Abstract: China is rich in deep and ultra-deep natural gas resources. The cumulative proven geological reserves of natural gas are nearly 5×10¹² m³, and the cumulative natural gas production exceeds 5 000 ×10⁸ m³. It is an important strategic field for ensuring national energy security. However, deep and ultra-deep gas reservoirs are all water-bearing gas reservoirs and are generally developed using sparse well patterns. Under the condition of sparse well pattern development, it is difficult to accurately depict the leading edge of water invasion, which has become a key factor restricting the efficient development of deep/ultra-deep water-bearing gas reservoirs. This study leveraged the advantages of the wide field electromagnetic method that could distinguish gas zones, gas-water transition zones, and water zones through differences in inversion resistivity. Taking well group 1 of the Longwangmiao Formation gas reservoir, Moxi area, Sichuan Basin as the research object, a three-dimensional wide field electromagnetic detection of 2 km² was conducted. The geoelectric characteristics from 5 000 m underground were obtained, a set of fluid identification methods integrating vibration and electricity was formed, and a geoelectric model was constructed. The wide field electromagnetic method was used for the first time to identify the leading edge of water invasion in deep edge-water gas reservoirs. The results showed that: (1) based on the linear regression relationship between well-logging resistivity and the wide field inversion resistivity, it was determined that the wide field electromagnetic inversion resistivity in the water zones of well group 1 was less than 227 Ω·m, the wide field electromagnetic inversion resistivity in the gas-water transition zones ranged from 227 Ω·m to 383 Ω·m, and the wide field electromagnetic inversion resistivity in the pure gas zones was greater than 383 Ω·m. (2) The edge water advanced relatively uniformly from well 1 into the interior of the gas reservoir without obvious water invasion channels. The leading edge of the water invasion showed uneven water invasion characteristics, with an overall water invasion rate of approximately 50 m/a. (3) The well group should adopt a water control strategy combining drainage and control. The daily drainage capacity of well 1 was 300 to 400 m³/d, and the daily gas production capacity of the internal wells should be reduced from the current 200×10⁴ m³/d to below 150×10⁴ m³/d. This achievement has broad application prospects in the description of gas-water distribution in deep/ultra-deep gas reservoirs, the characterization of the leading edge of water invasion, and precise water control.

Key words: wide field electromagnetic method, deep edge-water gas reservoir, resistivity, water invasion front, water control strategy