Zonal fracture treatment of well formations

Abstract

Methods are provided for treating an underground well formation whereby the treatment is confined to a desired zone within the formation. The methods comprise introducing one or more preflush fluids into one or more fractures in the formation followed by the introduction of a treating fluid having a density differing sufficiently from the density of the preflush fluids whereby the treating fluid is segregated and caused to flow into a desired zone within the formation.

We claim: .[.1. A method for placing an acidic treating fluid into a desired zone of a fracture in an underground well formation comprising: 
     
        fracture..]. .[.9.  The method of claim 8 wherein the specific gravity of said second preflush fluid in said fracture is at least about 0.05 less than the specific gravity of said first preflush fluid in said fracture..]. .[.10. The method of claim 9 which is further characterized to include the step of continuously introducing successive quantities of said first preflush fluid, said second preflush fluid and said treating fluid into said fracture so that the flow of said treating fluid along said interface is maintained while said treating fluid is flowed through said fracture..]. .[.11. The method of claim 10 wherein said first preflush fluid and said second preflush fluid are selected from the group consisting of hydrocarbon liquids, water, aqueous sodium chloride solutions, aqueous calcium chloride solutions, and aqueous potassium chloride solutions..]. .[.12. The method of claim 11 wherein said treating fluid is selected from the group consisting of hydrochloric acid, hydrochloric acid-organic acid mixtures and methanol-hydrochloric acid mixtures..]. .[.13. The method of claim 12 wherein the apparent viscosities of said first and second preflush fluids and said treating fluid at the temperature existing in said fractures are less than about 100 cps..]. .[.14. The method of claim 13 wherein said first and second preflush fluids are aqueous solutions having specific gravities in the range of from about 1 to about 1.4 at room temperature and wherein said treating fluid is an aqueous acid solution having a specific gravity in the range of from about 1.075 to about 1.15 at room temperature..]. .[.15. The method of claim 9 which is further characterized to include the initial step of inducing one or more of said fractures..]. .Iadd. 16. A method for placing a treating fluid into a desired zone of a fracture in an underground well formation comprising: introducing a preflush fluid having a known specific gravity into at least one substantially vertically-oriented fracture selected from the group consisting of natural and induced fractures, said introducing of said pre-flush fluid being performed via a well bore penetrating said formation in fluid communication with said fracture at a treating pressure at least equal to a hydraulic pressure sufficient to open said fracture and to maintain said fracture in an open position, and immediately thereafter while maintaining said treating pressure and ceasing introduction of said preflush fluid   introducing into said fracture via said well bore a treating fluid having a specific gravity not equal to the specific gravity of said preflush fluid, the specific gravity of said treating fluid being at least about 0.1 less than the specific gravity of said preflush fluid; whereby said treating fluid having a lower specific gravity than said preflush fluid is caused to override said preflush fluid into a desired upper zone of said fracture;   wherein said preflush fluid is selected from the group consisting of hydrocarbon liquids, water, aqueous sodium chloride solutions, aqueous calcium chloride solutions, and aqueous potassium chloride solutions.   
     
     
        .Iaddend. .Iadd. 17.  The method of claim 16 wherein said treating fluid is selected from the group consisting of hydrochloric acid, hydrochloric acid-organic acid mixtures and methanolhydrochloric acid mixtures. .Iaddend..Iadd. 18. The method of claim 16 which is further characterized to include the additional step of: continuously introducing successive quantities of said preflush fluid and said treating fluid into said fracture so that the overriding of said treating fluid into said upper zone is maintained while said treating   
     
