Simulation Of EWR-phase4Instrument On The Invasion Characteristics In Horizontal Well In Sandstone Reservoir

With the development of LWD technology, LWD has been applied to more and more research fields and oilfields. On the one hand, through LWD technology, we can timely control well trajectory and improve reservoir drilling rate in the drilling of highly-deviated wells and horizontal wells, on the other hand, stratum data from LWD, because of the two characteristics of immediacy and authenticity, can help improve the fine evaluation of reservoir. So that the study of LWD response characteristics using numerical simulation method is very meaningful, it can promote and accelerate real-time trajectory control, reservoir fine evaluation and development of LWD tools.Based on the edge-based finite element method, combined with the electromagnetic field theory, this paper develops a numerical simulation method, which is designed to solve the electromagnetic resistivity in horizontal wells. The main contents include unstructured tetrahedral mesh generation techniques, processing method of boundary conditions and excitation coils and large sparse linear equations solving techniques based on incomplete decomposition preconditioning.Unstructured tetrahedral mesh generation techniques, compared with structured mesh and hexahedral mesh, have at least two advantages. First, it has a better adaptability to complex models. Second, it is able to get higher simulation accuracy. In this paper, we put the excitation coils as linear current according to the principle of equivalence and deduce the general analytical expression of the corresponding integral in finite element equations. The usage of equivalent model overcomes the difficult problem about excitation coils processing, at the same time it is easy programming. Three-dimensional geological model is partitioned into tetrahedrons, in which electric field is represented by linear combination of vector basis functions. In finite element equations, the total number of unknows about electric field in solving region tends to more than100000and the stiffness matrix is seriously ill conditioned. So that the common solver, such as Gauss-Seidel and SOR iteration method, is incapable to solve the discretized equations. In such a scenario, based on the previous, this paper further studies the precondition techniques and realizes the fill-in ILU with the CSR storage strategy. Combined with generalized minimal residual method, this paper tries to optimize the parameters of incomplete decomposition and gets a more suitable preconditioning parameters, which effectively improves the speed of solving and the solution accuracy and can achieve the convergence precision le-7in500iterations.Based on the previous research on numerical simulation methods, in this paper, taking the Halliburton non-compensated LWD EWR-phase4tool as an example, we study the response rules in electromagnetic wave logging while drilling in the mud invasion condition, both in symmetric and asymmetric invasion. The simulation results consist with the theoretical condition and this method provides the tool development and logging data evaluation with a good theoretical basis.