不同物源三角洲前缘砂岩储层致密化过程定量研究

With the intensification of oil and gas exploration, tight sandstone reservoirs have received an increasing amount of attention. However, predicting “sweet point” is so hard. There are clear differences of densification process between microfacies in delta fronts. It is important to establish different pore evolution models for reservoir quality prediction in microfacies sandstones. The Chang 4 & 5 Members of Upper Triassic Yanchang Formation in the Ordos Basin have developed a typical tight, oil-bearing, clastic reservoir. The proven reserves are approximately 200 million tons. The two provenance systems of the southwest and northeast developed in the Longdong area. Tight sandstone reservoirs have been found in two delta fronts. Sedimentary characteristics of microfacies in delta fronts will be compared and the distribution and its controlling factors of sand bodies will be studied by using many cores and drilling/logging data. According to the observation and identification under microscopes and the geochemical analysis, diagenetic differences and diagenetic sequence in tight sandstone reservoirs in two delta fronts will be systematically analyzed. The genesis of tight reservoir rocks should be studied and the densification process and the models of reservoir quality prediction of different microfacies sandstones will be quantitatively reconstructed based on the relationships among burial history, thermal history, oil and gas filling history, etc. Above all, main control factors of reservoir quality will be identified, and a prediction model of sweet point will be established. Influences of microfacies, grain size, rock composition, diagenesis and diagenetic evolution on tight sandstone reservoirs in delta front will be systematically summarized in this project, providing a theoretical basis for tight oil exploration.

随着油气勘探的不断深入，致密砂岩储层越来越受到人们的重视，但“甜点”预测难度大。不同物源、不同微相储层致密化过程差异明显，分别建立孔隙演化模型能够有效预测储层质量。鄂尔多斯盆地三叠系延长组长4+5油层组发育典型的致密油储层。在陇东地区存在东北和西南两个物源体系，（辫状河）三角洲前缘普遍发育致密砂岩储层。本项目将利用大量的岩心、钻测井等资料，对比分析坳陷湖盆浅水缓坡不同物源三角洲前缘的沉积微相特征，明确砂体展布规律及其控制因素。通过岩石学和岩石地球化学手段，重点分析不同物源、不同微相储层成岩特征和成岩演化差异。进而明确致密储层成因机制；多史耦合，定量恢复不同微相储层致密化过程，明确优质储层发育的主控因素，构建不同微相砂岩孔隙演化数学模型。最后，建立“甜点”预测模型。本项目将系统总结微相、粒度、岩石成分、成岩作用及演化等对致密储层的影响，以期准确预测储层质量，为致密油勘探提供理论依据。

随着油气勘探程度的不断提高，致密储层越来越受到人们的重视，尤其是对致密储层成因的研究。本项目以鄂尔多斯盆地陇东地区长4+5油层组为研究实例，对比分析东北和西南两个物源体系在坳陷湖盆浅水缓坡背景下形成的三角洲前缘致密砂岩储层成因，明确沉积特征（如岩石组分、微相等）和成岩改造（如压实作用、多种自生矿物成岩胶结等）对储层孔喉结构的影响。.研究区发育了典型的致密砂岩油储层，粒径主要为0.1~0.3 mm。在西南部，辫状河三角洲前缘分流河道下部砂岩较粗，石英加大和铁白云石胶结物较少，储层质量较好(孔隙度约12%，渗透率约1mD)。在东北部，曲流河三角洲前缘水下河道砂岩(孔隙度约14%，渗透率约2mD)的绿泥石包膜较河口坝砂岩厚(>4vol%)。分流河道上部砂岩较细，渗透率较低(约0.1mD)。自生铁白云石主要出现在碎屑白云岩周围，为再生长胶结。石英加大中的SiO2主要来自蒙脱石向伊利石的转变和长石的溶蚀。在东北部，只需2vol%的绿泥石包膜，即对石英加大胶结具有显著的抑制作用，但它们可能阻止和延缓了有机酸对长石的溶解。研究区砂岩塑性易变形组分含量较高，储层经历早期缓慢浅埋-中压强胶减孔、中期持续深埋-强压强胶弱溶减孔、晚期充填交代的埋藏成岩过程。对两个地区储层孔隙演化进行了定量研究。.项目研究表明，三角洲前缘砂岩的成岩差异受沉积物粒度大小、成熟度和碎屑成分影响；形成自生矿物的物质主要来自于砂岩内部矿物的蚀变。该项目系统总结三角洲致密砂岩储层的研究思路和相关技术方法，为致密油勘探提供理论依据。