Flow and Heat Transfer of Liquid Nitrogen in Rock Pores Based on Lattice Boltzmann Method.

Liquid nitrogen (LN2) is of great potential in stimulating reservoirs. Thanks to the low viscosity and ultralow temperature, which makes it easy to penetrate rock pores and intensified rock failure. However, the flow and heat transfer characteristics of LN2 in rock pores are still not well understood, which limits the development of LN2 fracturing technology. To address this issue, a flow and heat transfer model was established based on Lattice Boltzmann Method (LBM). A connectivity sandstone pore model was presented, combining CT scanning and the improved connectivity algorithm proposed in this paper. A series of simulations were conducted to investigate how the existence of pores and the fluid flow affect heat transfer. Moreover, a pore-scale Lattice Boltzmann Method (LBM) simulation optimization method was proposed to improve the calculation efficiency. The results indicate that the existence of pores and fluid flow will inhibit and assist the heat transfer, respectively. Besides, the effect of pore itself on heat transfer is greater than that of pore flow. Meanwhile, the flow and heat transfer of LN2 and two other common fracturing fluids were compared. Under the same condition, the velocity of LN2 and its rate of cooling rock are the greatest, followed by supercritical carbon dioxide (SC-CO2) and water. As a kind of fracturing fluid, LN2 is better than the other two fluids in terms of flow and heat transfer characteristics. This study provides an in-depth understanding of the mechanism of heat transfer between rocks and LN2. [ABSTRACT FROM AUTHOR]