Ultrasonic P and S Wave Velocities in Carbonates From the Arab Formation, Saudi Arabia, and the Western Canada Sedimentary Basin, Canada

The fact that many of the giant hydrocarbon reservoirs, such as Ghawar field in Saudi Arabia and the Grosmont formation in Alberta, are carbonates make such rocks an important research topic. This is particularly true the bulk of laboratory investigations have focused on siliclatic reservoir materials; more work on carbonates is necessary. Anselmetti and Eberli (1993) have shown that the influence of mineral compositions in carbonates is minimal, and cannot be a reason for large changes in velocities. They found that the velocity variation in carbonates is mainly controlled by porosity and pore type. Assefa et al. (2003) showed that the velocities of rocks with high aspect ratio pores are greater than those with low aspect ratio. In this study, we are investigating the effect of pressure, porosity, permeability and saturation in carbonate rock. To date, we have measured the ultrasonic compressional and shear wave velocities for forty carbonate rocks, thirty eight of them are from Arab formation in Saudi Arabia and two from the Western Canad Sedimentary Basin (WCSB). The samples were measured both in dry and water saturated conditions under different confining pressures that varied from 2.5 MPa to 25 MPa for Arab-D samples and from 5 MPa to 70 MPa for WCSB samples. In order to study the effect of microcrack closure, one Arab and one WCSB samples were measured at confining pressure of 40 MPa and 90 MPa respectively. Higher confining pressures were avoided in order to lower the risk of damaging the samples. Some preliminary results from P and S wave velocity measurements on several samples under dry and water saturation conditions are presented. These measured results and the calculated water saturated velocities from Gassmann's equation are compared