Examples and New Applications in Applying Organic Geochemistry for Detection and Qualitative Assessment of Overlooked Petroleum Reservoirs

Daniel M. Jarvie, Robert J. Elsinger, Joe T. Sentfle, William B. Huges, and James J. Emme

Techniques of organic geochemistry can provide specific information on the presence and quality of petroleum in payzones that may be overlooked by exploration and production geologists This paper presents case histories where the use of basic geochemical techniques on rock and/or fluid samples were used to find reservoir intervals and predict the quality of the reservoired petroleum on both active and previously drilled wells.

Two examples are from wells drilled in the San Joaquin basin in California. TOC, Rock-Eval, and Thermal Extract Gas Chromatography analyses on cuttings from an actively drilling well were used to successfully identify missed reservoirs, qualify the hydrocarbons present, and identity the oil-water contact. The second San Joaquin Basin example used the same techniques on old cuttings samples to discover by passed shallow reserves of over 200,000 barrels of oil.

The use of Gas Chromatography on a RFT liquid sample successfully identified a gas condensate reservoir in a Gulf of Mexico Eocene Yegua trend well that was drilled with a diesel mud system. The diesel in the mud prevented the conventional evaluation techniques from identifying any liquid hydrocarbons in the well. A 50 API gravity liquid was tested from the sand interval.

Additional examples will be presented to illustrate other geochemical techniques and their usefulness in finding by-passed pay zones and assessing the quality of reservoired hydrocarbons.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California