共面感应测井仪探测地层裂缝的试验模型

Scale model Response of Fracture Zones to a Coplanar Induction Tool in a Borehole,

通过实验室模拟 ,研究了利用双线圈井眼共面感应测井仪探测地层裂缝的可行性。试验中 ,比例因子选为 10 ,用氯化铵溶液模拟实际地层电导率。所模拟的实际裂缝地层电阻率为 4Ω· m,非裂缝地层电阻率 2 0 0Ω· m。试验共研究两种类型的裂缝地层 :其一为垂直裂缝 ,裂缝至井壁的距离可以改变 ;其二为倾斜且与井眼相交的裂缝 ,倾斜角度分别为 0°、45°、6 0°。试验中所采用的信号主频为 10 0 k H z。试验结果表明 ,仪器灵敏度与线圈方位、裂缝厚度及裂缝距井壁的距离有关 ;在某种程度上 ,还取决于裂缝地层的倾斜程度。试验中还可以看出 ,共面线圈系存在测量盲区 ,它不可能获取线圈周围地层的所有地质信息。因而建议采用一种新的线圈系统——互补双耦线圈系统 (SN DC)。

The conventional induction logging tool cannot provide the orientation information with relation to fractures,because the field distribution of the tool is axisymmetry in a borehole.Otherwise,a coplanar induction dual coil system has a certain discriminability to the orientation angle of fractures.The suitability of using this system to detect a fracture zone is studied by scale model experiments in the laboratory.The result shows that the measurements are sensitive to coil orientations,thickness of fratures,their distance from the borehole wall,and,their dip.Since the information about all the formation arround the coils with this system cannot be obtained,the Semi Null Double Coupling(SNDC) system is suggested,because it provides a quick look technique to estimate the dip of the fracture zone qualitatively.The various logs recorded with this new system are presented.