Identification of plugging types and their formation mechanism based on production curves of coalbed methane wells

Abstract

Taking the production curves of coalbed methane (CBM) wells in Shizhuang south block in south-central Qinshui Basin (Shanxi Province, China) as a research subject, evaluation indices for the identification of plugging types of pulverized coal were constructed according to changes in daily water production and daily gas production. Four plugging types were classified based on the identification indices’ critical values. The results show when the proportion of soft coal in coal seam segments is not greater than 30%, mid-remote wave-shaped plugging is likely to occur. If the proportion of soft coal in coal seam segments is in the range of 30–50% and the daily water production or daily gas production is large, near-wellbore wave-shaped plugging occurs readily. Under the same proportion of soft coal, mid-remote complete plugging is liable to develop if the daily rates of water and gas production are low. Once soft coal accounts for a proportion equal to and greater than 50% in coal seam segments, near-wellbore regions are likely to be completely plugged. The research provides a method and reference for identifying the types of CBM well de-plugging and formulating de-plugging measures.