Basic Applied Research On Low Frequency Focused Electromagnetic Propagation Logging Response

With the progress of exploration and the complicated geological conditions of reservoir development, thin layer, thin interbed and oil-water layer have now became the challenges of research. And only by increasing the resolution of tools can they be identified effectively. From 1990s on, there has been a fast development on array induction log and high resolution induction log. This paper, based on Maxwell Equation, mainly focuses on the synthesis of real resolution, resolution matching, inversion modeling, and new inversion methods for array induction log. By numerically simulating array induction log, its responses under all kinds of geological conditions can be better analyzed, providing a theoretical basis for real data processing. From the main focuses in this paper, a feasible method platform for practical problems is provided. The application conditions of Doll geometric factor, Gianzero geometric factor, Moran geometric factor and Born geometric factor are mainly analyzed. And finally the right one for focusing array induction log is determined. Using amplitude and slope basis functions given by Mr. Gengji Zhang, applies the mode matching method to 2-D computation of electromagnetic field, computing the respective logging responses of subarray under borehole and borehole-absence conditions. With respect to different borehole diameters, data base for borehole correction are established, providing theoretical support for borehole correction while synthesizing array induction log. Gianzero geometric factor, with the information of formation conductivity, is adopted in stead of Doll geometric factor to focus array induction log. The resolution focusing model is simplified to a multi-objective constrained optimization problem, which is transformed into a single objective unconstrained problem by using optimization method. And synthesis filter of real resolution is obtained by solving this problem. Through testing of all kinds of formation model, Gianzero geometric factor is shown to be suitable for synthesizing array induction filter. While simulating formations with different contrast ratios, the synthesized curves are found to be an unreasonable while proceeding array induction synthesis for high contrast ratio formation, resulting from the synthesized subarray data failing to be improved to an accurate objective function according to the structure of real coil system. Finally the influencing factors of synthesized carves are analyzed, providing a theoretical basis for logging data interpretation. According to oil-water two-phase flow theory, we simulate formation invasion profile, and establishe a new inversion model of array induction log. Inversion problem is a multi-objective non-linear optimization problem, in which conventional Marquette method is adopted. After inversion of array induction curves under noisy and noise-free conditions, results suggest that this method is greatly influenced by initial values. On this basis, differential evolution and memetic algorithms are used for inversion. Through the inversion of differential algorithm of array induction curves, this algorithm presents a characteristic of global optimization, does not need jacobian matrix, and shows a strong stability. The memetic algorithm maintains the advantages of fast local optimization of conventional optimization algorithm and strong global searching ability of differential evolution algorithm, providing a theoretical basis for array induction inversion. At last, given the slow inversion speed, multi-core parallel technology is proposed for accelerating. Through the inversion of practical field data and comparison of the inverted results and results inverted from self supplied tools, the inverted resistivity profile is more reasonable.