Productivity Analysis Of Hydraulic Fracturing In Shale Gas Horizontal Wells Based On Triple-porosity/dual-permeability Model

Shale gas exists in shale with low porosity and permeability which is both source rock and reservoir stratum in either absorbed or free state.Based on the features of the shale reservoirs and origin mechanism of zone,this paper comes up with a triple medium model and does research on the rule of resolution-diffusion-seepage,establishes the triple-porosity and dual-permeability mathematical equations which considered the gravity of the fluid and the impact of capillary force.According to the typical geologic information of shale gas reservoirs and its physical properties,the geologic model of fractured horizontal wells for shale gas were built.After the simulation study of its production performance,the process of shale gas produntion could be divided into three stages,which contains the increase of gas production the decrease of reservoir pressure in the early stage;the increase of gas desorption from reservoirs matrix in the middle stage;the decrease of production in the end stage.Through the whole process,both gas saturation and recovery ratio increase from the wellbore and the fracture to the reservoirs.With the analysis of the factors during the process of desorption,diffusion and transfusion,the paper did some research on the influence of reservoir thickness,Langmuir parameters,fracture interval,fracture length,fracture conductivity and so on.The conclusions can be reached that:(1)The product process of shale gas is controlled by three links of gas desorption,diffusion and transfusion,which are related with each other closely and affects each other mutually.(2)The smaller the substrate size is,and the bigger the Langmuir pressure is,and the smaller the Langmuir volume is,the easier the gas will be desorb and the higher the production in early stage will be.(3)The concentration difference between matrix and fracture system is the main factor which influence the gas diffusion velocity greatly when compared with the diffusion coefficient.(4)The reservoir matrix and the microfracture permeability are the main factors that influence gas seepage.(5)The fracture conductivity has a great impact on the production capacity and the higher the conductivity is,the larger the gas production will be.(6)The impact of the fracture length on the production capacity need to be optimized according to the dimensionless fracture conductivity.On the basis of understanding of shale gas reservoirs,this paper preliminarily established the basic model of fractured horizontal Wells for shale gas productivity analysis and itsperformance.Some guiding principles and conclusions were drawn for further study on exploration of shale gas reservoirs.