Integrated Characterization of the Thin-Bedded 8 Reservoir, Green Canyon 18, Gulf of Mexico

Abstract

Abstract The thin-bedded, channelized-turbidite 8 reservoir of the Green Canyon 18 field (GC-18) had previously been difficult to describe owing to its complex architecture and limitations in seismic data resolution. The reservoir has high rock compressibility. Its complex geology had, before this study, prevented the delineation of its hydrocarbon accumulation and determination of the different resource volumes. An integrated approach has been used to develop a geologically consistent model of the reservoir. Seismic interpretation and attribute extraction provided the reservoir geometry and stratigraphy, which show the preeminent role of salt tectonics in the shaping of the reservoir before and after deposition. Geostatistical methods were used to construct gross and net thickness maps and to infer lateral variations in the quality of the 8 sand. Lithofacies description from cores showed 3 distinct facies - channel, levee, and overbank deposits - that were sufficient to describe the reservoir. Fine-scale heterogeneity in each zone was determined from core and log lithological descriptions. Truncated Gaussian sequential simulation was performed to distribute facies and reservoir properties throughout the reservoir volume. The resulting geological model was used to construct a dynamic flow model that matched historical production and pressure data. This work shows the efficiency of the integrated approach in describing complex reservoirs where the internal variability is a major control of flow efficiency. This approach is especially valuable in reservoirs like the GC-18 8 reservoir where the well information is scarce or not uniformly distributed. Introduction and Method The Gulf of Mexico (GOM) is a major petroleum-producing province with considerable importance to the U.S. economy. The move into deeper waters has provided new opportunities for petroleum production, but it has also provided new challenges as different reservoir problems are encountered. A significant fraction of the reservoirs in the Outer Continental Shelf consist of thin-bedded deposits of submarine fan systems. These reservoirs are typically very heterogeneous, consisting of turbidite channel deposits combined with sheet-like levee and overbank deposits. Stratigraphic features are subtle and difficult to detect because sand response is often close to shale response except where they are cut by channels. They are often heavily faulted. Green Canyon 18 field (GC-18) is a 5900-acre field located some 70 miles off the Louisiana coast in the GOM, approximately 120 miles south of Morgan City (Fig. 1).1 The field is a channel-levee-overbank system deposited between shallow salt bodies.2 Deposition of the 8 reservoir resulted from fine-grained turbidity currents in a mid-basin slope. The GC-18 field has enjoyed continuous development since 1982. To date thirty wells have been drilled in the field, of which twenty-six penetrated the 8 reservoir. The field came on stream in May 1987, but the 8 reservoir started producing in November 1987. As of 9/2001, cumulative production from the 8 reservoir was 8.18 MMSTB, 10.59 BCF, and 5.28 MMSTB of oil, gas and water, respectively.