【摘 要】
：
In recent years,significant progress in shale gas exploration has been achieved in the Upper Ordovician(Wufeng Formation)-Lower Silurian(Longmaxi Formation)shales in the Upper Yangtze area,South China.Although many studies have been carried out on the Upp
【机 构】
：
Research Institute of Petroleum Exploration and Development,CNPC,Beijing 100083,China;National Energ
论文部分内容阅读
In recent years,significant progress in shale gas exploration has been achieved in the Upper Ordovician(Wufeng Formation)-Lower Silurian(Longmaxi Formation)shales in the Upper Yangtze area,South China.Although many studies have been carried out on the Upper Ordovician-Lower Silu-rian shales,the controlling factors causing organic matter accumulation of these shales remain contro-versial.This study uses trace-element geochemistry and sedimentological methods to evaluate terri-genous input,redox conditions and primary productivity to explore the mechanisms of organic matter accumulation.The variation of terrigenous fraction elements(Al,Th and Sc)concentrations reflect a mixed influence of sea-level change and weathering.The sea-level of the Upper Yangtze Sea went through two cycles of transgression to regression during the Ordovician-Silurian transition.The Linxiang For-mation,Kuanyinchiao Bed and the upper part of Longmaxi Formation developed during the periods of regression,whereas the Wufeng Formation and the lower part of the Longmaxi Formation developed during the periods of transgression.The paleo-productivity indexes of TOC content,ratios of Ba/Al and P/Al,and redox conditions proxies of Mo concentration,ratios of U/Th and V/Cr generally display simi-lar variation patterns with respect to the sea-level changes.High TOC contents and Ba/Al and P/Al ratios indicate the paleo-productivity was high on the sea surface,as shown by relatively good positive correla-tions between Th vs.TOC,and Sc vs.TOC.This indicates that the paleo-productivity was controlled by the nutrients input through weathering.The good positive correlations between redox conditions indexes(U/Th and V/Cr ratios)with TOC content reflects reductive preservation conditions(anoxic to euxinic),thus implying they were an important controlling factor for organic matter accumulation.Nevertheless,redox conditions were closely associated with sea level change and organic matter decomposition.There-fore,the sea-level change and weathering were the primary controlling factors for organic matter en-richment across the Ordovician to Silurian transition.
其他文献
In the Middle and Upper Yangtze region of South China,there are well developed sets of marine shale strata.Currently only Wufeng Longmaxi shale gas has been developed in scale,while the Sinian and Cambrian shale gas are still under exploration.The various
In this paper,a calculation model for the breakdown time delay and jitter of gas switches under hundred-nanosecond pulses is proposed and applied in a self-triggered pre-ionized switch.The effects of injection time of pre-ionization,pulse rise time,and th
We present lithofacies classifications for a tight gas sandstone reservoir by analyzing hierarchies of heterogeneities.We use principal component analysis(PCA)to overcome the two level of heterogeneities,which results in a better lithofacies classificatio
It is of great significance to study the spatial distribution patterns and petrophysical com-plexity of volcanic vesicles which determine whether the reservoir spaces of the volcanic rocks can accu-mulate oil and gas and enrich high yields or not.In this
The microscopic pore structure of sand-conglomerate rocks plays a decisive role in its exploration and development of such reservoirs.Due to complex gravels-cements configurations and resultant high heterogeneity in sand-conglomerate rocks,the conventiona
A reliable and effective model for reservoir physical property prediction is a key to reservoir characterization and management.At present,using well logging data to estimate reservoir physical parameters is an important means for reservoir evaluation.Bas
Seismic and rock physics play important roles in gas hydrate exploration and production.To provide a clear cognition of the applications of geophysical methods on gas hydrate,this work presents a review of the seismic techniques,rock physics models,and pr
Fluid mobility has been important topic for unconventional reservoir evaluation.The tight sandstones in Chang 7 Member of the Ordos Basin has been selected to investigate the fluid mobility based on the application of core flooding-NMR combined method and
Reconstruction of the diagenetic evolution of reservoirs is one of the most significant tasks in oil and gas exploration and development.Assessing the accurate timing of diagenetic events is critical to better understand the process of reservoir evolution
Carbonates are considered to be important hosts of oxidized carbon during subduction processes.Here we investigate the redox interactions between dolomite and metallic iron in laser-heated diamond anvil cells up to～20 GPa.The identification of recovered s