Gas-bearing deposits in the Lower Mingyuefeng Formation of Paleogene, Lishui Sag, East China Sea Shelf Basin consist of shoreface sandstones of the highstand systems tract（HST） and transgressive systems tract（TST）...Gas-bearing deposits in the Lower Mingyuefeng Formation of Paleogene, Lishui Sag, East China Sea Shelf Basin consist of shoreface sandstones of the highstand systems tract（HST） and transgressive systems tract（TST）, and deltaic sandstones of the lowstand systems tract（LST） and falling stage systems tract（FSST）.Detailed petrographic observations suggest that the diagenetic features and related evolution of these deposits cannot be simply characterized and demonstrated in the depth domain.However, the occurrence of diagenetic minerals systematically depends on the studied interval within the HST, TST, LST, and FSST; therefore, diagenesis in this region can be better constrained when studied in the context of the depositional environments and sequence stratigraphic framework.The eogenetic processes in such settings include：（1） microcrystalline siderite precipitated as concretions in almost all environments and systems tracts, which inhibited further mechanical compaction;（2） grain dissolution and kaolinitization occurred in shoreface HST sandstones and deltaic LST and FSST sandstones;（3） glaucony was locally observed, which did not clearly reflect the controls of facies or sequence stratigraphy; and（4） cementation by pyrite aggregates occurred in the shoreface HST sandstones and deltaic LST sandstones.The mesogenetic diagenesis includes：（1） partial conversion of kaolinite into dickite in deltaic LST sandstones, and minor chlorite cementation in deltaic FSST sandstones;（2） transformation of kaolinite into illite and quartz cementation in deltaic LST and FSST sandstones;（3） frequent precipitation of ankerite and ferroan calcite in shoreface TST sandstones and early HST sandstones, forming baffles and barriers for fluid flow, with common calcite in shoreface HST sandstones as a late diagenetic cement; and（4） formation of dawsonite in the deltaic LST and FSST sandstones, which is interpreted to be a product of the invasion of a CO2-rich fluid, and acts as a good indicator of CO2-bearing reservoirs.This study has thus constructed a reliable conceptual model to describe the spatial and temporal distribution of diagenetic alterations.The results may provide an entirely new conceptual framework and methodology for successful gas exploration in the continental margins of offshore China, thus allowing us to predict and unravel the distribution and quality evolution of clastic reservoirs at a more detailed and reliable scale.展开更多
西湖凹陷中央洼陷带发育一系列挤压大背斜,是寻找大中型油气田的勘探区域之一,一直以来以构造油气藏评价和研究为主。应用钻井、岩心、实验分析及地震资料,系统开展了中央洼陷带中部花港组岩性油气藏主控因素分析,建立了该地区岩性油气...西湖凹陷中央洼陷带发育一系列挤压大背斜,是寻找大中型油气田的勘探区域之一,一直以来以构造油气藏评价和研究为主。应用钻井、岩心、实验分析及地震资料,系统开展了中央洼陷带中部花港组岩性油气藏主控因素分析,建立了该地区岩性油气藏形成的地质模式,并预测了勘探有利区分布。研究结果表明,广覆式厚层平湖组煤系烃源岩发育为岩性油气藏的形成提供了雄厚的物质基础,辫状河三角洲—湖泊沉积背景下花港组多期水道与分流间湾交互发育有利于岩性尖灭型圈闭的形成,H1—H2层区域性盖层遮挡下可形成多套良好的储盖组合,早期NNE向油源断裂高效输导是岩性油气藏源外成藏的关键因素。大背斜北翼受北部物源控制,大背斜西翼受西部物源控制,分别发育多期水道尖灭;后期的龙井运动导致地层遭受强烈挤压,水道砂反转抬升形成上倾尖灭型岩性圈闭;同时,先存油源断层活化,沟通平湖组煤系烃源岩和上部水下分流河道砂体,最终形成多个岩性油气藏。综合分析认为,中央洼陷带中部A1、N1、Y1、N2等4个井区是H1—H2、H3—H5两套气层有利区叠合分布范围,面积达700 km 2,是最有利的勘探指向区。展开更多
