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碎屑岩储层成岩作用复杂而强烈,对储层物性有着重要影响。应用岩相学研究方法,在对鄂尔多斯盆地姬塬地区延长组长4+5低渗砂岩储层成岩作用及其对物性影响定量研究基础上,探讨了低渗储层成因机理。成岩作用和孔隙演化研究表明,压实作用虽然造成12%~20%的孔隙度损失,但是压实后剩余孔隙度仍高达15%~23%;早期胶结作用使孔隙度损失很小,压实作用和早期胶结作用并没有使储层致密,不影响油气渗流。溶蚀作用进一步改善了储层,晚成岩阶段A期-B期形成的钠长石、亮晶方解石、白云石、自生高龄石和铁绿泥石等大量胶结物的晚期胶结作用使储层孔隙度仅有4%~6%,储层因此而致密,由此影响油气渗流。晚期裂隙作用对储层孔隙度贡献为6%~8%,改善了储层物性而使其成为有效储层。盆地演化及与之对应的成岩事件研究认为,印支运动前,姬塬地区长4+5储层处于浅埋藏阶段,经历压实作用和早期胶结作用;早-中侏罗世长7烃源岩进入未成熟-低熟阶段,形成富含有机酸流体进入储层而发生溶蚀作用;早白垩世中-晚期进入深埋藏成岩阶段,晚期胶结物大量形成而使储层致密。生烃增压作用导致的裂隙以及晚白垩世以来的构造运动形成的裂缝对研究区长4+5有效储层形成具有非常重要意义,同时对低渗油气藏勘探也具有指导意义。
The diagenesis of clastic reservoir is complicated and strong, which has an important influence on reservoir physical properties. Based on the study of petrography, based on the quantitative study on the diagenesis of the 4 + 5 low permeability sandstone reservoirs of Yanchang Formation in Jiyuan area, Ordos Basin, and the quantitative research on its physical property, the formation mechanism of low permeability reservoir is discussed. Diagenesis and pore evolution studies show that although the compaction results in a porosity loss of 12% -20%, the residual porosity after compaction is still as high as 15% -23%; early cementation makes the porosity loss small and compaction The role and early cementation did not densify the reservoir and did not affect oil and gas seepage. The dissolution effect further improves the reservoir formation. The late cementation of large amounts of cements, such as albite, brilliant calcite, dolomite, autorlite and iron chlorite, formed in late-diagenetic stage A-B makes the reservoir porosity only There are 4% ~ 6%, so the reservoir is dense, thus affecting oil and gas seepage. Late fractures contribute 6% to 8% to reservoir porosity, improving reservoir physical properties and making them effective reservoirs. The basin evolution and corresponding diagenetic events suggest that before the Indo-Chinese Movement, the 4 + 5 reservoirs in the Jiyuan area were in the shallow burial stage and underwent compaction and early cementation. Early-Middle Jurassic Chang 7 source rocks entered In the immature-low maturity stage, the fluid rich in organic acids was formed and dissolved into the reservoir. During the Early Cretaceous, it entered the deep-burial diagenetic stage. Late cementation materials formed in large quantities to densify the reservoir. The fractures caused by hydrocarbon generation and compression and the tectonic movements since the Late Cretaceous are very important for the formation of 4 + 5 effective reservoirs in the study area, and are also instructive for the exploration of low permeability reservoirs.