Stimulation Techniques for Low-Permeability Reservoirs with Horizontal Completions that Do Not Have Cemented Casing

Abstract

Abstract Existing literature offers numerous success stories for stimulating cased/cemented horizontal completions in low-permeability reservoirs.1–8 However, operators who are faced with limited producing potential need to reduce well costs. Completing the horizontal section openhole or with a noncemented liner is attractive. In low-permeability reservoirs, production from such completions has often been below expectations, and sometimes even commercially unfeasible. This is especially true when we consider only completions in reservoirs other than fractured chalks. To achieve proper stimulation with a technique such as fracture acidizing or hydraulic fracturing with proppants, operators must incorporate an economic and effective method for controlling the fluid or proppant placement. Currently, few well-proven technologies exist for controlling fracture placement in noncemented wellbores. In some cases, high risk or very high cost is associated with these technologies, depending on reservoir conditions or the potential for production improvement. This paper examines several approaches that have been used to solve these problems, and presents some of the reasons for their mechanical and/or economical success or failure. Generally, the successful use of either conventional fracturing treatments or waterfracs (with very little or no proppant) will require some method of controlling fracture placement along the horizontal for significant production improvement. Controlling fracture placement is usually also required for effective fracture-acidizing of carbonate formations. Case histories from Canada and west Texas are included, and other examples within the literature are cited. Introduction When an operator considers a horizontal completion in a low-permeability carbonate or sandstone reservoir, cost containment becomes a prime drilling and completion consideration. For many recent and currently planned projects throughout the world, the opportunity for openhole horizontals to give increased production per completion dollar economically may be what justifies the development of a new field, or additional drilling in an existing field. Also, the re-entry of older vertical wells for a horizontal recompletion will often dictate that the completion is openhole, due to hole-size limitations. The global reality that our industry seems slow to accept is that many horizontal completions in low-permeability reservoirs require significant stimulation for achieving truly economic production rates. Several horizontal-drilling programs have been based on assumptions that long openhole laterals will eliminate the expensive stimulation treatments that are normally required with vertical-well completions in a given reservoir. Except for Austin Chalk reservoirs, only a few such projects have achieved this goal. Among the many low-permeability, horizontal openhole drilling projects with disappointing production results, a few operators have found methods for effective stimulation treatments that significantly improved the economic return.7–8 Most operators have found no low-cost stimulation processes available that could be consistently effective in a particular reservoir or with their well-completion conditions without some placement control technique.