川东北地区上三叠统须家河组致密气成藏地质特征及成藏模式

Geological characteristics and gas accumulation pattern of tight gas reservoirs in the Upper Triassic Xujiahe Formation in northeastern Sichuan Basin

一直以来,四川盆地上三叠统须家河组致密气勘探主要集中在川西、川中和川北地区,川东地区因处于川东隔档式褶皱构造带,致密气勘探一直未引起重视,勘探程度低。近年来,川东北地区须家河组致密气勘探不断取得新突破,测试的两口井均获高产工业气流,展示出川东向斜区须家河组具有一定的勘探潜力。从烃源、储集与构造等地质条件入手,分析川东北地区须家河组致密气成藏地质特征,以期揭开川东地区致密气勘探新局面,研究认为:(1)川东北地区须家河组气藏烃源主要来自上三叠统须家河组和上二叠统吴家坪组,生烃强度大,具有“双源供烃”的特点,具备致密气成藏的烃源基础;(2)川东北地区须家河组基质孔隙欠发育,优质储层主要表现为“缝砂体”,须家河组五段(须五段)大面积分布的储集砂体与准连续分布的裂缝为形成规模性“缝砂体”创造了有利的地质条件,储集条件优越;(3)川东北地区须五段气藏具有“双源供烃、两期成藏、准连续性分布”的特点,成藏条件优越。因此,川东北地区须家河组具备形成大面积“准连续性”气藏的条件,具有较大的勘探潜力,对推动川东隔档式褶皱构造带向斜区致密气勘探具有重要意义。

The exploration of tight gas in the Upper Triassic Xujiahe Formation in Sichuan Basin has always focused in western,central and northern Sichuan Basin,while that in eastern Sichuan Basin has not been attached emphasis due to its complex structural location in ejective fold structural belt,resulting in a low exploration level.In recent years,new breakthroughs have successively been made in the exploration of tight gas in Xujiahe Formation in northeastern Sichuan Basin,and high-yield commercial gas flows have been tested in two wells,which show tight gas potential in Xujiahe Formation in the syncline area in eastern Sichuan Basin.From the perspective of source rock,reservoir and structural conditions,the geological characteristics of tight gas reservoir in Xujiahe Formation in northeastern Sichuan Basin are analyzed,so as to open a new prelude to the tight gas exploration in eastern Sichuan Basin.The study results show that:(1)The hydrocarbon source of Xujiahe Formation gas reservoir in northeastern Sichuan Basin was mainly supplied by source rocks in the Upper Triassic Xujiahe Formation and the Upper Permian Wujiaping Formation,with high intensity of hydrocarbon generation and characteristics of“hydrocarbon supply by dual sources”,which had the material basis for tight gas accumulation;(2)The matrix pores were underdeveloped in Xujiahe Formation reservoir in northeastern Sichuan Basin,and the“fracture-sand body”served as high-quality reservoir.The large-area sand bodies and quasi-continuous fractures in the fifth member of Xujiahe Formation delivered favorable conditions for the formation of large-scale superior“fracture-sand body”reservoir;(3)The gas reservoir in the fifth member of Xujiahe Formation in northeastern Sichuan Basin is characterized by“hydrocarbon supply by dual sources,two-stage gas accumulation and quasi-continuous distribution”,showing superior conditions for gas accumulation.To sum up,Xujiahe Formation in northeastern Sichuan Basin has the conditions for forming large-area and“quasi-continuous”gas reservoir,which has great exploration potential and is of great significance for promoting the exploration of tight gas in the syncline area in the ejective fold structural belt in eastern Sichuan Basin.