Lithologic reservoirs are characterized by subtle locations and complex architectures. Conventional structure and deposition interpretations based on seismic and logging data are beneficial to the distribution forecast of lithologic reservoirs. But they are not enough to predict remaining oil in the late development stage. A new fine remaining oil prediction method of lithologic reservoir based on the integration analysis of reservoir architecture and time-lapse (4D) seismic is proposed and applied successfully to Reservoir H11.
H11 is a complex delta lithologic reservoir in the Pearly River Mouth Basin. By the end of 2014, its water cut has been up to 98.5%, but EOR is only 35.1%. It is urgency to study remaining oil distribution. There are three key techniques involved, including the dynamic interpretation of reservoir depositional evolutions, fine characterization of sand body architectures & flow barrier distributions and the analysis of 4D seismic difference.
Firstly, constrained by sequence frameworks, stratal slices between the top and base of H11 are extracted at 1ms interval and calibrated with logging. These slices are relatively isochronous and contain the depositional information. According to seismic sedimentology theory, integral interpretations of slices and log facies are used to study spatial evolutions and distributions of H11. Secondly, based on investigations of delta front deposits cropping out in the Ordos Basin, sand body contacts are understood. These contacts are further analogized by core, logging, 3D seismic and acoustic impendence data in subsurface. Whether the contact boundaries are seepage flow barriers is further distinguished through the analysis of development performances or pre-stack inversion data. Finally, remaining oil of H11 was successfully delineated by 4D seismic analysis. The 4D difference data shows significant water movement from the north and west. The presence of bypassed pay at the southern and eastern scattered areas is obvious. Based on these understandings, a proposed well is completed at the southern prediction area in the late 2014 and the result is consistent with the 4D response. Currently, the oil production of this well is up to 2800 barrels per day.
Besides the imperfect well pattern, the complex contacts and lithologic flow barriers among sand bodies are the other reasons leading to the subtle 4D seismic difference. The static reservoir architecture analysis and 4D seismic difference analysis are integrated to improve the precision of remaining oil prediction of H11. This method has been popularized to other lithologic reservoirs of the Pearl River Mouth Basin, and enriches the approach and technique of remaining oil delineation.