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 microearthquake 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.

Effect of Geometry and Number of Seismic Stations on Micro-Earthquake (MEQ) Hypocenters in Geothermal Fields

“…with a strength of less than 3 Richter Scale (SR) can indicate the presence of faults (Kato et al, 2021;Toledo et al, 2020;Utama et al, 2021;Wildan Perdana et al, 2020). MEQ is used to identify subsurface dynamics related to the presence of faults and weak zones in geothermal field reservoirs, MEQ hypocenter determination is carried out based on seismic data recorded by seismic stations which are then processed by the inversion method and then analyzed to describe the subsurface conditions of the geothermal field (Pennington et al, 2022;Utama, Ardhya, et al, 2022). Generally, after the identification of the hypocenter is carried out, analysis and validation of the suitability with geological data of the geothermal field area or research area are carried out (Halim et al, 2020;Intani et al, 2020;Sicking & Malin, 2019;.…”