Seismic and geological characteristics of Cenozoic plastic layers in Qaidam Basin and their significance
LI Xuhang1, WANG Bo2, ZHANG Junyong1, GUO Bo1, TAN Wei1, JIANG Liwei3
1. Geological Research Center, GRI, BGP Inc., CNPC, Zhuozhou, Hebei 072751, China; 2. Research Institute of Exploration and Development, PetroChina Qinghai Oilfield Company, Dunhuang, Gansu 736201, China; 3. AI Research Center, Research Institute of PetroleumExploration and Development, PetroChina, Beijing 100086, China
Abstract：In recent years, owing to the improved quality of seismic data, three sets of plastic layers have been found in the Neozoic Lulehe Formation, Lower Ganchaigou Formation, and Upper Youshashan Formation in the Qaidam Basin. These plastic la-yers are closely related to the tectonic deformation and oil and gas accumulation in the Qaidam Basin. The previous research on the plastic layers in the Lower Ganchaigou Formation has made some progress. Nevertheless, systematic and in-depth research on the plastic layers in the Lulehe Formation and the Upper Youshashan Formation is still absent, resulting in the unclarity of the tectonic formation mechanism. For this reason, high-quality seismic data, regional geology, and drilling and logging data were availed to determine the seismic identification marks, lithological characteristics, distribution range, and thickness of the three sets of Neozoic plastic layers in the Qaidam Basin. The relationship between the development characteristics of the plastic layers and tectonic style was analyzed, and the main controlling factor of the decoupling between the deep and shallow tectonic layers in the Qaidam Basin was clarified. The results show that the plastic layers have mainly developed in the Altyn piedmont tectonic belt, the Lenghu tectonic belt, and the Yingxiongling tectonic belt. These layers are also the main controlling factor of the decoupling between the deep and shallow tectonic layers in the Qaidam Basin. As for the tectonic style, thin-skinned structures dominate the areas with developed plastic layers while basement-involved structures dominate the areas without plastic layers. The plastic layers cause the up-down stratification and planar zoning of the structures in the Qaidam Basin. Furthermore, these plastic layers control the development of tectonic traps. As stable regional cover layers in the Qai-dam Basin, they also control the local enrichment of oil and gas, ultimately enabling the formation of various types of oil and gas reservoirs. The results can guide the exploration of plastic layer-related oil and gas reservoirs in the Qaidam Basin.
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