Steamflooding in a Waterdrive Reservoir: Upper Tulare Sands, South Belridge Field
- James K. Dietrich (The Dietrich Corp.)
- Document ID
- Society of Petroleum Engineers
- SPE Reservoir Engineering
- Publication Date
- August 1990
- Document Type
- Journal Paper
- 275 - 284
- 1990. Society of Petroleum Engineers
- 5.3.4 Reduction of Residual Oil Saturation, 5.2 Reservoir Fluid Dynamics, 5.8.5 Oil Sand, Oil Shale, Bitumen, 4.1.5 Processing Equipment, 5.4.6 Thermal Methods, 1.6 Drilling Operations, 2.4.5 Gravel pack design & evaluation, 5.5.8 History Matching, 2.4.3 Sand/Solids Control, 5.1 Reservoir Characterisation, 5.5 Reservoir Simulation, 1.2.3 Rock properties, 2.2.2 Perforating, 5.1.1 Exploration, Development, Structural Geology, 4.2 Pipelines, Flowlines and Risers, 4.3.4 Scale, 4.1.2 Separation and Treating, 4.1.9 Tanks and storage systems
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A steamflood project in the strong edgewater-drive Upper Tulare reservoir at South Belridge recovered about 31% the original oil in place (OOIP) at a cumulative steam/oil ratio (SOR) of 2.7 vol/vol. Seven years of downdip steam injection depressed water influx and created an oil bank updip from the injectors. Response continued under the influence of returning aquifer water heat scavenging after the injectors were shut down. Numerical reservoir simulation of the historical steamflood performance indicated that the high production/injection capacity (1 ratio induced early water encroachment and partial quenching of the growing steam zone. Restarting downdip steam injection at m higher rates after 6 years without injection was shown to recover more oil than continuing the steamflood with either a seven-spot inverted nine-spot pattern. An efficient steamflood operating policy in am edgewater-drive environment involves overproducing in the oil column to reduce reservoir pressure combined with high-rate downdip pumping of the aquifer to reduce water inflow during steam injection. Downdip stream injection rates greater than 100 B/D-acre and P/I ratios of about 1.4 STB/STB emerged as reasonable operating parameters in several projects.
Few published results exist concerning steamflooding in the presence of strong aquifer influx. Reports from Europe and the U.S. on this topic indicate that successful field projects were designed on the basis of results from physical models and thermal reservoir simulators. In each case. the handling of water influx was the critical design parameter. During early project years. steamzone growth and oil recovery were enhanced by injecting steam at rates high enough to depress water influx, overproducing the oil column to reduce reservoir pressure, and pumping a series of downdip water wells to reduce aquifer pressure. During later years, the critical design parameter was the time of steam-injection termination because oil production continued under the influence of returning aquifer water and heat scavenging after injectors were shut down. Review of several mature steamfloods conducted in the heavy-oil Tulare sands at South Belridge indicates that Upper Tulare performance was controlled by strong edgewater drive, whereas Lower Tulare performance was controlled by gravity drainage. This paper describes the field results achieved in these highly dissimilar flooding environments. emphasizing the Upper Tulare edgewater drive to augment the limited number of publications in this area.
South Belridge Development
The South Belridge field (Fig. 1) is located about 40 miles west of Bakersfield, CA, in the San Joaquin Valley. The Tulare sands produce 130 API oil in response to thermal operations conducted at depths ranging from 400 to 1,200 ft. Belridge Oil Co. began thermal development operations in the Tulare heavy-oil accumulation at South Belridge in 1963. Upper and lower zones of approximately equal thickness within the Tulare formation (Fig. 2) were developed and steamed separately. Since 1963, 20 separate steamflood projects have been conducted in the Upper Tulare sands; 16 were still in progress when Shell Oil Co. acquired the Belridge holdings in 1979. The majority of these steamfloods were moderately successful and used unconfined. staggered linedrive patterns with a single row of injectors placed downdip near the oil/water contact (OWC) and multiple rows of producers drilled updip on 5/8-acre well spacing. Steamflood projects in the Lower Tulare sands were not as successful. Five projects using the same flood pattern and well spacing as those used in the Upper Tulare have been conducted in the Lower Tulare since 1965. Response from these projects was generally less favorable, partly because the Lower Tulare sands are not extensively continuous and are intermixed with poor-quality rock.
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