*Integrated Exploration Workflow for Maturing the Shallow Gas Play

J.H. ten Veen¹, H. Verweij¹, G. de Bruin¹, K. Geel¹, and T.H. Donders²

Abstract

Recent exploration activities in two of the largest deltas in the world, the Nile delta and the Cenozoic Southern North Sea (SNS) deltas, proved the economic potential of shallow gas resources. Like in many other parts of the world, including the Gulf of Mexico and offshore West Africa, the Nile Delta and SNS shallow gas was previously seen as a hazard or, at its best, as exploration tool for deeper HC’s. More and more, the shallow gas accumulations are seen as a valuable additional hydrocarbon resource, especially if located near existing infrastructures. Nonetheless, shallow gas production is still limited due to a lack of insight in the petroleum system, especially with respect to the relation between the anatomy of the delta and charging/trapping conditions. In order to mature the shallow gas play, a multidisciplinary workflow was applied to the SNS delta that involves 1) the reconstruction of the internally complex delta body, 2) a combined deterministic/stochastic approach to make reservoir property predictions, 3) evaluation of the HC origin, and 4) a grain-size based method to predict the seal-integrity of the sealing clay layers. The results present the first steps towards de-risking the shallow gas play in terms of trapping geometry, seal capacity, sourcing and migration. The presented workflow is applicable to areas were limited exploration data is available, but where critical production data is (still) missing. One such an area is the Nile delta. By reviewing the HC systems of the Nile and SNS deltas many similarities emerge that are expressed by 1) the control of sea-level and climate on the distribution of reservoirs, seals and organic material, 2) the presence of stratigraphic traps and 3) the role of deeper salt and faults in the formation of structural traps. For both settings, the origin of the shallow gas may be deep subsurface thermogenic sources or biogenic sources in shallower strata, or a mixture. For both areas, reserve estimates for shallow gas are often hard to make using conventional exploration techniques due to the inability to discriminate high vs. low saturation shallow gas. We briefly elucidate on the incorporation of pre-stack seismic inversions and other geophysical techniques such as CSEM that may appear essential in further maturing the Shallow Gas play.

AAPG Search and Discovery Article #90188 ©GEO-2014, 11th Middle East Geosciences Conference and Exhibition, 10-12 March 2014, Manama, Bahrain