Study On Inversion Of Array Induction Logging In The Inclined Layered Formation Based On The Forward Modelling

With the increasing of horizontal wells, high angle wells, branch wells and cluster wells, dip correction become the bottleneck of the correct oil and gas evaluation. Inversion method of array induction logging in deviated well is study in this paper, which is based on fast forward algorithm. It not only inverses the layered formation conductivity, but also eliminates the dip influence. The results have an important theoretical and practical significance for logging interpretation and evaluation.Firstly, the theory of induction logging in the uniform formation and electric anisotropy deviated well are studied from the Maxwell equations. The formula of induction logging in electric anisotropy deviated well is detailedly derived and its correctness is checked by the numerical simulation.Secondly, the response characteristics of array induction logging about formations with electric isotropic and electrical anisotropy are studied. The effect on measurement results are analyzed, such as angle, thickness, and conductivity. Results show that:①When the dip increases to certain angle, abnormal "spike" phenomenon can appear near the boundary of formation.②Short array has higher resolution and smaller effect of angle than long array.③In electrical anisotropic formations, apparent conductivity is not as apparent linear relationship with the conductivity of formation in electrical isotropic formation, but it is influenced by both horizontal conductivity and vertical conductivity, and with the increasing of dip, apparent conductivity tends to the vertical conductivity.④With the increasing of the target layer thickness, the shoulder effect is reduced. Short array performance is influenced by skin effect, and long array is also affected by the angle.Finally, inversion methods based on the damped least square method and the dichotomy are studied. According to the studying the division of layer from logging data, estimation of the initial parameters and the error characteristics, three layer, four layer, five layer and electrical anisotropy oblique formation are bulit. The results of inversion show that:①When dip is0degrees, horizontal conductivity of inversion close true value of layer, and the vertical conductivity can not be inverted.②In electric isotropic formation, when the angle is greater than30degrees, due to the macroscopic electrical anisotropy, horizontal conductivity is different from vertical conductivity, both of that is inverted by the damped least square method.The horizontal conductivity inverted by the dichotomy which is proposed by this paper isclose to true value of layer.③For the electrical anisotropic formations, horizontal conductivityand vertical conductivity inverted by the dichotomy are closer true value of layer than bydamped least square method.