川西坳陷东坡地区沙溪庙组断裂对天然气富集的控制作用

Controlling effect of Shaximiao Formation fault on gas accumulation in eastern slope area of Western Sichuan Depression

【研究目的】川西坳陷东坡侏罗系沙溪庙组气藏常规构造优势区挖掘潜力已不大、对于勘探程度较低的复杂断裂夹持区的气藏地质认识明显滞后。【研究方法】基于近年来的勘探开发资料和数据,运用构造控藏理论,本文研究了断裂断面形态类型和流体势差对油气成藏的控制,探讨了断裂夹持区内的油气分布规律,总结了南北断裂系统油气富集的差异性。【研究结果】断裂断面形态中以坡坪式断裂所控制的河道油气充注程度高、有利于高效成藏,低角度铲式断裂次之,高角度平直-铲式断裂成藏性最差;流体势差使得烃源岩天然气途径高势区向远距离砂体充注困难;断裂夹持区虽然在较窄的两端裂缝网络发育导致油气逸散很难成藏,但较宽的中部若由坡坪式断裂和低角度铲状断裂夹持输导则可形成相对较好的油气富集带。【结论】综合认为南部构造总体上优于北部、中部夹持区具有一定潜力,成藏的关键因素仍然受断裂形态特征和输导能力的控制。

[Objective]The exploration potential of conventional structural advantage area of gas reservoir in Jurassic Shaximiao Formation in the eastern slope of western Sichuan depression is not great,and the geological understanding of the gas reservoir in the complex fault clamping area with low degree of exploration is obviously lagging behind.[Methods]Based on the data in exploration and developent in recent years,using the theory of structural reservoir control,this paper studies the control of fault section morphology type and fluid potential difference on oil and gas accumulation,discusses the oil and gas distribution in the fault clamping area,and summarizes the difference of oil and gas enrichment in the north-south fault system.[Results]The study shows that the river channel controlled by slope-flat fault has a high degree of oil and gas filling,which is conducive to high-efficiency reservoir formation,followed by low-angle shovel-like fault,and high-angle flat shovel-like fault has the worst reservoir formation.[Conclusions]Fluid potential difference makes it difficult for hydrocarbon source cliff gas to fill long-distance sand bodies through high potential areas.Although it is difficult to form reservoirs due to the escape of oil and gas in the development of a narrow fracture network at both ends of the fracture clamping area,a relatively good oil and gas enrichment zone can be formed in the wider middle if the slope-flat fault and low-angle shovel-like fault are clamped and transported together.Therefore,it is believed that the structure in the south is superior to that in the northern and central clamping areas and has certain potential.The key factors of reservoir formation are still controlled by the fracture morphology and transportation capability.