Evaluation of Subsurface Fluid Movement by Using High Precision Tiltmeters

Abstract

The New Energy and Industrial Technology Development Organization(NEDO) has initiated a research program titled ì Development of Technology for Reservoir Mass and Heat Flow Characterizationî. As part of the research project, Japan Petroleum Exploration Co., Ltd. ( JAPEX) has been studying the application of surface tilt surveys for monitoring change in geothermal reservoirs. Tiltmeters have undergone rapid evolution in recent year, and can provide higher accuracy and greater resolution at depth. Surface tilt can be directly related to volume change in the subsurface associated with fluid injection or withdrawal, and inversion or forward modeling techniques for calculating displacements due to volume changes in elastic and poro-elastic media have existed for quite some time. We outline the results of the tiltmeter survey for injections conducted in the Hijiori geothermal area and inversion analysis for the tilt data to estimate subsurface fluid movement. The inversion generated images of fluid withdraw from a deep complex fracture zone due to injection in this field. The tiltmeter survey promises to provide a non-invasive method for directly monitoring subsurface volume change due to injection or production.