     
        fluid is flowed through said fracture. .Iaddend. .Iadd. 19.  The method of claim 18 wherein the apparent viscosities of said preflush fluid and said treating fluid at the temperature existing in said fractures are less than about 100 cps. .Iaddend. .Iadd. 20. The method of claim 16 which is further characterized to include the initial step of inducing one or more of said fractures. .Iaddend. .Iadd. 21. The method of claim 16 wherein said treating fluid contains propping agents for placement in said desired zone. .Iaddend. .Iadd. 22. A method for placing an acidic treating fluid into a desired zone of a fracture in an underground well formation comprising: introducing a preflush fluid having a known specific gravity into at least one substantially vertically-oriented fracture selected from the group consisting of natural and induced fractures, said introducing of said preflush fluid being performed via a well bore penetrating said formation in fluid communication with said fracture at a treating pressure at least equal to a hydraulic pressure sufficient to open said fracture and to maintain said fracture in an open position, and immediately thereafter while maintaining said treating pressure and ceasing introduction of said preflush fluid   introducing into said fracture via said well bore an acidic treating fluid having a specific gravity not equal to the specific gravity of said preflush fluid, the specific gravity of said acidic treating fluid being at least about 0.1 less than the specific gravity of said preflush fluid; whereby said acidic treating fluid having a lower specific gravity than said preflush fluid is caused to override said preflush fluid into a desired upper zone of said fracture; and thereafter while maintaining said treating pressure   continuously introducing successive quantities of said preflush fluid and said acidic treating fluid into said fracture so that the overriding of said acidic treating fluid into said upper zone is maintained while said acidic treating fluid is flowed through said fracture wherein said acidic treating fluid has a specific gravity in the range of from about 1.02 to about 1.34 at room temperature. .Iaddend..Iadd. 23. A method for placing a treating fluid into a desired zone of a fracture in an underground well formation comprising:   introducing a first preflush fluid having a known specific gravity into at least one substantially vertically-oriented fracture selected from the group consisting of natural and induced fractures, said introducing of said first preflush fluid being performed via a well bore penetrating said formation in fluid communication with said fracture at a treating pressure at least equal to a hydraulic pressure sufficient to open said fracture and to maintain said fracture in an open position, and immediately thereafter while maintaining said treating pressure and ceasing introduction of said first preflush fluid,   introducing a second preflush fluid into said fracture via said well bore, said second preflush fluid having a specific gravity sufficiently lower than the specific gravity of said first preflush fluid so that said second preflush fluid overrides said first preflush fluid, producing an interface between said first preflush fluid and said second preflush fluid, and immediately thereafter while maintaining said treating pressure and ceasing introduction of said second preflush fluid   introducing a treating fluid into said fracture via said well bore, said treating fluid having a specific gravity of at least about 0.1 less than the specific gravity of said first preflush fluid and at least about 0.04 more than the specific gravity of said second preflush fluid; whereby said treating fluid is caused to override said first preflush fluid and to underride said second preflush fluid and to flow along said interface between said first preflush fluid and said second preflush fluid into a desired zone of said fracture. .Iaddend. .Iadd. 24. The method of claim 23 wherein the specific gravity of said second preflush fluid in said fracture is at least about 0.20 less than the specific gravity of said first preflush fluid in said fracture. .Iaddend. .Iadd. 25. The method of claim 24 which is further characterized to include the step of continuously introducing successive quantities of said first preflush fluid, said second preflush fluid and said treating fluid into said fracture so that the flow of said treating fluid along said interface is maintained while said treating fluid is flowed through said fracture. .Iaddend. .Iadd. 26. The method of claim 24 which is further characterized to include the initial step of inducing one or more of said fractures. .Iaddend. .Iadd. 27. A method for placing a treating fluid into a desired zone of a fracture in an underground well formation comprising:   introducing a first preflush fluid having a known specific gravity into at least one substantially vertically-oriented fracture selected from the group consisting of natural and induced fractures, said introducing of said preflush fluid being performed via a well bore penetrating said formation in fluid communication with said fracture at a treating pressure at least equal to a hydraulic pressure sufficient to open said fracture and to maintain said fracture in an open position, and immediately thereafter while maintaining said treating pressure, and ceasing introduction of said first preflush fluid   introducing a second preflush fluid into said fracture via said well bore, said second preflush fluid having a specific gravity sufficiently lower than the specific gravity of said first preflush fluid so that said second preflush fluid overrides said first preflush fluid, producing an interface between said first preflush fluid and said second preflush fluid, and immediately thereafter while maintaining said treating pressure and ceasing introduction of said second preflush fluid   introducing a treating fluid into said fracture via said well bore, said treating fluid having a specific gravity of at least about 0.1 less than the specific gravity of said first preflush fluid and at least about 0.04 more than the specific gravity of said second preflush fluid; whereby said treating fluid is caused to override said first preflush fluid and to underride said second preflush fluid and to flow along said interface between said first preflush fluid and said second preflush fluid into a desired zone of said fracture, wherein the specific gravity of said second preflush fluid in said fracture is at least about 0.20 less than the specific gravity of said first preflush fluid in said fracture, and thereafter while maintaining said treating pressure   continuously introducing successive quantities of said first preflush fluid, said second preflush fluid and said treating fluid into said fracture so that the flow of said treating fluid along said interface is maintained while said treating fluid is flowed through said fracture, and wherein   said first preflush fluid and said second preflush fluid are selected from the group consisting of hydrocarbon liquids, water, aqueous sodium chloride solutions, aqueous calcium chloride solutions, and aqueous   
     
