差异性沉积—成岩演化过程对砂砾岩储层致密化的影响——以准噶尔盆地东部二叠系上乌尔禾组为例

Influence of differential sedimentary-diagenetic evolution on the densification of the sandy conglomerate reservoir:A case study of the Permian Upper Wuerhe formation in eastern Junggar Basin

为研究差异性沉积—成岩演化对准噶尔盆地东部砂砾岩储层致密化的影响,明确沉积—成岩作用影响下砂砾岩储层的差异性致密化过程,通过铸体薄片、扫描电镜、阴极发光、全岩及自生黏土矿物X射线衍射、图像孔喉、实测物性、岩屑录井、测井成像等资料,对准噶尔盆地东部东道海子凹陷与白家海凸起二叠系上乌尔禾组进行分析,认为受差异性沉积—成岩演化影响,凹陷带上乌尔禾组有利储层主要位于裂缝发育地带的相对高渗区,凸起带上乌尔禾组有利储层主要位于高孔隙发育地带的相对高渗区.研究结果表明:沉积作用导致的结构成熟度是决定储层致密化程度的基础条件,压实与胶结作用分别是增强储层致密化的主要与次要因素,溶蚀作用与构造裂缝在一定程度上降低了储层的致密化程度.由于沉积—构造运动—成岩—孔隙演化过程的不同,凹陷带与凸起带上乌尔禾组储层致密化过程具有一定差异.凹陷带离物源较近,以连续沉降为主,现今埋藏较深,储层经历了低初始孔隙度→强-中等压实减孔→中等-强胶结减孔→强-中等溶蚀增孔的致密化过程,成岩阶段达中成岩A亚期,致密化程度较高,孔隙度从最初的36.6%减少到现今的7.5%.凸起带离物源较远,具有多期抬升的特点,现今埋藏较浅,经历了高初始孔隙度→中等压实减孔→中等-强胶结减孔→中等-弱溶蚀增孔的致密化过程,成岩阶段达中成岩A亚期,致密化程度较低,孔隙度从最初的40.3%减少到现今的10.7%.相比较凸起带,凹陷带储层初始孔隙度较低、压实与溶蚀作用较强、成岩阶段较晚,储层较为致密,但构造运动产生的构造裂缝降低了其致密化程度.

In order to study the influence of differential sedimentary-diagenetic evolution on the densification of the sandy conglomerate reservoir in eastern Junggar Basin,this research clarified the differential densification process of the sandy conglomerate reservoir,and analyzed the Permian Upper Wuerhe formation in the Dongdaohaizi sag and the Baijiahai uplift in eastern Junggar Basin using the casting thin sections,scanning electron microscopy,cathodoluminescence,X-ray diffraction of whole rock and authigenic clay minerals,image pore throat,physical properties,rock debris logging,logging imaging.This study considered that:due to the influence of differential sedimentary-diagenetic evolution,the favorable reservoir of the Upper Wuerhe formation in the Dongdaohaizi sag is mainly located in relatively high permeability zone with structure fractures developed;and the favorable reservoir of the Upper Wuerhe formation in the Baijiahai uplift is dominantly situated in relatively high permeability area of the pore developed zone.The results show that:textural maturity caused by sedimentation is the basic condition for determining the degree of the reservoir densification;compaction and cementation are the main and secondary factors to enhance the reservoir densification,respectively;and dissolution and structural fractures weakened the degree of the reservoir densification to a certain extent.There were certain differences in densification process of the sandy conglomerate reservoir of the Upper Wuerhe formation in the Dongdaohaizi sag and Baijiahai uplift,due to the different evolution processes of sedimentation-tectonic movement-diagenesis-porosity.The Dongdaohaizi sag was close to the provenance with continuous subsidencing,resulting in deeper buried depths and relatively low initial porosity of the reservoir,and then experienced a medium to strong compaction decreasing porosity→medium to strong cementation decreasing porosity→strong to medium dissolution increasing porosity,with relatively intensified densification.The diagenetic stage has reached Asub-stage of mesodiagenesis.The porosity decreased from the primary of 36.6%to 7.5%at present.The Baijiahai Uplift was far away from the provenance with the characteristics of multi-stage uplifting,leading to shallower buried depths and relatively high initial porosity of the reservoir,and then experienced the medium compaction decreasing porosity→medium to strong cementation decreasing porosity→medium to weak dissolution increasing porosity,with relatively weaker densification.The diagenetic stage has reached Asub-stage of mesodiagenesis.The porosity decreased from the primary of 40.3%to 10.7%at present.Compared with the Baijiahai uplift,the reservoir in the Dongdaohaizi sag has low initial porosity,and experienced strong compaction,dissolution,and high degree of densification,with a relatively later diagenetic stage.However,structural fractures caused by tectonic movement reduced the degree of reservoir densification to some extent.