Analysis and modeling of induced seismicity in petroleum reservoirs

Abstract

Since 1998, a producing oil field in Oman has been experiencing microearthquake activity. The aim of this project is to compare numerical models of wave propagation using simple source representations to a small subset of these microearthquakes, with three goals in mind: 1) to understand whether the microearthquakes are generated by movement along a known fault system in the field, or by some other mechanism; 2) if the source is fault related, to better understand what kind of movement is occurring on the fault; and 3) to see if this simple modeling method provides useful results, and forms a basis for future work. Synthetic waveforms are generated using a one-dimensional, discrete wavenumber numerical model (Bouchon, 1980) with two simple source representations: an explosive point source and a vertical force. Comparison of the synthetic waveforms to the microearthquake data indicates that the vertical force results in a better match than the explosive point source. In addition, a simple model consisting of the superposition of four vertical forces (representing vertical fault rupture), results in waveforms that are very similar to the recorded events. These results suggest that the source of the microearthquakes is motion along a near-vertical normal fault system that has been mapped in the field. These results are also consistent with work by Sze and Toksoz (2001) in which relocation of the same events imaged a near-vertical normal fault in the field. Further work using fault rupture source modeling may provide additional insight into the amount of fault motion that is occurring in relation to these events.