鄂尔多斯盆地陕北地区长10_1高渗储层的控制因素

Control factors for the high-permeability reservoirs of Chang 10_1 Reservoir Group of Yanchang Formation in northern Shaanxi Province,Ordos basin

鄂尔多斯盆地中部的陕北地区,是盆地中生界油藏最为丰富的区带之一,主要含油层系为三叠系延长组长6层,其次是侏罗系延安组,以往的研究也多集中于以上含油层。长101层是近几年勘探评价的新层系,利用现代测试技术和数理统计研究了长101层的沉积、成岩特征,分析高渗储层控制因素。结果表明,沉积环境控制长101高渗储层分布,成岩作用对长101高渗储层的形成起主导作用。主河道砂岩厚度大、粒度粗、孔喉大、孔隙连通性好,河道侧翼砂岩厚度薄、粒度细、孔喉小、孔隙连通性差。因此,压实作用后主河道砂岩粒间孔含量多于河道侧翼砂岩,导致主河道砂岩胶结作用弱于河道侧翼砂岩,而溶蚀作用强于河道侧翼砂岩,主河道砂岩物性明显好于河道侧翼。沉积、成岩作用共同造成长101高渗储层发育于河道主带和分流交汇部位。

Northern Shaanxi area in central Ordos basin is one of the richest Mesozoic hydrocarbon accumulation zones, where the previous studies of Mesozoic oil-bearing series focused on Chang 6 and Jurassic Yan＇an Formation. The Chang 101 reservoir group is a new layer explored and evaluated in the past few years. In this paper, sedimentary characteristics and diagenesis of Chang 101 reservoir group were studied and control factors for the high-permeability reservoirs were analyzed by using various modern analytic techniques and mathematical statistics. The research results indicate that the distribution of the high-permeability reservoirs was controlled by the sedimentary environment, and the formation of high-permeability reservoirs was mainly affected by diagenesis. The sand body of the main channel is characterized by great thickness, coarse grain size, large porethroat and good connectivity between the pores, whereas the distributary channel has thin thickness, fine grain size, small porethroat and poor connectivity between the pores. Therefore, there existed more intergranular pores in the main channel than in the distributary channel after compaction, which led to more dissolution and less cementation in the main channel than in the distributary channel; as a result, the reservoir property of the main channel is much better than that of the distributary channel. The Chang 101 high-permeability reservoir was developed in the main channel and the interface of interdistributary rivers which were influenced by sedimentation and diagenesis.