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Abstract: Predicting Oil Quality from Sidewall Cores Using PFID, TEC, and NIR Analytical Techniques in Sandstone Reservoirs, Offshore Cameroon

W. O. Bement, R. I. McNeil, R. G. Lippincott

Cameroon reservoirs contain oil and gas that have migrated vertically from deeper buried thermally mature marine shales. Several shallow reservoirs also contain biogenic gas. Generally, lower gravity oils found in the shallow reservoirs have undergone various degrees of biodegradation. Deeper accumulations are higher gravity 'primary' oils. The biodegraded oils are characterized by lower gravities, higher acid numbers, higher sulfur contents, and higher viscosities than their non-biodegraded counterparts.

Oil quality (API gravity and acid number) has a significant impact on the development economics. It is important to obtain as much geochemical information as possible from the limited volume of oil contained in conventional sidewall samples because borehole conditions often preclude the possibility of running a wireline test tool (the MDT) to obtain a fluid sample. An analytical program of PFID (Pyrolysis Flame Ionization Detection), TEC (Thermal Extraction Chromatography) and NIR (Near Infra-Red spectroscopy) was conducted on a set of 'calibration' oils and the data were used to develop both empirical and quantitative predictive criteria for estimating crude oil properties of gravity, acid number, sulfur content, and viscosity. Sidewall samples provide sufficient material for these m cro-analytical techniques. The individual sidewalls were split for geochemical analysis with the remaining material available for petrographic analysis. The PFID and TEC techniques were run on the 'rock' sample containing the oil. For the NIR technique, the oil was extracted from the sample with an organic solvent and the 'extract' evaluated. Results will be presented for sidewall core samples obtained from four oil sands encountered during a two well exploratory program.

AAPG Search and Discovery Article #90951©1996 AAPG International Conference and Exhibition, Caracas, Venezuela