Detection of Pay Zones and Pay Quality, Gulf of Mexico
D. M. Jarvie
Humble Geochemical Services, Humble, TX
Evaluation of stacked sand pay zones in the Gulf of Mexico is quite costly when up to 11 zones must be tested and possibly completed. This is complicated by the fact that oil-based or synthetic muds are used during drilling, and make it difficult to evaluate formation fluids. Well site testing operations are definitive, but very expensive.
An alternative approach is to perform simple and inexpensive geochemical analyses of frozen sidewall core (SWC) samples. This approach is frequently used by certain companies, but is not well known. The technique of thermal extraction fast gas chromatographic (TEfGC) fingerprinting provides the relative yield and distribution of condensate or oil present in a sample. An organic mud system will have a definitive, recognizable fingerprint that dominates one portion of the fingerprint. However, the presence of producible fluids can be identified by their presence around the mud fingerprint. The presence of low quality biodegraded oil can readily be determined. By using high temperature analysis, the presence of high molecular weight waxes can be detected. These waxes can precipitate in the delivery lines, e.g., Joilet Field. These data may be used to determine the zones for testing and completion in a very short time frame (less than 6 hours after receipt of samples). Prediction of physico-chemical properties (API, viscosity, pour and cloud points) can also be completed.
AAPG Search and Discovery Article #90901©2001 GCAGS, Annual Meeting, Shreveport, Louisiana