Gas drainage efficiency: an input–output model for evaluating gas drainage projects

Gas drainage not only ensures safety in coal mine but also produces clean energy and reduces emission of greenhouse gases. However, a good method to evaluate the efficiency of gas drainage is still absent. In this study, we firstly propose a definition of gas drainage efficiency which is defined as the ratio of the real output–input efficiency to the ideal output–input efficiency. The definition combines both engineering parameters such as radius, length of borehole and economical parameters such as drilling cost to develop a comprehensive index for the assessment of the engineering–economical efficiency. Then, three important factors to determine gas drainage efficiency including the difficulty level, the input and output, namely investment and production, and the attenuation characteristic of gas drainage are discussed. Based on the relative standards, the index can reasonably evaluate gas drainage projects with different difficulty levels, thereby avoiding dependence on an absolute standard for the evaluation of overall difficulty levels. The indicator can also take both input and output into consideration and reflect the reduction of gas drainage flow with time. Besides, we investigate the relationship between gas drainage efficiency and several engineering parameters, including borehole radius, borehole length and the quality of borehole sealing. The results show the possibility of optimizing engineering parameters to maximize gas drainage efficiency. Finally, the evaluation method is proven efficient by performing case studies. Copyright Springer Science+Business Media Dordrecht 2014