Inorganic mineral plugging removal characteristics by acid etching and foam drainage in low-producing coalbed methane well

The blocking of inorganic minerals in coalbed methane development will cause the low production of coalbed methane well, which will seriously restrict the continuous and stable production of coalbed methane well. Acid dissolution is an effective means to clean up inorganic minerals. Based on the experiment of multi-component acid dissolution of inorganic minerals, combined with the wetting and carrying effect of foam drainage on inorganic minerals, the inorganic mineral plugging removal characteristics by acid etching and foam drainage in low-production coalbed methane wells were studied. The results indicate that hydrofluoric acid has better dissolution effect on inorganic minerals with silicate rock as the main component than hydrochloric acid and acetic acid. The dissolution rate of inorganic minerals does not increase significantly when the acid concentration exceeds 12%. The multi-component acid has higher dissolution rate of minerals than single component acid, generally reaching 40%−80%. When the concentration of foaming agent is less than 0.6%, the surface tension of the solution and the contact angle between the solution and inorganic minerals gradually decrease with the increase of the concentration of foaming agent. Under the action of foam discharge, the foam becomes denser, the foaming ability gradually increases, the foam half-life gradually prolongates, and the foam powder carrying content is higher with the increase of the concentration of foaming agent. When the concentration of foaming agent exceeds 0.6%, the surface tension tends to be disturbed and the foam stability becomes worse. The large bubble diameter of BS-12 foam system has more serious influence on the foam half-life than that of AEO foam system. The surface tension of APG compound acid is minimal with the stable and dense foam, and it has the best wettability to inorganic minerals. APG as non-ionic surfactant with strong acid resistance is selected as the foaming agent, compound with acid is the preferred solution to etch inorganic minerals. Foam drainage promotes the dissolution rate of inorganic minerals to increase slightly, and the acid concentration inhibited the stability and foam half-life, with the smaller particle size of inorganic minerals discharged from the foam and the narrower particle size range.