| Abstract |
Continuous microearthquake (MEQ) monitoring has been conducted since 1995 at Salak geothermal field. During 1995 to 2005, a five-station telemetered analog monitoring array was deployed. Since 2005, MEQ monitoring has been performed using a network of 10-13 portable 24-bit digital stations. So far, more than 12,000 MEQ events have been recorded at Salak field, and analyses show that microseismicity is induced by both injection and production activities and during stimulation of wells. Until 2016, in-house MEQ processing and analysis were limited to just event determination and correlation with field activities. More advanced MEQ processing was implemented in 2016 including velocity tomography inversion to provide models for the compressional (Vp) and shear wave (Vs) velocity structures. In 2018, two new velocity models were developed: an updated 1D and a new 3D model. The relocated MEQs using the new 3D velocity model showed very little change in the epicenters, but, field wide, the hypocenters tended to deepen and show a tighter clustering. Initial results of the MEQ 3D tomography study at Salak field show this method’s potential to provide valuable information for reservoir characterization. Current results of the tomographic modeling define systematic lateral and vertical changes of the Salak geothermal reservoir’s velocity structure. This includes a lower Vp centered over the productive field. Preliminary cross-plot analysis of Vp with pressure, matrix porosity, and fracture permeability suggest these may play a role in the Vp distribution across the field. Further analysis is underway to understand the link between Vp, Vs, and Vp/Vs with other reservoir parameters. The insights from these studies are being used to provide a better conceptual understanding of the Salak reservoir. This includes a mapping of the depth extent of the stimulated connected fracture network (Base of Reservoir) used in the dynamic numerical simulation model. |