Geochemical Exploration in Deserts of North Africa and the Middle East: Strategies for Success

Schumacher, Dietmar, Luis Clavijo, Daniel Hitzman, Geo-Microbial Technologies, Inc, Ochelata, OK

Surface geochemical exploration for petroleum is the search for surface or near-surface occurrences of hydrocarbons and their alteration products. It has been well documented that most oil and gas accumulations leak, that this leakage is predominantly vertical, that it is dynamic, and that this leakage can be detected and mapped using any of several direct and indirect methods. Hydrocarbon microseepage surveys in deserts require careful plan­ning and implementation. Microseepage data are inherently noisy and require adequate sample density to distinguish between anomalous and background areas. To optimize the recognition of a seepage anomaly, the sampling pattern and sample density must reflect sur­vey objectives, expected size and shape of the target, and expected variation in surface measurements. Defining background values adequately is an essential part of anomaly recognition and delineation. Undersampling and/or the use of improper analytical tech­niques is a major cause of ambiguity and interpretation failures.

Results of microbial and soil gas surveys in the deserts of Algeria, Tunisia, Egypt, Yemen, and Oman will be presented. These results illustrate the value of hydrocarbon microseepage data for high-grading basins, plays, and prospects. Surveys in Algeria and Tunisia document hydrocarbon microseepage to the surface in spite of the presence of 200­400 meters of halite above Triassic reservoirs, and the composition of the migrating hydro­carbons correctly predicted the composition of the reservoired hydrocarbons. Results from surveys in Egypt, Yemen, Oman, and Algeria successfully discriminated prospects on basis of hydrocarbon charge. Geochemical exploration surveys such as these require close sam­ple spacing and are most effective when results are integrated with subsurface data.