The exploitation of deep oil and gas resources in China is gradually developing.However,the signal transmission of mud pulse measurement-while-drilling is limited by the nature of drilling fluid,and cannot be applied to drilling in air,foam and leaky formation.In addition,electromagnetic measurement-while-drilling(EM-MWD)cannot meet the needs of the exploitation of deep resources due to signal attenuation.Thus,it is urgent to put forward a new technical scheme to increase the application depth of EM-MWD.For cluster wells of deep resources,a technical scheme of crosswell transmit-receive of signal transmission is proposed.To reveal the signal transmission mechanism and advantages of the scheme,a numerical model of signal transmission considering cluster wells,layered formation,drilling fluid and invasion zone is established.The influence of receiving insulated gap position,signal frequency,drill pipe conductivity,drilling fluid conductivity,borehole diameter,invasion depth,invasion type on the transmission signal intensity of crosswell transmit-receive EM-MWD is analyzed.The transmission signal response characteristics of the bit when it passes through the target layer are analyzed.Results show that installing the receiving insulated gap on the horizontal section and close to the inclining section of the receiving casing helps to achieve greater transmission signal intensity.The transmission signal intensity increases with the decrease of the angle between the horizontal section of the receiving casing and the drill pipe.Some conditions such as the lower signal frequency,lower drilling fluid conductivity,higher drill pipe conductivity and high invasion type are conducive to increase the transmission signal intensity.The transmission signal intensity will change abruptly when the bit goes out of the coal seam.In addition,the transmission signal intensity of the crosswell transmit-receive scheme is compared with that of the traditional scheme under the same conditions.Results show that the crosswell transmit-receive scheme can significantly increase the transmission signal intensity,and has a larger applicable signal frequency.Thus,the crosswell transmit-receive scheme can increase the application depth and data transmission rate of EM-MWD.
electromagnetic measurement-while-drillingsignal transmission mechanismtransmission signal intensitycrosswell transmit-receivecluster wells
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