致密储层储集空间特征及影响因素——以准噶尔盆地吉木萨尔凹陷二叠系芦草沟组为例

Tight reservoir space characteristics and controlling factors:An example from Permian Lucaogou formation in Jimsar sag,Junggar basin,northwest China

综合利用薄片鉴定、氩离子抛光、聚焦双离子束扫描电镜、能谱、XRD、恒速压汞等技术手段,结合岩心观察,综合分析了准噶尔盆地吉木萨尔凹陷二叠系芦草沟组致密储层岩石学特征、物性特征、储集空间特征及其影响因素.认为储集空间特征受沉积作用、成岩作用、生烃作用及构造作用的共同控制,压实作用是导致储层致密化的主要原因,长石、岩屑和凝灰物质的溶蚀是形成"高孔高渗"储层的关键.研究结果表明:芦草沟组致密储层低成分和结构成熟度特点导致储层抗压能力弱,原生粒间孔空间变小,储层平均孔隙半径为124.5μm,平均喉道半径为0.3μm,平均孔喉半径比为339.1;生烃作用产生的有机酸导致次生溶孔发育,次生溶孔和原生粒间孔占总孔隙的80%以上;受沉积作用控制,储集空间类型组合由湖盆边缘的原生粒间孔+次生溶孔组合向湖盆中心的次生溶孔+原生粒间孔+晶间孔组合过渡;生烃产生的异常高压与构造作用可形成微裂缝,改善储层渗流能力.

In this study, thin Section authentication, argon ion beam milling, dual beam focused ion beam scanning electron microscope （FIB-SEM）, X-ray diffraction and rate-controlled mer- cury injection were employed to characterize the tight reservoir space properties of Permian Lu- caogou formation in Jimsar sag of Junggar basin, aiming at analyzing petrologic feature and physical property, clarifying pore types and factors that affect these properties. It is considered that the pore types of the reservoirs are jointly controlled by sedimentation, diagenesis, hydro- carbon generation and tectonic process. Compaction is the principal cause of reservoir densifica- tion in the study area, and the dissolution of feldspars, detritus and tuffaceous particles is sig- nificant for forming the high porosity and permeability reservoir zones. The results show that low compositional and structural maturity of the tight reservoirs in Lucaogou formation result in low reservoir compression capability, and the space of the primary porosity decrease under o verburden pressure. The average pore radius is 124.5 μm and the average throat radius is 0.3μm with an average pore-throat radius ratio of 339. 1. Organic acid released by hydrocarbon generation is evidenced to be in favor of forming secondary solution pores, which account for over 80% along with primary intergranular pores. The assemblage of reservoir space is primary intergranular pore plus secondary solution pore in the marginal area of the lacustrine, mean while it is secondary solution pore plus primary intergranular pore and intercrystalline pore in the central area of the lacustrine. Abnormal pressure generated by hydrocarbon generation and tectonic process can contribute to the formation of microcracks, which can increase the permea- bility of tight reservoirs significantly.