The Pressure Transient Characteristics And Production Decline Analysis In Shale Gas Reservoirs

Shale gas is a very important unconventional resource which reserve in ultralow premebility shale reservoirs as free gas or absorbed gas.It is hard to obtain industrial gas flow by vertical drilling as usual.After decades improving,horizontal well drilling and hydrofracture have been widely used all over the world,especially in the US,the development of shale gas reservoirs can obtain industrial gas flow by these advanced technologies and it may change the world energy structure.Numerous research literatures about shale gas development have been carried out,and have acquired important theory cognitions and technologies.However,as a new-born resource,shale gas still has too much unknown waiting for us to discover.There even has no book which systematic describes fluid flow inside the shale gas reservoirs after absorbed gas desorbed.After hydrofracture,two-phase flow which caused by gas and water flow appeared in the fractures of shale gas reservoirs,with this phenomenon the flow characteristics have become more complicated than ever before.Therefore,it is crucial to understand the characteristics of fluid flow in shale gas reservoirs and quantify the influence of formation parameters during shale gas wells production.During the research,some important results were obtained,specifically as follows:1)On the basis of special flow behavior of shale gas,Langmuir isothermal adsorption law and Fick diffusion law are employed to study the desorbed gas flow characteristics in the shale gas reservoirs,obtained the expressions to express the desorbed gas pseudo steady diffusion and transient diffusion phenomenon.2)Based on the fundamental of poromechanics and reservoir engineering,employed the laws of desoiption,separately established the fractured horizontal well mathematics model of double medium shale gas reservoirs,the fractured horizontal well mathematics model of homogeneous and double medium shale gas reservoirs with the consideration of trigger pressure gradient and slippage.After soluted each models by some mathematical methods such as Laplace transform,point source function and so on,the exact solutions under the Laplace domain have been obtained.3)While considering the effect of gas-water two-phase flow in shale gas reservoirs after hydrofracture,the fractured horizontal well mathematics model under two-phase flow of double medium shale gas reservoirs has been established.After soluted the two-phase flow model by some mathematical methods such as Laplace transform,eignvalue method and orthogonal transformation,the exact solution under the Laplace space have been obtained.4)The exact solutions have been transformed to real space by Stehfest numerical inversion method and Duhamel's principle.The type curves of dimensionless pseudo-pressure and its derivative,the type curves of dimensionless production integral and its derivative have been plotted for each model.The flow periods of each model have been detail divided.5)Considering the effect of some parameters such as skin factor,fracture stages,dimensionless wellbore storage coefficient,desorption index,storativity ratio and inter-porosity,the sensitivities of each model have been analysised.On the basis of shale gas reservoirs fluid flow behavior theory,the researches in this thesis deepen shale gas reservoirs well testing theory and production decline analysis,they will provide theoretical basis for parameter optimization of fractured horizontal well in shale gas reservoirs.