A SEISMOTECTONIC STUDY AND STRESS ANALYSIS OF THE KERMIT SEISMIC ZONE, TEXAS (SEISMOTECTONIC, WEST, FINITE ELEMENT ANALYSIS, HYDRAULIC FRACTURING, EARTHQUAKE)

摘要

The purpose of this study was to investigate the seismicity and contemporary stress regime (seismotectonics) of the Delaware basin and the Central Basin platform of west Texas and southeastern New Mexico. Microearthquake data, hydraulic fracturing results, and geologic indicators were compiled in order to provide new information about lithospheric stresses. A finite element analysis incorporating geophysical and geological data as constraints was used to investigate the various stress responses of a spectrum of plausible models. Two distinct areas of seismic activity were delineated during the course of the earthquake monitoring and were named the Kermit seismic zone because of their proximity to the town of Kermit, Texas. One area of pronounced seismic activity was located in the Delaware basin in the vicinity of the War-Wink South gas field. A second area of seismic activity occurred on the Central Basin platform in the vicinity of the Keystone field. Focal mechanisms were derived for the two areas and were applied as indicators of tectonic stress. It is possible that the earthquake activity in the Keystone field area may be associated with a specific fault but the earthquake activity in the War-Wink South field area cannot be associated with certainty to any particular fault. An analysis of the stress distribution due to extraction and injection volumes throughout the entire history of both fields was performed. The pressures in the War-Wink South and Keystone fields fell below the values required to reduce the effective normal stress and induce shear failure resulting in an earthquake. The stress distribution within west Texas and southeast New Mexico appear to reflect a transitional area of stress between the Southern Great Plains and the Rio Grande Rift stress provinces. Finite element analysis was performed on two oversimplified crustal models derived from a detailed gravity survey along a 60 km cross-sectional area between the War-Wink South and Keystone fields. The suite of models was stressed by forces due to gravitational loading plus horizontal compressional and extensional forces or vertical uplift. The results of the finite element analysis point out areas of stress change which correlated with area of microearthquake activity.