Study On Electromagnetic Wave Propagation Resistivity Logging While Drilling Inversion Methods In Deviated Well

With the wide application of deviated wells in oilfield production,the importance of electromagnetic wave resistivity logging while drilling(LWD)with functions like data aquisition,interpretation and geosteering has become increasingly prominent.But the recorded orginal logging responses cannot fully represent the true state of the formation for that the electromagnetic wave resistivity measurement is easily affected by environment situations.If the necessary environment correction is not performed on the original data,the subsequent geological interpretation evaluation results and actual conditions assessment may be inaccurate.Therefore,we use data inversion technique to make the obtained parameters closer to the real situation of the formation.Onedimensional inversion has become the mainstream algorithm for current geosteering realtime inversion because of its precise and efficient characteristics.Therefore,we need to select one-dimensional inversion method with the stablility and accuracy to do inversion works.It is an urgent need to learn the prinple of diverse inversion methods and make adaption to them for actual well-logging problem.In this paper,we firstly build one-dimention formation model without considering the borehole effect and mud invasion,and study on the logging responses characteristics with different surrounding rock thickness and resistivity contrast,dip angle and resistivity anisotropy,which are based on exsited well-logging forward simulation.According to the demand of well-logging application,we introduce the prinple and algorithm of inversion methods like Gauss Newton method and conjugate gradient method.Then,nonlinear conjugate gradient inversion algorithm is proposed,based on the preassumed stratigraphic interface,to conduct fast one-dimensional electromagnetic wave resistivity measurement inversion in different formation models.Finally,we introduce the multipoint inversion technique for the thin target layer due to its sensitivity to surrounding rock,and apply it to complex formation to test its effectiveness.This inversion technique gives a more realistic reflection of the true formation situation,providing theoretical guidance and technical support for geosteering and real-time interpretation of LWD tools.