Geophysical monitoring technologies, such as Microearthquake (MEQ) and Microgravity, have been consistently employed to observe fluid dynamics in the Ulubelu geothermal reservoir over the past decade during its exploitation phase. The primary objective of this research is to monitor changes in the reservoir's fluid properties, specifically its velocity and density, resulting from production and injection activities. MEQ monitoring utilized eight surface sensors, while Microgravity measurements were conducted at over 105 local sites encompassing production and injection zones, as well as the broader Ulubelu field. The latest additions of 110 MW power plants from unit 3 and 4 involves the introduction of additional injection fluids to the newly established injection pads in the southern section of the field. To oversee the impact of production and injection activities on the reservoir, continuous Microearthquake (MEQ) and periodic Microgravity monitoring was conducted. Throughout the monitoring duration, MEQ recorded more than 12,800 observations of P and S waves. Earthquakes with gap angles of less than 180 degrees were selected for analysis, and the initial 1D velocity structure's shallow portion was determined using various sonic log readings. Ray tracing calculations were carried out using the pseudo-bending technique, and the tomographic parameters, including grid geometry and damping, were assessed through a checkerboard resolution test, yielding satisfactory outcomes. The microgravity data collected during monitoring exhibited very good quality, with an average precision and repeatability of around 15 microgal. The time-lapse tomography results revealed a distinct high ΔVp/Vs value near the injection pads with geometry trending relatively W – E at the reservoir level (+0.05 relative to initial velocity value). This discovery was consistent with the time-lapse microgravity result, which also identified as strong increase in gravity anomalies (up to 40 microgal). These anomalies were attributed to the introduction of fluids from injection wells, indicating that most of the fluids flowed toward the production zone controlled by proven major geological fault with trend NW-SE, while some portions moved in a southeastward direction. The integration of time-lapse seismic tomography and microgravity analysis stands out as a crucial tool for reservoir management in geothermal fields.

Press the Back button in your browser, or search again.

Copyright 2024, Stanford Geothermal Program: Readers who download papers from this site should honor the copyright of the original authors and may not copy or distribute the work further without the permission of the original publisher.