EVOLUTION OF SINIAN-CAMBRIAN SUBSALT CARBONATE SEDIMENTA-RY MODEL AND ITS PETROLEUM GEOLOGICAL IMPLICATION IN NORTHERN TARIM BASIN
The source-reservoir-cap distribution and assemblage characteristics of the Sinian-Cambrian reservoirs in the north Tarim Basin were studied using more than 20 2D seismic lines,3D seismic data,and nearly 30 drilling data points from the region.Combined with outcrop profiles from the northwest margin of the basin,this study analyzes the lithofacies paleogeography,sedimentary model evolution,source-reservoir-cap development patterns,and reservoir-forming assemblages of the Late Sinian-Middle Cambrian period.The results indicate the presence of three carbonate sedimentary models in the northern Tarim Basin during the Late Sinian-Middle Cambrian:carbonate ramp,weakly rimmed platform,and strongly rimmed platform.Specifically,the carbonate ramp developed in the Upper Qigebulak Formation and Lower Cambrian Xiaoerbulak Formation,the weakly rimmed platform developed in the Middle Cam-brian Wusongger-Shaylike Formation,and the strongly rimmed platform emerged during the deposition period of the Middle Cambrian Awatag Formation.The sedimentary evolution in this area underwent five stages:carbonate ramp→ clastic shore-shelf → carbonate ramp→ weakly rimmed platform→strongly rimmed platform.This evolutionary process controlled the scale of different reservoir types and deter-mined the locations of favorable areas.In the Qigebulake Formation,biological mound reservoirs devel-oped along the inner and middle ramp of the northern margin of the paleo-uplift.In the Xioerbulak Forma-tion,algal mound-shoal reservoirs formed along the inner and middle ramp of the Tazhong and Keping are-as.The Shaylik Formation was mainly controlled by the platform margin belt,where shoal facies reser-voirs distributed along the platform margin.High-quality source rocks of the Lower Cambrian Yurtus For-mation and potential source rocks of the Xiaoerbulak Formation and the Sinian rocks developed in northern Tarim Basin.Three large-scale dolomite reservoirs were identified in the Upper Sinian Qigebulak Forma-tion,the Lower Cambrian Xiaoerbulak Formation,and the Middle Cambrian Shaylik Formation.These reservoirs,in conjunction with two sets of salt-rock cap Layers in the Wusongger and Awatag Formations,form three sets of oil-gas reservoir-cap assemblages in northern Tarim Basin.
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