mesh, 40-60 mesh, etc.

In general a 20-40 mesh sand is employed as the sand component because of its ready availability and its adaptability for use in stabilizing most formations. In addition the use of a 20-40 mesh sand appears to prevent premature bridging which is likely to be more prevalent with finer mesh sands.

Sand particles which are coarser than about 12 mesh and finer than about 80 mesh are unsuitable for use in the composition of the present invention. The coarser particles are not satisfactory because the resultant set cement barrier has too great a permeability to prevent the flow of very fine unconsolidated sand particles therethrough when the well is placed on production. Very fine sand particles, that is sand particles finer than about 80 mesh, are unsuitable because the resultant set cement has too low a permeability to permit the flow of desired formation fluids therethrough.

Use of a sand:cement ratio of less than about 3:1 results in a very low or no permeability when the cement 40 hardens, while a ratio greater than about 8 or 9:1 is too low in compressive strength when using 20-40 mesh sand.

The cement component of the composition of the present invention should be present in the dry mixture in a ratio of about 1 part by weight of cement to from about 3 to about 9 parts by weight of sand. The cement component of the composition of the present invention may be any of the cements normally used in oil well cementing operations as well as a plaster of Paris cement, a sodium silicate cement, a silicophosphate cement, an acid phosphate cement or a pozzolan cement, a sorel cement or a litharge cement. It is preferred that the cement component be a light weight Portland cement having a density of about 75 pounds per cubic foot and a chemical analysis approximately as follows: silicon dioxide 38.3%. aluminum oxide 13.0%, ferric oxide 5.2%, calcium oxide 35.7%, magnesium oxide 1.6% and sulfur trioxide 2.4%, with a loss on ignition of approximately 3.3%, This particular lightweight cement has been found to be njost suitable in the composition of the present invention 60 since permeable cements made from this cement are most stable to attack by formation brines containing sodium chloride or sodium sulfate. Other oil well cements are not as resistant to attack by formation brines or sulfate solutions and therefore are not as practical for use in the cement composition of the present invention. These other cements appear to lose some of their compressive strength and become eroded from contact with sodium chloride and sodium sulfate solutions. In contrast the cements of the composition of the present invention are very resistant 70 to erosion by sodium chloride or sodium sulfate solutions and do not lose their compressive strengths even after prolonged exposure thereto.

The water component of the slurry is employed in an amount sufficient to wet the sand particles and the ce10

5a component of the slurry and make a workable mixIt has been found that from about 0.5 to about 1.5 by weight of water, per part by weight of cement

3.389.751 mation fluids therefrom. The resinous material must be one that is water and oil insoluble when polymerized.

Representative resinous materials that have been found useful in this embodiment include the known phenolic, furfuryl alcohol and epoxy type resin materials. Representative phenolics include the acid and alkali catalyzed lower molecular weight hydroxy aryl compounds condensed with lower alkyl aldehydes such as a phenol-formaldehyde condensation product which may also contain a silane bonding or coupling agent. Representative furfuryl alcohol resins include the acid catalyzed furfuryl alcohol polymers. Representative epoxy resins include polymeric polyepoxides such as l,3-bis(2,3-epoxypropoxy)benzene, l,4'-bis(2,3-epoxypropoxy)diphenyl ether, 1,8 - bis(2,3epoxypropoxy) octane, epoxy ethers of polyhydric phenols such as 2,2-bis(4-hydroxy-phenyl)propane (Bisphenol A) etc. Amine curing agents are preferred for the epoxy resins while a combination of heat and catalyst is preferred for the phenol-formaldehyde type and furfuryl alcohol type resins.

The resinous materia] is used in the composition of the present invention in an amount of from about 3 to 6% by wt. based on the weight of the sand component of the composition. Amounts below about 3% are ineffective since relatively low strengths are attained therewith while excessive amounts are to be avoided because of cost.

The curing agent for the resinous material can be incorporated in the composition or it is possible to first emplace the composition against the sandy formation then to contact the composition with the resin curing agent.

Addition of the resin to the composition provides added strength to the permeable resulting formed cement barrier and also forms an additional barrier film with the sand component outside of the cement layer. This additional resin/sand barrier serves as a further screen against the entry of the fine formation sands into the cement barrier and then into the producing tubing while remaining permeable to formation fluids.

