Zanarol Oilfield is a giant carbonate reservoir with condensate cap, weakly volatile oil, and bioclastic limestone of low porosity and permeability. During the waterflooding stage, formation pressure decreased stcp by step resulting from the former depleting development and the strong heterogeneity of carbonate reservoirs. The gas cap spread outwards with the formation pressure dropping, causing gas breakthrough in production wells near the oil and gas contact, GOR increased and oil density decreased. In the internal oil region far from the oil-gas contact, the dropping reservoir pressure led to dissolved gas separating out from oil, making crude oil change to black oil from weak volatile oil. With the separated solution gas, the oil density, produced gas oil ratio and oil viscosity increased, the oil well productivity decrcased, all these make waterflooding more difficult. The main method for improving development response is to keep formation pressure and improve the utilization factor of water injection.%让纳若尔油田是一个带凝析气顶的大型碳酸盐岩油藏,原油为弱挥发性原油,储集层为低孔低渗生物碎屑灰岩.由于早期衰竭式开发和碳酸盐岩储集层的强非均质性,在注水开发过程中,油藏地层压力逐渐下降.随着地层压力的下降,凝析气顶向外扩大,导致油气界面附近的生产井发生气窜,气油比上升,原油密度降低;同时,在远离油气界面的油环内部,由于地层压力下降,大量溶解气析出,地层原油性质发生变化,由弱挥发性原油逐渐转变成普通黑油,原油密度增大,地层原油黏度增大,油井生产气油比升高,油井产能降低,油藏水驱开发难度增大.保持一定的地层压力水平,提高注水利用率是进一步改善和提高该油田注水开发效果的主要手段.
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