| Oil plays an irreplaceable role in the process of a country’s development.A large number of oil reserves exist in the underground reservoir in the form of residual oil.Therefore,in order to improve the oil recovery,it is necessary to improve the recovery rate of residual oil,and the area near the derrick is a main area of residual oil.The exploration of abnormal bodies near the derrick can not only find residual oil,but also detect various nearby resources.Therefore,it is of great significance to explore the abnormal body near the derrick.Based on this,this paper carries out basic research combined with pseudo-random signal and well ground electromagnetic method,so as to improve the efficiency of exploration.Firstly,the general scheme of well ground pseudo-random electromagnetic exploration is given,and the principle of pseudo-random signal correlation identification technology based on Wiener Hoff equation is analyzed;Secondly,the characteristics of several common pseudo-random sequences are analyzed,and m sequence is selected as the system input signal,and the generation method,properties and parameter selection of m sequence are analyzed and studied;According to the identification effect and anti noise analysis of the signal,the m-sequence with order 14,symbol width 1 / 10000 s and cycle number 3 is selected as the transmission signal of the calculation model in this paper.Thirdly,based on the line source theory,the well ground detection model is established by using COMSOL multiphysics software,and the uniform and non-uniform well ground detection models are given respectively.The effects of conductivity change,buried depth change and thickness change of abnormal body on the potential distribution of non-uniform well ground detection model are studied.The research results show that when the abnormal body is a low resistivity body,it is easier to be discovered by exploration;The decrease of the burial depth of the abnormal body and the increase of the thickness of the abnormal body can improve the probability of exploration and discovery of the abnormal body.Based on the above conclusion,the author sets a series of specific conditions,in which the resistivity,buried depth and thickness of the abnormal body are studied respectively.Finally,the ground impulse response of the uniform well ground model and the non-uniform well ground model are obtained and compared.It is concluded that the peak value of the ground impulse response of the non-uniform model is lower than that of the uniform model,and in the later stage of the ground impulse,the pulse fluctuation of the non-uniform model is slightly larger than that of the uniform model.The above conclusions lay a good foundation for well ground pseudo-random electromagnetic exploration and provide a theoretical basis for the design of relevant instruments. |
