鄂尔多斯盆地合水地区三叠系长7段夹层型页岩油储层特征及主控因素

Characteristics and main controlling factors of interbedded shale oil reservoirs of Triassic Chang 7 member in Heshui area,Ordos Basin

运用铸体薄片、扫描电镜、黏土矿物X射线衍射、电子探针、阴极发光、高压压汞、物性测试等资料,对鄂尔多斯盆地西南部合水地区三叠系延长组长7段夹层型页岩油储层特征及储层致密化主控因素进行了研究,建立了储层定量评价标准,并预测出有利储层分布。研究结果表明:(1)鄂尔多斯盆地合水地区三叠系长7段夹层型页岩油储层主要为岩屑长石砂岩与长石岩屑砂岩,成分成熟度低、填隙物含量高、孔喉结构复杂,具有高孔低渗特征。(2)胶结作用是研究区长7段夹层型页岩油储层致密化的主控因素,储层平均视胶结率为86.3%,达到强胶结程度,以自生黏土矿物中的伊利石胶结为主;压实作用对储层致密化起次要作用,储层平均视压实率为46.0%,为中等压实程度;溶蚀作用降低了储层的致密化程度,但储层渗流能力较低,酸性流体难以大规模溶蚀,平均视溶蚀率仅为13.8%,为弱溶蚀程度。(3)受中等压实—弱溶蚀—强胶结成岩作用的影响,储层非均质性较强,成岩系数差异较大。Ⅰ类储层成岩系数大于2.4,Ⅱ1类储层成岩系数为1.8~2.4,Ⅱ2类储层成岩系数为1.2~<1.8,Ⅲ类储层成岩系数小于1.2,Ⅰ类与Ⅱ1类储层为有利储层。区域上中部混源区有利储层发育规模最大,是勘探的主要目标区。

Based on the data of cast thin sections,scanning electron microscopy,clay mineral X-ray diffraction,electron probe,cathodoluminescence,high-pressure mercury injection and physical properties testing,the characteristics and main controlling factors of reservoir densification of the interbedded shale oil reservoirs of Triassic Chang 7 member in Heshui area of Ordos Basin were studied,a quantitative evaluation standard of the reservoirs was established,and favorable reservoirs distribution was predicted.The results show that:(1)The interbedded shale oil reservoirs of Triassic Chang 7 member in Heshui area of Ordos Basin are mainly composed of lithic feldsparthic sandstone and feldspathic litharenite,with low compositional maturity,high interstitial content,complex pore throat structure,high porosity and low permeability.(2)Cementation is the main controlling factor for the densification of the interbedded shale oil reservoirs of Chang 7 member in the study area,with an average apparent cementation rate of 86.3%,reaching a strong degree of cementation,and dominated by illite cementation in authigenic clay minerals.Compaction has relatively low effect on the reservoir densification,with an average apparent compaction rate of 46.0%,reaching medium compaction degree.Dissolution reduces the degree of the reservoir densification,but the reservoir seepage ability is low,making it difficult for acidic fluids to undergo large-scale dissolution.The average apparent dissolution rate is only 13.8%,indicating a weak degree of dissolution.(3)Due to the influence of medium compaction,weak dissolution and strong cementation,the reservoir heterogeneity is strong,and the diagenetic coefficients vary greatly.The type-Ⅰreservoirs have a diagenetic coefficient greater than 2.4,the diagenetic coefficients of the type-Ⅱ1 and type-Ⅱ2 reservoirs range from 1.8 to 2.4 and 1.2 to 1.8,respectively,and the diagenetic coefficient of the type-Ⅲreservoirs is less than 2.4.Among them,type-Ⅰand type-Ⅱ1 are favorable reservoirs.The central mixed source area in the study area has the largest scale of favorable reservoir development,so it is the main target area for exploration.