Prediction of P-wave velocity with respect to differential pressure under fluid injection condition in underground energy storage

Abstract

Depleted gas reservoirs and saline aquifers have been widely used to store natural gas. In addition, recently researches related to carbon capture usage and storage (CCUS) and underground hydrogen storage (UHS) have been actively conducted to reduce greenhouse emissions. During the operation of underground gas storages, differential pressure variations occur due to fluid injection rate, which causes seismic velocity changes in reservoir. Therefore, if it is possible to predict accurate velocity changes with respect to differential pressure in advance, we can determine not only the rock property changes but also the feasibility of geophysical monitoring techniques such as time-lapse seismic monitoring. Eberhart-Phillips et al. (1989) proposed a representative empirical relationship between compressional velocity and differential pressure through a large number of laboratory measurements. However, this relationship does not correspond well to velocity changes with respect to differential pressure under reservoir condition. To overcome this problem, in this thesis, I propose a method to predict accurate compressional velocity changes with respect to differential pressure under reservoir condition using Eberhart-Phillips et al. (1989) empirical relationship and effective pressure. The proposed method was verified with the experimental data from different regions (Siggins et al., 2004; Prasad et al., 1997; Vasquez et al., 2009; Ma, X., 2019) and it was confirmed that the prediction corresponded well with experimental data.