四川盆地潼南—合川区块中二叠统白云岩储层形成主控因素与勘探区带预测

Main controlling factors of the Middle Permian dolomite reservoir and prediction of exploration zone in Tongnan-Hechuan block,Sichuan Basin

近年来,除川西地区和川南地区外,川中地区潼南—合川区块中二叠统栖霞组—茅口组多口钻井也钻遇白云岩储层并获得高产,展现了川中地区栖霞组—茅口组巨大的勘探潜力。但是前期针对川中地区栖霞组—茅口组研究认识较少,白云岩储层的成因与分布也存在较大争议。为弄清潼南—合川区块地层分布、沉积与储层特征,特别是优质白云岩储层形成的主控因素,充分利用最新的油气勘探成果和丰富的基础资料开展研究。结果表明:(1)潼南—合川区块栖霞组—茅口组划分为2个三级层序和6个四级层序,优质白云岩储层发育在层序的高位体系域。(2)栖霞组—茅口组均具有发育台内滩的沉积背景,大量发育台内生屑滩,白云岩储层主要发育在台内中高能滩相带内。(3)栖霞组白云岩储层单层厚度薄,垂向叠置发育;茅口组白云岩储层单层厚度较大,横向较连续;栖霞组—茅口组储集空间均以原生孔和准同生期溶蚀孔为主,台内中高能滩、受层序控制的岩溶作用和早期白云石化作用控制了白云岩储层的发育。(4)栖霞组白云岩储层环洼分布,有利勘探区带分布在潼南—合川区块中西部;茅口组白云岩储层主要发育在微古地貌高地的边缘斜坡部位,合深4井东北侧地区是最有利的勘探区带。

In recent years,in addition to the western and southern Sichuan Basin,dolomite reservoirs of the Middle Permian Qixia FormationMaokou Formation have been penetrated in multiple wells in Tongnan-Hechuan block in the central Sichuan Basin and high production has been achieved,showing promising exploration potential in the central Sichuan Basin.However,there is little understanding on Qixia Formation-Maokou Formation in the central Sichuan Basin from previous study,and great disputes appear on the genesis and distribution of dolomite reservoirs.The latest petroleum exploration results and a large number of basic data are analyzed to identify the stratigraphic distribution,sedimentary and reservoir characteristics,especially the main controlling factors of the high-quality dolomite reservoir.The results show that:(1)Qixia Formation-Maokou Formation in Tongnan-Hechuan block is divided into two third-order sequences and six fourth-order sequences,and the high-quality dolomite reservoir is developed in the highstand system tract.(2)The sedimentary facies of Qixia FormationMaokou Formation in Tongnan-Hechuan block was conducive to the deposition of granular beach,with a large number of bioclastic beach developed.The dolomite reservoir was mainly developed in high-energy beach facies zone.(3)The single layer of dolomite reservoir of Qixia Formation is thin and vertically superimposed,while that of Maokou Formation is greater and continuous in lateral.The reservoir space is dominated by primary pores and quasi syngenetic dissolution pores.The development of dolomite reservoir is mainly controlled by highenergy granular beach,sequence related karstification and early dolomitization.(4)The dolomite reservoir of Qixia Formation is mainly distributed in the circum subsag and the western part of Tongnan-Hechuan block is a favorable exploration zone.The dolomite reservoir of Maokou Formation is mainly developed in the edge slope of micro paleogeomorphologic high area and the northeast side of Well Heshen 4 is the most favorable exploration zone.