川北地区震旦系灯影组储层特征与主控因素

Characteristics and controlling factors of the reservoir of Sinian Dengying Formation in northern Sichuan Basin

近年来,四川盆地震旦系灯影组的油气勘探开发不断深入推进,川北地区作为后续勘探接替区,其灯影组储层的相关研究亟待进行。综合川北地区灯影组的地层、岩石及矿物特征,采用分析化验等手段揭示其储层特征,结果表明:灯二段、灯四段为川北地区灯影组储层发育层段,颗粒粘连白云岩、叠层状微生物白云岩和粉晶白云岩为主要储集岩类,次生溶孔、溶洞为主要储集空间;灯影组储层类型多样,发育孔-洞型、孔隙型、孔隙-裂缝型及溶洞型储层,以孔隙-裂缝型储层质量最佳。储层发育特征表明:滩丘沉积是灯影组储层发育的物质基础,后期岩溶改造是储层发育的关键;灯二段滩丘厚度相对更大,而储层物性相比灯四段较差。基于宏观储层演化和微观孔隙特征,建立了川北地区灯影组2种储层发育模式:灯二段以表生岩溶为储层发育的主控因素,见有不同期次白云石胶结和上覆地层细粒沉积物充填;灯四段以埋藏溶蚀为储层发育的主控因素,存在广泛的重结晶造成的溶蚀、溶蚀流体中硅质组分对孔隙的充填、以及溶蚀孔隙中沥青对储层的保护。依据不同的岩溶模式,可预测灯二段、灯四段有利储层的发育位置:在潜流带与滩丘沉积体叠加的部位,灯二段储层发育最佳;自顶部向下,自台缘向台内,灯四段储层质量逐渐下降。

Dolomite reservoir of Sinian Dengying Formation in northern Sichuan Basin, an important field for following exploration, some issues about that need to be studied. Based on petrology observation and experimental analysis, it is shown that reservoirs mainly developed in rocks such as particle adhesion dolomite, laminated microorganism dolomite,and grained dolomite in Dengying Member-2 and Member-4, with major reservoir spaces of secondary dissolution pores and vugs. Among the four types of reservoirs including pore-vug, pore, pore-fracture, and vug, the reservoir quality of pore-fracture type is the best. As for the development of dolomite reservoir in Dengying Formation, the sediment of mound-shoal facies is the material basis, and the reconstruction of diagenesis is the key element. The total thickness of mound-shoal sediment of Member-2 is bigger than that of Member-4, but the porosity and permeability of Member-2 is smaller. Based on macroscopic evolution and microscopic pore features of the reservoir, two models are setup for Member-2 and Member-4 respectively. The epigenic karstification is predominant in Member-2 with the cementation of dolomites and the filling of slim sediments from overlying strata, while the burial dissolution is predominant in Member-4 with extensive dissolution accompanied by recrystallization and the filling of silicoide and asphalt in dissolution pores. According to the models, the good reservoirs in Dengying Member-2 develop at the overlap parts of hyporheic zone and mound-shoal, and the reservoirs in Member-4 go poor towards the inner part of the carbonate platform, and towards the lower part of the member.