Hydrocarbon accumulation principles in troughs within faulted depressions and their significance in exploration

Previously, troughs in continental faulted depressions were usually considered as a zone of hydrocarbon generation and expulsion rather than a zone for hydrocarbon accumulation. If they were confirmed to be the source kitchen, the possibility that they could constitute potential plays would be overlooked in the subsequent exploration program. Based on the hydrocarbon exploration practice of the Jizhong Depression and the Erlian Basin in the past several years, this paper discusses a new understanding that reservoir distribution is controlled by multiple factors and lithological accumulations are more likely to form in trough areas. It further documents the three main factors controlling the formation of large lithological hydrocarbon accumulations in trough areas. The paper also discusses the new concept that structural and lithological accumulations not only co-exist but also complement each other. We propose that fan-delta fronts on inverted steep slopes in troughs, delta fronts and sublacustrine fans on gentle slopes, channel sands along toes of fault scarps are favorable locations for discovery of new oil accumulations. The application of this concept has led to the discovery of several hundreds of million tonnes of oil in place in trough areas in the Jizhong Depression and the Erlian Basin.