Theoretical Study On The Response Characteristics Of Electromagnetic Tensors In The Time Domain In A Hole

Typical geological structures such as faults and fissures can imply the characteristics of macroscopic or microscopic electrical anisotropy to a certain extent.In oil and gas formations,the electrical anisotropy of thin alternating layers of sand and mudstone,as well as coal and shale oil and gas layers is more prominent.The theoretical research on timedomain electromagnetic tensor logging in boreholes was carried out in this thesis.And the anisotropic characteristics of the target formation from an analytical point of view,laying the foundation was discussed for subsequent theoretical and technical research.Based on the Maxwell equations,the integral equation method was taken to solve the dyadic Green’s function under the magnetic source,and the frequency-time conversion is carried out by numerical filtering algorithm to obtain the electromagnetic tensor response in the time domain.By comparing the induced voltage,the accuracy of the method adopted in this paper is verified.The homogeneous isotropic and uniaxial anisotropic layered medium models are calculated respectively,and it is found that the horizontal cross component electromagnetic response signal cannot be obtained in the homogeneous isotropic layered medium under the condition of vertical wells,but in the uniaxial anisotropy A complete 9-component electromagnetic tensor response signal can be obtained in a layered medium;The complete electromagnetic tensor response can be obtained under inclined well conditions.Compared with the vertical well condition,the tensor response intensity is lower,and it takes longer observation time to obtain the transient abnormal response.Based on the uniaxial anisotropic inclined well condition,the characteristic law of the transient response of each component under different observation parameters is obtained.By changing the horizontal conductivity or the vertical conductivity,the electrical anisotropy coefficient changed at the same time,and found that the transient response characteristics of each component are consistent as a whole,and the transient response intensity decreases as the electrical anisotropy coefficient increases.The vertical principal component zz component is not affected by the change of the vertical conductivity.Compared with the horizontal principal and cross components,the horizontal and vertical cross components are less affected by the vertical conductivity.The research results of the multi-channel response of each component induced voltage under different borehole inclination conditions show that the wellbore inclination does not have much influence on the overall detection effect,the multi-channel curves of each component induced voltage can fit the model well,and the stratigraphic boundary is obvious.