Comparing The Langmuir And Bet Isotherms

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Figure 3- Comparison of the Langmuir and BET isotherms

Fig. 3 compares Langmuir and BET isotherm shapes: gas adsorption along the BET isotherm contributes more significantly at early time of production than that of Langmuir isotherm curve. The reason for this is the slope of the BET isotherm curve at higher pressure is larger than that of the Langmuir isotherm curve, resulting in more adsorbed gas releasing at early production times. The amount of released adsorbed gas with BET isotherm curve is larger than that with Langmuir isotherm curve under the same pressure drop from the initial reservoir pressure to the bottom hole pressure.
Dubinin-Astakhov equation
To describe adsorption in micro porous material, Dubinin-Astakhov have proposed form of Dubinin-Rudishkevich equation which has the form: a=W_0 ρ_L exp{-D[Tln(P_s/P)]^n }
a - concentration (adsorbed mass per unit adsorbent mass)
W_0 - Maximum adsorption capacity (volume of adsorbate/mass of adsorbent) ρ_L - Specific mass of the liquid adsorbate
D - Coefficient of affinity n - Characteristic parameter of the adsorbent-adsorbate pair
Adsorption Isotherm Models for Multi- Components
Shale reservoir would rarely contain a pure hydrocarbon fluid. Sometimes the fluid type dry gas may have two or three components accounting for more than 99% of the composition. In some cases, the liquid fluid may contain more than 40 components. There is a large transition zone between the dry gas and the liquid areas. In this

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