Research On The Electromagnetic Responses Of Electromagnetic LWD In Heterogeneous Formations

As a popular method of petroleum exploration, electromagnetic logging while drilling has the advantages of high efficiency and real-time measurement. It is more accurate since logging information can be obtained before the mud invades the formations. The forward simulation of electromagnetic logging while drilling is researched. Given the parameters of formations and the source, we can simulate the propagation of the electromagnetic wave in the given formations and get the electromagnetic responses of the electromagnetic logging while drilling tools by using finite-difference time-domain (FDTD) method. The forward simulation can provide useful information for the recovery of the logging information and the optimized design of the tools.FDTD is a numerical computing method to analyze the transmission of electromagnetic wave by solving Maxwell equations in time domain. Maxwell equations are transformed into difference equations by discretizing the electric fields and the magnetic fields alternatively in time and space domain. In this way can the electromagnetic fields be updated. The space and time step of FDTD have to be small enough to satisfy the numerical dispersion and numerical stability conditions. So it takes a long time to analyze the fine figures or electrically large structures.Because of the inherently data parallel algorithm, parallel FDTD computing can efficiently reduce the simulation time and be established easily. Restricted by the speed of network and expensive cost, parallel FDTD computing based on computer network is not cost-effective. However, parallel computing on GPU is easy to implement and has a high computing speed after the appearance of compute unified device architecture (CUDA) model. Basic three-dimensional cylindrical coordinate non-uniform cell FDTD theory and relative knowledge are introduced in detail. Then the hardware, software environment and programming model of CUDA model are discussed. Finally three-dimensional cylindrical coordinate non-uniform cell FDTD parallel computing on GPU is implemented for the first time and can work as a fast and effective tool to research the responses of electromagnetic logging while drilling tools. The main achievements of my research are as following: Firstly, the high-speed simulation platform is implemented. Three-dimensional cylindrical coordinate non-uniform cell FDTD parallel computing on GPU is implemented for the first time. According to the mandrel and coil geometries, FDTD in a three-dimensional cylindrical grid is chosen to research the response of electromagnetic logging while drilling tools. The cell size in radial p direction is non-uniform to lower the requirement of memory. The formula of three-dimensional cylindrical coordinate non-uniform cell FDTD and UPML-FDTD are deduced. In CUDA model, CPU and GPU work in the heterogeneous system, GPU is in charge of the heavy calculation and CPU is responsible for the logic judgments and control. According to the arrangement of CUDA thread, three-dimensional calculation area is mapped by two-dimensional thread. Shared Memory, Texture Memory and reasonable way of memory alignment are used to optimize the program, in this way can the delay of memory access be reduced and computing speed be accelerated.Secondly, we simulate the responses of traditional electromagnetic logging while drilling tool, iso-spacing compensated tool and aniso-spacing compensated tool in heterogeneous formations using the high-speed simulation platform. We analyze how the heterogeneous formations influence the borehole errors and the responses of the two kinds of compensated tools. This work can provide a reference value to evaluate formation and interpret logging data.Thirdly, a system is designed to measure the permittivity of down-hole bilayer materials. The system uses open-ended coaxial wire as a probe. The probe and the measured materials are modeled as two parallel capacitances. The high-frequency signals produced by a sweep frequency signal generator propagate into the materials through the open-ended coaxial wire. The permittivity of down-hole bilayer materials can be calculated by measuring the reflection coefficient at the interface of open-ended coaxial wire and the materials. According to the structure of the probe, the system is calibrated by four kinds of saline to get higher accuracy.