This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 134092, ’Integration of 3D Seismics and Reservoir Simulation for Remaining-Oil Exploitation in a Heavy- Oil Field: A Case Study,’ by Yun Ling, BGP CNPC; Xuri Huang, SPE, SunRise PetroSolutions Tech; and Xiangyu Guo and Yintao Cai, BGP CNPC, prepared for the 2010 SPE Annual Technical Conference and Exhibition, Florence, Italy, 19-22 September. The paper has not been peer reviewed.
Integrated research on steam-assisted gravity-drainage (SAGD) production was carried out for an oil field in north-eastern China by use of full-azimuth 3D seismics (cell size 6.25×6.25 m with a coverage area of 14 km2) and reservoir simulation on a well group [40 vertical wells and five horizontal wells in an area of 600×375 m (Fig. 1)]. The research indicated that the configuration of steam chambers caused by steam injection could be delineated from the high-resolution 3D-seismics results, and that this is more accurate than the reservoir-simulation model alone in the local-variation description of the chambers.
It has been observed in laboratories that a large seismic-velocity change can occur in rocks containing heavy oil when the oil is replaced by steam. The Duri heavy-oil field in Indonesia uses steam injection, and time-lapse seismics is used to monitor production. However, the effectiveness and reliability of the method depend on the quality and repeatability of the surveys. The technique of combining 3D-seismic exploration for the remaining oil with historical production data (called 3.5D seismics) avoids the nonrepeatability problem commonly associated with time-lapse seismic. This technique was applied to the Ng reservoir in northeastern China.
Geological and Seismic Background
The main producing reservoir, Ng, is on a monoclinal structure covering 1.95 km2. Its maximum thickness is 145 m and is found at a depth between 540 and 800 m. The reservoir porosity is 36%, permeability is 5.5 darcies, and the reservoir has edge, top, and bottom water. Production started in 1997, and 10 to 12 cycles of steam stimulation have been implemented in a well interval of 70 m. Enhanced oil recovery (EOR) reached 20 to 25%. Starting in 2005, five SAGD well pairs were used, and they are still in production. The SAGD process raised the EOR by 5 to 10%. A high-density 3D-seismic survey (with a wide azimuth and an aspect ratio of 0.874) was acquired in February 2009. The processing procedure that was used enhances the vertical resolution and preserves reservoir information.