煤系地层岩石渗透特性试验研究

基于MTS815.02型岩石伺服渗透试验系统,应用两种实验方法测定了岩石的渗透特性,给出煤系地层中多种岩石全应力-应变过程中渗透率变化范围,对几种岩石的渗透特征进行了分析和讨论。研究表明:1)煤系地层岩石全应力-应变过程的渗透率通常在10-9到10-4Darcy量级之间;2)不同岩石在应力峰值前后其渗透性呈现不同的变化趋势;3)岩石渗透率的离散性很大,即使在相同的试验条件下,渗透率变异系数大多在0.65以上,其离散性按粗砂岩、泥岩、砂质页岩、中砂岩、细砂岩、砾岩、石灰岩顺序逐渐增大;4)在MTS815.02系统上,当所测岩样渗透率小于10-4Darcy量级时,应采用瞬态法,当渗透率量级大于10-4Darcy时,可改用稳态法测定。岩石变形过程中应力场和渗流场的耦合作用十分复杂,渗透率受孔隙压力、围压、试件尺寸、饱和程度等因素影响。

Experimental Research on Permeability of Rocks of Coal-Bearing Strata

The permeability of rock samples collected from coal-bearing strata was tested on MTS 815.02 Rock Mechanics Test System by using two different methods.Variation ranges of permeability for several kinds of rocks in the total stress-strain process were obtained.And permeability characteristics of these rocks were analyzed and discussed.Some remarks can be obtained from the results.The permeability of the tested rocks is usually between 10~-9 and 10~-4 Darcy.The permeability near peak values of stress of different rocks shows different variation tendencies.The discreteness of permeability is quite obvious,even under the same testing condition,the variation coefficients of permeability of most rocks are greater than 0.65 and the discreteness of permeability of different rocks is in the order,from small to great,of gritstone,mudstone,sandy shale,mid-stone,fine stone,conglomerate,and limestone.In allusion to the MTS 815.02 system,transient penetrating method should be used to test the permeability of a sample if its permeability is smaller than 10~-4 Darcy,while if the permeability is greater than 10~-4 Darcy, steady penetrating method is preferred.The results also show that the coupling between stress and seepage flow is very complicated.Therefore the permeability is affected by many factors,such as porous pressure,confining pressure,dimension of specimen,degree of saturation,and so on.