Simulation And Applied Basic Research Of Directional Electromagnetic LWD Tool In Complex Media

Electromagnetic Logging-While-Drilling Tools, which can provide Real-TimeGeosteering and Formation Evaluation, is the key to reservoir characterization and wellplacement in complex scenarios. In order to improve the drilling success rate in High Angleand Horizontal Wells (HA/HZ), implement real-time geosteering and formation evaluation, aswell as provide useful guidance for the development of new Electromagnetic LWDinstruments, in this paper, To the Directional Electromagnetic LWD tool responses weresimulated and analyzed, and the data processing of and inversion algorithm of Distance toBoundary (DTB) and anisotropy resistivity were researched and established.In the second chapter, based on the logging environment of HA/HZ and the measurementprinciples of Directional Electromagnetic LWD Tool, one-dimension layered formation modelis establish, then, the transmitter coil is treated as a magnetic dipole, which is then dividedinto two components of vertical one and horizontal one. Through deduction of the analyticalsolution of the fields excited by each component, the field distribution of the originalmagnetic dipole with arbitrary direction can be obtained. By utilizing Gauss numericalintegration algorithm combined with Fast Henkel Transform (FHT), the integration includingBessel function in the analytical solution is accurately calculated. Thereby, fast simulation ofthe response of Directional Electromagnetic LWD Tool in layered formation is implemented.In the third chapter, first the finite difference time domain (FDTD) method in cylindricalcoordinates is adopted to model the response of Directional Electromagnetic LWD Tool undercomplicated formation conditions. The non-uniform meshing and local refinement techniqueis used to achieve fine discretization of borehole, drill collar and coil. The amplificationstrategy of dielectric constant is implemented to overcome the constraint of small iterationstep, and speed up the simulation time in low frequency. The anisotropic resistivity of thedipping formation in Cartesian coordinate is transformed into cylindrical coordinates based on coordinate transformation. The response of Directional Electromagnetic LWD Tool in dippinganisotropic formations is simulated and analyzed by using a finite-difference time-domain(FDTD) scheme. The numerical simulation results show that: the simulation time inanisotropy formation can be reduced by80%using amplification strategy, and the boreholecorrection is needed when the resistivity of drilling mud lower than0.1Ωm and Resistivitycontrast greater than100.In the fourth chapter, the Alternative Direction Implicit Finite-Difference Time-Domain(ADI-FDTD) method is introduced to the simulation of Directional Electromagnetic LWDTool responses. Two different schemes (Alternative Directional Implicit Method: ADI-FDTDand Split Step Method: SS-FDTD) are adopted and corresponding calculation accuracy andconvergence rate are compared. The numerical experiments show that: both the ADI-FDTDand SS-FDTD methods are able to overcome the time step size limit of FDTD, and the timestep can be magnified10times, but the calculation accuracy will not be affected.In the fifth chapter, based on numerical simulation method, the response characteristicsand corresponding sensitivity of Directional Electromagnetic LWD Tool under differentinfluential factor conditions are further analyzed. The simulation results of the tool underfactors such as layer thickness, borehole deviation angle, resistivity difference show that:compared with conventional LWD tools, The Directional Electromagnetic LWD Tools whichhas titled or orthogonal coils can provide more precise information about the relative positionof logging tool and the boundary; The amplitude attenuation of the DirectionalElectromagnetic LWD tool responses (phase shift, amplitude ratio or voltage) show goodlinear relationship in logarithmic coordinate; It is useful to determine the orientation, angle ofthe boundary from Directional signal imagine.In the sixth chapter, the methods for determining the borehole size, tool position, andrelative angle of tool and boundary are summarized, the correction charts of borehole anddielectric constant are calculated. The equivalent surrounding formation theory is adopted toachieve the inversion of formation resistivity. And the inversion algorithms of DTBestablished. The inversion results of Theoretical and field data show that: The environmentalcorrection is needed before further processing of LWD data. It is important to combine theLWD data with the geological and seismic data to inverse DTB considering the uncertainty of relative position determined by conversional LWD tool. However, the inversion method basedon the Directional Electromagnetic LWD data can overcome the non-uniqueness of inversion,and calculate the DTB precisely.In the seventh chapter, first, the causes of resistivity anisotropy were summarized and theElectromagnetic LWD logging responses in anisotropy dipping formation were analyzed.Furthermore, the inversion algorithm and chapter to calculate anisotropy resistivity wereestablished. The inversion results of theoretical and field data show that: With higherdeviation angle, frequency, lower horizontal resistivity, the electromagnetic response is moreaffected by formation anisotropy and the phase shift resistivity is more sensitive than theattenuation resistivity. Both the chapter and inversion method which can process the LWDdata point-by-point or layer-by-layer can get the anisotropy resistivity and they agree wellwith each other. However, when the resistivity radio is very large, the inversion results basedon the chapter will distort from the true resistivity of the formation.