Numerical Simulation Of Azimuthal Electromagnetic LWD Response In Anisotropic Formation

With the deepening exploration and development of complicated reservoirs, the wideapplication of complicated technological wells such as high deviated well and horizontal well,and the rapid development of azimuthal LWD technology abroad, our country is in urgentneed for research of azimuthal LWD technology, especially in anisotropic formation, toprovide help for real-tome geosteering and reservoir evaluation. This thesis simulates theresponses of electromagnetic LWD in one dimensional anisotropic formation and threedimensional anisotropic formation considering complex borehole conditions, also analyzesthe response characteristics and the directionality of the azimuthal electromagnetic response.Firstly, based on one-dimension layered anisotropic formation model, a free orientedmagnetic dipole is divided into horizontal and vertical sub-sources which are solvedrespectively on the basis of Hertz potential function. Gauss integral and Hankel transformintegral are adopted in low angle and high angle, respectively, to compute the generalizedintegral with Bessel function，thereby realizing simulation of electromagnetic loggingresponse while drilling in anisotropic dipping formation.In view of the actual complex logging environment during drilling, a reasonableformation model is constructed. Considering the outline of the tool and the shape of theborehole, the finite difference time-domain in cylindrical coordinates is adopted to model theresponse of electromagnetic LWD under complicated formation conditions. The anisotropicresistivity of the dipping formation in Cartesian coordinate is transformed into cylindricalcoordinates based on coordinate transformation. The non-uniform meshing and localrefinement technique is utilized to achieve fine discretization of borehole, drill collar and coil.The amplification strategy of dielectric constant is implemented to overcome the constraint ofsmall iteration step, and speed up the simulation time in low frequency. Finally, three dimensional simulation of electromagnetic LWD response in anisotropic formationconditions is realized.Based on the numerical simulation technique of electromagnetic LWD tool, the responsecharacteristics under different medium conditions are further analyzed, and the effect of thefactors including layer thickness, shoulder bed resistivity, borehole deviation angle, mudfiltrate resistivity and anisotropic ratio are analyzed. Through the comparison with traditionalelectromagnetic LWD response, the directionality of the azimuthal electromagnetic LWD toolis studied.In order to improve the three dimensional simulation efficiency of electromagneticLWD tool, the alternating direction implicit (ADI)-FDTD algorithmis adopted to overcomethe disadvantage of the traditional FDTD where the time step is constraint by space step. Inaddition, the simulation results of the (ADI)-FDTD are verified by comparing with thesimulation results of FDTD.