鄂尔多斯盆地塔巴庙地区上古生界砂岩储层“酸性+碱性”叠加溶蚀作用与储层质量主控因素

Superimposing Controls of Acidic and Alkaline Dissolutions on Sandstone Reservoir Quality of the Paleozoic Xiashihezi and Shanxi Formations in Tabamiao Area, Ordos Basin

从岩石学薄片观察、埋藏史恢复、成岩流体包裹体检测、地层水化学特征和砂岩、粘土矿物成岩作用及储层性能评价等入手,对鄂尔多斯盆地塔巴庙地区上古生界下石盒子-山西组砂岩储层储集性能主控因素进行了初步探讨.研究成果认为:(1)工区下石盒子-山西组砂岩储层在早白垩世达到最大埋深(约4500m),强压实和高含量岩屑变形以及杂基充填粒间,使得砂岩原生粒间孔隙几乎完全丧失,储集空间主要为次生溶蚀孔隙,原生孔隙不发育;(2)碳酸盐胶结物和少量长石及岩屑在中等埋藏深度发生酸性溶蚀,而石英骨架颗粒和泥质、微晶石英杂基在深埋藏阶段发生碱性溶蚀,从而形成“酸性+碱性”叠加溶蚀次生孔隙带,成为控制工区目的层储层质量的主控因素;(3)粘土矿物演化剖面、地层水化学剖面和储层物性与储层岩屑、方解石、自生硅质和填隙物含量关系对比剖面,揭示大约在2670m附近存在一个重要的界面,在此界面之上为酸性溶蚀带,在此界面之下为先期酸性、后期叠加碱性溶蚀的深部次生孔隙带,其中在2670～2740m深度段为高孔高渗带,天然气沿此深度带优先充注.因此,这个带也是一个天然气高产带,在今后的勘探应给予高度重视.

The main factors controlling the quality of the sandstone reservoirs of the Xiashihezi and Shanxi formations in Tabamiao area, Ordos basin, are discussed through the synthetic investigation of petrologic observation of thin sections, the restoration of burial history, fluid inclusion measurement, a comparison of formation water chemistry with clay minerals and porosity, and a statistical analysis of permeability. The study reveals that at about the end of the Early Cretaceous, the primary porosity of the sandstones seemed to be almost lost due to deep burial （about 4 500 m） and strong compaction, causing the soft debris deformation to fill the intergranular pores. However, the acidic dissolution of carbonate minerals and some feldspar, which occurred during the middle diagenesis, produced some secondary pores. During the late diagenetic stage, the alkaline dissolution raised in quartz grains and aluminosilic debris of the same sandstones to form a superimposed secondary porous belt, which has been thought to be the main controlling factor on reservoir quality. The profile of clay mineral contents coupled with formation water chemistry, porosity and permeability, contents of debris, calcite, authigenic quartz and matrix clearly indicates that there is a very important contact at about 2 670 m. At this depth, an acidic dissolution in sandstones developed, and beneath this depth, the sandstones underwent the late alkaline dissolution which superimposed on the early acidic dissolution. The strongest dissolution belt occurs between 2 670 and 2 740 m, and was filled with natural gases. Attention should therefore be paid to this belt in future exploration and development.