Using RFT Data for Elastic Rock Properties' Dependency on Pore Pressure in 4D Quantitative Analysis

Formation pressure data (RFT) for the Brent formation of the Gullfaks Field has been used together with quality checked well log data to estimate the dependency of elastic rock properties on in situ formation pressure. Acoustic impedance versus RFT pore pressure shows a decrease in acoustic impedance with increasing pore pressure. The observed trend in the acoustic impedance-RFT pore pressure domain shows a slight correlation with porosity, but no correlation with clay content and burial of depth. The analysis is focused on brine saturated points, as the estimation is very sensitive to fluid content. We suggest that the dependency of elastic rock properties on pore pressure estimated from well log and formation pressure data (RFT) may be used as an alternative to, or in combination with, core measurements, and in this way improve the understanding of the pressure component in 4D quantitative analysis.