Abstract

The importance of understanding the propagation of seismic waves in porous media containing fluids is now recognized by most reservoir geophysicists and engineers. This study covers a field under development that for this paper has been called the ITS field, South Sumatra basin, where stratigraphic traps are found in limestones of the Baturaja Formation. Values for some physical properties of the Baturaja Limestone from wells ITS-01, ITS-02, and ITS-03 were measured. Compression wave (P-wave) velocity, shear wave (S-wave) velocity, water saturation and bulk density were obtained from wireline logging data, and interval velocity from check-shot surveys conducted in each well. These parameters were investigated for their relationship with porosity derived from Neutron-Density cross-plots from wireline logging. Established modeling equations like the Time Average Equation, Raymer Equation, and Raymer-Hunt-Gardner Equation were tested against the base data of measured values. Results of detailed mapping in 2D and 3D of velocity-porosity modeling vs Acoustic Impedance and velocity-porosity-water saturation in this study are shown.

The scatter of values in velocity-porosity cross-plots most probably indicates variations of porosity in the Baturaja limestone, impure limestone lithology, and the properties of microscopic composition. The results of modeling velocity-porosity are that the Raymer Equation calculates velocity in best agreement with the data from the ITS-01 well for a gas-bearing reservoir. Raymer-Hunt-Gardner Equation is the best fit for the ITS-02 well for a gas and oil-bearing reservoir, and the Time Average Equation is the best fit for the ITS-03 well with an oil-bearing reservoir.

By mapping the detailed 2D and 3D velocity-porosity-acoustic impedance and the velocity-porosity-water saturation, we can estimate porosity and help to identify locations for future wells.