基于密度测井资料计算上覆岩层压力的不确定性分析

Uncertainty analysis of calculating overburden pressure based on density logging data

上覆岩层压力准确计算是地层孔隙压力预测的基础。应用不确定度理论,考虑密度测井仪器误差、测量井筒环境、地层横向变化、数据缺失以及函数拟合初值选择等因素,建立基于Taylor级数的上覆岩层压力估计的不确定度计算模型,以川东北探区某区块上覆岩层压力梯度为例进行不确定度评价。结果表明：研究区基于密度测井资料计算的上覆岩层压力梯度的相对不确定度为5.2%～16.3%,上覆岩层压力梯度的不确定性对地层压力预测精度的影响不可忽略;该评价方法为上覆岩层压力不确定度的计算与控制提供了一种分析方法和手段。

The accurate calculation of overburden pressure is the basis of formation pore pressure prediction.According to the uncertainty theory,considering the instrument error for density logging,the uncertainty for testing environment,formation lateral variation,density logging data missing and the initial values selected for fitting,an uncertainty model of overburden pressure was established based on the Taylor series expansion.Taking a block in the northeast Sichuan Basin as an example,the uncertainty overburden pressure gradient was estimated using this model.The calculation results show that the relative uncertainty of overburden pressure gradient is 5.2%-16.3% with density logging,the effect of uncertainty of overburden pressure gradient on the pore pressure prediction could not be ignored in new exploration area.The evaluation method provides a way for calculating and controlling of uncertainty of overburden pressure.