Application of Field Emission Scanning Electron Microscopy in Liquid CO2 Gas Fracturing Technology

Abstract

In the process of coal mining, gas disaster is an important problem that restricts the safe and efficient production of coal mine. Gas extraction is an effective way to control gas disaster, but the efficiency of gas extraction can not reach the expected effect due to the complicated geological conditions and low permeability of coal seam in China. Gas fracturing with Liquid CO₂ is a new and efficient gas treatment technology, but there are few theoretical and laboratory studies on the physical process of gas fracturing, lack of understanding on the micro-characteristics of coal sample destruction and the mechanism of increasing permeability and preventing outburst. This weak theory limits the further development and safe application of CO₂ gas phase fracturing technology. Faced with this research situation, the team designed and developed a coal-rock fracturing device using liquid CO₂ gas phase fracturing, and applied the coal samples from Pingmei No. 8 mine in Pingdingshan, Henan province, fourteen coal samples were tested under three high pressure conditions of 120 MPa, 150 MPa and 185 MPa. With the aid of field emission Scanning electron microscope experiment, the corresponding micro-morphology, fracture observation and analysis were completed, in this paper, the microscopic characteristics of coal and rock failure caused by CO₂ gas phase fracturing are systematically studied, and the main research results are as follows. A large number of “Erosion damage pits” and radial “Three wings” branching fissures were found on the surface of coal matrix by field emission scanning electron microscopy, this is the result of alternating stress wave produced by multiphase CO₂ jet impinging on coal and rock.