川中南河包场须家河组砂岩沉积-成岩作用

Depositional-diagenetic coupling complex of Xujiahe sandstone in Hebaochang Block in the south part of the Central Sichuan Basin

四川盆地上三叠统须家河组砂岩是盆地内主要天然气储层,其形成与演化的影响因素较为复杂。其中,沉积作用不仅控制着主要储层的宏观分布特征,而且影响着后期的成岩作用类型和强度;成岩作用使埋藏时期储层被改造,不仅影响了储集空间的演化过程和孔隙结构特征,还最终决定了现今储层的面貌和分布规律。对大量实测物性参数的统计分析表明,河包场区块须家河组储层物性从上到下逐渐变好,下部须二段砂岩中出现大量石英溶蚀产生的次生孔隙,其物性明显好于上部须四段、须六段,是导致深部储层物性变好的主要原因。综合考虑不同沉积微相砂岩所经历的成岩改造作用类型及其储层的响应特征,根据研究区的实际地质情况,归纳出6种沉积—成岩相组合类型。对这些组合类型造成的储层效应进行了建设性和破坏性的划分,初步建立了研究区的沉积—成岩相组合类型的分布模式。

As the main reservoir of natural gas resources, the sandstone reservoirs of Xujiahe Formation in the Upper Triassic of Sichuan Basin were influenced by many geological factors. The sedimentation controls the spatial distribution of reservoir framework and affects the events and intensity of the subsequential diagenesis. During burial period, diagenesis is the key factor for reservoir evolution, because it influences both the reservoir spaces and porosity structures, and finally decides the present reservoir property and their distribution law. The numerable measured data of porosity and permeability show that the reservoir property gets better gradually from top to bottom in Xujiahe Formation of Hebaochang Block in the south part of the Central Sichuan Basin. The lowest sandstone in Section Ⅱ of Xujiahe Formation keeps the better quality than those distributed in Section 1V and V[ of Xujiahe Forma- tion. Pervasive occurrence of the secondary pores produced by quartz dissolution is the main reason for the better quality of Xujiahe sandstones. In combination with the geological background of the study area, six types of depositional-diagenetic coupling complex in the Triassic clastic reservoirs were recognized according to the superimposition of diagenetic events of different sedimentary microfacies and the response of reservoir. The detailed information of the reservoir parameters for these coupling complexes was described. The constructive and destructive coupling types of reservoir parameters were subdivided. A distribution model of depositional-diagenetic coupling complex in the studied area was established.