川东北地区须家河组构造差异及其对天然气富集的影响

Structural difference and its influence on gas accumulation:An example from Xujiahe Formation,northeastern Sichuan Basin

四川盆地川东北地区上三叠统须家河组致密砂岩大面积含气,天然气资源潜力大,但不同地区不同层段的天然气产能具有显著差异,天然气成藏富集规律复杂,主力勘探目标不明确。为了明确川东北须家河组不同地区天然气成藏富集主控因素、落实有利勘探目标,基于大量分析测试资料、地震资料和勘探实践,以川东北元坝西部地区、元坝中东部地区及通南巴地区为研究对象,分析了须家河组构造差异及其对天然气成藏富集的影响,指出了川东北不同地区构造改造对须家河组致密砂岩成储、成藏和富集具有重要的控制作用,明确了有利勘探目标。研究结果表明:(1)元坝西部地区为弱构造变形区,断层不发育,具有源内成藏优势的须三段钙屑砂岩气藏是下一步勘探的主要目标;(2)元坝中东部地区为构造过渡变形区,须家河组断层发育,具备下生上储成藏优势的须四段气藏是有利的勘探目标;(3)通南巴地区为海相断层、陆相断层叠加强构造变形区,沟通海相地层的深大断层发育,具备"海陆双源供烃"优势的区域是最有利的油气勘探目标区。

In tight sandstone reservoirs of the Upper Triassic Xujiahe Formation,northeastern Sichuan Basin,there is large amount of gas with huge resource potential.But its productivity varies greatly in different members and areas,and the gas accumulation and enrichment laws are also complicated,bringing about some difficultly in determining the principal exploration targets.In order to clarify the main factors controlling the gas accumulation and enrichment of Xujiahe Formation in different areas of northeastern Basin and determine favorable targets,some Xujiahe Formation in three areas in northeastern basin(including western Yuanba,central-eastern Yuanba,and Tongnanba areas)was taken an objective to analyze the structural difference and its influence on gas accumulation and enrichment based on abundant analysis,test,and seismic data as well as exploration practice.Then,it’s pointed out that tectonic reworking in these different areas plays an important control role in reservoir-forming and hydrocarbon accumulation and enrichment in these tight sandstone reservoirs of Xujiahe Formation.Finally,some favorable exploration targets were determined.Results show that(1)the western Yuanba area is just an area with weaker structural deformation,where faults are not developed,and some calcarenaceous sandstone gas reservoirs of Xujiahe 3 Member with the advantage of intra-source hydrocarbon accumulation should be the principal targets for next exploration;(2)the central-eastern Yuanba area is a transitional deformation area,in which faults are developed in Xujiahe Formation,and Xujiahe 4 gas reservoirs with the advantage of upper reservoir and lower source should be favorable exploration targets;and(3)in the Tongnanba area as a stronger structural deformation area with superimposed marine and continental movement,discordogenic faults connecting marine strata are developed,and this area with the advantage of"marine-terrestrial dual-source hydrocarbon supply"should be the most favorable for exploration.