Development and Field Application of a Coalbed Methane Coring Tool with Pressure Maintenance, Thermal Insulation, and Shape Preservation Capabilities

In the process of lifting the coalbed methane (CBM) cores from the subsurface to ground, free gas escapes, adsorbed gas is partially desorbed and pore-permeability test data is distorted, seriously hampering the establishment of the CBM development plan. Therefore, a CBM coring tool with pressure maintenance, thermal insulation and shape preservation capabilities was developed. By designing an arc closed ball-valve, the failure in the pressure-maintenance seal was overcome by using a fully sealed ball-valve chamber that can withstand a pressure of 60 MPa. Using rubber tubes to hold cores and silica aeroge for thermal insulation, a composite coring inner barrel with thermal insulation function was designed, which allowed the coring tool to achieve the advantages of both pressure confinement and thermal insulation.The surface-set and impregnated composite diamond coring bit was optimized, thereby improving the coring bit footage. The CBM coring tool was applied to Well G-X20 for three times, obtaining a cumulative footage of 9.60 m, with a coring recovery rate of 94.48%, and a pressure maintenance rate up to 80%. The results showed that the proposed coring tool for CBM was very effective in pressure maintenance and gas preservation. Combined with sophisticated field construction technology, the coring tool can provide technical support for fine exploration and development of unconventional oil and gas resources such as coalbed methane and shale gas.