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SPE 132990 Petrophysical Evaluation for Enhancing Hydraulic Stimulation in Horizontal Shale Gas Wells

Dan Buller, Simon Hughes, Jennifer Market, and Erik Petre, Halliburton, and David Spain and Tobi Odumosu, BP America

Copyright 2010, Society of Petroleum Engineers This paper was prepared for presentation at the SPE Annual Technical Conference and Exhibition held in Florence, Italy, 19­22 September 2010. This paper was selected for presentation by an SPE program committee following review of information contained in an abstract submitted by the author(s). Contents of the paper have not been reviewed by the Society of Petroleum Engineers and are subject to correction by the author(s). The material does not necessarily reflect any position of the Society of Petroleum Engineers, its officers, or members. Electronic reproduction, distribution, or storage of any part of this paper without the written consent of the Society of Petroleum Engineers is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgment of SPE copyright.

Abstract The economic recovery of gas from shale reservoirs requires optimal multistage hydraulic stimulation in horizontal wells. Important parameters to consider in shale-gas evaluation include gas-filled porosity and total organic content. Mechanical rock properties, including a calculated brittleness index, along with mineralogy, are also required to target and design individual horizontal fracture stages in the best zones. This type of formation evaluation in horizontal wells requires careful correlation and calibration to petrophysical measurements obtained in either vertical pilot holes or direct offset wells. This paper presents a comprehensive approach to the evaluation of an unconventional resource play drilled in the Haynesville Shale in east Texas. Using openhole and logging-while-drilling (LWD) logs, conventional core analysis, and a chemostratigraphy analysis of drill cuttings, a shale analysis linking mineralogy, free gas, effective porosity, a shale brittleness index, and a clay linked transverse anisotropy is verified on separate vertical and horizontal control wells. Beyond that, pulsed neutron spectroscopy logs were run to develop a cased-hole evaluation solution from N-N (neural network) modeling that could replicate openhole wireline or LWD logs, and chemostratigraphy mineralogy results. Subsequently, two horizontal wells were logged with LWD tools and afterward, through casing, using the pulsed neutron log and neural network calibration. Fracture stages for the logged horizontal wells were then evaluated vs. the log data. Generally, lower normalized treating pressures per fracture stage are noted where lower clay volumes exhibit less transverse anisotropy and a higher calculated shale brittleness index. Radioactive tracer and production log data also confirm lower amounts of gas production from zones that are apparently fractured, but are more ductile and clay-rich. Introduction The Haynesville Shale is a black, organic-rich, shale that covers Caddo, Bossier, De Soto, Red River, and Bienville parishes in north Louisiana and primarily Harrison, Panola, Shelby, and San Augustine counties in east Texas The depth ranges from approximately 10,300 ft in the northwest part of the play to approximately 14,000 ft in the southeast. The Bossier Shale lies above the Haynesville Shale; the Haynesville Lime or Smackover Lime lie below it throughout the area. Both of these formations can be drilling targets, but the Haynesville Shale is of special interest because of generally thicker net pay and higher reservoir pressure with a gradient between 0.85 and 0.9 psi/ft. Varying depositional environments have left the shale with a thickness that varies between 80 and 350 ft, and facies that varies between a calcite-rich shale with little clay to a silica-rich shale with large amounts of bedded clay and lesser amounts of calcite (Parker et al. 2009). Advanced evaluation suites can provide an abundance of reservoir information. The primary purpose is resource identification and a calculation of original gas in place. However, new formation analysis and presentation techniques are required for a comprehensive mechanical description of this shale to select an optimum horizontal target (Rickman et al. 2008; Mullen et al. 2007). Subsequently, the same type of information can be used to select and design optimum fracture stages along the horizontal well. Currently, a few operators are beginning to log their horizontal wells, but are not using any log data to strategically locate or plan the horizontal fractures. The current completion practice is still evolutionary because more fracture stages per lateral have achieved better results as more surface area is contacted. Perforation clusters and spacing per fracture stage have been increased or decreased, depending on whether at the location or on the operator. The one constant is that fracture treating pressures and rates, depending on job design, all indicate serious stratigraphic formation differences that must be accounted for. Post-fracture


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