Multicomponent Gas Transport In Shale And Its Effect On Fractured Horizontal Shale Gas Well Performance

Shale gas is an important energy source.The shale gas revolution in the United States has stimulated worldwide research on shale gas.Acceleration of shale gas development has a strategic significance for China.Shale contains abundant micro– and nano–sized pores and is characterized by ultra–low permeability.Currently,horizontal well with multi–stage hydraulic fracturing is the common completion technique for shale gas development.Shale gas involves multiple storage mechanisms and complex transport mechanisms,especially for multicomponent gas transport and adsorption,which poses a great challenge for production prediction and hydraulic fracturing optimization.Thus,a shale gas production model that takes into account multicomponent gas transport and adsorption is needed,which is the objective of this dissertation.The main work is as follows:(1)The gas composition of eight different shale gas plays in American and China(a total of 112 gas samples)is summarized,which provides a basis for subsequent research?(2)The mineralogy and pore structure of shale is investigated by laboratory experiments.The controlling factor of pore structure is analyzed,and the pore space for shale gas transport and storage is determined.(3)Based on the multicomponent potential theory of adsorption,a multicomponent gas adsorption model,named hPC–SAFT–MPTA,is established.In this model,the adsorbent–adsorbate interaction is modeled using the Dubinin–Astakhov potential and the adsorbate–adsorbate interaction is described by the hPC–SAFT.This model provides a good description of adsorption isotherms near the critical point and reveals the mechanism of supercritical adsorption.Extending hPC–SAFT–MPTA to excess adsorption is straightforward and has no need to estimate the adsorbed phase density.Moreover,hPC–SAFT–MPTA can be used for reservoir simulation due to its less computational requirement and satisfactory precision.(4)The binary friction model involves an empirical parameter and is limited to slip flow regime.To solve these problems,the general slip boundary condition is introduced in the binary friction model,a new wall friction factor is proposed.This wall friction factor has clear physical meaning.Based on this wall friction factor,a multicomponent gas transport model is developed and validated by available experimental data.This model can be used in the continuum regime,slip flow regime,transition flow regime,and free molecular flow regime.(5)For multi–fractured shale gas horizontal well,a production model that considers stress sensitivity,multicomponent gas transport and adsorption is established.Hydraulic fractures are described using the discrete fracture model and matrix(stimulated and unstimulated regions)is handled by the continuum approach.To solve this model,a finite element programme is developed using COMSOL.According to the factorial design,senstivity studies are carried out with four parameters such as the number of stages,initial hydraulic fracture permeability,and permeability enhancement factor to find the critical parameters.An optimization analysis for these parameters is performed.Moreover,a well completion optimization method is developed.This work can contribute to provide some theoretical support for production evaluation and well completion optimization for shale gas wells.