Bulk Density Estimation from Well Log Data Using a Rock Model Including Diagenesis

A method to estimate density using other existing logs, like sonic, gamma ray and resistivity logs in a unified rock model is proposed. An empirically derived rock model is an efficient way to compute density information by transform from velocity to porosity and from porosity to density, including pore pressure and diagenetic effects, like of cementation and dissolution. One immediate benefit of estimating bulk density using well-log data in low porosity rocks is its value to verify the integrity of the log data. Another benefit of this method is that by performing fluid replacement in the rock model it provides an effective mean of predicting zones prone to gas accumulation sometimes by-passed by the incorrect values or absence of data in the density logs. The rock model is constructed as a mixture of two lithologies, sand and shale, with variable proportions of each mineral and brine as the pore fluid using porosity velocity relationship based in Issler’s transform. Diagenesis factor is applied to correct the porosity. The bulk density estimation is then straigthforward. This study assesses the effectiveness of the density prediction from a rock model and the zones likely to have gas accumulation after fluid substitution.