     
        potassium chloride solutions. .Iaddend..Iadd. 28.  The method of claim 27 wherein said treating fluid is selected from the group consisting of hydrochloric acid, hydrochloric acid-organic acid mixtures and methanol-hydrochloric acid mixtures. .Iaddend..Iadd. 29. The method of claim 28 wherein the apparent viscosities of said first and second preflush fluids and said treating fluid at the temperature existing in said fractures are less than about 100 cps. .Iaddend..Iadd. 30. The method of claim 29 wherein said first and second preflush fluids are aqueous solutions having specific gravities in the range of from about 1 to about 1.4 at room temperature and wherein said treating fluid is an aqueous acid solution having a specific gravity in the range of from about 1.075 to about 1.15 at room temperature. .Iaddend. .Iadd. 31. A method for placing a treating fluid into a desired zone of a fracture in an underground well formation comprising: introducing a first preflush fluid having a known specific gravity into at least one substantially vertically-oriented fracture selected from the group consisting of natural and induced fractures, said introducing of said preflush fluid being performed via a well bore penetrating said formation in fluid communication with said fracture at a treating pressure at least equal to a hydraulic pressure sufficient to open said fracture and to maintain said fracture in an open position, and immediately thereafter while maintaining said treating pressure, and ceasing introduction of said first preflush fluid   introducing a second preflush fluid into said fracture via said well bore, said second preflush fluid having a specific gravity sufficiently different from the specific gravity of said first preflush fluid so that said second preflush fluid and said first preflush fluid produce an interface between said first preflush fluid and said second preflush fluid, and immediately thereafter while maintaining said treating pressure and ceasing introduction of said second preflush fluid   introducing a treating fluid into said fracture via said well bore, said treating fluid having a specific gravity of at least about 0.1 less than the specific gravity of one of said preflush fluids and at least about 0.04 more than the specific gravity of the other of said preflush fluids; whereby said treating fluid is caused to override said one preflush fluid and to underride said other preflush fluid and to flow along said interface between said first preflush fluid and said second preflush fluid into a desired zone of said fracture and thereafter while maintaining said treating pressure   continuously introducing successive quantities of said first preflush fluid, said second preflush fluid and said treating fluid into said fracture so that the flow of said treating fluid along said interface is maintained while said treating fluid is flowed through said fracture, and wherein   said first preflush fluid and said second preflush fluid are selected from the group consisting of hydrocarbon liquids, water, aqueous sodium chloride solutions, aqueous calcium chloride solutions, and aqueous potassium chloride solutions. .Iaddend..Iadd. 32. The method of claim 31 wherein said treating fluid is selected from the group consisting of hydrochloric acid, hydrochloric acid-organic acid mixtures and methanol-hydrochloric acid mixtures. .Iaddend..Iadd. 33. The method of claim 32 wherein the apparent viscosities of said first and second preflush fluids and said treating fluid at the temperature existing in said fractures are less than about 100 cps. .Iaddend..Iadd. 34. The method of claim 32 wherein said first and second preflush fluids are aqueous solutions having specific gravities in the range of from about 1 to about 1.4 at room temperature and wherein said treating fluid is an aqueous acid solution having a specific gravity in the range of from about 1.075 to about 1.15 at room temperature. .Iaddend. .Iadd. 35. A method for placing a treating fluid into a desired zone of a fracture in an underground well formation comprising:   introducing a first preflush fluid having a known specific gravity into at least one substantially vertically-oriented fracture selected from the group consisting of natural and induced fractures, said introducing of said preflush fluid being performed via a well bore penetrating said formation in fluid communication with said fracture at a treating pressure at least equal to a hydraulic pressure sufficient to open said fracture and to maintain said fracture in an open position, and immediately thereafter while maintaining said treating pressure, and ceasing introduction of said first preflush fluid   introducing a second preflush fluid into said fracture via said well bore, said second preflush fluid having a specific gravity sufficiently lower than the specific gravity of said first preflush fluid so that said second preflush fluid overrides said first preflush fluid, producing an interface between said first preflush fluid and said second preflush fluid, and immediately thereafter while maintaining said treating pressure and ceasing introduction of said second preflush fluid   introducing a treating fluid into said fracture via said well bore, said treating fluid having a specific gravity of at least about 0.1 less than the specific gravity of said first preflush fluid and at least about 0.04 more than the specific gravity of said second preflush fluid; whereby said treating fluid is caused to override said first preflush fluid and to underride said second preflush fluid and to flow along said interface between said first preflush fluid and said second preflush fluid into a desired zone of said fracture, and wherein   said treating fluid contains propping agents for placement in said desired zone. .Iaddend. .Iadd. 36. A method for placing a treating fluid into a desired zone of at least one vertically oriented fracture induced in an underground well formation, the vertically-oriented fracture extending laterally outwardly from a well bore penetrating the formation, which