Abstract
A vug porosity system, in addition to a matrix, is also the target rocks for the acidizing. In this work, the acidizing process in two typical core-scale separate-vug porosity systems is studied in detail. Numerous cases are conducted to discuss a parametric study on the acidizing process and hydraulic behavior. Results indicate that the presence of vug reduces the pore volume of acid solution consumed to achieve a breakthrough, which is consistent with experimental observations. Increasing the vug diameter and porosity decreases pore volume to breakthrough both for a vugular carbonate rock and isolated vug carbonate rock. In comparison, the acid mass does not change a lot. Typical dissolution patterns can also be observed in the acidizing process when a vug exists. Compared to matrix dissolution patterns, the presence of vug induces wormhole to pass through the vug region.
Highlights
Reactive flow in porous media plays an essential role in various physical, chemical, and biological processes in nature and has many applications (Fredd and Scott Fogler, 1998; Acharya et al, 2007; Li et al, 2008; Bijeljic et al, 2013; Nick et al, 2013; Menke et al, 2015; Li et al, 2018)
Vug in vugular carbonate rock is supposed uniformly embedded in the matrix region, and each vug initially has a diameter of 3 mm (Casar-Gonzalez and Suro-Perez, 2000; Izgec et al, 2010)
The results show that the difference of pore volume to breakthrough (PVBT) values between the current and previous two-scale continuum model is not noticeable when acid acquires a very high injection rate
Summary
Reactive flow in porous media plays an essential role in various physical, chemical, and biological processes in nature and has many applications (Fredd and Scott Fogler, 1998; Acharya et al, 2007; Li et al, 2008; Bijeljic et al, 2013; Nick et al, 2013; Menke et al, 2015; Li et al, 2018). Izgec et al (2009) developed a two-scale continuum model to simulate the acidizing process in the separate-vug porosity system, in which vuggy carbonates are divided into two distinct regions of the matrix region and the vuggy region. The continuum approaches behave pretty well in vug well-developed reservoirs, but the challenging part of this mode is that it is hard to determine accurate rock properties such as porosity and permeability (Yao et al, 2010) Another popular approach is based on the coupled Stokes and Darcy equations, in which the Darcy equation is only used in the porous region, and the Stokes equation is used in the free-flow region. Where n is the boundary unit direction vector, u0 is the injection velocity, c0 is the injection concentration, pe is the pressure at the core outside, and Δφ0 is the initial heterogeneity magnitude of porosity
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