摘要
In recent years,the Yanchang shale-oil formations of the Ordos Basin are rich in reserves with complex lithology and structure characteristics,low porosity and low permeability,and weak anomalies for oil and water discriminations,have been the key targets of unconventional oil/gas resource exploration and development in the relevant areas.The joint acoustic-electrical(AE)properties can be used to interpret reservoir lithology,mineralogy,pore structure,and fluid saturation.To conduct tests of thin section analysis,X-ray diff raction,and ultrasonic and electrical experiments at diff erent pressures and saturation degrees,cores from the shale-oil formations in the Q area of the basin are collected.The variations in AE properties with respect to clay content,porosity,pressure(microfracture),and saturation are analyzed.The experimental results indicate that the rock physics behaviors of sandstones with diff erent clay contents vary significantly.The AE properties of clean sandstones are basically dependent on the microfractures(pressure),while for muddy sandstones,the clay content is an important factor affecting the responses.The target reservoir consists of interbedded sandstone and shale layers.The AE equivalent medium equations and the Gurevich theory are applied to establish the joint models for the diff erent lithologies and simulate the variations in AE properties with respect to fluid type,pore structure,and mineral components.The three-dimensional joint templates of clean and muddy sandstones,as well as shale,are developed based on the elastic and electrical attributes and then calibrated using the experimental and well-log data.The reservoir properties are estimated with the templates and validated by the log data.The results indicate that the joint templates based on lithology characteristics can eff ectively characterize the properties of interbedded sandstone and shale layers.Furthermore,the combined application of AE data provides more beneficial information for the assessment of rock properties,leading to precise estimates that conform with the actual formation conditions.
鄂尔多斯盆地延长组页岩油层系是近年来相关地区非常规油气勘探开发的重点目标,其资源量丰富,具有岩性结构复杂、低孔低渗、微裂隙发育及油水分异不明显的特点。联合岩石声波和电学特性可被用于查明、表征储层岩性、矿物组分、孔隙结构及流体饱和度。本研究针对鄂尔多斯盆地Q区页岩油层系的7块岩心样本,进行X射线衍射、铸体薄片鉴定,以及开展不同围压和流体饱和度下的超声波及电导率实验,分析了声电特性随孔隙度、泥质含量、压力(微裂隙)及饱和度的变化规律。实验结果显示,砂岩的岩石物理响应在含有不同泥质含量的情况下差异显著,其中,纯砂岩的声电特性受微裂隙含量(压力)的影响较大,而对于泥质砂岩,泥质含量成为岩石物理响应特征的主控因素之一。针对工区由砂岩、页岩薄层组成的交互层特点,本研究采用声电等效介质方程及Gurevich喷射流理论,建立砂岩、页岩岩石物理模型,模拟了不同岩性的声电特性随流体类型、孔隙结构、矿物组分的变化特征。基于弹性及电学参数构建了砂岩、泥质砂岩及页岩段的三维声电联合岩石物理图板,并利用岩心样本及工区测井数据对图板进行校正。随后,将建立的声电联合图板应用到研究区目的层,预测各岩性段的储层物性参数,并基于测井解释结果进行验证。对比显示,本文根据岩性构建的声电联合图板能够有效的预测砂岩与页岩互层的储层参数,并且,综合应用声波和电学数据可以提供更多可用于评估岩石属性所需的有用信息,使得预测结果更符合实际地层情况。
基金
supported by the National Natural Science Foundation of China (Nos.41974123,42174161)
the Jiangsu Innovation and Entrepreneurship Plan and the Jiangsu Province Science Fund for Distinguished Young Scholars (grant no.BK20200021).
