Computational Methods And Analysis Of Productivity In Shale Gas Reservoir

The shortage of conventional reserves seriously restricts national economy development.With the rapid decline in conventional oil and gas resources,the efficient development of unconventional reserves can protect our energy supply.Shale gas is an important unconventional resources,with the large reserves and wide-ranging distribution.Due to the multiscale pore size,complex pore types and various storage types spaces,the gas transport mechanisms in shale multi-stage fractured horizontal well are complex.The traditional fluid flow theory is no longer suitable to shale gas reservoir.Therefore,it is necessary to establish a new method for flow simulation and production analysis in shale gas reservoir.Based on the literature review,some models are selected to describe the multiple transport mechanisms in shales,including viscous flow,Knudsen diffusion,surface diffusion,adsorption and desorption,stress dependence,real gas effects and phase behavior in nanopores are also taken into account.Firstly,two fully coupled conductivity model are developed to describe gas transport in organic and inorganic pores separately.Then combined with capillary model,the influences of transport mechanisms and other parameters on production rate are analyzed.Secondly,based on multiple transport mechanisms,including adsorption/desorption,viscous flow,diffusive flow in shale matrix and pressure dependent phenomenon,two semi-analytical models for multi-stage fractured horizontal well(MFHW)in shale gas reservoirs are presented: one contains stimulated reservoir volume(SRV)and the other contains SRV and un-stimulated reservoir volume(USRV).Perturbation method is applied to linearize the model.Then the line source solution is solved by Laplace transformation.Production rate of MFHW is obtained using principle of superposition,and the effects of relevant parameters on production rate are analyzed.Thirdly,a unified model of MFHW in shale gas reservoir is presented,which incorporates real-gas transport,multiple flowing mechanisms,pressure dependent phenomenon and discrete fracture model which has the capability of handling fractured media.In order to simulate more efficiently,a unit SRV of hydraulic fracture is selected.The model is solved by finite element method and used to predict shale-gas production under different reservoir scenarios and investigate which factors control its decline trend.Fourthly,a unified model able to incorporate matrix-microfracture and hydraulic fracture is presented.The hydraulic fractures are explicitly represented by the discrete fracture network model and embedded in the microfracture grid.The MINC method is used to accurately evaluate the transfer function between matrix and microfracture.The mathematical model is solved by finite volume method.The factors that impact the production of MFHW are analyzed,such as transport,adsorption/desorption,matrix parameters,SRV size,microfracture parameters,and the pressure dependent phenomenon.Finally,the numerical simulation method of thermal recovery in shale gas reservoir is introduced.A fully coupled numerical model of MFHW is developed.The model incorporates multiple flowing mechanisms,real gas flow,pressure dependent phenomenon,as well as heat diffusion processes within the shale reservoir.The mathematical model is solved by finite element method.The potential of thermal recovery based on hydraulic fracture heating is investigated and the factors that impact the production decline of thermal recovery are analyzed,which provides a technology guidance for thermal recovery in unconventional gas reservoir.