Abstract:
A method for diverting steam injection in injection wells by the use of perforation ball sealers composed of polymer compounds covered with a thin coating of elastomer of low enough density to float in the injected fluids, yet able to stand the adverse temperatures of steam injection.

Description:
In many steam injection wells, it is desirable to alter the injectivity of steam to improve sweep of the formation. However, polymers frequently used for this purpose in lower temperature environments are not effective in steam injection because the intense temperatures break down the profile altering polymer rendering it ineffective. Mechanical isolation or diversion is not practical due to the cost of equipment. Most packers and packer components are not capable of withstanding the adverse temperature environment for long periods of time. 
     Perforation ball sealers are used effectively in various stimulation treatments to divert treating fluids such as acids, solvents, and fracturing fluids. The adaptation and effective use of perforation ball sealers is well documented in the literature. U.S. Pat. Nos. 4,102,401; 4,244,425; and 4,287,952 issued to Exxon Corporation are examples of where perforation ball sealers have been used to divert treating liquids in formations. The prior art references do not show use of ball sealers in a steam injection process during the recovery of hydrocarbonaceous fluids from a reservoir of formation. Therefore, what is needed is a method for utilization of ball sealers with a steam injection process which follows a liquid treatment of a formation. 
     SUMMARY OF THE INVENTION 
     This invention is directed to a method to control the injection profile in a steam injection well which has at least two perforations fluidly connected with zones of different permeabilities in a hydrocarbonaceous bearing formation. In the practice of this invention, a carrier liquid having ball sealers suspended therein is downwardly flowed into said well. Said ball sealers have a density less than the density of said carrier liquid, while being of a size sufficient to plug said perforations. Said ball sealers are of a composition sufficient to withstand the steam injection temperature and pressure. The flow velocity of said carrier liquid is maintained at a rate sufficient to overcome the bouyancy of said sealers and is also sufficient to transport said sealers to the perforations, thereby closing off at least one zone of high permeability. Thereafter, steam of a flow and a pressure sufficient to keep said sealers seated on the perforations is injected into the well. This causes the steam to enter at least one zone of a lesser permeability while driving said carrier liquid ahead of said steam. The water and steam combine to drive the hydrocarbonaceous fluids to a production well for removal from said well. 
     It is therefore an object of this invention to control the formation profile with ball sealers during steam injection to remove hydrocarbonaceous fluids from areas of less permeability. 
     It is another object of this invention to use ball sealers to control the profile of a hydrocarbonaceous formation which formation has at least two zones of differing permeability fluidly connected to perforations in said well. 
     It is a further object of this invention to lower the cost of a steam injection process through the use of ball sealers. 
     It is yet a further object of this invention to provide a method which gives greater flexibility when following a water flood process with a steam injection process. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The drawing is a schematic representation showing a hydrocarbonaceous formation penetrated by an injection well and a production well where ball sealers have closed perforations in the injection well so that steam can enter through perforations into a zone of lesser permeability to remove hydrocarbonaceous fluids from the formation. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the practice of this invention, referring to the drawing, hot water is pumped through conduit 19 into injection well 10. Included in the hot water or carrier liquid are perforation ball sealers 22. The hot water can be either fresh water or salt water and preferably should be substantially near the boiling temperature of the water. Well 10 is surrounded by a casing 12 which penetrates formation 30 and contains a zone of at least two different permeabilities. Well casing 12 contains perforations 24 which enter into the hydrocarbonaceous fluid producing formation. 