method comprises   while applying sufficient hydraulic pressure to open said fracture and to maintain the vertical fracture in an open position, introducing a first preflush fluid having a known specific gravity into said vertical fracture via said well bore and thereafter   while applying sufficient hydraulic pressure to maintain the vertical fracture in an open position, and ceasing introduction of said first preflush fluid introducing a second preflush fluid into said vertical fracture via said well bore, said second preflush fluid having a specific gravity sufficiently different from the specific gravity of said first preflush fluid so that said second preflush fluid and said first preflush fluid produce an interface between said first preflush fluid and said second preflush fluid, and thereafter   while applying sufficient hydraulic pressure to maintain the vertical fracture in an open position, and ceasing introduction of said second preflush fluid introducing a treating fluid into said vertical fracture via said well bore, said treating fluid having a specific gravity of at least about 0.1 less than the specific gravity of one of said preflush fluids and at least about 0.04 more than the specific gravity of the other of said preflush fluids; whereby said treating fluid is caused to override said one preflush fluid and to underride said other preflush fluid and to flow along said interface between said first preflush fluid and said second preflush fluid into a desired zone of said vertical fracture, said treating fluid being forced by said hydraulic pressure to flow outwardly in the fracture from the well bore, extending the fracture and simultaneously treating the desired zone therewithin. .Iaddend..Iadd. 37. The method of claim 36 which is further characterized to include the initial step of inducing one or more of said vertical fractures, and wherein said treating fluid is an acidic treating fluid having a specific gravity in the range of from about 1.02 to about 1.34 at room temperature. .Iaddend. .Iadd. 38. The method of claim 36 wherein said treating fluid contains propping agents for placement in said desired zone. .Iaddend. .Iadd. 39. A method for placing an acidic treating fluid into a desired zone of at least one vertically-oriented fracture induced in an underground well formation, the vertically-oriented fracture extending laterally outwardly from a well bore penetrating the formation, which method comprises:   while applying sufficient hydraulic pressure to open said fracture and to maintain the vertical fracture in an open position, introducing a preflush fluid having a known specific gravity into said vertical fracture via said well bore, and thereafter   while applying sufficient hydraulic pressure to maintain the vertical fracture in an open position, and ceasing introduction of said preflush fluid introducing into said fracture via said well bore an acidic treating fluid having a specific gravity not equal to the specific gravity of said preflush fluid, the specific gravity of said acidic treating fluid being at least about 0.1 less than the specific gravity of said preflush fluid, whereby said acidic treating fluid having a lower specific gravity than said preflush fluid is caused to override said preflush fluid into a desired upper zone of said vertical fracture, said acidic treating fluid etching flow channels in faces of the vertical fracture in the formation, said flow channels after said hydraulic pressure is lessened and said fracture closes, remaining in the formation to allow desired fluid contained in the formation to flow relative to the well bore wherein said acidic treating fluid has a specific gravity in the range of from about 1.02 to about 1.34 at room temperature, and wherein the hydraulic pressure is sufficient to extend the vertical fracture laterally from the well bore. .Iaddend. .Iadd. 40. A method for placing a treating fluid into a desired zone of a fracture in an underground well formation comprising:   introducing a first preflush fluid having a known specific gravity into at least one substantially vertically-oriented fracture selected from the group consisting of natural and induced fractures, said introducing of said preflush fluid being performed via a well bore penetrating said formation in fluid communication with said fracture at a treating pressure at least equal to a hydraulic pressure sufficient to open said fracture and to maintain said fracture in an open position and immediately thereafter while maintaining said treating pressure, and ceasing introduction of said first preflush fluid,   introducing a second preflush fluid into said fracture via said well bore, said second preflush fluid having a specific gravity sufficiently different from the specific gravity of said first preflush fluid so that said second preflush fluid and said first preflush fluid produce an interface between said first preflush fluid and said second preflush fluid, and immediately thereafter while maintaining said treating pressure, and ceasing introduction of said second preflush fluid   introducing a treating fluid into said fracture via said well bore, said treating fluid having a specific gravity of at least about 0.1 less than the specific gravity of one of said preflush fluids and at least about 0.04 more than the specific gravity of the other of said preflush fluids; whereby said treating fluid is caused to override said one preflush fluid and to underride said other preflush fluid and to flow along said interface between said first preflush fluid and said second preflush fluid into a desired zone of said fracture   continuously introducing successive quantities of said first preflush fluid, said second preflush fluid and said treating fluid into said fracture so that the flow of said treating fluid along said interface is maintained while said treating fluid is flowed through said fracture.   
     
     
        .Iaddend. .Iadd. 41.  The method of claim 40 which is further characterized to include the intial step of inducing one or more of said fractures. .Iaddend.