Characteristics of Pore Pressure and Effective Stress Changes in Sandstone Reservoir Through Velocity Analysis Approach Due to Hydrocarbon Production

Abstract

This paper focuses on the use of velocity analysis to identify and characterize the pore pressure and effective stress changes during oil field production since the pore pressure estimation takes an important role in oil and gas industry. Pore pressure estimation is a substantial prerequisite to start drilling and production. Moreover, the precise pore pressure estimation will determine the safety, profits and success in both production and recovery. In order to accomplish the objective of this study, the methodology is composed of several broad stages. It consisted of field mapping to create stratigraphy model, coring/sampling, velocity measurement with saturation and pressure (i.e., pore and confining) variations, velocity analysis for constructing the empirical equation of pressure, saturation, and pore pressure relationship in each facies, pore pressure and effective stress changes estimation model from interval velocity and transit time analysis. The result shows that pore pressure value was reduced due to the decrease in fluid content to represent the production history. The decreasing in pore pressure might soften the elastic mineral frame and has the tendency to possess high velocity. Regarding depth, the pore pressure was slightly increasing where the effective stress decreased gradually; the enhancement of pore pressure values was due to the increasing overburden pressure. In consistent depth or constant overburden pressure (confining pressure), increasing of pore pressure would decrease the velocity gradually. This occurs due to the increase in inflicted interval time (ti) as a consequence of reduced medium (samples) velocity. The alteration in pore pressure by the changes in fluid content or saturation resulted in the alteration of velocity value that had proportionate trend with the effective stress.