基于邻井距离测量误差的救援井磁测距工具优选方法

Optimal Selection Method of Magnetic Ranging Tools for Relief Well Engineering Based on the Measurement Error of the Adjacent Well Distance

为了确保能在可探测的前提下选用测量精度更高、作业风险更小的磁测距工具探测事故井,进行了救援井与事故井相对距离测量误差计算。由于“梯形”误差模型无法与井眼轨迹误差相耦合,通过协方差传播率,建立了磁测距工具测量误差模型。将磁测距工具测量误差与井眼轨迹误差相耦合,可得到磁测距工具工作平面内的总协方差矩阵,进而给出由总协方差矩阵确定的误差椭圆和救援井磁测距工具的优选方法。实例计算结果显示,救援井当前井底与事故井相距7.41 m时,磁测距工具测量误差椭圆长、短半轴长度分别为1.26 m和0.33 m。测距作业后,救援井继续钻进,当两井相对距离为6.68 m时,推荐使用Wellspot工具;当两井相对距离为5.21 m或2.07 m时,推荐使用RGRⅠ工具。研究结果表明,测距作业后,随着救援井继续钻进,两井相对距离的减小趋势大于两井相对距离测量误差的增大趋势;当磁测距工具探测范围完全包覆两井相对距离测量误差椭圆时,可以选用作业距离更小、但测量精度更高的磁测距工具。

Measurement errors of the relative distance from an accident well to its relief well were calculated from magnetic ranging tools with higher measurement accuracy and lower operational risks on the premise that the accident well was within the tools’ detection ranges. As the error calculated by the “trapezoidal” error model could not be coupled with the wellbore trajectory error, a measurement error model for magnetic ranging tools was built through the covariance propagation rate. The measurement errors of magnetic ranging tools were coupled with the wellbore trajectory errors to obtain the total covariance matrixes in the working planes of the magnetic ranging tools. The error ellipses and the optimal selection method of magnetic ranging tools for the relief well were thereby derived. The example calculation showed that when the current bottom of the relief well was 7.41 m away from the accident well, the semi-axis lengths of the measurement error ellipses were 1.26 m and 0.33 m. After the ranging operation, the relief well drilling continued to drill. The wellspot tool or RGR-Ⅰ tool were recommended when the relative distance between the two wells was 6.68 m or was shortened to 5.21 m and then to 2.07 m, respectively. The research results show that the decreasing trend of the relative distance between the two wells is greater than the increasing trend of the measurement error of the relative distance after the range measuring operations and as relief well drilling continues. When the detection range of a magnetic ranging tool fully covers the measurement error ellipse of the relative distance between the two wells,magnetic ranging tools with shorter measurement ranges but higher accuracy can be used.