四川盆地华蓥山五峰组—龙马溪组剖面特征及其勘探意义

Characteristics and exploration significance of Wufeng-Longmaxi Formation stratigraphic section in Mount Huaying,Sichuan Basin

近年来,四川盆地龙马溪组页岩气勘探已全面展开,但复杂构造带领域攻坚还在探索,开展四川盆地内高陡构造带华蓥山地区三百梯剖面的系统研究,可为复杂构造带页岩气的勘探突破提供思路。通过开展剖面岩性、古生物、矿物成分、地化特征、孔隙类型及结构等多方面研究,并与邻区钻井进行对比后认为:(1)华蓥山剖面出露良好,五峰组至龙马溪组底部页岩地层完整连续,五峰组分为2段,龙马溪组(未见顶)分为3段,WF2-LM9笔石带发育齐全。由下至上沉积环境由还原向氧化过渡,生物硅质环境遭受破坏,陆源碎屑含量增加,有机质丰度呈下降趋势。五峰组—龙一段有机质较为富集,脆性矿物含量高,储集空间以有机孔为主,无机孔、微裂缝发育,孔隙结构以墨水瓶孔为主,少量狭缝形孔。(2)在赫南特期—鲁丹期,川南地区华蓥山三百梯剖面尽管仍位于深水陆棚相带,但局部发育水下高地微古地貌,由于底流作用、可容纳空间等因素影响,富有机质页岩沉积厚度较薄,微古地貌对于页岩气形成的物质基础具有重要的影响,可为下一步龙马溪组选区评价提供思路。(3)五峰组—龙一段优质页岩储层形成主要受控于火山作用、物源供给、还原环境的共同作用。

In recent years,the exploration of Longmaxi Formation in Sichuan Basin has been successful,but the shale gas of the complex structural belt’s Longmaxi Formation are still the next areas for exploration.Therefore,it is necessary to carry out systematic researches on the Sanbaiti section in Mount Huaying of high-steep structural belt in Sichuan Basin,so as to provide ideas for the further exploration breakthrough.The section’s lithology,paleontology,mineral composition,geochemical characteristics,pore type and structure are studied,and compared with the drilling wells of adjacent areas.The findings are as follows.(1)The outcrop in Mount Huaying section is well exposed.The shale strata from Wufeng Formation to the bottom of Longmaxi Formation are complete and continuous.Wufeng Formation is divided into two sections,and the Longmaxi Formation(no top)is divided into three sections.The WF2-LM9 graptolite biozone is well developed.From the bottom to the top,the sedimentary environment changed from reduction to oxidation,and the biogenic siliceous environment has been destroyed.The injection amount of terrigenous debris increases,and the abundance of organic matter shows a downward trend.The organic matter in Long-1 member of Wufeng Formation is relatively rich,and the content of brittle minerals is high.The reservoir space is dominated by organic pores,followed by inorganic pores and microfractures.The pore structure is dominated by ink bottles,and a small amount of slit pores.(2)For the Hirnantian-Rhuddanian,although the Sanbaiti section of Mount Huaying is located in the deep-water shelf zone in southern Sichuan,the underwater highland micro-paleogeomorphology is locally developed.Due to the influence of undercurrent and other factors,the deposition thickness of organic-rich shale is thin.So that,the micro-paleogeomorphology has an important influence on the material basis of shale gas formation,which can provide ideas for the further evaluation of Longmaxi Formation.(3)The formation of organic-rich shale reservoirs in Long-1 member of Wufeng Formation is mainly controlled by the combined action of volcanism,source supply and reduction environment.