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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 65 (1981)

Issue: 5. (May)

First Page: 907

Last Page: 907

Title: Surface Detection of Free Hydrocarbon Microseepage from Subsurface Petroleum Accumulation: Case Study: ABSTRACT

Author(s): Stephen W. Brown, Joab Salce

Article Type: Meeting abstract


In January 1979, PEMEX began a 2-year test project designed to evaluate the surface detection of free hydrocarbon microseepage as an integrated exploration tool. The tests were performed by analyzing samples collected over fields selected to represent various hydrocarbon entrapment conditions (differing hydrocarbon type, differing trap mechanisms, varying depths, etc). All analyses were performed in the field, and the sample types, sample depths, and collection procedures were varied to determine the best procedures for detecting microseepage anomalies.

In addition to summarizing the various sample collection and analytical procedures utilized in the field operation, results are presented from one of the successful tests conducted over a known producing structure. The analytical field procedures used were C1-C7 gas chromatography and C10+ spectrum fluorescence analysis of cuttings and core samples collected at varying depths between 2 and 30 m. The structure selected is a lenticular anticline that produces oil from an Austin equivalent at 2,500 m and dry gas from the Jurassic at approximately 3,500 m.

The 350 surface samples definitely indicate that methane is seeping into the near-surface sediments and forming a distinct anomaly directly above the two superimposed reservoirs. Apparently, only the methane is able to migrate through the stratigraphic section, and the heavier components, if they were able to escape from the Cretaceous reservoir, have been stripped and retained by the sediments.

The surface anomaly appears to contain elements of both a circular halo and a centralized anomaly that overlies the apex of the producing structure. The intensity of the anomaly was of a sufficient degree that its detection should have been possible using blind reconnaissance sampling.

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Copyright 1997 American Association of Petroleum Geologists