Development of Seismic Measurement Technology to Detect Changes in Reservoirs Using Active Sources

Abstract

The project entitled ìStudy on Geothermal Resource Exploration Technologyî was launched by NEDO in 1997 in order to develop adequate technologies useful for the characterization of reservoir mass and heat flows in geothermal environments. Following this theme, the research project was divided into several categories, one of them being a seismic monitoring project. Its purpose and aim is to develop a seismic technology to detect hydrothermal changes in the reservoir. It is expected that the detection and analysis of precise changes in the microearthquake distributions and velocity structures within the geothermal area can be correlated to allow for the extraction or reinjection of geothermal fluids. If the development of such technology becomes feasible, it would contribute not only to evaluate the behavior of the geothermal reservoir in the early stage of exploitation, but also to optimize the decrease in power generation and to explore new areas related to the existing reservoir.

In the first year of this project, a feasibility study was conducted and a conceptual design created to determine measurements related to the changes in seismic velocity distributions within the geothermal structure. In the second year, model simulations using the Sumikawa geothermal field conditions were carried out in order to design an appropriate seismic method capable of obtaining vertical seismic profiles. Due to the lack of measurable changes in the seismic velocity structure within the Sumikawa area, the VSP survey will be re-scheduled in the Akinomiya geothermal area where better field conditions are expected. It is expected that data analysis will include the after phase and amplitude of several kind of waves including the direct P wave by using seismic tomography techniques.

If the results of this yearís model simulation are promising, field surveys in geothermal fields will be scheduled during the years 1999 and 2000 to confirm the applicability of the method.