Numerical Evaluation of Mass Transfer Process on Acid Reactive Flow in Carbonate Rocks

Acid stimulation in carbonate rocks represents a quintessential application of reactive flow in subsurface porous media. Unlike chemical reactions that occur in solution, the chemical reactions involved in acid stimulation are essentially heterogeneous reactions. During the reaction process, the acid fluid and the solid matrix are accompanied by the mass transfer of reactants and products. This work is motivated to investigate the effect of the mass transfer process on the acid stimulation process. The two-scale continuum model is employed for capturing mass and momentum transfer, updating rock property parameters and acid fluid transport and reaction process parameters in response to pore structure changes. A comprehensive parametric study is conducted to examine the effect of the mass transfer rate on the acid breakthrough volume. The results show that compared with the influence of velocity and viscosity of the fluid phase, the ratio of surface reaction rate and mass transfer rate of the acid fluid is more sensitive to changes in pore radius and molecular diffusion rate. A smaller breakthrough volume is calculated with consideration of acid mass transfer compared to that calculated without consideration of acid mass transfer and less solid matrix being dissolved. 1. INTRODUCTION Carbonate reservoirs contain a significant portion of the world oil and gas resources (Fredd and Fogler 1999, Panga, Ziauddin 2005). The complex nature of carbonates, including strong heterogeneity and the presence of fractures and vugs, represent technical challenges (Jia, Huang 2021, Jia, Sepehrnoori 2021). During oil and gas production, eroded particles accumulate near the wellbore and impede flow, thus diminishing the connection between the well and the reservoir and impacting productivity (Jia, Alkaabi 2023, Cunqi, Saif 2023). To combat this, acid is injected into the formation to dissolve carbonate minerals and form wormholes in a process known as matrix acidizing. This process provides higher conductivity pathways between the well and reservoir, bypassing formation damage and stimulating productivity (Dong 2018, Dong, Zhu 2018).