鄂尔多斯盆地陕北地区延长组长7段致密油储层特征及其主控因素

Characteristics and main controlling factors of tight oil reservoirs in Chang 7 Member of Yanchang Formation in Ordos Basin,North Shaanxi

鄂尔多斯盆地延长组石油资源丰富,储层致密,为了查明湖盆致密砂岩储层发育机理,综合利用岩心观察、铸体薄片鉴定、X射线衍射分析、扫描电镜观察、高压压汞测试等方法,对鄂尔多斯盆地陕北地区长7段致密油储层特征及其发育主控因素进行了分析。研究结果显示,研究区长7段长石含量高,主要发育长石砂岩和岩屑长石砂岩。致密砂岩储层孔隙类型以长石粒内溶蚀孔隙和粒间溶蚀孔隙为主,同时晶间微孔和微裂缝较为发育。研究区长7段时期主要为三角洲前缘与滨浅湖沉积环境,水动力较弱,发育砂岩中泥质含量较高。中等强度压实作用及早期的方解石胶结作用使原生孔隙消失殆尽,胶结作用进一步使孔隙减小。由于长石及黏土含量较高,其受溶蚀作用形成溶蚀孔隙,改善储层质量,同时也是研究区长7段致密砂岩储层发育的主要控制因素。

To explore the mechanism of tight-sandstone reservoir development in the Chang 7 Member of the Yanchang Formation in the Ordos Basin,North Shaanxi,the characteristics of the sedimentary rocks and the main control factors were analyzed by using the core data,thin section of cast,X-ray diffraction,scanning electron microscopy,and high-pressure mercury compression.Results show that the sedimentary rocks of Chang 7 Member are rich in feldspar,and mainly are feldspathic and lithic feldspar sandstones.The pore types of tight sandstone reservoir are mostly intra-grain dissolution pores and inter-grain dissolution pores of feldspar,and intergranular micropores and microfractures are also developed.The Chang 7 Period in the study area was mainly a deltaic foreland and shallow lakeside depositional environment with weak hydrodynamics as reflected by high mud content in the sandstones.The medium-intensity compaction and early calcite cementation caused the primary pore space to disappear,and the cementation further made the pore space smaller.Due to the high content of feldspar and clay,they were subject to dissolution and then formed dissolution pores and improved the reservoir quality,which is also the main controlling factors on the development of dense-sandstone reservoirs in the Chang 7 Member of the study area.