Results of a highly-instrumented multiple well field test to characterize a dual-porosity gas reservoir are presented. The field test consisted of two pulse tests between four wells drilled into a naturally fractured, highly anisotropic gas reservoir. The test procedure utilized constant flow rate pulses in the production wells and bottomhole shut-off techniques in the observation wells to minimize wellbore storage distortion of the pressure responses.
Field test results were analyzed using conventional pulse test analysis techniques. Coring and geophysical logging data were used to further characterize the reservoir within the test area and to provide porosity and permeability data for the analysis. The tests confirmed the continuity of the reservoir, provided estimates of permeability and porosity, and provided insight into requirements for conducting pulse tests in reservoirs having similar characteristics.
The pulse test described in this paper is one of a series of field tests being executed by the BDM Corporation for the U.S. Department of Energy to obtain reservoir data on the Chattanooga Shale. in Whitley County, Kentucky. The Chattanooga Shale is an organic-rich southwestern Appalachian Basin shale of Devonian age that correlates with several shale members in the thicker Devonian section in the central part of the Basin. These shales are gas-productive over much of eastern Kentucky, western Virginia, southern West Virginia, and southeastern Ohio. Production from the shales is highly-dependent upon natural fracture systems to transport the gas from the shale reservoir rock to the wellbore. The objective of this test was to verify the continuity of the reservoir and to determine the approximate permeability and porosity of the fracture system.
The field test facility consisted of 4 wells, one of which was a hydraulically-fractured production well. The other three wells were very close offsets at distances of 124 feet (38 m.), 262 feet (80 m.), and 315 feet (96 m.') from the production well. All wells were surveyed and distances are given for bottomhole locations. Figure I shows the location of the wells. The producing well was selected for the first pulse test because it had been stimulated and was known to be capable of generating an adequate pulse. The unstimulated wells were capable of sustaining only very low flow rates of less than 10,000 scf/d (283 standard m3/d).
Pulse testing has received considerable attention over the last several years and has been shown to provide useful reservoir information using test procedures that require a relatively short period of time. Many excellent papers on interference and pulses testing have been reviewed and summarized by Kama. Although many of the papers were relevant to the planned field test, none directly addressed the specific problem; i.e., pulse tests conducted in a dual-porosity natural gas reservoir believed to have a high degree of anisotropy. Because there were no directly applicable analytical tools found in the literature, a series of computer simulations were run to obtain a qualitative evaluation of the impact of the dual-porosity system on pulse test analysis.