基于时变卡尔曼滤波的中途VSP钻前速度反演及在地层压力预测中应用

Inversion of midway VSP pre-drilling velocity based on time-varying Kalman filter and its applicationin formation pressure prediction

地层速度的变化是孔隙压力预测过程中的敏感参数之一,而岩层的性质、岩石的成分等众多因素则影响着速度的变化,导致其预测和估计的复杂性和困难性。本文首先利用中途垂直地震剖面(VSP)获得的已钻井段的时深关系及钻头前方未钻井段反射波场信息使用多元回归模型对地层速度预测问题进行建模,其显著特点是众多影响因素以属性形式作为输入模型,然后使用卡尔曼滤波器来求解该多元回归模型的参数,预测得到钻头前方地层速度。鉴于输入的VSP走廊叠加资料及衍生属性具有比常规地震更高的分辨率,从而使得预测得到地层速度也具有更高分辨率。基于以上工作基础上,我们将基于VSP预测获得的速度应用在地层压力预测中,并实际应用在琼东南盆地高温高压井中,预测了钻头前方300 m的地层速度,进而估算钻头前方地层的孔隙压力。后续的实测结果表明,预测结果较为可靠,为安全钻井提供了技术支持,验证了本文方法可行性。

The variation of formation velocity is one of the sensitive parameters in the prediction of pore pressure,while many factors such as lithology,rock composition,and other geological properties affect the change of velocity,leading to the complexity and difficulty of its prediction and estimation.In this paper,by using The time-depth relationship of the VSP in the drilled well section and the reflected wave field information in the undrilled section ahead of the bit,we first model the problem of formation velocity prediction using a multivariate regression model,which is characterized by numerous influencing factors as attribute inputs to the model.Then,we use a Kalman filter to solve the parameters of the multivariate regression model,to predict the formation velocity ahead of the bit.The input VSP corridor stacking data and derived attributes have higher resolution compared to conventional seismic data,leading to higher-resolution predictions of formation velocity.Building upon this foundation,we apply the velocity obtained from VSP prediction to the prediction of formation pressure.Using this mothed at high-temperature and high-pressure wells in the Qiongdongnan Basin,predicting the formation velocity 300 meters ahead of the drill bit,and estimating the pore pressure ahead of the drill bit.The subsequent drilling and measured results indicate that the predicted results are relatively reliable,can provide technical support for safe drilling and verify the feasibility of the proposed method.