Study on Eliminating the Water Blocking Effect in Coal Seams Using Gas-Wetting Reversal Technology.

Abstract

To eliminate or alleviate the water blocking effect (WBE) encountered while hydraulic fracturing of coal seams, the wettability of the coal body was changed, using gas-wetting reversal technology, thus improving gas drainage. After initial measurements of contact angles, surface tension, surface free energies, erosion resistance, self-absorption capacities, and self-absorption rates of coal samples, a hydrophobic and low-surface-tension gas surfactant was selected. After comparing the results of four candidate surfactants, two surfactants were selected, FC117 and FC134, which were both hydrophobic and exhibited low surface tension, to achieve the desired effect. Testing showed that with increased surfactant concentration contact angles increased and surface tension gradually decreased. After surfactant treatment, the coal surface energy decreased, self-absorption capacities and rates of coal samples decreased significantly, and their erosion resistance was good. After determination and verification of several evaluation parameters, the results showed that the two surfactants performed well and achieved the expected effect. By optimizing and evaluating gas-wetting reversal agents, our work has provided a theoretical basis and scientific guidelines for eliminating the WBE from coal seams, thereby facilitating gas drainage.