EXAMPLE I

A well in the Golden Meadow Field in Louisiana having perforations from the 2637 to 2641 feet intervals was washed with a perforation washer and 500 gallons of 15% by weight hydrochloric acid to remove the formation sands from behind the perforations. A packer with 90 feet of tailpipe was then run and set with the tailpipe about 1 foot off the bottom at 2659 feet. A quantity of a diesel oil fraction was spotted across the perforated interval and up past the packer. The tailpipe was picked up about 10 feet above the perforations and the packer set. Approximately two barrels of a gelled refined oil comprising 120 grade aircraft engine oil containing 5% by volume of polybutylene solution known by the trade name Dowell J—105 gelling agent were introduced into the tubing followed by about 7.5 barrels of the sand-cement gelled oil slurry. The gelled oil and sand-cement gelled oil slurry in the tubing were squeezed into the formation using fresh water as the displacement fluid at a rate of about 1 barrel per minute and at a pressure of 1000 to 3000 p.s.i.g. In all, about 3 barrels of the sand-cement gelled oil slurry were squeezed into the formation and the final squeeze pressure was 3000 p.s.i.g. The excess slurry was reversed out of the tubing. After a 12 hour interval waiting on cement the soft cement was drilled out to a depth 4 feet above the upper perforation. An additional interval of 36 hours elapsed to permit hardening of the cement. The remainder of the cement was drilled out. The well was equipped for production and produced about 45 barrels of sand-free wash water and oil for 3 days. On the fourth day of production, a small amount of sand was produced but thereafter for over a four month period the well produced i.s allowable of sand-free oil after which direct observations were discontinued.

Example II

A slurry composed of 50 grams of portland cement, 150 grams of sand having a particle size between 20 and mesh and 40 ml. of a 20% by weight aqueous calcium chloride solution was prepared and incorporated into 20 mL of gelled 120 Grade aircraft engine oil containing 5% by volume of Dowell J—105 in solution. The gelled 5 oil slurry was placed in a filter press and subjected to a pressure of 250 p.s.i, The cement was permitted to harden while the pressure was maintained thereon. The permeability was found to be 0.8 darcy

Example III

The procedure of Example II above was repeated using the same amounts of the same materials except that 50 ml. of calcium chloride solution was employed The hardened cement had a permeability of about 2 15 darcies.

Example IV

A mixture of 52 grams of litharge and 20 ml. of an aqueous 66% glycerine solution was prepared. The mixture was then slurried with 150 grams of 20 to 40 mesh ²⁰ Ottawa sand. This mixture was further mixed with 15 grams of gelled oil Grade 120 aircraft engine oil containing 5% solution of Dowell J—105 gel agent and squeezed in a filter press at a pressure of 750 p.s.i. The permeability of the set cement was found to be 6.35 ²³ darcies.

Example V

A slurry containing 30 to 40 mesh sand and portland cement in the weight ratio of 3:1 was prepared with suf30 ficient water to form a workable mix. The resultant slurry was suspended in a gelled heavy viscous hydrocarbon oil in an amount of 4 parts of the sand-cement mixture to 0.7 part by weight of the gelled oil. The suspended slurry was placed in a filter press and subjected 35 to a pressure of 1000 p.s.i.g. for 10 minutes. After the cement had hardened, it was found that the permeability was 1.89 darcies and the twenty-four hour compressive strength was 1210 p.s.i.

Example VI

A cement slurry containing 3 parts by weight of 20 to 40 mesh sand, one part portland cement. 0.7 part water and 0.7 part of a heat curable resinous mixture, comprising 10 ml. of formalin, 4 ml. of meta-cresol and 1 gram of guanidine carbonate was mixed with 0.7 part 45 of a gelled grade 120 aircraft engine oil containing 5% of Dowell J—105 gel agent. The resulting suspended slurry in the gelled oil was squeezed in a filter press at a pressure of 1000-7000 p.s.i.g. Thereafter hot water was used to cure the resin by immersing the press in a 50 hot water bath. The alkali released by the cement during hardening also aided in curing the resin. The permeability of the set resin coated cement was good,

Example VII

A slurry was formed of 4 parts by weight of 20 to 40 mesh sand, 1 part of finely ground pozzolan, 140 ml. epoxy resin known as and by the trade name Bakelite ERL-2774,” 40 ml. of l,2-epoxy-3-phenoxypropane solvent for the resin, and incorporated in 379 ml. of 60 gelled 120 grade aircraft engine oil containing 5% by volume of Dowell 1-105 as the gelling agent. The gelled oil also contained 20 ml. of a tertiary amine catalyst known by the trade name “DMP-30” as the epoxy curing agent. The resulting suspension of water wet sand65 cement and epoxy resin in the gelled oil was forced at a pressure of 1500 p.s.i. into a section of pipe about 12 in diameter containing about 1 cubic foot of loose formation sand. The pressure was maintained for about 10 min. and then the mixture was allowed to harden for about two hours. Thereafter the formed barrier was backflowed with hot water. Subsequent examination of the consolidated sands revealed that the resin had consolidated the major portion of the loose sand particles nearest the pipe end from which the pressure was applied. A lower permeability pozzolan sand-resin layer

3,389,751 had been formed beneath the major portion of the consolidated sands and a still lower pack sand layer had been consolidated by the polymerized resin.

The epoxy resin “ERL-2774” is a condensation copolymer of bisphenol and epichlorohydrin having a vis- 5 cosity at 77° F. of 11,000-13,500 cps,, a maximum hydrolyzable chlorine content of 0.18 weight percent and a specific gravity of 1.15-1.17. The hardener “DMP-30” is a tertiary amine catalyst comprising tris(dimethylaminomethyl)phenol.

Obviously, many modifications and variations of the invention as hereinbefore set forth may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims. jj