The mechanism of "Multi-grade controlling sandbodies" under the guidance of "Source-to-Sink" system theory: a case study from the third member of Shahejie Formation in Liuzan area, Nanpu Sag

Liuzan Area is located in the northeast of Nanpu Sag in Bohai Bay Basin of China. It is obvious that oil pools are controlled by lithology. However, the researches of development characteristics and controlling factors of... [ view full abstract ]

Liuzan Area is located in the northeast of Nanpu Sag in Bohai Bay Basin of China. It is obvious that oil pools are controlled by lithology. However, the researches of development characteristics and controlling factors of sand-bodies are relatively rare. Under the guidance of source-to-sink system and the introduction of the multi-grade controlling sand-bodies mechanism, the development characteristics and the controlling factors of sand-bodies are deeply studied based on the 3D seismic data, well logs and cores. The model of three grades controlling sand-bodies is summarized. 1) Tectonic uplift and subsidence control the development characteristics of provenances. The previous researches have demonstrated that basin edge faults controlled the migration of deposition and subsidence, which leaded to the change of strata thickness as a “teeterboard”. Namely, because of the tectonic inversion, the thickness of strata clockwise migrated from thick in west and thin in east to thick in east and thin in west. Based on the seismic reflection characteristics and ZTR coefficient of heavy mineral, the development characteristics of provenances match with the above tectonic inversion. Therefore, the tectonic uplift and subsidence control discrepant superimposition in vertical and clockwise distribution in plane of the three main provenances. Namely, the tectonic uplift and subsidence control the development of “source” in source-to-sink system. 2) The structural slope-break zone and the lake level changes co-control the reservoir facies types. The study on the structural slope-break zone and lake level changes in Liuzan Area indicates that both structural slope-break zone and lake level changes constrain the accommodation space changes as well as the “sink” in source-to-sink system, which means the structural slope-break zone and lake level changes control the reservoir facies types. 3) The reservoir facies types control the sand-bodies distribution. In Liuzan Area, favourable sand-bodies developing in different reservoir facies types include distributary channel sand-bodies, front sand sheet and near submerged fan sand-conglomerates means the different reservoir facies types control the different sand-bodies distribution and types. Hence, the “contents” of the “sink” in source-to-sink is depicted in this way. This research provides the guidance and the basis for the breakthrough of oil and gas exploration.