Key factors in hole-sealing and pressure-relief failure of hydraulic fracturing straddle packer in coal mine

Abstract

Hydraulic fracturing technology is widely used in coal mines, and straddle packers are a key component of this technology. However, during the application of a straddle packer, potential problems occur, including hole-sealing failure and shooting rod events at the pressure-relief stage, which may result in serious harm to on-site personnel. Therefore, we here investigated the application of straddle packers in five coal mines. The failure type, rock layer in which failure occurred, and frequency of use of straddle packers were analyzed. The most common failure type was packer capsule rupture, and this mostly occurred in sandstone and mudstone strata. The frequency of use was directly related to the rock stratum structure, while hole-sealing failure occurred most easily near to rock stratum interfaces. Analysis of the mechanical behavior of straddle packer hole-sealing failure showed that soft rock strata and capsule rupture were the key factors leading to such failures. Hard and stable rock formations, appropriate expansion of the diameter of boreholes, and strict manufacturing quality control can play important roles in preventing hole-sealing failures of straddle packers. Residual high-pressure water in the packer section or upper part of the straddle packer was the key factor causing pressure-relief failure and shooting rod events; to prevent these issues, high-pressure water should be fully released, anti-channeling chains should be used, and existing straddle packer technology should be optimized.