Simulation Of Shale Oil Flow Based On Multi-scale Multi-component Pore Network Model

The development of conventional oil and gas resources is not sufficient for the increasing demand of energy consumption.Shale oil is a typical type of unconventional resource.With a vast reserve,it is the key to the increasing of oil & gas storage and production for China.The characteristics of shale formations are complex: multi-scale in pore sizes and mineral components,strong heterogeneity,multiple forms of fluid occurrence.The surface interaction is strong in nano-scale pore-throat channels,leading to complicated flow mechanisms and obvious micro-scale effect.In response to the above issues,in this dissertation,based on the digital rock technique and pore network model,we constructed micro-scale rock model and simulated fluid flow in shale reservoir.Based on pore network models with regular structures,the subdivide method was used to insert the organic pores,and multi-scale multi-component pore network models were generated by assigning different pore size distributions for organic and inorganic pores.A three-dimensional multi-component digital rock was reconstructed based on two-dimensional SEM images,then a watershed-based algorithm was used to extract the pore network model and quantify organic and inorganic components in each pore.In regular pore network models,we changed the value of volumetric total organic content.By incorporating the single-tube flow equation modified with adsorption and slippage effect,we computed the apparent permeability,analyzed the effects of flow properties(slip length,et al.)and pore structure properties(coordination number,et al.)on fluid flow.The pore network model with complex pore structure was used to simulate the effects of spatial distribution of mineral components.A two-phase flow model was derived by considering the micro-scale effect,then,pore-network simulations combined with the percolation theory was performed to obtain the two-phase relative permeability curves.Our results show that the pore diameter,specific surface area,and coordination number exhibit obvious differences between organic and inorganic pore systems,the constructed multi-component multi-scale pore network models can effectively characterize the pore space of shale formations.The apparent permeability of shale medium is mainly determined by slip length,the effect of viscosity variation is slight.The overall seepage capacity of shale rock is governed by the flow in inorganic pores.Compared with simplified treatments,the model with realistic organic-matter spatial distribution can predict the permeability more accurately.The oil-water two-phase flow in water-wet medium is influenced by water slip length,viscosity ratio and adsorption layer thickness.The interconnected adsorptive water layer with relatively low viscosity increases the water saturation when the drainage is finished,and the layer also enhances the seepage capacity of oil phase.