Forward Modeling And Response Feature Extraction Of Pseudo-Random Electromagnetic Method For Inter-Well Detection

In the 21 st century,the energy demand is becoming more and more severe,and the exploration and development of oil and gas resources has become an important strategic resource affecting my country’s development.With the deepening of the exploration work,the oil and gas resources are decreasing day by day,and the exploration target has shifted from the surface or near the surface to the hidden oil and gas reservoirs deep underground.It is urgent to study the methods and theories related to the detection of inter-well reservoirs.Due to its low exploration efficiency,the traditional single-frequency electromagnetic method cannot meet the requirements of the future development of electromagnetic exploration systems.In view of this,this paper selects pseudo-random electromagnetic method as the basic theory of the subject,establishes the measurement system of "multiple receivers with one transmitter",and puts both the transmitter and receiver in the well,and adopts the "well-well" working method.For the selection of excitation field source,through spectrum analysis of square wave,triangular wave and pseudo-random sequence,m-sequence with better correlation performance and richer spectrum is selected as excitation signal,and the correlation properties of m-sequence are simulated and analyzed by MATLAB software.Based on the excitation field source m-sequence determined in this paper,first,optimize the parameters of the m-sequence to determine the m-sequence order and symbol width required in this paper.Secondly,the correlation identification technology based on m-sequence is analyzed,the power frequency noise and Gaussian noise of different parameters are superimposed on the output response of the system,the input signal and the output signal are convolved to obtain the ground impulse response,and the impulse response under noise interference is compared.It is consistent with the theoretical impulse response,and the strong anti-interference performance of the pseudo-random sequence is verified.Then,the COMSOL Multiphysics finite element simulation software is used to establish the interwell exploration model,and the response characteristics of the interwell reservoir are studied through numerical calculation.Response variation characteristics of a typical stratigraphic model.Finally,the apparent resistivity of the model was extracted by the method of defining the apparent resistivity at the peak time of the impulse response,and the resistivity distribution map was drawn.Both are close to the resistivity set by the model,but for the middle layer,the apparent resistivity curve changes greatly with the change of the measuring points,and there is apparent resistivity distortion in the transition field stage.The above results show that the pseudo-random electromagnetic method can effectively detect the reservoir between wells,suppress the strong electromagnetic interference in the work area,improve the accuracy and efficiency of the system exploration,and make up for the shortcomings of the traditional single-frequency electromagnetic method.Broad application prospects.