塔河油田T738井区奥陶系碳酸盐岩岩溶发育特征及储层控制因素分析

Karst development characteristics and reservoir controlling factors of Ordovician carbonate rocks in T738 well area of Tahe oilfield

塔河油田T738井区地处岩溶高地向岩溶盆地过渡的斜坡带,为上奥陶统浅覆盖区域,大型岩溶缝洞型储层发育。结合古生物、地震、钻井、地球化学等资料,对该区奥陶系碳酸盐岩岩溶发育特征及储层主控因素展开分析。研究表明:井区奥陶系一间房组、鹰山组两套缝洞型储层主要是加里东运动中期I幕、海西运动早期两期岩溶作用叠加改造而成。古水系侧向输入,沿上奥陶统良里塔格组、恰尔巴克组地层尖灭带发生顺层溶蚀,并沿着深大断裂垂向渗入、水平溶蚀,纵向形成垂向渗滤与水平径流两个溶蚀带。岩溶作用过程中,岩溶水系通过贯穿型深大断裂泄水,形成完整的补给—径流—排泄系统。区域上,广泛发育的断裂对储集体具有明显的控制作用,根据三组不同走向的断裂与主水流方向的交互关系,总结了三种储层发育模式,其中,北西向断裂带是最有利的储层发育部位。

T738 well area of Tahe oilfield is located in the slope zone of transition from Karst highland to karst basin,which is a shallow covered area of upper Ordovician with large-scale karst fractured-vuggy reservoirs.On the basis of Paleogeomorphology restoration,combined with paleontology,seismic,drilling and geochemical data,this paper analyzes the karst development characteristics of Ordovician carbonate rocks and the main controlling factors of reservoirs in this area.The results show that the fractured-vuggy reservoirs of Yijianfang and Yingshan formations of Ordovician in the well area are mainly the result of the superimposition and transformation of karst process in the middle Caledonian and the Early Hercynian.The ancient water system undergoes layer by layer dissolution along the pinch-out line of Lianglitage and Chalbac formations,and vertically infiltrates and horizontally erodes along the deep fractures.Vertically,two erosion zones,vertical infiltration and horizontal runoff,are developed.At the same time,water is discharged along the through deep fractures,forming a complete supply-runoff-discharge system.Regionally,the widely developed faults have obvious control over the reservoir.According to the interaction between three groups of faults with summarized,among which the northwest fault zone is the most favorable reservoir development location.