阿姆河盆地中-下侏罗统砂岩储层特征

Characteristics of lower-middle Jurassic sandstone reservoirs in Amu Darya Basin,Turkmenistan

根据铸体薄片鉴定和扫描电镜、物性、压汞、镜质体反射率及声发射实验等分析,认为阿姆河盆地中-下侏罗统砂岩储层以细-中粒岩屑砂岩为主,控制储层发育的成岩作用有压实、胶结、溶解和破裂作用。以早期占据原始孔隙,晚期充填次生孔隙的多期次碳酸盐、硅质及粘土矿物的胶结作用影响最大,以长石、岩屑和方解石等不稳定组分溶解产生次生孔隙对形成储层的贡献最重要。储集空间为少量剩余原生粒间孔、粒间和粒内溶孔、晶间微孔及少量裂缝组合,储层具特低孔、特低渗性质。储层发育受多种因素控制:沉积微相控制储层发育位置;持续稳定的构造沉降决定了早-中成岩阶段成岩作用的发育程度;压实作用、早期碳酸盐和后期硅质的胶结作用是造成储层致密化的主要原因;孔隙流体性质的变化是促使不稳定颗粒组分和胶结物溶解、形成次生孔隙、晚期高岭石及伊利石沉淀的主要因素;破裂作用极大程度地改善储层渗透性,但储层发育程度有限。以物性和孔隙结构参数将储层分为3类,Ⅰ类储层发育弱,Ⅱ类储集性能差,储层开发风险超大。

Analyses based on data of casting thin sections,SEM,porosity and permeability analysis,mercury injection test,vitrinite reflectance and acoustic emission test reveal that lithic sandstone with fine to medium grain sizes dominate the sandstone reservoirs in the Lower-Middle Jurassic in Amu Darya Basin. Their formation was controlled by various genesis processes including compaction,cementation,dissolution and fracturing,among which,the most predominant is the multi-stage cementation of carbonate,siliceous and clay minerals that filled up primary pores first and later secondary pores. Secondary pores formed by the dissolution of the unstable components such as feldspar,debris and calcite,contributed the most to the formation of the reservoirs. Reservoir space was composed of remanent intergranular pores,intergranular and intragranular dissolved pores,intercrystalline micropores and fractures,causing ultra-low porosity and permeability in reservoirs. The development of the reservoir was interfered by many factors： sedimentary microfacies determined the location of the reservoirs; sustained steady tectonic subsidence controlled the early and middle stages of diagenesis; compaction and cementation caused tight formations; pore fluid changes facilitated dissolution of unstable components and cements and formed secondary pores,and the precipitation of later kaolinite and illite; and facturing activities improved the permeability of the reservoirs. However,development of the reservoirs was confined to some extent. The reservoir may be grouped into three classes based on physical parameters and pore structures. Among them,classes I and II are poor in quality,assuming high development risk.