Abstract
Hydraulic fracturing is a necessary method to develop shale gas reservoirs effectively and economically. However, the flow behavior in multi-porosity fractured reservoirs is difficult to characterize by conventional methods. In this paper, combined with apparent porosity/permeability model of organic matter, inorganic matter and induced fractures, considering the water film in unstimulated reservoir volume (USRV) region water and bulk water in effectively stimulated reservoir volume (ESRV) region, a multi-media water-gas two-phase flow model was established. The finite difference is used to solve the model and the water-gas two-phase flow behavior of multi-fractured horizontal wells is obtained. Mass transfer between different-scale media, the effects of pore pressure on reservoirs and fluid properties at different production stages were considered in this model. The influence of the dynamic reservoir physical parameters on flow behavior and gas production in multi-fractured horizontal wells is studied. The results show that the properties of the total organic content (TOC) and the inherent porosity of the organic matter affect gas production after 40 days. With the gradual increase of production time, the gas production rate decreases rapidly compared with the water production rate, and the gas saturation in the inorganic matter of the ESRV region gradually decreases. The ignorance of stress sensitivity would cause the gas production increase, and the ignorance of organic matter shrinkage decrease the gas production gradually. The water film mainly affects gas production after 100 days, while the bulk water has a greater impact on gas production throughout the whole period. The research provides a new method to accurately describe the two-phase fluid flow behavior in different scale media of fractured shale gas reservoirs.
Highlights
With the gradual increase of production time, the gas production rate decreases rapidly compared with the water production rate, and the gas saturation in the inorganic matter of the effectively stimulated reservoir volume (ESRV) region gradually decreases
Fluid flow in shale gas reservoirs is affected by multiple migration mechanisms [1,2], static structure characteristics of porous media [3,4] and dynamic changes of pore size [5,6]
Σi
Summary
Fluid flow in shale gas reservoirs is affected by multiple migration mechanisms [1,2], static structure characteristics of porous media [3,4] and dynamic changes of pore size [5,6]. Based on the apparent porosity/permeability model, conventional numerical simulation methods can be used to describe the flow mechanism of organic and inorganic matter in shale gas reservoirs. Numerical simulation models can handle more complex fracture networks, but the method is computationally time-consuming, requiring high expertise when building models [46] This method can characterize the influence of pressure changes on reservoir physical parameters at different production moments, and can accurately characterize the fluid migration mechanism of shale gas reservoirs. The complex migration mechanisms of fluids in the micro-scale pores of organic and inorganic media, the static structural characteristics of porous media, the dynamic changes of pore size, and the distribution of induced fractures spacing/aperture of shale gas reservoirs are comprehensively considered. The complex water distribution in different reservoir volume (ultra-low water saturation in unstimulated reservoir volume (USRV) and high water saturation in ESRV) and its influence on flow behavior (single gas flow in pores with ultra-low water saturation and water-gas flow in pores with high water saturation) can considered in the model
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