Abstract
Acidizing technology is an effective reformation method of oil and gas reservoirs. It can also remove the reservoir pollution near wellbore zones and enhance the fluid transmissibility. The optimal injection rate of acid is one of the key factors to reduce cost and improve the effect of acidizing. Therefore, the key issue is to find the optimal injection rate during acid corrosion in fractured carbonate rock. In this work, a novel reactive flow mathematical model based on two-scale model and discrete fracture model is established for fractured carbonate reservoirs. The matrix and fracture are described by a two-scale model and a discrete fracture model, respectively. Firstly, the two-scale model for matrix is combined with the discrete fracture model. Then, an efficient numerical scheme based on the finite element method is implemented to solve the corresponding dimensionless equations. Finally, several important aspects, such as the influence of the injection rate of acid on the dissolution patterns, the influence of fracture aperture and fracture orientations on the dissolution structure, the breakthrough volume of injected acid, and the dynamic change of fracture aperture during acidizing, are analyzed. The numerical simulation results show that there is an optimal injection rate in fractured carbonate rock. However, the fractures do not have an impact on the optimal acid injection rate, they only have an impact on the dissolution structure.
Highlights
Since the 1980s, many scholars have conducted systematic research on matrix acidizing
Hoefner (Hoefner and Fogler, 1989; Fredd et al, 1997) and (Fredd et al, 1997) first undertook studies on the dissolution patterns of porous media. They injected the inorganic acid into limestone, injected the low melting point alloy into limestone after acid etching. They studied the dissolution structure of porous media by observing the shape of the alloy. (Hoefner and Fogler, 1988) used the network model to study the wormhole propagation and formation in the porous media and performed a series of experiments to analyze the mechanism of wormhole formation and many numerical simulations to study the characteristics of the mass-transfer limited regime and reaction-limited regime
These results suggested that the branch length of the main channel will never exceed the distance between the branch and the main channel. Based on this mathematical model, (Budek and Szymczak, 2012) improved the extended pore network model to qualitatively characterize the dissolution patterns at different Damköhler numbers and analyze optimal injection velocity. (Kim and Santamarina, 2015) explored how CO2 dissolves into water and flows into the reservoir with a 2-D pore network model. (Wang et al, 1993) adopted the core displacement method to study the Reactive Flow in Fractured Medium influence of temperature, acid concentration, and the velocity of the injected acid on the wormhole
Summary
Since the 1980s, many scholars have conducted systematic research on matrix acidizing. (Wang et al, 1993) adopted the core displacement method to study the Reactive Flow in Fractured Medium influence of temperature, acid concentration, and the velocity of the injected acid on the wormhole. (Nierode and Williams, 1971) established description equation for reactive flow based on the reaction kinetics, indicating that the mass transfer coefficient of solute in acid affects the result of acidizing treatment, and the effect of matrix acidizing was related to the injection rate of acid in the ground.
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