海上油田注水过程中，为防止由于注水压力不合理而导致盖层完整性被破坏，需要对极限注水压力的不确定性及敏感因素对其的影响规律进行分析。以PL19‐3油田某注水井为研究对象，利用FLAC3D软件建立了储盖层模型，模拟计算了盖层开始发生破坏时的注水压力即极限注水压力，分析了渗透率、内聚力和内摩擦角等参数对极限注水压力的影响，并采用蒙特卡洛模拟方法分析了极限注水压力的不确定性。结果表明：当注水压力达到极限注水压力时，盖层开始发生破坏；随着渗透率增大，极限注水压力呈现出先增大后减小再缓慢增大的趋势；随着内聚力和内摩擦角的增大，极限注水压力分别呈现线性增大和二次函数增大的趋势。确定性极限注水压力只是不确定性分析结果的一部分，而通过不确定性分析可以得到盖层发生破坏可能性较大的极限注水压力区间，能够对极限注水压力进行全面评估，可以为现场注水安全管理提供理论指导。%In order to avoid caprock integrity failure caused by unreasonable water injection pressure during water injection in offshore oil fields ,it is necessary to conduct an uncertainty analysis on extreme injection pressure and the controlling influences of sensitive factors on extreme injection pressure .In this paper ,a water injector in the PL19 3 Oilfield was taken as a research object and a caprock model was es‐tablished by using FLAC3D software .Based on this model ,the extreme water injection pressure (i .e .the water injection pressure when the caprock is initially broken ) was calculated .Then ,the effect of sensitive parameters (e .g .permeability ,cohesive force and internal friction angle ) on extreme injection pressure was analyzed .Furthermore ,the uncertainty of extreme water injection pressure was studied by means of Monte Carlo simulation (MCS) .It is shown that cap rocks begin to break when the extreme injection pres‐sure is reached .As the permeability increases ,extreme injection pressure varies ,first in the trend of in‐creasing ,decreasing then increasing slowly .The extreme injection pressure increases linearly as the cohe‐sive force increases ,but in the form of quadratic function with the increasing of the internal friction angle . A deterministic result of extreme injection pressure is only a part of the uncertainty analysis .Through un‐certainty analysis ,the range of extreme injection pressure with higher probability of caprock failure can be revealed and extreme injection pressure can be evaluated comprehensively so as to provide the theoretical guidance in the secure management of water injection .
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