粗粒沉积次生孔隙发育模式——以准噶尔盆地西北缘二叠系夏子街组为例

近源扇三角洲粗粒砂砾岩体往往沉积规律复杂，具有块状构造、砾石大小混杂、粒径变化大、泥质杂基含量高、物性整体偏差且横向变化快等特征，导致对该类致密砂砾岩油气富集规律的区带评价及勘探目标的落实难度大。基于井-震一体化研究方法，通过三维地震、铸体薄片、岩石物性及地球化学等资料，对准噶尔盆地西北缘夏子街组沉积相划分、岩石学特征、物性规律、孔隙类型及成岩作用进行分析，认为夏子街组砂砾岩储层成分成熟度及结构成熟度均低，孔隙类型主要为次生溶蚀孔，保留少量残余粒间孔，物性整体较差。利用孔隙度演化定量分析方法，建立了准噶尔盆地西北缘夏子街组粗粒沉积孔隙演化模式。结果表明，准噶尔盆地西北缘夏子街组孔隙的演化先后经历了快速压实、早期胶结、有机酸溶蚀及晚期碳酸盐胶结等4个成岩阶段。在快速压实阶段，强烈的机械压实导致原始孔隙急剧减少，孔隙度由29.8%下降至15.1%；成岩早期形成的黏土、杂基及沸石类胶结物对储集空间造成破坏，孔隙度平均减小6.5%；有机酸溶蚀是对储层物性起关键改善的成岩作用，主要是对沸石类胶结物形成溶蚀，孔隙度由早期胶结后的8.6%增至12.1%，同时溶蚀作用与烃源岩的主要排烃期相吻合，有利于油气的有效充注；成岩晚期随埋深加大，压溶作用增强，硅质及碳酸盐胶结物相继沉淀，使颗粒支撑方式由点—线接触演变为线接触为主，储层物性再次变差，孔隙度损失约3.4%，一系列复杂的成岩作用下演变为现今的致密砂砾岩储层，孔隙度约8.7%。该研究成果可为研究区夏子街组储层预测提供参考。

Development model of secondary pores in coarse-grained deposits:a case study of Permian Xiazijie Formation in northwestern margin of Junggar Basin

Coarse-grained glutenite bodies in near-source fan delta,generally with complex sedimentary regularities,are characterized by massive structure,different gravel sizes,large variations in grain size,high argillaceous matrix content,poor reservoir physical properties and rapid lateral changes,leading to difficulties in assessment and exploration of oil and gas enrichment regularities of tight glutenite. Based on well-seismic integrated research method,the data of three-dimensional seismic,casting thin sections,rock physical properties,geochemistry were used to analyze the sedimentary facies division,petrologic features,physical properties,pore types and diagenesis of Xiazijie Formation in the northwestern margin of Junggar Basin. The tight glutenite reservoir was dominated by lithic sandstone with low compositional and structural maturity and the pore type was mainly secondary dissolved pore,with a small amount of residual intergranular pores and poor physical properties. The evolution model of reservoir pores of Xiazijie Formation was established by quantitative analysis of porosity evolution. The results show that the pore evolution of Xiazijie Formation in northwestern margin of Junggar Basin has undergone four diagenetic stages:rapid compaction,early cementation,organic acid dissolution and late carbonate cementation. In the rapid compaction stage,strong mechanical compaction resulted in a sharp decrease in the original porosity from 29.8% to 15.1%. The clay,matrix and zeolite cements formed in the early diagenetic stage destroyed the reservoir space and the porosity decreased by 6.5% on average. Organic acid dissolution was the diagenesis that plays a key role in improving reservoir physical properties and was mainly for zeolite cements. Porosity increased from 8.6% to 12.1% after early cementation and reservoir properties were greatly improved. Additionally,the dissolution coincided with the main hydrocarbon expulsion period of source rocks,which was conducive to effective filling of oil and gas. In the late diagenetic stage,with the increase of burial depth and pressure dissolution and precipitation of siliceous and carbonate cements,grain-support mode changed from point-line contact to line contact, the reservoir physical properties deteriorated again and the porosity loss was about 3.4%. In the context of a series of complex diagenesis,the current tight glutenite reservoir was developed,with a porosity of about 8.7%. The results of this study can provide a reference for the reservoir prediction of Xiazijie Formation in the study area.