Technology Helps Revitalize Maturing Giant Gas Field: Horizontal-Well Redevelopment

Abstract

This article, written by Technology Editor Dennis Denney, contains highlights of paper SPE 109948, "Applied Technology Helps Revitalize a Maturing Giant Gas Field: Learnings From the Cleveland Formation's Horizontal-Well Redevelopment Program," by Neil C. Decker, SPE, David B. Bumbaugh, SPE, Ron L. Brogdon, and David C. Gardner, SPE, BP plc; Stephen P. Roberts, SPE, Jones Energy; and Sean D. Petersen, BP plc, prepared for the 2007 SPE Annual Technical Conference and Exhibition, Anaheim, California, 11–14 November. The paper has not been peer reviewed. The Cleveland formation is a giant tight gas reservoir under a large area of the northeastern Texas Panhandle and western Oklahoma. Operator strategies have shifted in recent years to infill drilling with horizontal wells. Challenges include optimizing horizontal-well orientation, lateral length, completion type, and the number and length of hydraulic fractures, all within the context of a partially depleted reservoir. Operators have become active in acquiring data to improve their understanding of the reservoir and to quantify the variables driving well performance. Introduction The Cleveland reservoir exists throughout much of the northeastern Texas Panhandle and western Oklahoma, with the majority of production in Lipscomb and Ochiltree Counties of Texas and Ellis County, Oklahoma. The formation was dis-covered during exploration for deeper Morrow objectives in the late 1950s. Initially, it was developed with traditional hydraulically fractured vertical wells on 640-acre (1-section) spacing, but much of the reservoir has been downspaced to optional 160-acre spacing. The Cleveland produces from depths of 6,500 to 8,200 ft true vertical depth. Pay thickness varies from approximately 20 to 80 ft, with porosity values ranging from 4 to 14%. Calculated water saturations are high because of the influence of interbedded sequences of sand with thin shale laminations and the fine-grained sandstone, as observed in core samples. However, the Cleveland does not produce significant volumes of formation water. Cleveland wells with significant water production historically have downhole mechanical problems. Permeabilities are estimated to range between 0.003 and 0.015 md on the basis of injection-falloff tests performed in horizontal Cleveland wells and Agarwal-Gardner type-curve analysis of vertical Cleveland producers incorporating rate/time superposition. The first horizontal Cleveland well in this area was drilled in late 1997. Performance results and reservoir pressures that indicated the reservoir was not being depleted effectively supported the shift to development with horizontal infill drilling. This inefficient drainage results from the overall low permeability of the reservoir, compounded by the effects of reservoir heterogeneity creating permeability barriers. Cost inflation has continued to place economic pressures on Cleveland development. Operators continue to explore ways to achieve improved and consistent well performance while lowering development costs. Major efforts have been made to acquire data to improve operators’ understanding of the reservoir and identify key variables to optimize horizontal-well development.