Quantitative Analysis On The Gravity Filed Response of Granites Under Geothermal Reservoir Conditions

Geophysical property variations estimate of hot dry rock (HDR) under geothermal reservoir conditions, i.e. high temperature, high pressure and extremely low porosity, is the foundation of its exploration and characterization. On one hand, a comprehensive understanding of the reservoir stratum provides guidance for geothermal resource assessment and exploitation. On the other hand, the forward calculation of property variations would provide a feedback for geophysical field anomalies interpretation. The related study is in deficiency currently, especially for the latter one. In this paper, the variation of density parameter of HDR is simulated and we calculate the corresponding response (forward process) of gravity and gravity gradient field. Gravity and its gradient field is mainly related to crustal density heterogeneity, which would be caused by tectonic boundary, fault, vertical and lateral stratum distribution and changes of environment (temperature and pressure). As the gravity measurements above the ground are a superimposed effect of underground heterogeneous density distribution, the signal intensity of gravity field caused by density variation would be estimated firstly. To further evaluate the ‘possibility’ of target signal detection, it is essential to make a quantitative comparison between it and other gravity signals. The target signal will be extracted when we could obtain an adequate ‘detection rate’ and on this basis, the interpretation results (inverse process) could reflect geothermal reservoir characteristics more accurately.