Multidisciplinary Insights from Analysis of Borehole Microseismic Data from the Cotton Valley Tight Gas Formation in East Texas, U.S.A.

摘要

Microseismic data were acquired during the hydraulic fracture stimulation of a horizontal well in the Cotton Valley tight gas formation in east Texas, U.S.A., using a borehole observation array. The ~3700 feet horizontal well was successfully stimulated in six stages using slickwater cross-linked treatment at 80 – 88 barrels/minute. The resulting microseismic events were recorded in a vertical observation well using an array of seven sensors spaced at 100 feet intervals, spanning ~600 feet along the wellbore, and ~125 feet above the target reservoir. Based on 148 microseismic events, the inferred, dominant fracture orientations range between ~S59°W and ~S65°W, consistent with the regional orientations of SHmax. At least one ~N-S oriented fracture intersected the dominant orientations. Using all microseismic event locations, the derived fracture lengths are between ~2,257 feet and ~2,529 feet, independently confirmed by observed inter-well fracture hits in the area. Calculated fracture heights range between ~125 feet and ~387 feet indicating that the stimulations were contained within the ~400 feet target reservoir. The dominant linear fractures initiated in intervals within the tight sand where gamma ray log values are < ~70 gAPI units, thereby indicating a potential diagnostic range of frac-ability, consistent with independent field-wide rock typing study within the Cotton Valley formation. While the number and size of microseismic events varied amongst stages, treatment pressures and proppant concentration >~4,000 psi and ~1.3 ppg respectively, influenced stimulation of the reservoir, resulting in larger and more frequent microseismic events. Production characteristics of the treatment well, and tracer data collected from it, indicate that only part of the inferred fracture network volume from microseismic events, is effectively stimulated. These multidisciplinary insights guide improvements in future horizontal well stimulations in tight gas formations.