论文详情
页岩油藏岩相复杂, 纵向变化较快且非均质性强等因素导致“甜点”地震预测存在困难。明确复杂岩相地层的地震岩石物理特征, 对提高测井解释和地震定量预测的精度具有重要意义。为此, 对陈沱口凹陷新沟嘴组下段Ⅱ油组页岩油层系的33块取芯样品进行了物性和跨频段(低频1~1 000 Hz, 超声频段1 MHz)岩石物理参数测试。结合地质认识, 分析了岩石弹性各向异性与成岩矿物、微观孔隙结构之间的机理联系, 从而以岩石物理手段提供可识别有利岩相的跨频弹性属性。研究结果表明, 新沟嘴组下段Ⅱ油组的页岩层系在该区具有极低孔隙度和超低渗透率, 其白云石晶间孔隙发育较少, 而纹层结构、陆源碎屑矿物及其含量对云质页岩的孔隙度有正向影响。此外, 基于矿物和微观结构等物性数据与超声实验测量的弹性参数之间的关系表明, 矿物组分和孔隙结构对页岩层系岩石的弹性性质影响较大; 纹层状构造、水平裂缝和黏土矿物的定向排列是研究区弹性各向异性的主要原因。最后, 基于典型岩心宽频测试数据和频散理论模型估算了全部岩心速度频散, 以此提供识别有利岩相的跨频段(2.2, 24.0, 1.0×104, 1.0×106 Hz)弹性参数组合分别为拉梅系数×密度和泊松比、纵波阻抗和纵横波速度比。研究结果可为岩石物理实验和理论建模为基础的跨频段(地震、测井和实验室超声)数据联合应用以及地震定量预测研究提供指导和数据支撑。
It is difficult to predict the "sweet spot" owing to the complex lithofacies, rapid longitudinal change, and strong heterogeneity of shale reservoirs.It is important to clarify the physical characteristics of shale strata with complex lithofacies to improve the accuracy of logging interpretations and quantitative seismic predictions.In this study, 33 samples were collected from the second oil group of the lower segment of the Xingouzui Formation in the Chentuokou Sag, and basic physical property measurements and cross-band rock physics experiments composed of low-frequency (1~1 000 Hz) strain-stress tests and ultrasonic band (1 MHz) tests were conducted to obtain the rock physical parameters of the shales.Combined with geological understanding, we studied the correlation mechanism between the elastic anisotropy and physical properties of the reservoir in terms of lithology, diagenetic minerals, and microscopic pore structure to provide cross-band elastic attributes for the seismic identification of favorable lithofacies in shale reservoirs.The results showed that the shale strata of oil group II, the lower member of the Xingouzui Formation had extremely low porosity and permeability.Dolomite intergranular pores were less developed, whereas the laminated structure, terrigenous clastic minerals, and their contents positively affected dolomitic shale porosity.Moreover, the relationship between the physical data of the mineral and microstructure and the elastic property data measured by ultrasonic testing showed that the mineral composition and pore structure were the main factors influencing the elastic properties of shale.The acoustic anisotropy of the shale in the area was controlled by the laminated structure, horizontal fractures, and oriented alignment of clay minerals.Finally, the velocity dispersion of all samples was estimated based on the cross-band experimental data and dispersion theoretical model to provide cross-band (2.2 Hz, 24.0 Hz, 1.0×104 Hz, and 1.0×106 Hz) elastic parameter combinations of λρ, ν, Zp, and vP/vS to identify favorable lithofacies.The results of this study can provide guidance and support for the joint application of cross-frequency (seismic, well-logging, and laboratory ultrasonic) data based on rock physics experiments and theoretical modelling, as well as quantitative seismic prediction studies.