鄂尔多斯盆地彬长地区长6储层成岩作用及有利成岩相带

摘要

The fine-grained sandstones associated with deep-lake mudstones predominate in the Chang-6 oil reservoirs as the favourable area for the heavy oil exploration in the Binxian-Changwu region, Ordos Basin. In the light of core observation, thin section examination and analytical data, the emphasis in this study is placed on porosity types and other physical properties, diagenetic evolution, classification of diagenetic facies and delineation of the favourable exploration areas based on the planar distribution of diagenetic facies zones. The diagenesis in the Chang-6 oil reservoirs is now developed into A to B stages of late diagenesis. The primary porosities have been lost due to compaction, and the permeabilities continued to be decreased by the kaolinite cementation. However, late dissolution of feldspar and lithic clastics led to the redistribution of the porosities and improvement of the physical properties. The diagenetic facies zones comprise strong compaction, strong dissolution, weak dissolution, strong carbonate cementation and microfracture diagenetic facies zones, of which the strong dissolution diagenetic facies sandstones are interpreted as the prolific zone in the Chang-6 oil reservoirs.%鄂尔多斯盆地彬长地区长6油层组发育与深湖相泥岩相伴生的细粒砂岩沉积，是致密油勘探的有利区域。根据岩心观察、铸体薄片鉴定及各类分析测试资料，研究彬长地区长6油层组砂岩储层的孔隙类型及物性特征、成岩演化过程，建立成岩相分类方案，并通过成岩相带平面展布指出勘探有利区。结果表明，研究区长6储层成岩阶段主要处于晚成岩A-B期，压实作用造成原始孔隙大量损失，后期高岭石胶结作用使得渗透率进一步降低。早期绿泥石薄膜的发育可以使原生孔隙得到保存；后期长石、岩屑等不稳定组分发生的溶蚀作用，使孔隙再次分配，物性得到提高。根据成岩作用对物性的影响，划分出强压实成岩相、强溶蚀成岩相、弱溶蚀成岩相、强钙质胶结成岩相，以及微裂缝成岩相等5种成岩相带。优质储层与成岩相密切相关，强溶蚀成岩相的砂体物性、含油性最好，是研究区长6储集层油气最为富集的成岩相带。