Production Analysis Of Multi-fractured Horizontal Shale Gas Wells Based On Heterogeous Model

With the rapid decline in conventional gas reserves,unconventional resources such as shale gas have been playing an increasingly important role in energy industry over recent years and gradually become a key component in energy supply of the world.Unlike conventional reserves,shale gas reservoirs(SGR)consist of rock matrix,discrete natural fractures and hydraulic fractures,which makes SGR are strongly heterogeneous.The heterogeneous SGR are investigated to study multi-scale flow regime of shale gas and production analysis of multi-fractured horizontal wells by means of theoretical research and numerical calculation.The main works and achievement of this thesis are summed up as follows:(1)Microcosmic gas diffusion mechanisms and flow behaviors are investigated by numerical computation method.Multiple flow mechanisms,determined by Knudsen number,are explored,including continuum flow,slip flow,transition flow and Knudsen flow.Apparent permeability is obtained with consideration of gas slippage and diffusion effect,and the sensitivity of parameters is analyzed.Langmuir adsorption isotherm is validated to be feasible and reliable for adsorption-desorption of shale gas.(2)A new analysis model(MNH),which considers the multiscale flow regimes,is developed for a heterogeneous shale gas reservoir.In this MNH model,gas flow in shale matrix is described by non-Darcy law and gas desorption is also considered.Gas flow in discrete natural fractures follows the cubic law in each fracture and these natural fractures are described by a discrete fracture model.Based on Brinkman-NS model,an equivalent method is put forward to describe the flow regime in hydraulic fractures.This MNH model is then use to analyze the pressure distribution and flow regimes of shale gas flow within a multi-stage fractured horizontal well.(3)The two-phase flow during flowback process of fracturing fluid is investigated.Based on the bubble flow model,the water-gas two-phase flow regime is studied in hydraulic fractures.The differences between single-and two-phase flow are discussed,and the variation tendency of gas water ratio(GWR)is analyzed.The water-gas twophase flow in equivalent region is expounded by means of two-phase Darcy flow,and flowback rate as a function of saturation is expressed.Gas phase permeability in equivalent region is developed to modify MNH model,and the influences of flowback rate on gas phase permeability are also discussed in detail.(4)The modified MNH model is employed on quantitative production analysis evaluation of multi-stage fractured horizontal wells.Two control factors,which control productivity of fractured horizontal wells,are put forward to explore decline of gas production rate.The influences of parameters,including gas desorption,natural fracture aperture,natural fracture density,hydraulic fracture aperture,and hydraulic fracture spacing,on gas production rate,cumulative production and control factors are respectively investigated.Eight cases with various combinations of influence factors are numerically studied to explore the total influence of these parameters on shale gas production.Furthermore,this thesis could lay a theoretical foundation for the efficient production in shale gas engineering.