鄂尔多斯盆地北部泊尔江海子断裂对上古生界天然气成藏的控制

为了揭示泊尔江海子断裂对鄂尔多斯盆地北部杭锦旗地区上古生界天然气成藏的控制作用，应用地震和钻井资料，在断裂活动性分析的基础上，根据断层泥比率和断层连通概率法对泊尔江海子断裂的侧向和垂向封闭性进行半定量评价，探讨断裂和天然气富集区的关系。结果表明：泊尔江海子断裂呈现3次明显的活动高峰期，分别为加里东期-早海西期的断裂形成期、印支期-早燕山期的挤压逆断裂活动期、中晚燕山期的走滑撕裂活动期，而中晚燕山期的走滑撕裂控制了上古生界天然气主要成藏期。断裂的封闭性具有“横向分段、纵向分层”的特点；横向上，以断层泥比率(SGR)等于0.3为界将泊尔江海子断裂分为侧向优势输导区和侧向封闭区；纵向上，在石千峰组和上石盒子组断裂启闭系数基本都小于1.0，断裂垂向封闭，在下石盒子组和山西组断裂启闭系数主要集中在4.0~10.0，断裂垂向开启。在断裂侧向优势输导区，断裂南部主力烃源区生成的天然气，经断裂发生垂向和侧向运移，易在断裂北部地区富集成藏；在侧向封闭区，则易在断裂南部地区富集成藏。

Control of Boerjianghaizi Fault on Gas Accumulation of Upper Paleozoic in Northern Ordos Basin

In order to reveal the control functions of Boerjianghaizi fault on natural gas accumulation of Upper Paleozoic in Hangjinqi block of the northern Ordos Basin, the history of the fault activity, the lateral and vertical sealing ability of the fault were studied by using fault growth index evolution, fault shale gouge ratio method and fault connectivity probability method through seismic and drilling data of this area. Then Boerjianghaizi fault effects on the natural gas enrichment zones were discussed. The results showed that Boerjianghaizi fault had three obvious peaks of activity in the history of evolution, which were Caledonian to Early Hercynian fracture period, Indosinian to Early Yanshanian squeezing thrust fault activity period, and Mid-late-Yanshanian strike-slip tearing activity period. Mid-late-Yanshanian strike-slip tearing activity period matched well with the main stage of gas accumulation of Upper Paleozoic. It was pointed out that sealing ability of Boerjianghaizi fault had the characteristics of “horizontal sectioning, vertical layering”. In the horizontal direction, Boerjianghaizi faults were divided into lateral migration fault areas and lateral sealed fault areas according to the shale gouge ratio (SGR) which equals to 0.3 as the dividing line. In the vertical direction , the fault plane was vertically sealed in Upper Shihezi and Shiqianfeng formations because the fault sealing coefficients were almost less than 1.0 in the section, while the fault plane was vertically open in Lower Shihezi and Shanxi formations because the fault sealing coefficients mostly range from 4.0 to 10.0 in the section. Meanwhile, in the lateral migration fault areas, natural gas generated from the main source areas which were in the south side of Boerjianghaizi fault was transmitted in the vertical and lateral direction through the fault, then natural gas accumulated in large amount in the north side of the fault easily, but in the lateral sealed fault areas, it is easy to find the natural gas pools in the south side of the fault.