The Effect of Drilling Fluid on Coal’s Gas-Water Two-Phase Seepage

Abstract

In the process of coal bed methane (CBM) production, the output of CBM is mainly related to the relative permeability of gas and water in coal seams. However, during the drilling process, the invasion of drilling fluid into CBM reservoirs changes the wettability, which may cause the gas and water’s redistribution through the pores and cracks, further changing their two-phase seepage characteristics and influencing CBM production. Therefore, studying the effect of drilling fluid on coal’s gas-water two-phase seepage has practical implications. Using a steady-state method, the influence of changing wettability and reducing the solution’s interfacial tension on relative permeability is investigated by adding different surfactants. The increase in coal’s hydrophilicity exhibits an impact on its relative gas-water permeability. At the same water saturation level, the relative gas permeability decreases and the relative water permeability increases. The hydrophilicity of coal was enhanced after adding anionic surfactants, which reduced gas permeability. Cationic surfactants are difficult to adsorb to the surface of coal due to the fact that the interfacial tension of the water and coal surface is reduced when the coal seam water is added to the cationic surfactants. After adding cationic surfactants, the gas permeability increased in favor of CBM production. The findings of this study could help to better understand the influence of drilling fluid intrusion on coal’s gas-water two-phase seepage and provide technical guidance for selecting better surfactants during the preparation of drilling fluids and help to increase CBM production.

Study on Seepage of Coalbed Methane in Pore-fracture Double - porosity Medium

“…Continued injection of the fracturing fluid causes these fractures to propagate further into the reservoir. Once a network of large fractures is established, a proppant-laden slurry (usually containing quartz sand or ceramic beads) is injected to support and keep the fractures from closing completely [5] .…”

Construction and Evaluation of a Degradable Drilling Fluid for Underground Coalbed Methane Extraction Boreholes

“…In recent decades, CBM has received increased attention, and wellbore instability and reservoir damage have become the most challenging issues in CBM drilling. , The low strength, low matrix permeability, and development of pores and natural fractures in coal formations make them highly susceptible to damage during the drilling process. , Researchers have used experiments such as core analysis, strength testing, and permeability testing to reveal the characteristics and mechanisms of drilling fluid damage on the strength, permeability, and gas ad/desorption of coal seams. − Coal seam damage is a result of several factors, including particle and polymer plugging, matrix adsorption expansion, water sensitivity damage, and water locking damage. − Preventing drilling fluid loss is crucial in reducing damage during the drilling process, and reasonable particles added to the drilling fluid can control drilling fluid loss in fractured reservoirs. , Nanoparticles have emerged as a new additive with superior performance in drilling fluids, with small amounts able to improve rheological and filtration properties while maintaining excellent stability. , Fuzzy ball drilling fluids are used to control the wellbore instability in the drilling of CBM wells. These fluids bond with the formation and change the rock’s mechanical properties, thereby preventing wellbore collapse. , Polymer drilling fluids have also been applied in CBM drilling, and their performance and degradation mechanism have been studied. , Clean water remains the primary flushing medium used in bedding borehole CBM extraction due to its strong cooling capacity and convenience. , However, it is difficult for water to transport cuttings and maintain fluid pressure in the pressurized drilling method.…”