Research On Shale Adsorption Isotherm

The researches on gas-solid,gas-liquid,liquid-solid and liquid-liquid adsorption isotherms have been carried out,and they can be categorized into four aspects: monolayer adsorption,multilayer adsorption,absorption(solution)and micropore filling.Shale,as an adsorbent,has complex components and various structure.It contains multiple clays and fragmented minerals.Different minerals have different adsorption capacities,which results in complicated adsorption in shale.Moreover,shale is porous media which includes macropore,mesopore and micropore.The size and structure of pore have influences on acting force and potential distribution of shale adsorption.When applied Langmuir,BET and Freundlich adsorption isotherms to match data from experiment respectively,we found that there are limitations for applying the three typical adsorption isotherms to depict shale adsorption.Due to shale adsorption isotherm includes monolayer adsorption,multilayer adsorption and capillary condensation,Therefore,the generated new adsorption isotherm equation for shale should depict these features.According to the three typical adsorption isotherm equations(Langmuir,BET and Freundlich),we built up the new shale adsorption isotherm equation based on process in shale adsorption.Furthermore,different pore type has different adsorption characteristics.This research chooses the cylindrical pore model to build adsorption isotherm.According to the process in shale adsorption,the adsorption volume was divided in two parts: the multilayer adsorption volume and capillary condensation volume,then built the adsorption isotherm based on pore model.The physical and chemical meanings of each parameter are figured out and ranges for each parameter are determined.The results of curve fitting for shale experiment data are in high accuracy by these adsorption isotherms,so the isotherms can be used to predict the adsorption volume for the pressure which had not been tested.The prediction result of isotherm based on adsorption process is better than the one based on pore model.When applied isotherms to calculate the specific surface area,the isotherm based on process is more effective.For representing the adsorption heat,the parameter ?b‘ in Langmuir adsorption isotherm and parameter ?c‘ in BET adsorption isotherm were calculated.The results shown that using the parameter ?c‘ to evaluate adsorption heat was more accurate.And calculated the surface tension and wetting angle by adsorption isotherm based on pore model to compare the surface characteristics among different shale samples.As an attempt,this research sought the relationship between parameters in adsorption isotherm and shale characteristics.Combined the physical and chemical meaning of each parameter,the results shown that the kaolinite,illite,feldspar and quartz constrain the adsorption of nitrogen on shale,as the content of these mineral increasing,the adsorption force becomes stronger,and leads the higher adsorption volume.The content of chlorite and calcite promote adsorption process.The content of these mineral increased,the adsorption force strengthen,and the adsorption volume becomes higher.In the aspect of shale physical property,the parameters have poor relationship with the porosity and permeability of shale due to the inconformity experimental conditions.At the same time,the amorphous bitumen in matrix causes the poor relationship between the parameters of adsorption isotherm and the organic properties.