地层孔隙压力在石油钻井中起着至关重要的作用, 是石油钻井中套管方案设计和泥浆比重优化不可缺少的基本参数。利用地震、测井和随钻录井资料可以预测地层孔隙压力。然而, 由于碳酸盐岩地层的隐蔽性和复杂性, 以及地震、测井和泥浆测井资料的固有误差, 地层孔隙压力一直难以准确预测。为了定量描述地层孔隙压力的不确定性, 提出了一种预测地层孔隙压力的概率方法。首先, 根据本文的方法得到了任意井深的伊顿指数和正常压实趋势线分布的统计性质。然后根据蒙特卡罗模拟方法, 生成相应分布特征对应的随机数, 计算任意深度的孔隙压力样本集, 最后选择正态分布拟合任意深度的孔隙压力样本集, 推导出孔隙压力在任意深度下的累积概率分布结果。选取各深度点上累积概率分别为0. 05和0. 95的孔隙压力值, 沿整个井段进行串联, 得到置信度为90%的地层压力区间剖面。实例结果显示, 该方法综合了测井和记录信息, 得到了更准确的孔隙压力预测结果, 不确定性分析后得到的结果为碳酸盐岩地层孔隙压力的预测提供了参考价值。

Formation pore pressure plays a vital role in oil drilling, and is an indispensable basic parameter for casing scheme design and mud specific gravity optimization in oil drilling. Formation pore pressures can be predicted through the data of seism, logging, and logging-while-drilling. However, due to the concealment and complexity of carbonate formations, as well as the inherent errors in the date of seism, logging, and mud loging, formation pore pressure is always difficult to predict accurately. Thus, a probabilistic method for predicting formation pore pressure is proposed to quantitatively describe the uncertainty of the pressure. Firstly, the method in this paper provides statistical properties of Eaton index and the normal compaction trend line distribution of random well depth. Then, with the Monte Carlo simulation method, the random number corresponding to the distribution features can be generated. And further the pore pressure sample set of any depth can be calculated. Finally a normal distribution is selected to fit the pore pressure sample set of any depth, and the cumulative probability distribution of pore pressure at any depth is derived. The pore pressure values with the cumulative probabilities of 0. 05 and 0. 95 at each depth point were selected and connected in series along the entire well section to obtain a formation pore pressure interval profile with a confidence of 90%. The case study shows that the method, integrating the logging and information recorded, obtains more accurate pore pressure prediction results, which provides a reference value for the uncertainty analysis of pore pressure in carbonate formation.