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为了揭示鄂尔多斯盆地石盒子组8段砂岩储层中长石异常分布及成因,在盆地尺度范围内,利用大量岩石薄片、阴极发光、扫描电镜分析手段,研究了储层岩石学特征及长石分布特征;并在此基础上,结合真实岩心酸溶蚀模拟实验、埋藏史、热史及成岩特征,探讨了长石异常分布的成因,认为长石的减少与成岩过程中溶蚀作用密切相关.研究结果表明:鄂尔多斯盆地腹部盒8段致密砂岩在成岩前存在大量长石(百分比平均为7.5%),而现今砂岩中低或无长石使得储层演化为具有“高成分成熟度”的石英砂岩和岩屑石英砂岩,这一现象与盆地周缘相对高长石含量形成明显的差异.现今长石的产状主要表现为完全溶蚀型,碳酸盐岩充填型及高岭石化型;地质历史时期长石的溶蚀需在高温条件下进行,而盒8段储层在溶蚀作用期叠加的一次热异常事件促使了上古生界煤系烃源岩的生烃作用,为长石的大量溶蚀提供了持续高温和酸性介质条件,使得在相对高热演化的腹部地区溶蚀作用强烈,储层中长石百分比小于1%,局部地区(苏里格地区)甚至为零,长石的大量溶蚀很好地改善了致密砂岩储集空间;而在热演化程度较低的边缘地区溶蚀作用较弱,长石保存相对较好,溶孔发育较少.对鄂尔多斯盆地砂岩储层中长石的异常分布研究有助于今后致密气甜点区的预测.
In order to reveal the anomaly distribution and genesis of the feldspar in the sandstone reservoir of Block 8, Shixianzi Formation, Ordos Basin, a large number of thin sections of rock, cathodoluminescence and SEM were used to study the petrological characteristics and feldspar distribution in the basin scale On the basis of the above, the causes of anomalous distribution of feldspar were discussed based on the simulation of true coring acid dissolution, burial history, thermal history and diagenesis, and the reduction of feldspar was closely related to the dissolution during diagenesis. The results show that there are a large number of feldspars (percentage average 7.5%) before the diagenesis in tight sandstone of Box 8 in the belly of the Ordos basin. However, the presence or absence of feldspar in sandstone now makes the reservoir evolve into quartz with “high component maturity” Sandstone and cuttings quartz sandstone, which is obviously different from the relatively high feldspar content in the peripheral margin of the basin.The occurrences of present-day feldspar mainly include complete dissolution type, carbonate filling type and kaolinite type. Geological history During the period, the dissolution of feldspar should be carried out under high temperature, and a thermal anomaly superimposed during the dissolution period of the Box 8 reservoir prompted the hydrocarbon generation of the Upper Paleozoic coal measures It provides continuous high temperature and acidic media conditions for extensive dissolution of feldspar, resulting in strong dissolution in the abdomen of relatively high thermal evolution, less than 1% feldspar in the reservoir and even zero in the local area (Sulig region) , Massive dissolution of feldspar well improved the tight sandstone reservoir space, whereas the dissolution in the marginal areas with low thermal evolution is relatively weak, the feldspar is relatively well preserved and the pores are less well developed.The sandstone reservoirs in the Ordos Basin The study of anomalous distribution of feldspar in the layer is helpful for the prediction of the dense gas-sweet dessert area in the future.