塔里木盆地玉北地区中-下奥陶统储层发育特征及控制因素

摘要

The Lower-Middle Ordovician carbonates in the Yubei Area,Tarim Basin,are considered promising exploration targets.However,the complexity of the controlling factors and distribution patterns of the reservoirs hindered the explora-tion process in the area.By using petrologic,physical and geochemical methods,we classified the reservoirs into five types:cavern type,dissolution pore type,fracture-vug type,vug-fracture type and fracture type.The main controlling fac-tors of the reservoirs were determined to be dissolution,dolomitization and fracturing.It is suggested that the relative low stand sea level during the Early-Middle Ordovician caused the relative paleogeomorphic highs being repeatedly exposed to penecontemporaneous dissolution,which resulted in the formation of centimeter-scale caves,millimeter-scale mold pores, along-bedding dissolution and geopetal cements that are not cotrolled by single uniform exposure surface.The dissolution degree in the Penglaiba Formation was overly stronger than that in the Yingshan Formation.The dolomitization processes that mainly occurred in penecontemporaneous and shallow burial stages strengthened the resistance of carbonates to com -paction and pressure dissolution,thus provided favorable condition for the preservation of early dissolution pores and ca-ves and contributed indirectly to the forming of reservoirs in the area.The fractures formed through multiple tectonic sta-ges.The fractures formed before the Late Hercynian epoch were filled up by calcite,dolomite and silica and made less contribution to the formation of reservoirs.However,the fractures formed during the Late Hercynian and Himalayan epoch were effective in contributing to the formation of reservoirs due to weak diagenetic processes.%塔里木盆地玉北地区中-下奥陶统碳酸盐岩具有良好油气勘探潜力,但储层发育的控制因素及分布规律不明制约了勘探进程.通过岩石学、物性测试与地化分析等手段,总结出玉北地区中-下奥陶统主要发育溶洞型、溶孔型、裂缝-溶蚀孔洞型、溶蚀孔洞-裂缝型与裂缝型等5种储层类型.溶蚀作用、白云岩化作用以及裂缝活动为储层发育的主要控制因素.早-中奥陶世相对较低的海平面,导致微古地貌高部位在准同生期反复暴露地表遭受溶蚀,形成不受单一统一暴露界面控制的小尺度溶蚀孔洞、顺层溶蚀与示顶底充填等现象.总体来看蓬莱坝组溶蚀作用强度大于鹰山组.主要发育于准同生阶段和浅埋藏阶段的白云岩化作用增强了岩石的抗压实压溶能力,有利于早期溶蚀孔洞的保存,对储层具有间接贡献.裂缝具有多期活动特征,海西晚期之前的裂缝多被方解石、白云石和硅质等流体充填,对储层贡献较少,海西晚期及喜马拉雅期裂缝经历的成岩改造较弱而成为有效裂缝.