Delay Time (δt) and Polarization Direction (φ) Analysis Based on Shear Wave Splitting (SWS) Method

Abstract

The information of dominant polarization direction and the mapping of fracture intensity are among the most important informations during the monitoring of geothermal field reservoir evaluation, as an effort to develop geothermal energy production. The appearance of geothermal reservoir fractures caused by fluid injection and the production activity resulting in the decreased pore pressure and appearance of open weak zone. The micro-earthquake activity around the area can represent these fractures that appear in the geothermal reservoir. Shear Wave Splitting (SWS) analysis can be done based on the polarization of S wave through the anisotropy medium recorded by seismograph. There are two parameters related to Shear Wave Splitting: the polarization direction (φ) related to the micro fracture direction with its delay time (δt), showing the fractures density and its permeability area. The result of Shear Wave Splitting Analysis of the field X geothermal shows that two dominant polarization directions are NW-SE and NE-SW. It is caused by the fractures around the X field geothermal with similar fractures direction, and it is compatible with the distribution micro-earthquake hypocenter of the previous study. Based on the map of fractures intensity, the value range shows a relatively dense intensity value around 6.6 – 8.0 ms/km. The high value of intensity fractures indicates a high value of anisotropy around the area, and it is also confirming the presumption of the high permeability potential of the X geothermal field.