Evolution of Horizontal Well Hydraulic Fracturing in the Granite Wash – Understanding Well Performance Drivers of a Liquids-Rich Anadarko Basin Formation

Abstract

The multi-zone Granite Wash is a mature vertical well play extending across 6 counties in the Texas Panhandle and Western Oklahoma. The laterally and vertically extensive formations were developed with close spaced vertical wells for several decades. In the last five years, almost all development has been horizontal, initially adapting drilling and completion technologies from shale gas development. With over 200 million barrels of proven Granite Wash reserves and low US natural gas prices, Anadarko basin E & P efforts are migrating towards higher rates of return from Granite Wash light oil, gas condensate and natural gas liquids. Driven by horizontal drilling and modern completion and fracturing techniques, horizontal well count and hydrocarbon liquid production have more than tripled over the last 4 years in this active U.S. mid-continent play.Unlike typical sandstone reservoirs, the Granite Wash has complex mineralogy including quartz, potassium and sodium feldspars, illite, chlorite, dolomite and calcite. Depositional environments range from near shoreline to continental slope events to deep marine. Many of the targets consist of compartmentalized sub-marine fan deposition. Due to high level of reservoir heterogeneity and GOR, it is difficult to characterize reservoir property changes between fields and horizons. Prior production driver studies on vertical wells in the Granite Wash did focus on both reservoir and completion parameters. The bulk of horizontal studies are limited to completions and stimulation without rigorous investigation of stratigraphic and reservoir quality variation. This paper correlates well performance with completion and fracturing practices in well samples of similar geographic and stratigraphic position, determined from public domain well, completion and well and log data.Using the large enormous public database of vertical wells, a three-dimensional sub-surface model of the reservoir is built for three geographic areas with multiple stratigraphic benches to reduce sample variation of reservoir quality. Reservoir quality is defined from petrophysical properties that affect the productivity of the well including but not limited to porosity, permeability, saturations and rock mineralogy, and accordingly, property distribution models are built for each property across study areas. Stimulation parameters investigated include, but are not limited to lateral length, number of fracturing stages, and normalized fluid and proppant volumes. Reservoir quality from the three dimensional model and parameters from the stimulation database are then correlated with well production to identify both stimulation and reservoir production drivers. The result sought is improved conclusions and recommendations for completion and stimulation in specific geographic areas and stratigraphic benches.