断裂及成岩作用对塔中奥陶系岩溶发育影响

Influence of Fracture and Diagenesis on Karst Development of Ordovician in Central Tarim

为明确塔中西部奥陶系鹰山组岩溶发育特征及沉积机理,通过岩心、薄片、野外露头和成像测井等资料的分析,识别了研究区主要的储集类型,镜下薄片观察出晶间孔、粒间孔、粒内溶孔、微裂缝等储集类型,发现了构造裂缝、缝合线、溶洞、针状和层状溶孔等接触类型。分析了断裂裂缝以及沉积微相对岩溶发育的影响,断层和断陷是溶洞崩塌最直接的产物,综合分析建立了鹰山组岩溶发育模型。该模型表明塔中鹰山组上部主要发育两套广泛分布的岩溶层,分别受顶部不整合和潜水面的控制。不整合面附近的大型溶洞被破坏充填严重,其下覆地层内的缝洞体系距不整合面较近,缺乏盖层,不能很好地储存油气。而潜水面附近产生的溶洞被角砾岩充填后,其洞底多被块状泥砂充填,形成对下覆地层发育的串珠状溶洞以及缝洞体形成良好的盖层,更易形成油气藏。对岩溶发育进一步认识能为水平井轨迹调整以及提高水平井储层钻遇率提供指导。

In order to clarify the karst development characteristics and sedimentary mechanism of the Ordovician Yingshan formation in the central and western Tarim basin,the main reservoir types in the study area were identified through the analysis of core,thin section,field outcrop and imaging logging data.Under the microscope,the reservoir types such as intercrystalline pore,intercrystalline pore,intragranular solution pore and microfracture were observed in thin section,and the connection types of structural fracture,suture,karst cave,needle like and layered solution pore were found.The influence of fracture and sedimentary microfacies on karst development was analyzed.Fault and fault depression are the most direct products of karst cave collapse.The karst development model of Yingshan formation was established by comprehensive analysis.The model showed that there were two sets of widely distributed karst layers in the upper part of Yingshan formation,which were controlled by the top unconformity and the water table.The large-scale karst caves near the unconformity surface were seriously damaged and filled,and the fracture cave system in the underlying strata was close to the unconformity surface,the lack of cap rock could not store oil and gas.After the karst cave near the water table was filled by breccia,the bottom of the cave was mostly filled by massive mud sand,forming a good cap layer for the beaded karst cave and fracture cave body developed in the underlying strata,which was more likely to form oil and gas reservoir.Further understanding of karst development can provide guidance for the adjustment of horizontal well trajectory and the improvement of drilling rate of horizontal well reservoir.