Research On The Design Of Coil System For Azimuthal Propagation Resistivity LWD Instrument

With the exploration and development of horizontal well and high angle wells,oilfield exploration and development cost is high,azimuthal propagation resistivity LWD appears.Azimuthal propagation resistivity LWD instrument can implement multi-depth formation resistivity test,at the same time it can implement azimuthal resistivity of the formation.The logging instrument also has deep exploration and high resolution test function,which can be accurately implement the function of geo-steering and formation evaluation.The logging instrument can reduce the exploration and development cost of the oilfield.Azimuthal propagation resistivity LWD instrument implement the function of different detection is the key to the design of the coil system.This thesis deeply studies the design method of the logging instrument's coil system,and complete the following innovative work.According to the logging instrument's different detection functions,a coil system parameter design method based on the Green function method was proposed in this thesis.First of all,the correspondence between the coil system's parameters and different detection of the logging instrument was deeply studied.The mathematical model between parameters of tilted coil system and the measured response based on Green function was established.By analyzing the influence of conventional tilted coil parameters and multi-parameter variation on the measurement response,the parameters of the tilted coil system was designed based on different detection and the various constraints.This method took full account of the influence of tilted coil system's multi-parameters,and designed the parameters of the tilted coil system with different detection for the logging instrument.Aiming at the active logging instrument's weak sensitivity of the azimuthal resistivity detection and shallow depth of the layer interface detection caused by receiving coil's effective area of the magnetic flux,the conventional tilted receiving coil was improved.The design method of the receiving coil based on the segmented composite structure was proposed.Firstly,the advantages and disadvantages of the active logging instrument's coil system were compared and analyzed.The shortcomings of the conventional inclined receiving coil in the actual logging process are clarified,and the design method of the coil system based on the segmented composite structure is proposed.Secondly,the mathematical model of the parameters of the segmented coil system and its measurement response is established by using the coil system parameter design method based on the Green function method.The design of the segmented coil system parameters under different functional requirements is completed.Aiming at the verification function of the logging instrument based on the tilted structure and the logging instrument based on the segmented composite structure,an analytical verification method for the detection function of the logging instrument was presented.Firstly,the induced electromagnetic wave signal at the receiving coil is simulated by the finite element forward simulation method.Secondly,the amplitude ratio and phase difference of the induced electromagnetic wave signal at the adjacent receiving coil are proposed by using the signal amplitude ratio and phase difference calculation method based on orthogonal sampling.By comparing the measurement response of different coil systems,the detection function of different logging instruments was analyzed and verified.