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Fault Structures Controlling Petroleum from Compressed Sedimentary Basin in the Front of Mountain — from Identical Example of Wushi Sag in Kuqa Depression of Tarim Basin, China

Zheng, Min 1; Jia, Chengzao 1; Li, Xiaodi 1; Feng, Zhiqiang 2; Qu, Hui 1
1 Research Inst of Petroleum Expl & Dev, Beijing, China.
2 PetroChina Daqing Oilfield Company, Daqing, China.

The compressed sedimentary basins, those in the front of mountains are important areas of petroleum exploration, are abundance of petroleum resources in western China. This study was performed in Wushi Sag of Tarim Basin and used the basin’s dynamic background and the basin’s deposition static attribute to analyze the fault structures’ influences to the deposit and the hydrocarbon accumulation factors.

Wushi Sag developed six sedimentary types and seventeen subfacies and was proved there was lacustrine sedimentary environment. The Cretaceous stratum underlied at the bottom of the Neogene stratum at the eastern sub-sag, Lower Cretaceous strata were absence and Jurassic strata were just distributed at the north-east mountain zone, and the Triassic strata were drilled from Cretaceous strata directly in the Wucan 1 well. There were Mesozoic strata and structures bellow the ramp thrust in the front of Tianshan. The Meso-Cenozoic strata could be divided, by the gypsum-salt bed in the Miocene Jidike Formation, into two structural layers. We considered that the hydrocarbon source might come from its north-east area such as Talake and the main target for the oil-gas exploration should be Triassic Huangshanjie Formation.

Wushi Sag mainly develops four groups of reverse fault: NE, NEE, NW, EW and one group of NNW trending strike-slip fault. It has three fault composite patterns including face to face thrust, back to back thrust, sphenoid thrust, and five fault regional structural patterns (fault-bend folds, fault-propagation folds, duplex structure and sphenoid- duplex structure, paroxysmal structure, growth structure). The deformation in the upper structural layer was characterized with back-thrust, and a basement-evolved ramp thrust occurred in the lower structural layer. These fault-structure patterns controlled many trap styles, structural hydrocarbon reservoirs was the best, such as Wucan 1 and Shenmu 1 reservoirs.

The range of nowadays Wushi Sag just is the southern half part of the prototype basin and its’ SN-trending stratum shortening rate of Wushi Sag was about 67% since the basin was formed in Mesozoic era. Wushi sag grows stable SN compressive principal stress and makes the oil and gas migrate from north edge to south. The Cenozoic fault- Xiatagake fault cut off the way of oil and gas migration and stopped them to move again. The new structure and accumulation was growed in the northern Wushi. Shenmu 1 well was guided by this concept and had breakthrough.


AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009