Experimental investigation on the effect of organic solvents on gas development of coalbed methane reservoir

CBM reservoirs are extremely vulnerable to damage due to their complex pore structure. So, changing pore structures in CBM reservoirs is of vital importance for reducing reservoirs damage. Organic solvents have been considered as additives into fracturing fluids to enhance production because they can enhance the pore connectivity and loosening macromolecular network structure. It is thus of great interests to investigate how organic solvents (ethanol and ethylene glycol ether) change micropore structures and fluid distribution. In this study, samples were selected from different wells completed in No. 3 coal seam, Zhaozhuang minefield. Low-pressure nitrogen adsorption (LP-N(2)GA) experiments were conducted on coal samples to evaluate the changes in pore-structure parameters including specific surface area (SSA), pore diameter, and pore volume. NMR experiments were conducted on coal samples to evaluate the changes in fluid distribution. Analyzing the LP-N(2)GA results suggests ethylene glycol ether and ethanol can effectively increase SSA, pore diameter, and opening degree of pores in coal samples. Comparative analysis of NMR results indicates that ethylene glycol ether consistently reduces the irreducible water saturation (S-wir) in samples. The average value of S-wir of raw samples is 0.8670 and the average value of S-wir of samples treated with ethylene glycol ether value is 0.7644. Considering the porestructure alterations, this study demonstrates that ethylene glycol ether is more preferable for enhancing recovery from CBM reservoirs compared with ethanol.

Automated summary

This study investigates the effects of organic solvents on the pore structure and fluid distribution in CBM reservoirs, finding that ethylene glycol ether and ethanol can effectively enhance pore structure parameters in coal samples, with ethylene glycol ether consistently reducing irreducible water saturation in samples. Considering the alterations in pore structure, ethylene glycol ether is shown to be more preferable for enhancing recovery from CBM reservoirs compared to ethanol.