塔河油田4区奥陶系缝洞型油藏特征及开发对策

Reservoir characteristics and development strategy of Ordovician fractured-vuggy reservoirs in block 4 of Tahe oilfield

塔河油田4区储集体主要分布在奥陶系风化壳,呈不规则网状。储集空间以溶洞、裂缝为主,溶洞高度大多数低于2 m,裂缝平均宽度大于0.1 mm的层段占总层段的58%。储集体的平面分布与古岩溶发育有关,古岩溶水道的地震反射特征呈串珠状强反射,深浅侧向测井异常具有幅度差。利用蒙特卡罗法计算缝洞型油藏储量,一种方法是利用测井解释的结果,统计孔隙度、有效厚度、含油饱和度的概率分布;另一种方法是假设孔隙度、有效厚度、含油饱和度为精确值,储集体面积符合某种概率分布,求得每口井的储量分布。塔河油田是块状底水油藏,油藏的水体主要由深部发育的古岩溶水道系统沟通底水。合理开发碳酸盐岩缝洞型油藏应以缝洞单元为基础,以循环注水、钻侧钻井为主要措施,宜采用“一井一策”方针。

Reservoirs in block 4 of Tahe oilfield are mainly distributed in Ordovician weathered crust and appear as irregular chicken-wire pattern. Solution cavities and fractures are the main types of reservoir space. The height of most solution caviteis is less than 2m, and the formation intervals with average fracture width of over 0.1 mm account for 58% of the total. Areal distribution of reservoirs is related with the development of fossil karst. Fossil karst channels appear as beaded strong seismic reflection, and magnitude differences exist between deep and shallow laterolog anomalies. Monte Carlo method is used to calculate reserves of fractured-vuggy reservoirs. One way is to achieve the probability distribution of porosity, net thickness and oil saturation based on interpretation of log data. Another one is to achieve reserves distribution of each well through assuming that the values of porosity, net thickness and oil saturation are accurate and the area of reservoir body accords with certain probability distribution. Tahe oilfield is a massive oil pool with bottom water, being communicated with deep fossil karst water channel system. Rational development of fractured-vuggy carbonate reservoirs should take fracture-vug units as bases, cyclic waterflooding and lateral drilling as the principal measures, and “one well one scheme” as the guiding principle.