Effects of pressure and fluid saturation changes on time‐lapse AVO response

Abstract

Summary Time-lapse seismic analysis has been successfully applied to monitor fluid saturation changes during production. Even though the seismic difference is observable in preferred environments, it might be produced not by changes in fluid saturation but by changes in other reservoir properties such as temperature or pore pressure. This might misdirect the interpretation of time-lapse seismic data. AVO attributes can also be useful tools to distinguish causes of some of these changes in reservoir properties. In this paper we investigate this problem by simulating timelapse AVO attributes in two different reservoir models. Our model examples show that amplitude changes for far offset data in a light oil saturated reservoir subjected to water injection are twice as large as analogous changes in zero offset data. The gas saturated reservoir also shows a large amplitude change in the far offset data, but it is relatively small compared to the oil saturated model. This is because the Vp/Vs ratio increases in the oil reservoir but changes by only a slight amount in the gas reservoir. The simulated time-lapse AVO is less sensitive to the pressure change than to changes in fluid type.