Research On Response Characteristics Of Electromagnetic Remote Detection Based On Half Coil

Remote detection while drilling is a key technology of geosteering.It is used to identify reservoir boundaries in directional wells,highly deviated wells,and horizontal wells to ensure that the drill bit is drilled along the best trajectory in the reservoir.In order to break the monopoly of foreign technology in this field,the national "Thirteenth Five-Year Plan" major project "Logging Interactive Fine Fusion Processing Platform" carried out research on technology for remote detection while drilling,and independently developed electromagnetic remote detection well instruments.Half-coil electromagnetic induction logging is a new method of electromagnetic remote detection well.This paper conducts in-depth research on this method.The research results provide a theoretical basis for the development,design and application analysis of semi-coil system electromagnetic remote detection well instruments.The main research content and results are divided into the following three partsThe first part studies the theory of semi-coil far detection boundary detection and constructs a three-dimensional horizontal well detection model.Starting from the theory of induction logging in homogeneous media,the basic principle of half-coil remote detection is studied,and the calculation formula of half-coil measurement voltage is deduced.Then a three-dimensional horizontal well edge exploration model was established in the COMSOL software,and the consistency of the numerical solution and the analytical solution of the lower half of the coil and the full coil of the uniform formation was compared to verify the rationality and accuracy of the model.The second part is the design of the parameters of the semi-coil remote detection instrument.First,study the influence of the rotation angle on the response of half-coil logging under different source distances,working frequencies,and instrument positions,and determine the orientation of the boundary through the positive and negative values of the signal and the change trend.Secondly,by studying the edge detection characteristics of the instrument under different source distances,combined with the engineering realization requirements of actual instrument design,the source distance range of the instrument is determined to be 1m?1.5m.Finally,by studying the influence of the working frequency on the half-coil logging response under different source distances and instrument positions,the edge detection distance of the instrument at different working frequencies and different source distances is calculated,taking into account the actual instrument's signal resolution ability,and finally determined The working frequency range of the instrument is 1k Hz?20k Hz.The third part studies the logging response characteristics of the electromagnetic remote detection instrument based on the half-coil in the three-layer formation.Mainly calculated and analyzed the well logging response law of wellbore,intrusion,surrounding rock,dip angle and other factors.In the wellbore impact study,it is mainly divided into two parts: the mud conductivity and the impact of the well diameter on the logging response.The larger the well diameter and mud conductivity,the greater the impact of the wellbore on the logging response.Secondly,the intrusive impact study is divided into two cases: wellbore formation and non-wellbore formation.In each case,the intrusion effects of low-resistance surrounding rocks and high-resistance surrounding rocks are studied separately,and different intrusive models,intrusive conductivity,and intrusive intrusions are summarized.Response characteristics at radius.In the study of surrounding rock influence,it is mainly divided into two parts: the conductivity contrast of surrounding rock and target layer and the influence of target layer thickness on logging response under the condition of no borehole and intrusion.The conductivity contrast is relatively large,and the target layer thickness When it is smaller,the surrounding rock has a greater influence on the logging response.In the study of the influence of the formation dip angle,numerical simulation calculations are mainly carried out for the formation dip angle of 0°to 90°,and the response characteristics of the instrument in the horizontal well are mainly studied.The greater the stratum dip,the more significant the boundary effect,the slower the signal attenuation,and the longer the edge detection distance of the instrument.Among them,the effect of identifying the interface and providing geosteering services in horizontal wells is the best.