Experimental study on goaf detection by small loop transient electromagnetic method in complex terrain

Due to the large terrain fluctuation and drop in Qianshuta well field, the layout of the ground large loop transient electromagnetic method detection device is limited. In order to find out the distribution range of goaf under the second Shanjing line of oil and gas pipeline in this area, numerical simulation and field test of small loop transient electromagnetic method were carried out to analyze the feasibility of ground detection, and optimized parameters were applied to the field. The results show that the numerical simulation confirms that the 3 m×3 m small loop transient electromagnetic method can effectively detect the goaf with a depth of more than 200 m and a mining height of more than 1 m, and has a more obvious effect on the water-filled goaf with low resistance; the field test adopts the small loop transient electromagnetic method with optimized parameters such as the length of the transmitting wire frame 3 m×3 m, the number of stacking times of 15, the transmitting frequency of 16 Hz, and more than 8 A transmitting current, which can achieve the purpose of effective detection and verify the correctness of the numerical simulation; a total of 5 abnormal areas were delineated and explained in the No.3 coal seam, which were inferred to be gobs or burned rock voids. The reliability of the small loop transient electromagnetic detection method is fully verified.