四川盆地及其周缘下寒武统沧浪铺组下段岩相古地理特征

Lithofacies and paleogeography of the lower Canglangpu Formation of the Lower Cambrian in Sichuan Basin and its periphery

川中—川北地区的风险探井角探1井、蓬探1井、川深1井在下寒武统沧浪铺组钻遇厚层鲕粒白云岩,测井解释气层厚17 m,证实了盆地内沧浪铺组发育优质滩相白云岩储层,可形成气藏。为了明确颗粒滩分布范围,需对沧浪铺组,特别是其下段岩相古地理特征进行研究。通过钻井、野外剖面及区域地质调查资料的统计,系统性编制单因素图件,综合分析认为沧浪铺组总体表现为西部古隆起区薄、裂陷区及盆地边缘厚、东南缘盆地相地层薄的特点,下段沉积在德阳—安岳裂陷中南部地区厚度较大。沧浪铺组下段可分为6种沉积相,自川西向黔东南地区依次为三角洲相、碎屑潮坪相、台洼相、碳酸盐岩台地、斜坡相及盆地相。最有利的储集相带是碳酸盐岩台地相中的高能颗粒滩亚相,经白云化作用更有利于形成规模储层,主要发育在川北—川中地区。经历早期、晚期加里东运动,川北—川中地区具备形成优质储层的条件,是最有利的勘探区域。

Risk exploration Wells JT1,PT1 and CS1 in the center-north of Sichuan Basin encountered thick oolitic dolomite in the Lower Cambrian Canglangpu Formation,and the logging interpretation of the gas reservoir was up to 17 m,which proves that the Canglangpu Formation in the basin has high-quality beach facies dolomite reservoir and can form gas reservoir.In order to determine the distribution of granular beach,it is necessary to study the strata and the lithofacies-paleogeography of Canglangpu Formation,particular the lower part.Based on the data statistics of drilling,field section and regional geological survey,the systematic single factor maps are compiled.The lower segment deposition is partially affected by Deyang-Anyue rift subsidence.There are six sedimentary facies in the lower part of Canglangpu Formation,which are delta facies,clastic tidal flat facies,platform depression facies,carbonate plateau facies,slope facies and basin facies.The most favorable reservoir facies belt in the lower part is the high energy grain beach subfacies in the carbonate plateau facies,which are mainly developed in the north-center of Sichuan Basin.Through the early and late Caledonian movement,the north-center of Sichuan Basin is the most favorable exploration area with the conditions to form high-quality reservoir.