| The recoverable resource of shale gas is rich in China,which is among the world's highest and has enormous economic value.Shale gas reservoir is different from conventional gas reservoir.It has complicated occurrence form and seepage mechanism that exist in porous medium with absorbed states and free states including desorption,darcy flow,slippage and diffusion.The adsorption and desorption of shale gas has an important influence on the development and exploitation of shale gas reservoir.Therefore,in-depth study of the supercritical adsorption of shale gas and the production of shale gas reservoir in shale gas reservoir are of great theoretical and practical significance for the economic and efficient development of shale gas resources.Experimental and theoretical methods are combined to carry out research in this paper.Firstly,the isothermal adsorption model of shale gas has been developed,and the isothermal adsorption model under high temperature and pressure supercritical condition is deduced,and its adsorption model is verified.A three dimensional,multi-phase flow numerical model of a fractured horizontal well producing in shale gas reservoirs under complex flow mechanisms is presented,which is valid for the entire Knudsen's range(continuum flow,slip flow,transition flow and free molecular flow)in shale gas reservoirs.After the developed model is verified by other models and actual field data,the effects of critical factors such as Knudsen diffusion and slippage effect,gas desorption,multi-phase flow,supercritical isothermal adsorption model,and fracturing treatment on gas production rate are discussed as well.The major conclusions of this dissertation can be summarized as follows:(1)The characteristics of microscopic pore structure of shales and gas storage mechanism are studied based on laboratory experiments,the physical description and mathematical representation of shale gas transport mechanism from different scales is illustrated.(2)The isothermal adsorption isotherm curves of shale gas at different temperatures were tested.The isothermal adsorption curve of shale gas shows that when the experimental pressure increases from OMPa to 3MPa,the adsorption capacity of shale gas increases exponentially;with the pressure continues to increase,the growth rate of shale gas adsorption gradually slows down.The adsorption amount of shale gas decreases with the increase of temperature.When the temperature increased from 25? to 40?,the adsorption gas of three shale samples decreased by an average of 12.23%.When the temperature increased from 40? to 60? the average amount of adsorbed shale gas decreased by 38.86%.(3)The adsorption amount of shale gas determined in supercritical state is excess adsorption.Combined with the Gibbs adsorption model,the modified Langmuir model was obtained.Considering the adsorption of shale gas in organic matter,the L-K adsorption model is deduced.the isothermal adsorption model was studied and showed that the fitting degree of fitting comparison,L-K model of shale isothermal adsorption curve is higher than other model fitting degree;under high temperature,the fitting precision of L-K model than Langmuir model fitting accuracy by an average of 11.21%.(4)A three dimensional,multi-phase flow numerical model of a fractured horizontal well producing in shale gas reservoirs is presented,which is valid for the entire Knudsen's range in shale gas reservoirs,and the effects of Knudsen diffusion and slip flow,gas desorption are taken into consideration.Grid refinement and equivalent fracture conductivity method are used to simulate hydraulic fracturing cracks.(5)The numerical model is validated with commercial software,other model and actural field data,and the effects of Knudsen diffusion and slip flow,gasdesorption,multi-phase flow,supercritical isothermal adsorption model and fracturing treatment on gas production rate of fractured horizontal are analyzed.The presented theoretical models provide theoretical basis for evaluating and predicting the productivity of shale gas well,and is of theoretical and practical significance to promote the efficiently development of shale gas reservoirs. |
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