Study of hydraulic fracturing for gas drainage in a coalmine in Iran

Hydraulic fracturing (HF) is one of the methods to make coalmining operation safer and more economic. One of the hazards in underground coal mining operation is the sudden coal gas emission leading to coal explosion. To reduce the risk of gas emissions to ensure safer mining, it is necessary to pre-drain coal seams and surrounding layers. The most important parameters affecting the HF process of a coal seam are: dip, thickness, seam uniformity, roof and floor conditions, reserve of coal seam and coal strength. This paper presents the development and application of a fuzzy model to predict the efficiency of hydraulic fracturing, considering the above factors. In the developed model, the efficiency of hydraulic fracturing of coal seams is calculated as a dimensionless numerical index within the range 0-100. The suggested numerical scale categorizes the efficiency of HF of seams to very low, low, medium, high and very high, each one being specified by a numerical range as a subset of the above range (0-100). The model is used to study the potential of hydraulic fracturing in a coal bed in PARVADEH 4 coalmine in Iran, which will be undergoing stress variation due to future mining activities. The mine consists of 5 seams C1, C2, B1, B2 and D with different characteristics. The results show that the seams C1 and B2 with predicted 94.6% and 81.2% efficiency, have high potential for gas drainage, and considering dip, uniformity and thickness it is suitable to use HF technique. The B1 seam with 31.8 percent efficiency has low potential for gas drainage by HF. HF would not be appropriate for both of C2 and D seams with 7.5 percent efficiency.