Natural gas production in central West Virginia is primarily from the shales of Devonian age upward to the sandstones of Pennsylvanian age. These productive intervals are typically low permeability, under pressured and adjacent pay zones can have similar closure pressures with only a minimally competent barrier separating them.
Such a scenario exists in the Weir and Injun sandstones of Nicholas, Fayette and Kanawha Counties, West Virginia. At a depth of 2000 to 2500 ft, both the underlying Weir and overlying Injun exhibit only a few hundred psi reservoir pressure, frac gradients in the 0.4 to 0.6 psi/ft range and are separated by 10 to 20 ft of sandy shale. To make either of these zones commercially productive, both must be hydraulically fractured.
Initially it was felt that historical treatment data and the comparison of conventional electric logs to offset wells would provide sufficient data to effectively fracture model stimulation treatments. This technique provided interesting computer simulations, but treatment and production results did not substantiate the modeling.
In an effort to better model and stimulate both zones, mechanical properties were obtained from a sonic log. Treatment parameters such as pressure, fluid efficiency/formation permeability and near wellbore connectivity characteristics were obtained from step-down and mini-frac tests. Real-time job monitoring, post-frac RA tracer survey and production testing were performed to verify the design simulation.
Treatment design history and current philosophy will be discussed in this paper. In addition, the results of the data gathering, treatment design and execution and RA tracer survey will be presented.
The Dickenson Field is located in Nicholas County, West Virginia, fig. 1, and consists of 61 wells, which have produced 37 BCFG, since the field discovery in 1944. Initial development targeted the Mississippian Big Lime limestone and Big Injun sandstone. It was not until the early 1980's that formations below the Big Injun were penetrated and the Mississippian Weir sandstone was added as a target zone.
The Big Lime is a limestone member of the Greenbrier Group, fig. 2, and unconformably overlies a clastic sequence called the Pocono or Price Formation1. The Big Lime in the Dickenson field is a stratigraphic trap where porous oolites laterally grade into nonporous, nonoolitic limestone. Depths to the top of the formation range from 1,400' to 2,200', with the gross interval being greater than 200 feet with net pay thickness in the range of 10 to 35 feet.
The Big Injun is a member of the Pocono or Price Formation; the term was often applied to any productive interval at the base of Big Lime formation. The pre-Greenbrier unconformity truncates the Lower Mississippian rocks across the field, which causes the variability of the stratigraphic terminology. The Big Injun in the Dickenson field is a medium to fine-grained sandstone representative of a distributary channel. Depths to the top of the formation range from 1,600' to 2,400', with net pay thickness in the range of 15 to 35 feet.