Wave speed measurement method

In order to determine whether we can see the 4D seismic changes, we first need to understand the cause of the reflection. Sonic logging data from the field shows that at the oil-water contact surface, the porosity does not change much, but the speed increases by about 9%. Similarly, the core measurements of a sandstone show an average 6% increase in P-wave velocity as the water saturation changes from 7% to about 60%. This indicates that the oil-water contact speed difference is due to the difference in the compression coefficient between the oil and the brine.

Oil-water contact (OWC) reflections and weak top sand events. The top sand is usually interpreted as an earthquake event that is sub-parallel to the Oligocene bottom. In the section, the full lenticular contact velocity in the channel increases significantly, while the porosity changes only slightly. This shows that the increase of the velocity of the oil-water interface is due to the difference in the fluid compression coefficient between the oil and the brine. We established a 3D seismic model using the geostatistical interpolation method in which the velocity and density reside in the model space. This guarantee represents an uneven distribution of the resistance values ​​in each of the zones in the model (oil, water and cap shale). The resulting model incorporates the water saturation distribution output from the Eclipse reservoir simulator. Reservoir and seismic simulations are easier to handle because Chevron's simulation environment is based on a well-balanced stratigraphic model developed on Gocad.

Wave speed determination. It shows that the increase in velocity seen at the oil-water contact surface is caused by the difference in the compressibility coefficient between oil and brine. The synthetic earthquake model predicts that the oil-water contact surface below the production well is a dark spot, possibly leaving behind the residual reflection of the original oil-water contact surface. .