Eaton’s equation is the most popularly used model for pore pressure prediction, but it is based on over-simplified stress velocity relation. A new model for pore prediction was brought up based on stress effect modeling of lab core measurement. The new model requires exactly the same inputs and should have better performance in pore pressure prediction. Then performances of pore pressure prediction by using differential pressure and effective pressure respectively are compared. Due to delicacy in estimating the effective stress coefficient and complexity of in-situ fluid properties, introduction of effective pressure might not improve pore pressure prediction results. Our new model has been successfully applied to field data.
We have measured velocity anisotropy on 13 core samples from an organic shale oil reservoir with differential pressure up to 3000 psi. The pressure effect on velocities is generally stronger in direction normal to the bedding than along the bedding, and thus the anisotropy decreases with increasing differential pressure. P-wave anisotropy and vertical Vp/Vs ratio have good correlation with TOC content: the higher is the TOC content, the stronger is P-wave anisotropy and the lower is Vp/Vs ratio. The measured P-wave anisotropy is generally greater than S-wave anisotropy. Sensitivity of c13 and δ to errors in velocity and angle measurement were analyzed. From the sensitivity analysis we conclude that both the angle and velocity measurement around 45° are critical for reliable anisotropy measurement.
An analysis of amplitude variation with offset (AVO) observations is applied in hydrate-bearing sands, free-gas- charged sands, and hydrate-over-gas sands. The elastic model parameters (Vp, Vs, and density) are obtained from well log measurements and a rock physics model. The study suggests that presence of gas hydrate and free gas affect the AVO of shallow unconsolidated sediments containing gas hydrate and free gas. Low-concentrated gas hydrate and low-concentrated gas hydrate overlying free gas have weak AVO behaviors while highly-concentrated gas hydrate and highly-concentrated gas hydrate overlying free gas have strong AVO behaviors. Both highly-concentrated gas hydrate and highly-concentrated gas hydrate overlying free gas are Class I AVO anomalies but the intercept of AVO is stronger negative for highly-concentrated gas hydrate overlying free gas. They may occur in different locations in the AVO intercept and gradient plane.
Understanding thermal effects on seismic properties of heavy oil sands is important for seismic reservoir monitoring with thermal process. Velocities of heavy oil sands as a function of temperature are revealed as mainly controlled by properties of heavy oil (Han et al., 2007). However, newly measured data suggest that the thermal damage of sand frame also plays a significant rule to reduce velocity. Thermal damage of sand frame is a quasi-static processing, and mainly deteriorates the heavy oil contribution to strength sand frame. We should count the thermal damage effect on sand frame when modeling velocity-temperature trend of heavy oil sands.
Different structure of CO2 from hydrocarbon gases and oils has a significant impact on properties of CO2-oil miscible mixtures in comparison with “live” oil with dissolved hydrocarbon gases. We have systematically investigated velocity and density of CO2 with different oil (API) mixtures above their bubble point. The measurement condition is ranged with CO2 GOR up to 310L/L, temperature from 40°C to 100°C, and pressure from 20MPa to 100MPa. Based on our updated database we have developed preliminary models for the velocity and density of the CO2-oil miscible mixtures.