Coalbed Methane Extraction Using the Self-Oscillating Water Jet Slotting Method

Abstract

Self-oscillating Water Jet (SOWJ) slotting in Coalbed Methane (CBM) is proposed to overcome low gas permeability, high gas desorption, and difficult mining in deep coal beds. SOWJ slotting excitation expands the fracture network, increases coal permeability, and strengthens gas desorption. The coupled effect of these three processes increases CBM extraction. Analysis of the characteristics of SOWJ, the effect of coal slotting, and changes in coal permeability shows that (1) SOWJ impacts on coal-rock mass, forming the erosion-peeling zone, fragmentation zone, and distal conical crack zone in the rock. The jet impact and cavitation sonic vibrating effect generate coal vibration; (2) The slots and fractures formed by the jets release the coal's elastic energy, depressurising the coal and changing the stress field. The stress redistribution further expands the fractures and the subsequent perforative fracture network; (3) Slot formation increases the coal's exposed area, changing the gas flow pattern. The decrease of effective stress increases coal permeability; the vibration characteristics of the jets and the cavitation sonic vibrating effect enhance gas desorption, which increases gas emission; (4) Extraction field tests showed that single-hole extraction of CBM from conventional boreholes was 1606 m 3 and the average standard scalar volume was 0.01 m 3 /min, compared to 7081 m 3 and 0.042 m 3 /min for SOWJ slotting boreholes, 4.41 and 4.2 times, respectively, of the conventional boreholes. Thus, SOWJ slotting can significantly improve CBM mining.

Experimental study of shock pressure and erosion characteristics of high‐pressure gas–liquid two‐phase jet: Exploration for improving coalbed methane extraction efficiency

“…Erosion characteristic is a vital factor in determining whether high‐pressure jet can be applied to coalbed methane extraction engineering 26,27 . According to the above experimental studies, high‐pressure gas–liquid two‐phase jet not only has good erosion characteristics but also has good water‐saving performance.…”

Effects of Organ-Pipe Chamber Geometry on the Frequency and Erosion Characteristics of the Self-Excited Cavitating Waterjet

“…Waterjet technology as a non-conventional processing method is widely used in mining [1,2], cleaning [3], rock breaking [4] and cutting [5]. Nevertheless, the high energy consumption and low efficiency of the traditional waterjet limited its application.…”

Effects of Stress and Temperature on the Permeability of Gas-Saturated Wet Coal

“…Coalbed methane (CBM) is a type of resource rich in the underground coal mines, but CBM reservoirs in China are generally characterized by low permeability, seriously hampering efficient extraction . In the past decades, in situ physical modification of coal seam based on multiple-field coupling theory has been widely accepted to enhance the permeability of CBM reservoirs. − Common modification methods include hydraulic fracturing, presplitting blasting, , water jet slotting method, , etc., for the purpose of enhancing fracture development and breakthrough. In addition, pressure gradient, which is a driving force of gas, can be increased by borehole spacing optimization or gas displacement. , Heat injection is considered an effective method for enhancing extraction recovery in deep coal seams; in other words, superheated steam at a temperature below 300 ° C is injected into the coal seam to ensure dissipation of moisture and free gas without altering the molecular structure of the coal .…”