Water Fracs and Sand Quantity: A Barnett Shale Example

Abstract

Abstract Chief Oil and Gas, LLC has an active drilling and completion program in the Barnett Shale, Newark East Field, Ft Worth Basin near Ft Worth, Texas, USA. This Mississippian age gas producing reservoir consists of naturally fractured shale. Most hydraulically induced fractures have been observed to be more of a network of fractures, referred to as fracture fairways, than the usual ‘planar’ fractures. These fairways apparently result from opening many of the natural fractures allowing for production. All wells must be hydraulically fractured for economic production. The Barnett Shale hydraulic fracturing trend in the last few years has been to water frac with small concentrations of sand. The water frac treatments reported on here have varied from approximately 600,000 to over 1,500,000 gallons and 120,000 to over 400,000 pounds of sand. Most of the wells have been completed in the lower Barnett with a lesser number in the upper and lower. Results from both types of completions are included in this work. Production histories versus treatment volume and pounds of sand are presented as well as production decline data. Results indicate a much better correlation of production history with sand quantity than with fluid volume. Introduction Chief Oil and Gas, LLC (Chief) began drilling and completing wells in the Barnett Shale in 1996. From that beginning to the end of 2003, they have drilled ~ 182 Barnett Shale wells. Most of these wells were in Denton and Tarrant counties of Texas. All but two of these wells have been hydraulically fractured using the ‘Water Frac’ approach. The early treatments contained only small amounts of sand; however, with time the amount of sand used in the treatments was increased. A comprehensive database was kept of these treatments as well as the production response from each well. The analysis of this database resulted in information to guide future treatment size and quantity of sand used. This paper discusses those results. Geological Setting The Geology of the Barnett Shale has been discussed in numerous technical papers. An overview has been presented by Kuuskraa1. Briefly, the Barnett Shale is a Mississippian age shale deposit made up of primarily quartz and clay. It was deposited unconformably on rocks of early to middle Ordovician age. These lower zones, the Viola/Simpson limestone, and in some cases the Ellenburger dolomite, form the lower boundary of the Barnett Shale. In some areas the Barnett Shale is divided into an upper and lower, being separated by the Forestburg Limestone. The Barnett Shale is overlain by the Pennsylvanian age Marble Falls Limestone. A type log is shown in Figure 1.