More than 100 million tons of tight oil reserves have been discovered in the Xin’anbian area of the Ordos basin in recent years, of which the main reservoir is the Chang-7 Member of the Yanchang Formation. To identify the characteristics of the tight sandstone reservoir and their the development of the Chang-7 Member in the study area, casting thin sections, scanning electron microscopy (SEM), high-pressure mercury injection, cathodoluminescence and other technical methods were used to analyze the reservoir rock types and their physical properties and pore structure. Based on reservoir diagenesis research and quantitative evaluations of reservoir pores, a reservoir pore evolution mode was established. The results showed that the main rock types in the tight sandstone reservoirs in the Chang-7 Member of the Xin’anbian area were lithic feldspathic sandstone and feldspathic detritus sandstone and that the reservoir space types were mainly feldspar dissolved pores, with a few residual intergranular pores, clay intercrystalline pores, and microfractures. The reservoirs were classified as having low porosity and low permeability and extra-low porosity and extra-low permeability. The porosity and permeability of the reservoirs were between 4 ~ 10% and 0.01 ~ 1 mD, respectively, and were mainly controlled by compaction, cementation, and dissolution. Compaction and cementation reduced the porosity and permeability, while dissolution increased the porosity and permeability. The Chang-7 Member reservoir mainly experienced weak-medium compaction, medium-strong cementation, and different degrees of dissolution. The average loss of porosity due to cementation was around 25%, while the average loss due to compaction was around 13%. This research determined four key stages in the porosity evolution of the Chang-7 Member in the study area: (1) the porosity was reduced to 26% from the Triassic to the Early Jurassic period, which was mainly due to compression compaction; (2) the reservoir was seriously damaged by cementation from the Middle Jurassic to Late Jurassic period, where the porosity decreased to 5%; (3) in the Early Cretaceous period, the porosity increased to 11% due to dissolution; and (4) the porosity was reduced to 7% from the late Early Cretaceous to early Late Cretaceous period, which was mainly due to cementation.

中文翻译：

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鄂尔多斯盆地新安边地区延长组长7段致密砂岩储层特征及孔隙演化

近年来，鄂尔多斯盆地新安边地区发现致密油储量超过1亿吨，其中主要储层为延长组长7段。为识别研究区长7段致密砂岩储层特征及其发育情况，采用铸造薄片、扫描电镜（SEM）、高压压汞、阴极发光等技术手段进行分析。储层岩石类型及其物理性质和孔隙结构。在储层成岩作用研究和储层孔隙定量评价的基础上，建立了储层孔隙演化模式。结果表明，新安边长7段致密砂岩储层的主要岩石类型为岩屑长石砂岩和长石碎屑砂岩，储集空间类型以长石溶孔为主，少量残留粒间孔隙、粘土晶间孔和微裂缝。储层分为低孔低渗和特低孔特低渗储层。储集层孔隙度和渗透率分别在4～10%和0.01～1 mD之间，主要受压实、胶结和溶蚀控制。压实和胶结作用降低了孔隙度和渗透率，而溶蚀作用增加了孔隙度和渗透率。长 7 段油藏主要经历弱-中压实，中强胶结作用，不同程度的溶解。胶结造成的平均孔隙度损失约为 25%，而压实造成的平均孔隙度损失约为 13%。本研究确定了研究区长7段孔隙度演化的四个关键阶段：(1)三叠纪至早侏罗世孔隙度降低至26%，主要是由于压实作用；(2) 中侏罗世至晚侏罗世胶结作用破坏储层严重，孔隙度下降至5%；(3)早白垩世，由于溶蚀作用，孔隙度增加到11%；(4)早白垩世晚期至晚白垩世早期孔隙度降低至7%，主要是胶结作用。胶结造成的平均孔隙度损失约为 25%，而压实造成的平均孔隙度损失约为 13%。本研究确定了研究区长7段孔隙度演化的四个关键阶段：（1）三叠纪至早侏罗世孔隙度降低至26%，主要受压实作用；(2) 中侏罗世至晚侏罗世胶结作用破坏储层严重，孔隙度下降至5%；(3)早白垩世，由于溶蚀作用，孔隙度增加到11%；(4)早白垩世晚期至晚白垩世早期孔隙度降低至7%，主要是胶结作用。胶结造成的平均孔隙度损失约为 25%，而压实造成的平均孔隙度损失约为 13%。本研究确定了研究区长7段孔隙度演化的四个关键阶段：（1）三叠纪至早侏罗世孔隙度降低至26%，主要受压实作用；(2) 中侏罗世至晚侏罗世胶结作用破坏储层严重，孔隙度下降至5%；(3)早白垩世，由于溶蚀作用，孔隙度增加到11%；(4)早白垩世晚期至晚白垩世早期孔隙度降低至7%，主要是胶结作用。本研究确定了研究区长7段孔隙度演化的四个关键阶段：（1）三叠纪至早侏罗世孔隙度降低至26%，主要受压实作用；(2) 中侏罗世至晚侏罗世胶结作用破坏储层严重，孔隙度下降至5%；(3)早白垩世，由于溶蚀作用，孔隙度增加到11%；(4)早白垩世晚期至晚白垩世早期孔隙度降低至7%，主要是胶结作用。本研究确定了研究区长7段孔隙度演化的四个关键阶段：（1）三叠纪至早侏罗世，孔隙度降低至26%，主要受压实作用；(2) 中侏罗世至晚侏罗世胶结作用破坏储层严重，孔隙度下降至5%；(3)早白垩世，由于溶蚀作用，孔隙度增加到11%；(4)早白垩世晚期至晚白垩世早期孔隙度降低至7%，主要是胶结作用。(2) 中侏罗世至晚侏罗世胶结作用破坏储层严重，孔隙度下降至5%；(3)早白垩世，由于溶蚀作用，孔隙度增加到11%；(4)早白垩世晚期至晚白垩世早期孔隙度降低至7%，主要是胶结作用。(2) 中侏罗世至晚侏罗世胶结作用破坏储层严重，孔隙度下降至5%；(3)早白垩世，由于溶蚀作用，孔隙度增加到11%；(4)早白垩世晚期至晚白垩世早期孔隙度降低至7%，主要是胶结作用。