四川盆地东南缘震旦系-下古生界储层特征及形成机制

Reservoir Characteristics and Formation Mechanism of Sinian-Lower Paleozoic in the Southeastern Margin of Sichuan Basin

利用岩石薄片、包裹体薄片及碳、氧同位素分析方法研究了四川盆地东南缘震旦系-下古生界储层特征及形成机制。结果表明,震旦系-下古生界(下组合)主要为一套浅海陆棚相碎屑岩与台地相碳酸盐岩沉积序列。储集岩石类型主要为晶粒白云岩、藻纹层白云岩、颗粒白云岩等,以及生物碎屑灰岩。储集空间主要有溶洞(孔),晶间(溶)孔,微裂缝和溶缝等。储集岩基质致密,孔隙度均值在0.98%～2.15%,但局部发育优质储层,孔洞面孔率可达10%。滩相与白云质潮坪相为有利储层发育的沉积相带,是震旦系-下古生界优质储层发育的先天条件。优质储层主要受控于桐湾运动期表生岩溶作用、热液白云岩蚀变作用及热液硅化作用。其中,热液白云质流体活动时期为早-中二叠世,其可使灯影组储层的晶间孔、次生溶蚀孔隙度在原基础上增加3%～10%;而硅化作用主要导致储层致密,但若硅质重结晶较强,硅质岩可作为天然气的储层。

By using petrographic and inclusion thin sections and carbon-oxygen isotope analysis,the reservoir characteristics and formation mechanism of Sinian to Lower Paleozoic system in the southeastern margin of Sichuan Basin were studied.The results indicate that there mainly develop a set of shallow marine shelf clastic sedimentary rocks and platform carbonate rocks during the Sinian-Lower Paleozoic(Lower Assemblage) period.The reservoirs are crystalline grain dolomite,algal-laminated dolomite and dolomitic grainstone,bioclastic limestone etc.The main pore spaces are dissolved caves(or pores),inter-crystal(dissolved) pores,micro-fractures and dissolved fractures etc.The reservoir is tight and its matrix porosity is 0.98% ～ 2.15% in average.However,high-quality reservoir develops locally and its plane porosity is up to 10%.The shoal facies and dolomitic tidal facies are the foundations of high quality reservoirs.High-quality reservoir formation was controlled by supergene karstification during Tongwan movement,hydrothermal dissolution and alteration of dolomite and hydrothermal silicification.The activity age of hydrothermal dolomitic fluid is early-middle Permian,which causes intercrystal and dissolved porosity increase of 3%～10% on the original basis of reservoirs in Dengying Formation.And the silicification densifies reservoir rocks,but chert should be also gas reservoir formed by the strong recrystallization of silica.