Experiment Study On Sensibility Of Coalbed Permeability For Eastern Ordos Basin

Coalbed methane(CBM)is a kind of important unconventional gas resources.A comprehensive understanding of coal permeability evolution facilitates the development of CBM.The coal seams of Ordos Basin which is the biggest CBM basin in China are usually deep and multiple superposed.What’s more,the main gas-producing seams always have different depth,which makes the influence of temperature and pressure on permeability have an obvious difference at different development period.Coalbed samples from 4# and 8# main seams in Baode district of Eastern Ordos Basin are selected.Experiment on temperature and pressure sensibility is done by using the innovative permeability evaluation experiment device.Combined with dimensional analysis and regression analysis,a permeability engineering prediction model is presented.This model takes into account 6 important parameters.Since the variation of temperature gradient is quite small while that of pore pressure decreases monotonically during the production,the coal seam depth can be characterized by temperature while the development stage characterized by pore pressure.To illustrate this further,the effective stress is converted into the dimensionless production time through the comparison with its original value.The results show that coal permeability variation with horizontal effective stress match the exponential law of dynamic cleat volume compressibility.The coal permeability changes with temperature may reverse as effective horizontal stress increase,and the inversion point is where the coal matrix has equal thermal expansion and compaction effects.Based on the experiment,a plate of dynamic cleat volume compressibility and a new coal permeability model are established.The average relative error between the predicted and experiment results is reasonable,8.8 % of 4# coal sample and 7.1% of 8#,which shows a good performance in predicting the permeability evolution for main coal seams in different burial depth at different development period.The study of this article helps to realize the permeability evolution and give a guidance to the evaluation of CBM well performance.