基于角道集速度建模的孔隙压力预测方法

Pore pressure prediction method based on angle domain common imaging gathers velocity modeling

准确预测地层孔隙压力是合理设计钻井液密度和井身结构的基础,也是保护油气层,降低钻探成本和提高钻探成功率的前提.地震层速度场是预测地层孔隙压力的关键参数,其准确性直接影响孔隙压力预测的精度.针对当地层存在低速异常体(欠压实主导的低速泥岩)时,传统的基于偏移距域共成像点道集层速度场建模方法存在射线多路径的假象,给层速度场建模带来较大的误差,导致孔隙压力预测精度严重不足的问题,本文利用角度域共成像点道集代替常规偏移距域道集,创新推导出以角道集剩余曲率为自变量,剩余速度为目标函数的关系式,利用该关系式可以有效地获得层速度场.该方法有效解决了低速异常带来的偏移距域射线多路径假象的问题,提高层速度场建模精度的同时,有效提高了孔隙压力预测的精度.由带有速度异常地层的实际数据应用证明,本文提出的方法是合理且可行的,该方法预测结果精度较高,可直接用于钻井液密度的设计.

Accurate prediction of formation pore pressure is the fundamental basis of reasonable design of drilling fluid density and the wellbore structure,and it is also a prerequisite for protecting oil and gas formation,reducing the cost of drilling and improving drilling success rate.The seismic Interval velocity field is a key parameter to predict the pore pressure of the formation,and its accuracy directly affects the accuracy of the pore pressure prediction.When there are low-velocity anomalous bodies in the local formation(low velocity mudstone dominated by under less-compaction),the traditional method of modeling the interval velocity field based on offset domain imaging gathers has the illusion of ray multipath,which gives the interval velocity field modeling large errors have resulted in a serious shortage of pore pressure prediction accuracy.In this paper,by using angle domain common imaging gathers instead of conventional offset domain gathers,and innovatively derive the residual curvature of the angular gather as the independent variable and relational expression of the residual velocity as the objective function,using the relational expression the interval velocity field can be effectively obtain.This method effectively solves the problem of ray multipath illusion in offset domain caused by low-velocity anomalies,improves the accuracy of interval velocity field modeling,and effectively improves the accuracy of pore pressure prediction.The application of actual data in formations with abnormal velocity proves that the method proposed in this paper is reasonable and feasible.The prediction result of this method has high accuracy and can be directly used in the design of drilling fluid density.