基于多孔介质弹性理论的碳酸盐岩地层超压预测

碳酸盐岩地层超压预测目前仍然是国内外研究的难点问题。碎屑岩超压预测方法均是建立在明显的超压测井、地震宏观响应规律基础上的经验关系,这些经验性方法不适用于因岩性致密使得超压地球物理响应微弱的碳酸盐岩地层。通过碳酸盐岩样品超压岩石物理模拟实验,分析了在应力-孔隙压力共同作用下岩石中声波速度、弹性参数的变化规律;基于多孔介质弹性理论和广义胡克定律推导并建立了表征孔隙压力与岩石弹性参数定量关系的理论模型,即多孔介质弹性理论的超压预测量化模型。以川东北地区典型碳酸盐岩超压钻井为例,开展了碳酸盐岩地层超压预测应用研究:针对碳酸盐岩地层选择油气水测井综合解释模型获取岩石物性参数;利用Voigt-Reuss-Hill平均模量模型计算岩石基质体积模量,利用Wood模型和Patchy模型计算孔隙流体体积模量,利用BISQ模型计算岩石骨架体积模量,然后通过多孔介质弹性理论量化模型预测超压。预测结果显示预测压力与钻杆实测压力(DST)吻合较好,与泥浆密度换算压力和随钻监测压力变化趋势相近,表明这种基于多孔介质弹性理论的超压预测量化模型是一种解决碳酸盐岩地层超压预测的新途径。

Overpressure Prediction in Carbonate Formation Based on Poroelasticity Theory

The prediction of overpressure in carbonate formations is still a difficult problem worldwide.The overpressure prediction methods in clastic rocks are formed with the empirical relationships based on the obvious logging and seismic macroscopic response law to overpressure.These empirical methods are not applicable to predict overpressure in carbonate strata with very weak geophysical response to overpressure due to tight lithology.In this paper,the overpressure rock physical simulation experiment on carbonate rock samples is used to analyze the variation of acoustic wave velocity and elastic parameters in rocks under the action of stress-pore pressure.Based on the poroelasticity theory and generalized Hooke’s law,a poroelasticity theoretical model namely a quantitative model of overpressure prediction is derived and established to characterize the quantitative relationship between pore pressure and rock elastic parameters.Taking the overpressured typical well-drilling that located in northeastern Sichuan Basin as an example,applied research on overpressure prediction in carbonate formation has been carried out in this paper.The physical parameters are obtained by choosing the oil-gas-water well-logging comprehensive interpretation model for carbonate formation.The Voigt-Reuss-Hill average modulus model is used to calculate the bulk modulus of the rock matrix and the Wood model is used to calculate the bulk modulus of pore fluid,then the BISQ model is used to calculate the bulk modulus of rock skeleton,and finally,overpressure is predicted by the quantitative model.The prediction result shows that the predicted pressure agrees well with the drill-stem-testing pressure and the trend of the predicted pressure change is similar to the monitoring pressure while drilling.This indicates that the quantitative model of overpressure prediction based on poroelasticity method to predict overpressure is a new approach to solve the problem of overpressure prediction in carbonate rocks.