基于DSI测井横波分裂的水平井压裂缝检测研究

利用偶极横波测井检测水平井压裂缝不同于直井压裂缝检测，目前还存在较多的理论和技术问题。针对直井、斜井和水平井等不同情况，给出了三维TTI介质中SH波和SV波的相速度和各向异性系数计算公式，从理论方面研究其横波各向异性系数与裂缝倾角、裂缝方位角、井斜方位角、井斜角之间的关系，开展水平井横向压裂缝的DSI实验模拟研究，并在实际水平井QP52井中进行压裂缝检测应用。研究发现，DSI可以检测水平井的纵向缝和斜交缝，但无法检测水平井的横向正交压裂缝。横波各向异性系数随裂缝倾角的增大而减小，随裂缝方位角与井斜方位角之差的增大而减小；而井斜角的改变不会影响横波分裂速度和各向异性系数的检测与计算。研究结果可为工区水平井实施压裂缝检测的DSI项目提供重要理论指导和依据，即通过压前、压后近井地带的横波各向异性对比来检测压裂缝与识别压开层段。

Detection of Hydraulic Fractures in Horizontal Wells Based on Shear Wave Splitting of DSI Logging

Many theoretical and technical challenges remain with the detection of hydraulic fractures in horizontal wells using dipole shear image (DSI) logging, which differs from the detection of hydraulic fractures in straight wells. Formulas for computing the phase velocity and coefficient of anisotropy of SH-waves and SV-waves in three-dimensional TTI media were derived for straight, inclined, and horizontal wells. The theoretical relationship between the coefficient of anisotropy of shear waves and the slope of fracture, azimuth of fracture, azimuth of borehole inclination, and angle of borehole inclination was then examined by performing a DSI experimental simulation of horizontal hydraulic fractures in horizontal wells. This was then applied to the field detection of hydraulic fractures in horizontal well QP52. The study found that DSI is capable of detecting vertical and diagonal fractures in horizontal wells, but not horizontal orthogonal fractures in horizontal wells. The coefficient of anisotropy of a shear wave decreases with increasing slope of the fracture and with increasing difference between the azimuth of the fracture and the azimuth of the borehole inclination. In addition, changes in borehole inclination have no impact on the detection and computation of splitting speed or the coefficient of anisotropy of shear waves. This study revealed that hydraulic fractures can be detected and fractured layers and sections can be identified by comparing the anisotropy of shear waves in areas adjacent to boreholes before and after fracturing. This provides important theoretical guidance and criteria for DSI logging projects involving the field detection of hydraulic fractures in horizontal wells.