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In the period of “11th Five-year Plan” (2006-2010), PetroChina proposed and developed a geological exploration theory for large oil and gas provinces, under which a group of major discoveries have been achieved. Large oil and gas provinces are large oil/gas-bearing areas consisting of several groups or belts of reservoirs (oil/gas fields) under the same large structural setting. These are determined by similar accumulation conditions, dominated by a certain type of hydrocarbon reservoir and overlaid vertically and connected horizontally. The combination of the large structural setting, favorable source rock and widely distributed heterogeneous reservoir is essential for development of large oil and gas provinces. Large oil and gas provinces are mainly developed in large structures such as continental depressions, foreland and marine craton basins, with large oil/gas-bearing areas and considerable reserves. Reservoirs are widely distributed, with low porosity and low permeability and high heterogeneity. Hydrocarbon distribution is not controlled by local structures and there is no uniform oil/gas/water contact but varying proportions of oil, gas and water. Based on the reservoir lithology, large oil and gas provinces are divided into clastics, carbonates and volcanic, which are subdivided into five sub-large oil and gas provinces, i.e. low porosity and permeability clastic; complex, steep and deep foreland structural; carbonate karst stratigraphic; carbonate platform margin reefal; and volcanic stratigraphic. Moreover, key technologies integrating seismic surveys, drilling, logging and formation tests have been developed. The exploration in large oil and gas provinces stresses the concept of “overall study, overall exploration and overall control”, and the evaluation method of “integrating exploration and development, and integrating production expansion and reserve growth”, to maximize the benefits of both exploration and development. Key words: litho-stratigraphic hydrocarbon reservoir, large oil and gas province, accumulation mechanism, geological characteristics, exploration concept, exploration method |
