ABSTRACT: Demonstration and Application of Thermal Desorption to Reservoir and Prospect Evaluation

John M. Bodard, Evan J. Evans, Garry Woodhouse

Thermal desorption-gas chromatography (TD-GC) has been used to analyze the volatile organic matter in sediments. By including an internal standard, the quantity and chemical characteristics of such material can be determined. TD-GC provides a cheap alternative to solvent extraction followed by gas chromatography for quantification and chemical typing. Comparably high-precision data are rapidly obtained. This permits more complete sample coverage when time and/or costs are limited. The method is especially useful where small amounts of material low extractable levels are involved (i.e., tight and/or dirty sands, or poor-quality samples). Drill cuttings and sidewall and conventional core samples of all sediment types are suitable for analysis.

TD-GC analysis is of particular value in the delineation and study of potential reservoir sequences. A key advantage of rapid determinations of extract yields and characteristics is in common discovery situations where a preliminary oil leg definition is ambiguous. TD-GC analysis is cost effective in reservoir evaluation and consideration of further formation testing and drilling while the drill remains on site. These data are ultimately useful in planning further reservoir development.

We demonstrate the application of TD-GC in evaluating a potential reservoir using a recent wildcat well situation. Yield and geochemical data are used to predict the gas-oil and oil-water contacts in this oil-on-rock discovery. Implications for the filling and subsequent history of the structure and others in the area are examined. Further applications from other drilling and different prospect evaluation experiences are also discussed.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990