Numerical simulation of gas-liquid two-phase flow in channel fracture pack

Abstract

Channel fracturing technique (CFT) is a stimulation method which can promote the generation of high-fracture-conductivity open channels and get higher production and less cost in fracturing operation. This paper presents the numerical simulations of the gas-liquid two-phase flow in channel fracture packs by establishing a new model. To model the multi-phase flow in channel fracture pack, a two-fluid basic model is adopted and extended by including slip velocity and friction force in the closure relations. The flow in channel and in pillars are coupled by pressure and this model is solved using finite volume method. Also, a series of laboratory experiments were carried out to obtain the structure of channel fracture packs, and the measurement of fracture conductivity was carried out and the fracture productivity formula was used to validate the model. The simulation results of pressure, velocity and streamline are analyzed and discussed in this paper, and it shows that the main reason for the significant decrease in the actual production compared to the expected value in channel fracturing well is that ideal continuous channels which has high-fracture-conductivity are not formed, and the structure of pore-channels which complicates the flow laws are formed. The appearance of the structure of pore-channels will change the expected main flow pattern which is along the continuous open channels to a complicated flow which will bring much friction resistance. The flow laws in the channel fracture pack are primarily dominated by the number and distribution of pore-channels. Also, the factors such as bottom hole flowing pressure (BHFP), viscosity and density of the mixture in the formation, numbers of phase states and mass flow rate have impact on it, mainly in the aspect of velocity distribution. The natural gas and the formation water both have a similar behavior in pore-channels but have different flow trends in proppant packs, and their velocity in pore-channels are relatively higher than them in proppant packs, and compared to the velocity of natural gas, the velocity of formation water in pore-channels is relatively high. The original flowing trend in proppant pack changes and tends to show a sudden inrush to pore-channels which will bring a large amount of inlet, outlet and linear losses.