鄂尔多斯盆地杭锦旗地区关键构造期与二叠系致密气成藏响应

Key structural periods and Permian tight gas accumulation response in Hangjinqi area,Ordos Basin

关键构造期是大型叠合盆地中表征构造作用与油气成藏之间成因联系和因果关系(成藏响应)的关键时间点,是分析油气成藏演化和油气聚集规律的重要“窗口”。基于鄂尔多斯盆地构造演化史,通过磷灰石裂变径迹等热年代学指标的约束,分析了鄂尔多斯盆地北部杭锦旗地区中生代以来构造演化及变形序列,厘定了该区J_(3)-K_(1)、K_(2)-E_(1)两个关键构造期,并结合石炭系—二叠系成烃—成藏史,认为J_(3)-K_(1)是杭锦旗地区现今“北东高、南西低”NE向构造格局的定型期,对应于烃源岩大量生排烃和砂岩致密化期,主要形成三眼井—乌兰吉林庙—泊尔江海子断层南部(简称南部)的石炭系太原组、二叠系山西组及石盒子组盒一段岩性气藏;K_(2)-E_(1)是主干断裂活化、北部NE向构造圈闭和NW向断裂形成期,导致南部先期岩性气藏调整和北部构造或构造—岩性气藏的形成;主干断裂两侧成藏差异明显,南部成藏早于北部,南部以岩性气藏为主,北部以构造—岩性气藏为主,南部含气层系以深层为主,北部深浅层均有,古近纪北部的隆升导致天然气散失。关键成藏期和关键改造期在空间和时间上转化,通过对成藏要素的差异化改造最终控制天然气的富集和贫化。

Critical tectonic period is a critical time point that characterizes the genetic connection and causal relation(accumulation response)between tectonic effect and oil/gas accumulation in large superposition basins,it is also an important"window"for analyzing accumulation evolution and accumulation regularity of oil/gas.Based on the systematic review of the tectonic evolution history of the Ordos Basin,the tectonic evolution and deformation sequence since the Mesozoic in Hangjinqi area in the northern part of Ordos Basin were studied through the constraints of apatite fission tracks and other thermal chronological indicators.Two key structural periods including J3-K1 and K2-E1 were proposed.It was believed by combining with the understanding of the Carboniferous-Permian hydrocarbon-generating and reservoir-forming histories that the J3-K1 was the period of design finalization in the Hangjinqi area which formed a currant NE-trending structural framework"high in the northeast and low in the southwest"during which,lithologic gas reservoirs including the Carboniferous Taiyuan and the Permian Shanxi formations,first member of the Permian Shihezi Formation to the north of the Sanyanjing-Wulan Jilin Temple-Bo’erjiang Haizi fault were formed and corresponding to the period of great amount of hydrocarbon generated and expulsed from source rocks as well as the densification of sandstones.On the other hand,the K2-E1 period was the major stage for fault reactivation and the formation of NE-trending tectonic trap and NW-trending fault that led to the adjustment of early lithologic gas reservoirs in the south and the formation of structural or structural-lithologic gas reservoirs in the north.The difference of accumulation on each sides of the main fault is obvious.The southern part was formed earlier than the northern part,and was dominated by lithologic gas reservoirs yet the northern part was dominated by structural-lithological gas reservoirs.The southern gas-bearing strata are dominated by deep strata,while those in the north are both shallow and deep ones.In Paleogene,lifting in the north caused loss of gas.The key accumulation and transformation periods transformed with space and time,which transformed accumulation factors differentially and finally constrained the enrichment and depletion of natural gas.