Numerical study of vug effects on acid-rock reactive flow in carbonate reservoirs

Abstract

Matrix acidizing is one of the most practical stimulation technologies for carbonate reservoirs, which effectively improve the region permeability near the wellbore. In addition to solid matrix, vugs are also very common in carbonate reservoirs. However, a few studies have been addressed with existence of vugs on carbonate acidizing process. In this work, a two-scale model is developed using dual domain method and discrete vugs model to study effect of vugs on acidizing process. Darcy equation is employed in solid matrix region. Navier Stokes equation is adopted for free flow region in vugs. The two regions are coupled by modified Beavers-Joseph-Saffman boundary condition. Numerical cases are conducted to present the effect of vug characteristics on acid-rock reaction process. The results show that acid solution has the largest effective reducing distance and the smallest breakthrough volume in circular vugs. Dominant wormhole is created when acid injection direction is parallel or vertical to the azimuth angle of vugs. Increasing amount of vugs in horizontal effectively reduces the flow distance and breakthrough volume of acid solution. Vugs with random distribution increases effective flow distance and breakthrough volume of acid solution compared to vugs with orderly distribution.

Transitions of Dissolution Patterns in Rough Fractures

“…Here Pe represents the relative effect of the advection to diffusion, and Da represents the relative effect of reaction to advection. A large number of flow‐through dissolution experiments were dedicated to the impacts of Pe and Da on the transitions of dissolution patterns (Al‐Khulaifi et al., 2018; Daccord et al., 1993a, 1993b; Deng et al., 2015, 2018; Detwiler et al., 2003; Dijk et al., 2002; Fredd & Fogler, 1998; Golfier et al., 2002; Z. Huang et al., 2020; Noiriel, 2015; Noiriel et al., 2009; Ott et al., 2015; Osselin et al., 2016; Smith et al., 2013). Generally, increasing Pe or Da triggers the transitions of dissolution patterns from face/compact dissolution to wormholes to uniform dissolution (Cohen et al., 2008; Daccord et al., 1993a; Hoefner & Fogler, 1988; Hu et al., 2021; Kiani et al., 2021; Singurindy & Berkowitz, 2005; Soulaine et al., 2017).…”

Research on high efficiency and retarded autogenous mud acid for plugging removal in a sandstone reservoir—Example of Bai 823 well area

“… Pore calculation model The porosity and permeability of the formation also change during the main acid injection process. Using the principle of mineral volume balance, the mathematical model of porosity and permeability distribution during the main body acid injection was derived with the consideration of silica gel precipitation 31,32 $$${\varphi }_{m}^{n+1}={\varphi }_{m}^{n}+(1-{\varphi }_{m}^{n})\sum _{i=1}^{2}({C}_{m,{mi}+1}^{n}-{C}_{m,{mi}+1}^{n+1})-{\varphi }_{m}^{n}({C}_{m,m4}^{n+1}-{C}_{m,m4}^{n}),$$$ $$$\frac{{k}_{m}^{n+1}}{{k}_{m}^{n}}=\frac{{\varphi }_{m}^{n+1}}{{\varphi }_{m}^{n}}{\left(\frac{{\varphi }_{m}^{n+1}\left(1-{\varphi }_{m}^{n}\right)}{{\varphi }_{m}^{n}\left(1-{\varphi }_{m}^{n+1}\right)}\right)}^{2\beta }$$$…”

“…Using the principle of mineral volume balance, the mathematical model of porosity and permeability distribution during the main body acid injection was derived with the consideration of silica gel precipitation. 31,32…”

Influence of Paleosedimentary Environment on Shale Oil Enrichment in the Raoyang Sag, Bohai Bay Basin

“…When the suspension balance condition was broken, fine-grained clay minerals carry organic matter and sink to the bottom of the lake, where they mix with native carbonate minerals to form clay shale. However, we should also pay attention to the fact that the strong influence of the source will cause "dilution effect", 75 and excessive terrigenous clastics will dilute the original organic matter. Moreover, the strong hydrodynamic conditions are also not conducive to the preservation of OM.…”