四川盆地中三叠统雷口坡组储层特征及勘探方向

Reservoir characteristics and exploration target of the Middle Triassic Leikoupo Formation in Sichuan Basin

四川盆地中三叠统雷口坡组是中国石油西南油气田公司的重要战略接替领域。随着勘探形势的变化,需要以全盆地为单元,明确储层平面分布规律,为下一步天然气勘探方向提供指导。基于丰富的岩心、测井、地震和野外露头等资料,通过层序格架下的岩相古地理深化认识和储层特征综合分析,认为:(1)四川盆地雷口坡组属于局限台地沉积环境,纵向上可划分为4个三级层序,有利沉积相带发育在海侵体系域,主要位于雷一1亚段、雷三3亚段和雷四3亚段;(2)雷口坡组“一洼两隆”的古地理格局控制着滩体分布,其中盆地西侧龙门山前带滩体为复合叠置发育,东侧膏盐湖边缘滩体为迁移叠置发育;(3)雷口坡组发育沉积型和岩溶改造型两类储层,其中沉积型储层以颗粒滩白云岩储层和微生物白云岩储层为主,主要发育于盆地边缘及盆内古地貌高处,而岩溶改造型储层主要发育于有利相带与岩溶残丘叠合处。综合考虑烃源岩、储层类型和圈闭条件等,指出四川盆地雷口坡组下一步勘探方向:剑阁—江油—名山一带是雷三段、雷四段颗粒滩白云岩储层和微生物白云岩储层有利勘探领域,资阳—南充地区和泸州古隆起西缘是雷一段滩相白云岩储层有利勘探领域,大川中地区是岩溶改造型储层有利勘探领域。

The Middle Triassic Leikoupo Formation is a major strategic replacement fi eld for petroleum exploration of PetroChina Southwest Oil and Gas Field Company in Sichuan Basin.The exploration situation is changing,and the rule of reservoir distribution in basin scale is necessary to be identifi ed,so as to provide guidance for gas exploration in the near future.The lithofacies paleogeography within sequence framework is further understood and reservoir characteristics are comprehensively analyzed by using a large number of core samples,well logging,seismic and outcrop data.The results show that:(1)It was a limited platform environment in Sichuan Basin during the deposition of Leikoupo Formation.The formation is subdivided into four tertiary sequences,and the favorable reservoirs are mainly developed in L11(1st sub-member of the 1st member of Leikoupo Formation),L33 and L43 sub-members of transgressive system tract;(2)The paleogeographic pattern of“one subsag and two uplifts”during the deposition of Leikoupo Formation controlled the distribution of beach reservoir,in which it was composite superimposed in the piedmont of Longmen Mountain in the western basin while it was migration superimposed of the marginal beach body of gypsum salt lake in the eastern basin;(3)There are two types of reservoirs of Leikoupo Formation,i.e.,the faciescontrolled reservoir and karst reservoir.The former is dominated by grain beach dolomite and microbial dolomite,which is mainly developed in the basin margin and paleo highs inside the basin,while the latter is developed in the superimposed area of favorable facies zones and karst residual mounds.Finally,the favorable exploration targets are proposed by comprehensively considering source rocks,reservoir types and trap conditions,including grain beach dolomite and microbial dolomite reservoirs of L_(3) and L_(4) members in Jiange-Jiangyou-Mingshan area,beach dolomite reservoirs of L_(1) member in Ziyang-Nanchong area and the western margin of Luzhou paleo uplift,and karst reservoir in central Sichuan region.