Infill Drilling in the Moxa Arch: A Case History of the Frontier Formation

Abstract

SPE Members Abstract A case history of the Moxa Arch in southwestern Wyoming details the initial development on 640 acre spacing in 1977 through 1982 and the results of subsequent infill wells drilled from 1989 to 1992. The engineering evaluation includes an integration of 3D hydraulic fracture modeling and reservoir simulation with petrophysical and geological studies. The study indicates that the Moxa Arch Frontier Formation is very heterogeneous with permeabilities ranging from 0.001 mD to more that 0.1 mD. The productive sand thicknesses vary from less than 10 ft to over 70 ft. Effective drainage areas range from over 640 acres to less than 100 acres, with ultimate gas recoveries estimated from less than 1 BCFG to over 5 BCFG. Reservoir and hydraulic fracture modeling indicate that infill drilling on 160 acre spacing (within a portion of the Moxa Arch) would increase reserves by 68% when compared to reserves for 320 acre spacing. Results from new CO2 foam/ISP stimulations did not show significant improvement compared to early water-based fluid and sand treatments. Introduction The Moxa Arch is located in the Green River Basin in southwestern Wyoming at the intersection of Lincoln, Uinta, and Sweetwater counties. The Frontier sandstone in this area is characterized as a "tight gas" formation with permeabilities of less than 0.1 mD at depths of about 11,000 to 12,000 ft. The development of the Moxa Arch Frontier was made possible through the advent of massive hydraulic fracturing (MHF) techniques in the late 1970's. Stimulations during initial development consisted of water-based fluids (220 Kgal) and 20/40 mesh sand (450 Klbs) with sporadic use of other fluids (emulsions and oil-based) and sintered bauxite. During the 1989–91 infill drilling, the majority of the fracture treatments utilized CO2 foam and intermediate strength proppants (ISP). Based on the performance of the 1989–91 treatments, current designs range from sand to ISP with either water-based borate gels or foams as the carrier fluids. The initial development was on 640 acre spacing with most of the drilling completed by 1982. Increased density drilling was initiated in 1989 with the drilling of an additional well on each 640 acre spacing unit. This infill program was completed in 1991. In December 1991 the Wyoming Oil and Gas Conservation Commission authorized further infill development by granting an optional third and fourth well per spacing unit in a limited area of the Moxa Arch. This program is currently in progress. Figure 1 illustrates the location of the Moxa Arch and shows the outline of the area targeted for 160 acre infill drilling. P. 533^