Geochemical Exploration Strategies for Papua New Guinea and other Geologically Complex Areas in Southeast Asia: Best Practices and Recent Exploration Case Histories

Abstract

The petroleum potential of geologically complex areas -- such as highly faulted and folded terrains -- is often poorly known due to technical challenges affecting seismic acquisition and imaging. When these areas occur in jungles and highlands, the logistical challenges only add to the difficulty of evaluating the petroleum potential of such regions. For such areas, surface geochemical and non-seismic hydrocarbon detection methods provide an opportunity to reliably detect and map the elevated hydrocarbon concentrations and hydrocarbon-induced changes commonly associated with undiscovered oil and gas accumulations. The surface manifestations of hydrocarbon microseepage can take many forms, including (1) anomalous hydrocarbon concentrations in soils, sediments, waters, and atmosphere; (2) microbiological anomalies; (3) mineralogic changes such as the formation of calcite, pyrite, uranium, elemental sulfur, and certain magnetic iron oxides and sulfides; (4) bleaching of red beds; (5) clay mineral changes; (6) acoustic anomalies; (7) electrochemical changes; (8) radiation anomalies; and (9) spectral and hyperspectral anomalies. These varied expressions of hydrocarbon seepage have led to the development of an equally diverse number of hydrocarbon detection methods. Some of these methods are geochemical, some are non-seismic geophysical methods, and some come under the category of remote sensing. Hydrocarbon detection surveys in geologically complex areas require careful planning and implementation due to extreme variations in topography and surface conditions. Based on effective logistical and security considerations, geochemical surveys have proven ideal for this region’s diverse exploration regions. To optimize recognition of hydrocarbon anomalies, survey patterns and sample numbers 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. Under-sampling and/or the use of improper sampling techniques represent a major cause of ambiguity which may lead to interpretation failures. Hydrocarbon detection surveys are most effective when results are integrated with satellite remote sensing data and available geophysical data. Such surveys are ideally suited for an early stage evaluation since they can quickly identify those parts of the area possessing the highest petroleum potential, as well as determine the characteristics of petroleum in the areas of interest. When used to high-grade exploration leads and prospects on the basis of their likely hydrocarbon charge, geochemical survey results predict 75% to 85% of subsequent discoveries, and 90% of subsequent dry holes. The inclusion of hydrocarbon detection surveys early in an exploration strategy focuses attention and resources on a relatively small number of high potential areas, thereby minimizing both risks and expenses. This presentation is illustrated with examples of surface geochemical results evaluating drilling sites, AOIs, prospects and post drilling surveys over dry and discovery wells from PNG, Australia, Indonesia, Laos, Malaysia, Philippines, Taiwan, and Thailand. The examples from PNG and some from Indonesia and the Philippines have not been published before.

AAPG Datapages/Search and Discovery Article #90371 © 2020 AAPG Asia Pacific Region, The 1st AAPG/EAGE PNG Geosciences Conference, PNG’s Oil and Gas Industry: Maturing Through Exploration and Production, Port Moresby, Papua New Guinea, February 25-27, 2020