Flow Performance Analysis For Re-fractured Shale Gas Reservoirs And Optimization Of Re-fracturing Time

It is impossible to imagine modern world without oil and gas production.In recent years,people's consumption has been revolutionized with technology progress,where oil and gas production increased considerably,while a priority is given to the development of shale gas productivity.New clean energy sources can be a complement for the gradual exhaustion of traditional energy sources.As a new source,shale gas has attracted much attentions and its extraction technology is becoming more and more mature.However,the gas production from shale gas horizontal wells decays rapidly after the early production peak.How to prolong the life of shale gas wells and increase the production capacity of shale gas wells has been an unsolved problem.In this study,the impact of refracturing on the life and productivity of a fractured shale gas reservoir is investigated through numerical simulations.The fractured reservoir is composed of a horizontal well,a single-porosity medium zone,a dualporosity medium zone,and hydraulic fractures.The deformation and gas flow in the fractured reservoir are mainly studied.That is,the governing equation for reservoir deformation is derived from the Hooke's law for elastic porous medium and the porosity and permeability models are established.Then,the governing equation for gas flow in the fractured reservoir is developed with the mass conservation law and the Darcy's law.This formulates a fluid-solid coupling model for a refractured shale gas reservoir.With proper initial and boundary conditions in each zone,numerical simulations for the multi-physical coupling are implemented within COMSOL Multiphysics platform.This coupling model is verified by the production data of a refractured shale gas reservoir from literature.Finally,the optimization of refracturing time,hydraulic fracture layout,hydraulic fracture permeability and fracture half-length are investigated through the evolutions of reservoir pressure,cumulative gas production and gas flow rate.Following conclusions are drawn through these numerical simulations:(1)Greater hydraulic fracture permeability can have higher gas flow rate at the initial stage.When the permeability is too low,less obvious effect of refracturing induces lower cumulative gas production.(2)The effect of hydraulic fracture layout on refracturing is less obvious if the total number of fractures after refracturing can achieve full extraction in the production area.(3)Within a certain range,the half-length of refracturing can increase the cumulative gas production.