克拉通盆地盆缘致密气藏封堵模式:以鄂尔多斯盆地北缘杭锦旗地区盒1段为例

Sealing model of tight gas reservoirs in the edge of Claraton Basin:A case study from the first Member of Lower Shihezi Formation in Hangjinqi area of the northern margin of the Ordos Basin

克拉通盆地大面积致密砂岩气藏边界带上的气水分布往往远比盆地内部复杂,圈闭类型多样,气藏上倾方向封堵模式尚存在争议。本研究以鄂尔多斯盆地北缘杭锦旗地区二叠系盒1段气藏为例,对比分析不同区带典型河道砂体厚度、岩相组合、砂体叠置关系、储层物性及横向宏观非均质性等多因素差异分布特征及其对气藏分布的控制作用,最终建立杭锦旗地区不同构造带内盒1段气藏封堵模式。研究表明,研究区自西向东发育3种河道沉积模式,分别是西部缓坡区浅水辫状河模式、中部陡坡区冲积扇-辫状河模式、东部深水道模式,3种沉积模式控制了河道上倾方向储层宏观非均质性差异,这种宏观非均质性变化是研究区致密砂岩气藏上倾方向封堵的主控因素。根据研究区上倾方向储层变化与圈闭类型关系,划分了3种天然气封堵模式:西部缓坡区岩性封堵模式、中部陡坡区地层-岩性封堵模式、东部岩性-构造过渡封堵模式。3种天然气封堵模式构成了鄂北盆缘盒1段大面积天然气连续成藏区的边界,同时控制了不同类型圈闭分布与天然气富集。

Gas and water distribution of large-scaled tight sandstone gas reservoirs in the margin of typical craton basin is generally much more complicated than that in the center of the basin,and there are various types of traps,therefore,the updip sealing models of gas reservoirs is controversial.This study takes the Permian gas reservoirsof the first Member of Lower Shihezi Formation(He-1 member)in Hangjinqi area of the northern margin of the Ordos Basin as an example,and aims to investigate the differential distribution characteristics,including sandbody thickness,lithofacies association,sandbody superimposition,reservoir physical properties and transverse connectivity of typical channels in the He-1 memberat different locations.The results suggest three types of river depositional models,including shallow-water braided river model in the western gentle slope zone,alluvial fan-braided river model in the central steep slope zone,and deep-water braided river model in the eastern slope break zone.The three depositional models control the difference of channel updipsealing conditions.Based on the relationship between updip reservoir variation and trap types,three models of natural gas migration and accumulation are proposed aslithologic sealing model in the western gentle slope zone,strata coupled with lithologic sealing model in the central steep slope zone,and transitional model of lithologic sealing-trap accumulation in the eastern zone.It is concluded that the upward sealing conditions under these three migration and accumulation models constitute the boundary of the large-scaled continuous reservoir-forming area of He-1 memberin the northern margin of the Ordos Basin,and also control the distribution of different traps and gas enrichment in the Hangjinqi area.