     Upon introducing the ball sealers 22 into the fluid upstream of the perforated areas of the casing 12, said sealers are carried down into the well 10 by the fluid flow. Once the fluid arrives at the perforated intervals 24, and into the strata being treated, the fluid is displaced outwardly through said perforations. The flow of the treating fluid through the perforations 24 carries the entrained ball sealers 22 toward said perforations 24 causing them to seat on the perforations 24. Once seated on the perforations, ball sealers 22 are held onto the perforations by the fluid pressure differential which exists between the inside of the casing and the producing strata of said formation on the outside of casing 12. Seated ball sealers 22 serve to effectively close the perforations 24 which have the greatest flow of the carrier liquid therethrough. Said perforations will remain sealed until such time as the pressure differential is reversed, and the ball sealers are released. 
     Said ball sealers 22 will tend to first seal the perforations through which the carrier liquid is flowing most rapidly. The preferential closing of the high flow rate perforation tends to equalize treatment of the production strata over the entire perforated interval. 
     For maximum effectiveness in seating on perforations 24, the ball sealers 22 preferably should have a density less than the density of the carrier liquid in the well bore at the temperature and pressure conditions encountered down hole. For example, it is not unusual for the bottom hole pressure to exceed 10,000 psi and even reach 15,000 psi during the well treatment procedure. Sealers and a method for use in well treatment with fluid diversions are discussed in U.S. Pat. Nos. 4,407,368 and 4,244,425 issued to Erbstoesser on Oct. 4, 1983 and Jan. 13, 1981, respectively. These patents are hereby incorporated by reference. 
     Once the ball sealers have seated themselves in the perforations, the carrier liquid injection is ceased. Thereafter, steam injection is commenced by the injection of steam into conduit 19 which forms a part of injection well 10. One method for injecting steam in a formation is discussed in U.S. Pat. No. 4,489,783 which issued to W. R. Shu on Dec. 24, 1984. Another is discussed in U.S. Pat. No. 4,417,620 which issued to E. G. Shafir on Nov. 29, 1983. Both of these patents are incorporated by reference. 
     Upon entering the injection well 10, the steam pressure forces the water into the unblocked perforations in the area of the zone of low permeability causing water in that area to be forced therethrough. Steam is injected into injection well 10 via conduit 19 and goes through the open perforations 24 where the ball sealers have not seated and force the hydrocarbonaceous fluid 18 as shown in the drawing into production well 14. The steam enters production well 14 through perforations 28 and the hydrocarbonaceous fluids along with the steam and water are removed from the production well 14 via conduit 32. Water in the hydrocarbonaceous formation remains in the high permeability zone 26 as is shown in the drawing. 
     Although an injection and a production well are shown in the drawing, the method will work where only one injection well is used. Following the sealing of the most permeable (thief) layer(s) of the reservoir by the ball sealers, steam is injected into well 10 to reduce the viscosity of the carbonaceous fluids, thereby helping their recovery from the less permeable layer(s). The ball sealers are then released from perforations 24 and well 10 is converted into a production well. This ball sealer aided huff-and-puff cycle can be repeated as desired. 
     Ball sealers which can be used in the practice of this invention and which are useful at the steam temperature encountered, are composed of polymer compounds covered with a thin coating of elastomer of low enough density to float in the injected carrier fluid. The densities generally will be low and will be from about 0.8 to about 0.9 g/cc. The ball sealers will generally be of a diameter of about 3/4 inch and will comprise a core wrapped therearound with an elastomer. Polymers which can be used to comprise the core include the following: 
     
         ______________________________________                      Melting             Density  PointPolymer           (g/cc)   (°C./°F.)______________________________________Polystyrene       1.11-1.12                      240/464Poly-4-methyl-1-pentene             0.81-0.83                      250/482Poly-3-methyl-1-hexene             0.83-0.86                      288/550Poly-3-methyl-1-butene             0.92-0.93                      310/590Poly-4,4-dimethyl-1-hexene             0.8-0.9  350/662Poly ortho-methylstyrene             1.07     360/680Poly 4,4-dimethyl-1-pentene             0.8-0.9  380/716______________________________________ 
    
     Ball sealers and a method of making same are disclosed in U.S. Pat. Nos. 4,244,425 and 4,410,387 which were issued to Erbstoesser and Halkerston et al. on Jan. 13, 1981 and Oct. 18, 1983, respectively. These patents are hereby incorporated by reference. 
     Obviously, many other variations and modifications of this invention, as previously set forth may be made without departing from the spirit and scope of this invention as those skilled in the art readily understand. Such variations and modifications are considered part of this invention and within the purview and scope of the appended claims.