The reef-shoal depositional system of the Ordovician carbonate platform margin is well exposed in the Yijianfang （一间房） outcrop of the Bachn （巴楚） uplift region, which offers an advantageous condition to study ...The reef-shoal depositional system of the Ordovician carbonate platform margin is well exposed in the Yijianfang （一间房） outcrop of the Bachn （巴楚） uplift region, which offers an advantageous condition to study their paleoecology. Using a detailed field geologic survey and illustrated profiles of typical depositional systems, three types of genetic facies associations can be recognized in the reef-shoal depositional system： an organic reef, an organic shoal, and an upper slope. The organic reef is composed of three types of genetic facies （a reef base, a reef core, and fore-reef breccias）; the organic shoal is formed from five types of genetic facies （tide channels, fore-reef inner shoals, fore-reef outer shoals, back-reef inner shoals, and back-reef outer shoals）. The studies of the paleontological assemblage in each genetic facies of the depositional system indicate that the fauna preserved in each genetic facies are varied. The calathium, archaeoscyphia, bryozoan, and calcareous alga are well preserved in the organic reefs. The organisms preserved in the organic shoals are generally fragmented, while weil-preserved girvanella and nuia siberica with a content of about 15% in the back-reef outer shoals are the most characteristic and different from others. The sinoceras, trilobites, and gastropods are well preserved in the upper slope deposits. The studies will demonstrate that the reef-shoal complexes developed above the base of the fair-weather wave base and that the original hydrodynamic conditions for the reef core forming is the stronger and become more and more low-energy from the inner part to outer part of the organic shoals.展开更多
Taking advantage of the successful experience in exploring and discovering the Puguang Gasfield,and targeting the Changxing Formation-Feixianguan Formation organic reef and shoal lithological trap,SINOPEC drilled Well...Taking advantage of the successful experience in exploring and discovering the Puguang Gasfield,and targeting the Changxing Formation-Feixianguan Formation organic reef and shoal lithological trap,SINOPEC drilled Well Yuanba 1 in the Bazhong area in Northeast Sichuan in 2006,and discovered the Yuanba Gasfield with a high-production commercial gas flow of 503×10^(3) m^(3)/d.As a normal-pressured lithological gas reservoir with high H_(2)S content,Yuanba Gasfield is characterized by weak tectonic deformation and deep burial,with an average depth of 6,600 m in the central part of the gas reservoir,and is the deepest marine gas field in the Sichuan Basin.Yuanba Gasfield is dominated by large-scale reef-shoal reservoirs of Changxing Formation.The formation of the reservoirs was primarily controlled by early meteoric freshwater dissolution and dolomitization,and less affected by deep-burial dissolution and tectonic movement.A comparative analysis was made on the characteristics of deep reef-shoal reservoirs in the Yuanba and Puguang gas fields so as to explore their formation mechanisms.It is concluded that the reservoir size and early pore development was controlled by early depositional-diagenetic environment.Fracture formation and dissolution were controlled by structure-fluid coupling,pore reworking and preservation is determined by fluid-rock interaction.展开更多
基金supported by the SINOPEC Forward Looking Project of China (No. YPH08114)
文摘The reef-shoal depositional system of the Ordovician carbonate platform margin is well exposed in the Yijianfang （一间房） outcrop of the Bachn （巴楚） uplift region, which offers an advantageous condition to study their paleoecology. Using a detailed field geologic survey and illustrated profiles of typical depositional systems, three types of genetic facies associations can be recognized in the reef-shoal depositional system： an organic reef, an organic shoal, and an upper slope. The organic reef is composed of three types of genetic facies （a reef base, a reef core, and fore-reef breccias）; the organic shoal is formed from five types of genetic facies （tide channels, fore-reef inner shoals, fore-reef outer shoals, back-reef inner shoals, and back-reef outer shoals）. The studies of the paleontological assemblage in each genetic facies of the depositional system indicate that the fauna preserved in each genetic facies are varied. The calathium, archaeoscyphia, bryozoan, and calcareous alga are well preserved in the organic reefs. The organisms preserved in the organic shoals are generally fragmented, while weil-preserved girvanella and nuia siberica with a content of about 15% in the back-reef outer shoals are the most characteristic and different from others. The sinoceras, trilobites, and gastropods are well preserved in the upper slope deposits. The studies will demonstrate that the reef-shoal complexes developed above the base of the fair-weather wave base and that the original hydrodynamic conditions for the reef core forming is the stronger and become more and more low-energy from the inner part to outer part of the organic shoals.
基金This study was supported by China Geological Survey(Zi[2012]02-029-006).
文摘Taking advantage of the successful experience in exploring and discovering the Puguang Gasfield,and targeting the Changxing Formation-Feixianguan Formation organic reef and shoal lithological trap,SINOPEC drilled Well Yuanba 1 in the Bazhong area in Northeast Sichuan in 2006,and discovered the Yuanba Gasfield with a high-production commercial gas flow of 503×10^(3) m^(3)/d.As a normal-pressured lithological gas reservoir with high H_(2)S content,Yuanba Gasfield is characterized by weak tectonic deformation and deep burial,with an average depth of 6,600 m in the central part of the gas reservoir,and is the deepest marine gas field in the Sichuan Basin.Yuanba Gasfield is dominated by large-scale reef-shoal reservoirs of Changxing Formation.The formation of the reservoirs was primarily controlled by early meteoric freshwater dissolution and dolomitization,and less affected by deep-burial dissolution and tectonic movement.A comparative analysis was made on the characteristics of deep reef-shoal reservoirs in the Yuanba and Puguang gas fields so as to explore their formation mechanisms.It is concluded that the reservoir size and early pore development was controlled by early depositional-diagenetic environment.Fracture formation and dissolution were controlled by structure-fluid coupling,pore reworking and preservation is determined by fluid-rock interaction.
