|
The Tarim Basin with an area of 56104 km2 is the largest basin in China. Although the basin hosts both the largest oil accumulation (Hadexun Field) in the marine sandstones and the largest oil accumulation (Tahe Field) in marine carbonate in China, there are still some problems to be resolved, especially the distribution of main source rocks. These problems hinder future oil exploration in the basin. However, the practice of the oil exploration in non-marine sequences in Eastern China is not suitable for the oil exploration in marine sequences due to the significant differences between the clastics and the carbonates. This study documents the distribution characteristics of the marine successions and discusses the exploration methods, which are suitable for the oil exploration in marine strata.
The tectonic setting, the sequence of the marine carbonate, the variation of the sea level, the distribution of the sedimentary facies, and seismic data are synthesized to analyze the distribution of the Cambrian and Ordovician hydrocarbon source rocks. Our detailed analyses indicate that there exists a significant difference in the type and distribution between the marine source rocks and the continental source rocks. In terms of lithology, the Cambrian-Ordovician source rocks in the Tarim Basin are divided into two types: the carbonate source rock and the mudstone source rock. The two sets of source rocks are mainly developed in three stratigraphic intervals: Middle-Lower Cambrian carbonate and mudstone source rocks, Middle-Lower Ordovician mudstone source rock and Upper Ordovician limestone source rock. The stratigraphic distribution of the source rocks is controlled by the sea level changes and their regional distribution by the sedimentary facies. The mudstone source rock was deposited in slope-semi deep sea environment. The source rock of the slope origin and that of semi-deep sea origin are related to the anoxic environment and the upward-flowing sea water respectively. The carbonate source rock was mainly developed in the platform slope of the highstand systems tract and it is usually intimately associated with the evaporites. The Middle-Lower Cambrian carbonate source rock was mainly developed in the Bachu, Tazhong, Tangguzibasi Depression and Yingmaili area.
The Middle-Lower Cambrian mudstone source rock is mainly distributed in areas east of the line of Kunan 1-Tadong 1. The Middle-Lower Ordovician mudstone source rock mainly occur in the east slope of the Manjiaer Depression. The Upper Ordovician carbonate source rock was mainly developed in the platform slope of the highstand systems tract in areas such as the south margin of Tabei, north slope of Tazhong, Bachu area and Keping area.
|
