Strategies for Surface Geochemical Surveys in Africa: Best Practice Designs and Recent Case Studies

Daniel C. Hitzman¹ and Luigi Clavareau^2
1Geo-Microbial Technologies (GMT), Ochelata, OK
²Geo-Microbial Technologies International, Paris, France

Geochemical exploration for petroleum is the search for surface hydrocarbons and their alteration products. Geochemical surveys document hydrocarbon microseepage originates from petroleum reservoirs and is common, widespread, predominantly vertical, and dynamic.

Direct geochemical exploration techniques analyze small quantities of hydrocarbons that occur in the pore space of soils, are adsorbed onto clay minerals, or are incorporated in soil cements. Indirect methods detect seepage-induced changes to soil and sediments. Microbes play a profound role in the oxidation of migrating hydrocarbons, and are directly responsible for many surface manifestations of petroleum seepage.

Onshore hydrocarbon microseepage surveys in Africa require careful planning and implementation. Based on effective logistical and security considerations, geochemical surveys have proven ideal for Africa’s diverse exploration regions. To optimize recognition of seepage anomalies, sampling patterns and quantities must reflect survey objectives, expected size and shape of targets, and expected variation in surface measurements. Defining background values is an essential part of anomaly recognition and delineation. Undersampling and/or the use of improper sampling techniques is a major cause of ambiguity which may lead to interpretation failures.

Geochemical exploration data have found their greatest value when integrated with geological and geophysical data. The integration of surface and subsurface exploration methods leads to better prospect evaluation and risk assessment. Recent African case studies will be presented.

AAPG International Conference and Exhibition, Cape Town, South Africa 2008 © AAPG Search and Discovery