基金Financial support was provided by the National Science and Technology Major Project of China (No.2011ZX05023-002-003)
文摘Gas-bearing deposits in the Lower Mingyuefeng Formation of Paleogene, Lishui Sag, East China Sea Shelf Basin consist of shoreface sandstones of the highstand systems tract（HST） and transgressive systems tract（TST）, and deltaic sandstones of the lowstand systems tract（LST） and falling stage systems tract（FSST）.Detailed petrographic observations suggest that the diagenetic features and related evolution of these deposits cannot be simply characterized and demonstrated in the depth domain.However, the occurrence of diagenetic minerals systematically depends on the studied interval within the HST, TST, LST, and FSST; therefore, diagenesis in this region can be better constrained when studied in the context of the depositional environments and sequence stratigraphic framework.The eogenetic processes in such settings include：（1） microcrystalline siderite precipitated as concretions in almost all environments and systems tracts, which inhibited further mechanical compaction;（2） grain dissolution and kaolinitization occurred in shoreface HST sandstones and deltaic LST and FSST sandstones;（3） glaucony was locally observed, which did not clearly reflect the controls of facies or sequence stratigraphy; and（4） cementation by pyrite aggregates occurred in the shoreface HST sandstones and deltaic LST sandstones.The mesogenetic diagenesis includes：（1） partial conversion of kaolinite into dickite in deltaic LST sandstones, and minor chlorite cementation in deltaic FSST sandstones;（2） transformation of kaolinite into illite and quartz cementation in deltaic LST and FSST sandstones;（3） frequent precipitation of ankerite and ferroan calcite in shoreface TST sandstones and early HST sandstones, forming baffles and barriers for fluid flow, with common calcite in shoreface HST sandstones as a late diagenetic cement; and（4） formation of dawsonite in the deltaic LST and FSST sandstones, which is interpreted to be a product of the invasion of a CO2-rich fluid, and acts as a good indicator of CO2-bearing reservoirs.This study has thus constructed a reliable conceptual model to describe the spatial and temporal distribution of diagenetic alterations.The results may provide an entirely new conceptual framework and methodology for successful gas exploration in the continental margins of offshore China, thus allowing us to predict and unravel the distribution and quality evolution of clastic reservoirs at a more detailed and reliable scale.
文摘西湖凹陷中央洼陷带发育一系列挤压大背斜,是寻找大中型油气田的勘探区域之一,一直以来以构造油气藏评价和研究为主。应用钻井、岩心、实验分析及地震资料,系统开展了中央洼陷带中部花港组岩性油气藏主控因素分析,建立了该地区岩性油气藏形成的地质模式,并预测了勘探有利区分布。研究结果表明,广覆式厚层平湖组煤系烃源岩发育为岩性油气藏的形成提供了雄厚的物质基础,辫状河三角洲—湖泊沉积背景下花港组多期水道与分流间湾交互发育有利于岩性尖灭型圈闭的形成,H1—H2层区域性盖层遮挡下可形成多套良好的储盖组合,早期NNE向油源断裂高效输导是岩性油气藏源外成藏的关键因素。大背斜北翼受北部物源控制,大背斜西翼受西部物源控制,分别发育多期水道尖灭;后期的龙井运动导致地层遭受强烈挤压,水道砂反转抬升形成上倾尖灭型岩性圈闭;同时,先存油源断层活化,沟通平湖组煤系烃源岩和上部水下分流河道砂体,最终形成多个岩性油气藏。综合分析认为,中央洼陷带中部A1、N1、Y1、N2等4个井区是H1—H2、H3—H5两套气层有利区叠合分布范围,面积达700 km 2,是最有利的勘探指向区。
