Fig 1.
Gas distribution in shale strata from macro-scale to micro-scale.
In the fracture there exist free gas and in the matrix free gas and adsorption gas co-exist.
Fig 2.
Idealization of the heterogeneous porous medium as DPM.
Fig 3.
Transport scheme of shale gas production in DPM.
Gas desorbed from the matrix surface and transferred to the fracture, then flow into the wellbore. Non-darcy flow, Knudsen diffusion, slip flow, and viscous flow have been considered.
Fig 4.
Gas flow mechanisms in a nano pore.
Red solid dots represent Knudsen diffusion, while blue ones represent viscous flow.
Fig 5.
Pore radius change due to gas desorption.
If single molecule gas desorption Langmuir isothermal is considered, when all the molecules have desorped from the surface, then the pore radius will increase as shown in the right part.
Fig 6.
Gas viscosity variation with the Knudsen number (from 0.01 to 1), also means from slip flow to transition flow.
Gas viscosity has changed a lot when the Knudsen number changes, which means it is necessary to consider the gas viscosity variation (Modified from [33]).
Fig 7.
Comparison between analytical solution and numerical simulation in this paper.
Fig 8.
Real reservoir and simplified 2-D reservoir simulation model.
Table 1.
Parameters used in the simulation model.
Fig 9.
Effect of adsorption on gas production performance.
(a) production rate vs. time; (b) cumulative production vs. time.
Fig 10.
Matrix and fracture permeability change with time.
(a) matrix permeability vs. time; (b) fracture permeability vs. time.
Fig 11.
Effect of Non-Darcy flow on gas production performance.
(a) production rate vs. time; (b) cumulative production vs. time.
Fig 12.
Effect of gas viscosity change on gas production.
(a) production rate vs. time; (b) cumulative production vs. time.
Fig 13.
Effect of pore radius increase due to gas desorption on gas production.
(a) production rate vs. time; (b) cumulative production vs. time.
Fig 14.
Comparison of five different models:
(1) basic model; (2) Considering adsorption; (3) Considering adsorption and non-Darcy permeability change; (4) Considering adsorption and non-Darcy permeability change, gas viscosity change; (5) Considering adsorption, non-Darcy permeability change, gas viscosity change and pore radius change.
Fig 15.
Effect of initial reservoir pressure on gas production.
(a) production rate vs. time; (b) cumulative production vs. time.
Fig 16.
Effect of matrix permeability on gas production.
(a) production rate vs. production time; (b) cumulative production vs. production time.
Fig 17.
Effect of fracture permeability on gas production.
(a) production rate vs. production time; (b) cumulative production vs. production time.
Fig 18.
Effect of matrix porosity on gas production.
(a) production rate vs. production time; (b) cumulative production vs. production time.
Fig 19.
Effect of fracture porosity on gas production.
(a) production rate vs. production time; (b) cumulative production vs. production time.