Abstract: To use horizontal wells,infill wells and cluster wells to exploit low-permeability oilfields,shale gas reservoirs and other low-quality hydrocarbon resources,it is necessary to eliminate the possibility of collisions with adjacent wells.Accordingly,while-drilling electromagnetic anti-collision tools have been developed to measure distances from adjacent wells accurately.In addition to perform researches related to algorithms for distance measuring and direction guiding,prototypes of the while-drilling electromagnetic anti-collision tools were designed and manufactured.Furthermore,simulation tests were conducted on the ground to analyze impacts of relative positions of the sensor and casing on accuracies in measuring of distances and azimuth of adjacent wells.Simulation test results showed the tool could accurately identify distances and azimuths of adjacent wells in cases with sensor and casing placed in parallel at distances of 0.50-3.00 m due to low strengths of magnetic fields.In cases with distances over 3.00 m,calculation results displayed significant deviations.Care should be taken during field applications to consider the impacts of casing joints on measurement results.In cases with included angles between the sensor and the casing are less than 50°,the calculation results of the tool were very accurate.In cases with included angles over 50°,anti-collision tools of other types should be deployed instead.Relevant research results validated the accuracy of the principle of the while-drilling electromagnetic anti-collision tool and provided reliable theoretical supports for the development of this electromagnetic detection tool.