The oolitic shoal reservoirs of the Lower Triassic Feixianguan Formation carbonates in the Sichuan Basin of southwest China are an important target for gas exploration in the basin.Their occurrence,like other cases wo...The oolitic shoal reservoirs of the Lower Triassic Feixianguan Formation carbonates in the Sichuan Basin of southwest China are an important target for gas exploration in the basin.Their occurrence,like other cases worldwide,can be divided into two locations in general,i.e.,platform interior and platform margin locations.Their differences of reservoir features and origins,however,have not been investigated comprehensively due to different exploration degrees.This issue is addressed in this paper,to provide basic data and information for the basin＇s hydrocarbon exploration and for the study of carbonate platform sedimentology and reservoir geology worldwide.We compared the features of these two types of reservoirs in detail,including the depositional and diagenetic features,pore types and petrophysical features.Based on the comparison,the origin of the reservoirs was further discussed.It is shown that the reservoirs in platform interior and platform margin locations differ significantly.The interior carbonates were deposited in moderate to high energy settings and the dominant lithologic type was limestone,which was weakly compacted and intensely cemented and has undergone meteoric dissolution.Pore types include intragranular dissolution and moldic pores,with low porosities（6%） and low permeabilities（0.1 mD）.By contrast,the platform margin carbonates were deposited in relatively high energy settings and mainly consisted of dolostones with some limestones.The rocks were strongly compacted but incompletely cemented.As a result,some primary intergranular pores were preserved.Both meteoric solution and burial solution have taken place.There are various types of pore spaces including intergranular and intercrystalline solution pores and residual intergranular pores.This type of reservoir generally has better petrophysical properties（9% porosity and 0.1 mD permeability） and pore-throat structures than the interior reservoirs.These differences were influenced by both primary depositional features and secondary diagenesis.For the interior carbonate reservoirs,early meteoric dissolution,weak compaction and strong cementation are important controlling factors.By contrast,the factors controlling the formation of the margin carbonate reservoirs mainly include dolomitization,preservation of primary pores and burial dissolution.展开更多
On the basis of systematic study of sedimentary facies, microfacies and geochemistry of measured strata sections and wells, the ooid shoals of the Cambrian Miaolingian Zhangxia Formation in the southern Ordos Basin ar...On the basis of systematic study of sedimentary facies, microfacies and geochemistry of measured strata sections and wells, the ooid shoals of the Cambrian Miaolingian Zhangxia Formation in the southern Ordos Basin are composed of both high-and low-energy ooid shoals. The characteristics of the high-energy shoals are sparry cementation, with moderate to well sorting, large grain size, high ooid content and low micrite, weak micritization, and well-preserved internal textures of the ooids. Macroscopically, the high-energy ooid shoals display a thick-bedded aggradational stacking pattern in upward coarsening and thickening sequences. The low-energy ooid shoals are mainly made up of micritic cementation, with moderate to poor sorting, relatively small grain size, lower ooid content and higher micrite, strong micritization, and poorly-preserved internal textures of the ooids. Macroscopically, the low-energy ooid shoals show a thin-bedded, interbedded stacking pattern in upward fining and thinning sequences. The sedimentological evidence and carbon isotope data show that the differences of internal fabric and sedimentary evolution of both high-and low-energy ooid shoals are closely related to the sea-level change.展开更多
A set of coal-bearing terrigenous clastic-carbonate cyclic shelf depositional sequences—Yoredale cyclic deposits are developed in the middle and upper parts of Taiyuan Formation of the Upper Carboniferous in the east...A set of coal-bearing terrigenous clastic-carbonate cyclic shelf depositional sequences—Yoredale cyclic deposits are developed in the middle and upper parts of Taiyuan Formation of the Upper Carboniferous in the eastern part of Ordos Block, North China. They are comparable to the Yoredale cycles, but possess their own character. Yoredale cycles were first discovered in beds of Viseen age in the Yoredale-Wensleydale area in展开更多
基金funded by the National Basic Research Development Program(973 project, Grant No. 2012CB214803)PetroChina Youth Innovation Foundation (Grant No. 2011D-5006-0105)Key Subject Construction Project of Sichuan Province, China(Grant No. SZD 0414)
文摘The oolitic shoal reservoirs of the Lower Triassic Feixianguan Formation carbonates in the Sichuan Basin of southwest China are an important target for gas exploration in the basin.Their occurrence,like other cases worldwide,can be divided into two locations in general,i.e.,platform interior and platform margin locations.Their differences of reservoir features and origins,however,have not been investigated comprehensively due to different exploration degrees.This issue is addressed in this paper,to provide basic data and information for the basin＇s hydrocarbon exploration and for the study of carbonate platform sedimentology and reservoir geology worldwide.We compared the features of these two types of reservoirs in detail,including the depositional and diagenetic features,pore types and petrophysical features.Based on the comparison,the origin of the reservoirs was further discussed.It is shown that the reservoirs in platform interior and platform margin locations differ significantly.The interior carbonates were deposited in moderate to high energy settings and the dominant lithologic type was limestone,which was weakly compacted and intensely cemented and has undergone meteoric dissolution.Pore types include intragranular dissolution and moldic pores,with low porosities（6%） and low permeabilities（0.1 mD）.By contrast,the platform margin carbonates were deposited in relatively high energy settings and mainly consisted of dolostones with some limestones.The rocks were strongly compacted but incompletely cemented.As a result,some primary intergranular pores were preserved.Both meteoric solution and burial solution have taken place.There are various types of pore spaces including intergranular and intercrystalline solution pores and residual intergranular pores.This type of reservoir generally has better petrophysical properties（9% porosity and 0.1 mD permeability） and pore-throat structures than the interior reservoirs.These differences were influenced by both primary depositional features and secondary diagenesis.For the interior carbonate reservoirs,early meteoric dissolution,weak compaction and strong cementation are important controlling factors.By contrast,the factors controlling the formation of the margin carbonate reservoirs mainly include dolomitization,preservation of primary pores and burial dissolution.
基金supported by the National Natural Science Foundation of China (Nos. 42272014, 41290260 and 41872034)。
文摘On the basis of systematic study of sedimentary facies, microfacies and geochemistry of measured strata sections and wells, the ooid shoals of the Cambrian Miaolingian Zhangxia Formation in the southern Ordos Basin are composed of both high-and low-energy ooid shoals. The characteristics of the high-energy shoals are sparry cementation, with moderate to well sorting, large grain size, high ooid content and low micrite, weak micritization, and well-preserved internal textures of the ooids. Macroscopically, the high-energy ooid shoals display a thick-bedded aggradational stacking pattern in upward coarsening and thickening sequences. The low-energy ooid shoals are mainly made up of micritic cementation, with moderate to poor sorting, relatively small grain size, lower ooid content and higher micrite, strong micritization, and poorly-preserved internal textures of the ooids. Macroscopically, the low-energy ooid shoals show a thin-bedded, interbedded stacking pattern in upward fining and thinning sequences. The sedimentological evidence and carbon isotope data show that the differences of internal fabric and sedimentary evolution of both high-and low-energy ooid shoals are closely related to the sea-level change.
文摘A set of coal-bearing terrigenous clastic-carbonate cyclic shelf depositional sequences—Yoredale cyclic deposits are developed in the middle and upper parts of Taiyuan Formation of the Upper Carboniferous in the eastern part of Ordos Block, North China. They are comparable to the Yoredale cycles, but possess their own character. Yoredale cycles were first discovered in beds of Viseen age in the Yoredale-Wensleydale area in
