Experimental study on the variation law of equivalent effective stress coefficient of the coal reservoir
The variation law of equivalent effective stress coefficient of the coal reservoir at the stage of the saturation single-phase gas flow is essential in evaluating the reservoir permeability.The coal samples with differ-ent degrees of metamorphism were collected and their equivalent effective stress coefficient was studied under dif-ferent applied loading and pore pressure conditions.The results showed that under a constant pore pressure,with the application of the loading,the equivalent effective stress coefficient of the coal decreases.Applied loading has a negative effect on the equivalent effective stress coefficient of coal reservoirs,and which is strong with the increase of applied loading.Whereas,at a certain loading,with the increase of pore pressure,the equivalent effec-tive stress coefficient of coal reservoirs increases.Pore pressure has a positive effect on the equivalent effective stress coefficient of coal reservoirs.Compared with the middle-and high-rank coal,there are much more pore types in the coal.And the its pore size is much larger.Under the coupling effect of applied loading and pore pressure,the equivalent effective stress coefficient of low-rank coal reservoir is less affected compared to the middle-and high-rank coal reservoirs.There is a significant difference in the equivalent effective stress coefficient of coal reservoir under different applied loading and pore pressure.Thus for the coal reservoir at the saturation single-phase gas flow stage,without considering the coalbed methane desorption-induced coal matrix shrinkage effect,the effective stress change of coal reservoir is not equivalent to the change of pore pressure.And it is closely related to the magnitude of geo-stress and pore pressure.Under the high in-situ geo-stress condition,due to the small equivalent effective stress coefficient,the change of effective stress for the coal reservoir is little with the decrease of pore pressure.
coalbed methanecoal reservoireffective stress coefficientvariation law
NETL
NSTL
万方数据
