Feasibility Study of Reservoir Monitoring Using Repeat Precision Gravity Measurements at the Sumikawa Geothermal Field

Abstract

In principle, repeat gravity surveys can help appraise changes in natural reservoir recharge in response to production-induced pressure decline. Unambiguous interpretation of gravity surveys (in isolation from other data) is, however, often impossible. One promising approach is to combine precision gravity survey measurements with numerical reservoir simulation studies. The synthesis of the two techniques is potentially capable of providing results which would be unobtainable using either technique alone. Preliminary numerical simulation studies (prior to full-scale field exploitation) have been used (1) to evaluate feasibility and (2) to design a specific gravity survey plan for the Sumikawa geothermal field. These results were processed to yield areal maps of "synthetic gravity anomaly change" corresponding to the changes in underground conditions calculated by the numerical reservoir model.