The Study On Numerical Simulation And Geosteering Application Of Electromagnetic Logging While Drilling Tools

Logging-while-drilling (LWD) technology has become a key method for oil field toget the maximum production, and it is worldwide used in the oil fields at home and abroad.Electromagnetic LWD tool is one of the core logging tools which is widely used information evaluation and geosteering. However, very little researches of systematic theoryof such instrument have been carried on. Thus in this thesis, based on forward andinversion numerical simulation, the geosteering applications of electromagnetic tool werestudied detailed.The forward numerical simulation was based on the dyadic Green’s functionproduced by magnetic dipole. The dyadic Green’s function of anisotropy formation withany number of layers was deduced using matrix recursive principle. This method is withhigh calculation speed and high accuracy, and it is suitable for the analysis of the responseof electromagnetic LWD tool with the coils placed in any direction. In the inversionnumerical simulation, adaptive damping Gauss Newton and distort Born iterative method,a new regularization method and inequality constraint imposed method were developed.In this thesis, the response rules and application in geosteering in highly deviatedwells of the electromagnetic LWD tool with conventional and tilted coils were simulatedby using the developed forward and inverse methods. The results showed that in highlydeviated wells, when the conventional electromagnetic LWD tool is near the formationboundary, there is a polarization angle phenomenon of the response which can indicatesexisting of the boundary, and the response is affected by the anisotropy and increases withthe increasing of relative angle. The thin alternating layers showing macroscopicanisotropy. The new generation tool with single transmitter and single receiver with tiltedcoils uses a lower operating frequency and the spacing is longer. When it is near the upperand lower formation boundaries, the response shows opposite signal characteristicsrespectively, and that can effectively help identifying the direction of the boundary. A newdefinition of directional signal was developed in the tool with two transmitters and tworeceivers with tilted coils, so that the tool had the capabilities of formation evaluation aswell as geosteering. The numerical simulation results showed that the resistivitymeasurement is more sensitive to anisotropy than conventional tools’ measrement, while the geosteering direction measurement is not affected, and the boundary responsecharacteristics of two tansmitters two receivers system is same with the single tansmittersingle receiver system. Geosteering vector angle theory was studied using numericalsimulation with space superposition algorithm. The results showed that the vector angle isalways pointing to the direction of greater conductivity. Combined with directional signalsof tilted coils, it can be determined that from which direction the tool is getting close tothe boundary. This theory can apply in the case in which the formation boundary is notparallel.Several formation models were built and the inversion numerical simulations ofelectromagnetic LWD tool were done using these models. A multi-initial method wasintroduced. The results showed that the method can resolve the problems of iterationdivergence and multiple solutions caused by the inappropriate initial value. The influencerule of relative dip and formation resistivity parameter errors were summarized and thefeasibility of the inversion of three layers model was verified. In the models of several thinlayers, the conventional electromagnetic resistivity curve is more effective than the deepdirectional curve in boundary identify, while in the models of thick layers, the deepdirectional curve is more effective.