鄂尔多斯盆地渭北地区长3致密砂岩沉积微相与储层非均质性

在对岩心、测井、分析化验等资料综合分析的基础上,结合区域地质背景与地震砂体预测,对鄂尔多斯盆地渭北地区长3油组沉积微相特征及其与致密砂岩储层非均质性的关系进行了研究。研究表明:该区沉积微相以纵向多期叠加、平面快速变化的浅水辫状河三角洲前缘水下分流河道微相为主。叠加河道砂体厚度在8~23.5m之间,各单期河道砂体厚度差异较大;在工区东、西部河道规模差异大,顺河道方向河道宽窄快速变化。叠加河道砂体的物性、含油性非均质性强,受单期河道规模影响较大。单期厚度较大的河道砂体中下部物性、含油性整体较好,单期厚度较小的河道砂体受钙质胶结和泥砾影响,物性、含油性整体较差。平面上,水下分流河道展布控制了物性、含油性分布,水下分流河道越宽,砂体规模越大,单期河道砂体越发育,物性、含油性越好,平面非均质性越弱。 

Tight Sandstone Microfacies and Reservoir Heterogeneity of Chang 3 of Yanchang Formation in Weibei Area,Ordos Basin

Based on the comprehensive core analysis,its experiment and logging data,combined with regional geological background and sand-body prediction by seismic data,the microfacies characteristics and its effects on reservoir heterogeneity of Chang 3in Weibei area are discussed.The results show that the delta front underwater distributaries channel of shallow braided delta,characterized by multiphase superposition on vertical section and rapid changes horizontally,is the main sedimentary microfacies.The thickness of this channel is between 8-23.5m,and the channel thickness of each single phase has a big difference.The scale of these channels differs significantly in eastern and western part of research area,and varies quickly along the river.The superposition sand channel has strong heterogeneity on physical property and oil saturation,mainly influenced by the scale of single phase channel.In thicker single phase channel the physical property and oil saturation gets fairly good,while as thickness of channel decreasing,it is much worse due to calcite cementation and boulder-clay.The distribution of physical property and oil saturation is controlled by underwater distributary channel.With wider channel and larger scale sand body,the porosity of single phase channel will be better and the horizontal heterogeneity will be weaker.