Geochemical characteristics of produced water from coalbed methane wells and its influence on productivity in Laochang Coalfield, China

The water produced from the coalbed methane (CBM) wells contains abundant geochemical information, which is of great significance in evaluating the productivity of these wells. Based on the data of water produced from five CBM wells, geochemical characteristics of the produced water and its influence on the productivity of the wells are analyzed in Laochang Block. The results show that with the increase in the produced water of the five wells, delta D and delta O-18 show a downward trend in general, reflecting that the influence of coal seams and surrounding rock on the produced water is weak, while the water-rock interaction of the Y-3 and Y-5 wells is more stable than that of the Y-1, Y-2, and Y-4 wells. Combining the water production characteristics of the Y-3 and Y-5 wells with better drainage and recovery effects, it is proposed that 0 <= sigma(M) < 0.3 and 0 <= sigma(Y) < 600 or 0.7 < sigma(M) < 0.8 and 1,200 < sigma(Y) < 1,300, and the fluctuation ranges of Ca2+, Mg2+, HCO3- and SO42- can provide a basis for quantitative characterization and evaluation of CBM well production.