Geosteering capability of the novel transient multicomponent electromagnetic logging while drilling method
Description
We have proposed a novel transient multicomponent electromagnetic (EM) logging while drilling (LWD) method and studied its capability in geosteering. Instead of using the transient triaxial measured data directly, a detection mode is defined to sense the bed boundary. By setting a noise threshold, the depth of detection (DOD) of this time domain EM LWD method can reach tens of meters. Based on the polarity of the signal, the directional measurements can be achieved. In addition, linear relationship between the distance to the boundary (DTB) and the time we observe it is established to effectively determine the DTB. We also find that the cross component decays much faster than the coaxial or coplanar component in the formation coordinate system. Thus, an algebraic method is proposed to determine the relative dip angle without inversion. When the tool is located in an isotropic layer and the shoulder is anisotropic, the apparent dip angle yields 0° at early time. During the transition time, the apparent dip angle becomes very sharp and gradually approaches to the true value at late time. However, when the tool is placed at an anisotropic layer, the apparent dip yields the true value at early time. After a transition period, the apparent dip angle gradually approaches to the true dip at late time again.