鄂尔多斯盆地镇北地区延长组长4+5致密油层成岩作用及成岩相

鄂尔多斯盆地镇北地区含凝灰质的延长组长4+5致密油层勘探潜力巨大,但因成岩作用研究薄弱,相对高孔高渗储层成因机理和分布规律认识不清,使该区勘探开发进程受到明显的制约。综合应用铸体薄片、扫描电镜、电子探针、阴极发光、显微荧光、X射线衍射、流体包裹体、高压压汞和常规物性等方法,对镇北地区的长4+5储层成岩作用及成岩相带进行了研究。研究结果表明:研究区长4+5储层主要处于中成岩阶段A期,石英自生加大等硅质胶结作用和铁白云石等碳酸盐胶结作用是造成储层低孔特低渗的根本原因;绿泥石膜胶结作用和早期油的充注抑制了机械压实作用和胶结作用,保护了储层孔隙;长石碎屑的溶蚀作用扩大了储集空间。划分出机械压实相、碳酸盐胶结相、绿泥石膜胶结相和长石溶蚀相四类主要成岩相,其中长石溶蚀相常形成相对高孔高渗储层发育区,一般面孔率大于6.0%,孔隙度大于14.0%,渗透率大于1.30×10-3 μm2,主要分布在辫状河三角洲前缘亚相水下分流河道微相砂体中部。综合研究表明,沉积作用和成岩作用共同控制着相对高孔高渗储层的分布。

Diagenesis and Diagenetic Lithofacies of Tight Reservoir of Chang4+5 Member of Yanchang Formation in Zhenbei,Ordos Basin

Though the prospective of oil reserves of tight reservoir of Chang 4+5 reservoir of Yanchang Formation, which contains tuffaceous component, is great in Zhenbei area, Ordos Basin, but the mechanism and distribution of relatively high porosity and permeability is not clear causing the speed of oil exploration and development slowly. Diagenesis and favorable diagenetic facies of Chang 4+5 Member of Yanchang Formation are researched by casting slice, scanning electron microscope, electron probe microanalysis, cathodeluminescence, micro fluorescence, X-ray diffraction and fluorescence, fluid inclusion, high pressure mercury, and physical properties technique. The results show that the quartz overgrowths of siliceous cementation and iron dolomite of carbonate cementation caused the background of low porosity and ultra low permeability reservoir of Chang 4+5 reservoir in the study area, and the diagenetic stage has reached the "A" middle now. Chlorite film cementation and early oil accumulation effectively protected pores, and limited the mechanical compaction and cementation. The intense dissolution of feldspar components could greatly improved the porosity and caused the relatively high porosity and permeability reservoir. There are mainly divided into four kinds of diagenetic facies, including mechanical compaction facies, carbonate cementation facies, chlorite cementation facies and feldspathic solution facies. The most favorable diagenetic facies is feldspathic solution facies, which mainly distributes in the middle sandbody of the underwater distributary channel, and it is favorable for the formation of relatively high porosity and permeability reservoir, which surface porosity is more than 6.0%, porosity is more than 14.0%, permeability is more than 1.30×10-3 μm2. Comprehensive studies have shown that the combination of sedimentation and diagenesis control the distribution of relatively high porosity and permeability reservoir.