Triple Porosity/Dual Permeability Model For Fracturing Shale Reservoirs And Its Application

Shale gas is considered as an important clean energy with abundant reserves,but the conditions for occurrence and exploit in China are significantly different from those of other countries.Therefore,substantive advances of the key works such as fracturing design of reservoir,detection and evaluation of fracture network,simulation of gas movement and prediction analysis of production are all deemed to be significant measures for realizing high-efficiency exploitation of shale gas.Now,the joint researches on the multi-media model of shale reservoirs after hydraulic fracturing,reservoir fracture and capacity are immature,which greatly restricts the development of shale gas mining technology in China.This paper is based on the traditional dual medium model,and the fracture medium is divided into microfissure-main crack system.A Triple Porosity/ Dual Permeability Model with matrix-microfracture-main crack system under the condition of ultra-low porosity is established.Monte-carlo method is used to construct multiple random fracture networks after hydraulic fracturing and reconstruct the numerical reconstruction of reservoir fracture network.The connectivity recognition and the conductance analysis of the cross fractures is conducted.The influence law of different main controlling factors to the efficiency of shale gas is simulated numerically.On the basis of simulation,the effect of different character,distribution and combination of fissures to the capacity of shale gas.The theoretical analysis and calculation show that the Triple Porosity/ Dual Permeability Model of matrix-microfracture-main crack after subdividing Fractured medium can effectively apply to shale reservoirs after hydraulic fracturing.And it has better calculation accuracy under ultra-low porosity.Shale reservoirs have a pronounced hopper pressure drop during mining.The gas production efficiency is positively related to reservoir fracture permeability,adsorption constant,gas content and reservoir pressure.And the Fracture permeability has important influence on reservoir permeability and shale gas migration.While The adsorption constant,gas content and reservoir pressure are directly related to the rate of gas production and cumulative gas production.Hydraulic fracturing of the main fissures can significantly increase the local permeability around the fissures.Evenly distributed secondary fissures can conduct deeper natural fissures and effectively improve the effective volume of the reservoir.The initial gas production efficiency of shale gas is mainly controlled by local permeability,the local permeability is increased by 21%,and the initial output is increased by nearly 30%.The cumulative gas production is mainly determined by the effective reconstruction volume of the reformed area,When the effective reconstruction volume is increased by 4%,the gas production will increase by 12%.