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The AAPG/Datapages Combined Publications Database

GCAGS Transactions


Gulf Coast Association of Geological Societies Transactions
Vol. 49 (1999), Pages 90-95

Reservoir Continuity and Architecture of the Genesis Field, Gulf of Mexico (Green Canyon 205): An Integration of Fluid Geochemistry within the Geologic and Engineering Framework

Mark A. Beeunas (1), Thomas A. Hudson (1), Josann A. Valley (1), David K. Baskin (2) and Wesley Y. Clark (1)

(1) Chevron Production Co., Gulf of Mexico Deepwater Business Unit, New Orleans, LA

(2)Chevron Research Technology Co., Integrated Laboratory Technology, La Habra, CA


Due to the high cost of developing deepwater reserves, it is imperative that all pertinent data be collected, analyzed and integrated into the reservoir model to insure the greatest possible accuracy. An area often overlooked is the compositional analyses of reservoir fluids collected from producing wells, DSTs, MDTs and core extracts. Traditionally, compositional analyses of reservoir fluids have been used for PVT-type engineering assessments and for identification of petroleum systems. However, detailed chromatographic analysis of reservoir hydrocarbons also provides information about the vertical and lateral connectivity.

Oil compositions are based on gas chromatogram fingerprints and compared with each other using Chevron's proprietary software, CP-Squared. The software rapidly scans the chromatograms and identifies peak ratios useful for comparing the oil samples. The application of hydrocarbon compositional analysis for continuity evaluation is based on the premise that oil samples from a single hydrocarbon accumulation (continuous reservoir) will have similar compositions, whereas production from separate hydrocarbon columns (e.g., different sand/fault block) will usually have discernibly different compositions. Compositional similarities are thought to be the result of hydrocarbon mixing within a reservoir, particularly in highly permeable reservoirs. Compositional differences between reservoirs can arise from the episodic charging of hydrocarbons having varying thermal maturities and/or sources. Additionally, post-charge alterations such as biodegradation, water washing, or evaporative fractionation can result in compositional differences within the reservoir.

Hydrocarbon compositional results from Genesis reservoirs have provided additional validation of suspected discontinuities within the major reservoir sands (N1, N2 and N3L). Of particular importance are suspected transmissibility restrictions interpreted in the N1 and N3L sands, based on pressure transient analyses and a corresponding area of lower seismic amplitude and minor vertical offset (Rafalowski et al., 1994). Significant hydrocarbon compositional differences across these restrictions support their existence and suggest potential barriers to production.

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