延安气田上古生界山西组致密砂岩储层微观特征及主控因素

Microscopic Characteristics and Main Controlling Factors of Tight SandstoneReservoirs in the Upper Paleozoic Shanxi Formation,Yan′an Gas Field

延安气田主力气层上古生界山西组储层非均质性较强,物性较差,属于典型的致密砂岩气藏,勘探有利区预测及气藏开采难度较大。为明确储层低孔低渗成因及发育主控因素,通过岩心薄片、扫描电镜、全岩X衍射等多种实验分析,按塑性颗粒含量差异性,将山西组致密砂岩划分为5种岩石相,以相控指导建模,应用三维地质建模软件进行岩石相随机建模。结果表明:沉积相、水动力条件及成岩作用共同影响砂岩孔隙的发育及储集性能;塑性物质机械压实是造成储层物性差的根本原因;纯石英砂岩与富石英低塑性颗粒岩屑砂岩孔隙发育、物性较好,为有效储层,其主要发育于水动力较强的水下分流河道与河口坝微相的中下部。通过岩石相建模能更好地认识岩石相三维空间分布规律,提高有效储层分布预测精度,对延安气田精细开采具有指导意义。

The reservoirs of the Shanxi Formation in the main gas-bearing layers of the Yan′an Gas Field exhibit strong heterogeneity and poor physical properties,typical of tight sandstone gas reservoirs.It is difficult to predict favorable exploration areas and exploit gas reservoirs.To clarify the causes of low porosity and permeability in the reservoir and identify the main controlling factors,various experimental analyses such as core thin sections,scanning electron microscopy,and whole-rock X-ray diffraction were conducted.Based on differences in plastic particle content,five lithofacies were identified within the tight sandstone of the Shanxi Formation.Phase control was used to guide modeling,and three-dimensional geological modeling software was employed for stochastic lithofacies modeling.The results indicate that sedimentary facies,hydrodynamic conditions,and diagenesis collectively influence sandstone pore development and reservoir performance.Mechanical compaction of plastic materials is identified as the fundamental cause of poor reservoir properties.Pure quartz sandstone and quartz-rich,low-plasticity lithic sandstone exhibit well-developed pores and better physical properties,representing effective reservoirs.These lithofacies are mainly distributed in the middle to lower parts of underwater distributary channels and deltaic barrier microfacies with strong hydrodynamic conditions.Lithofacies modeling provides a better understanding of the three-dimensional spatial distribution patterns,enhancing the accuracy of predicting effective reservoir distribution.This approach has significant implications for the fine development of the Yan′an Gas Field.