Comparison of Carbonate HCl Acidizing Experiments With 3D Simulations

Abstract

Acidization of carbonate rocks is a common practice to reduce formation damage near the wellbore. In this process, an acidic solution is injected to dissolve some of the rock, creating conductive channels called wormholes. These wormholes facilitate the flow of hydrocarbons to the wellbore. In the literature, there are several theoretical and experimental studies performed to understand this process. Recent work by Maheshwari et al. 2013 focused on a qualitative comparison of 3D numerical results for slow-reacting acids with experimental data and presented a sensitivity analysis of the acidization process with respect to various transport, reaction, and rock properties. There are very few 3D numerical studies that can predict the experimental results quantitatively, such as the optimum injection rate for fast-reacting acids such as hydrochloric acid (HCl). Therefore, the main objective of this study is to quantitatively predict the experimentally observed acidization curve and dissolution patterns in carbonates with HCl.We present 3D numerical simulations of carbonate acidization with HCl using a two-scale continuum (TSC) model. The model describes the reactive transport at Darcy scale and retains all porescale physics through structure-property relations. Unlike previous studies, we use a new two-parameter (pore-broadening and poreconnectivity) structure-property relation to describe the change in permeability, pore radius, and interfacial area per unit volume with porosity. We predict quantitatively the experimentally observed acidization curve for an HCl/limestone system and show the existence of a critical heterogeneity (that corresponds to the minimum amount of acid required to breakthrough). We also present scaling criteria to estimate the wormhole-tip diameter and optimum acidinjection rate for vuggy and nonvuggy carbonates. Finally, we present the flow dynamics of acid inside the wormhole.

Predicting the Performance of the Acid-Stimulation Treatments in Carbonate Reservoirs With Nondestructive Tracer Tests

“…It is important to note that Fredd and Fogler (1999) and Panga et al (2005) present scaling factors for the x-axis of the PV bt curve, such as Damköhler and Péclet numbers, to represent different mineral/acid reaction rates and dispersion coefficients on their master PV bt curves. They assume that the entire rock porosity is accessible to acid and thus provide no a priori scaling factors for the y-axis.…”

“…Both Fredd and Fogler (1999) and Panga et al (2005) do not provide a priori guidance on the scaling of the y-axis of the PV bt curve. Most of the data considered by Fredd and Fogler (1999) are on one rock type in which most of the porosity is accessible.…”

“…However, the use of their master curve requires a knowledge of PV btmin , and therefore it is of limited utility. Panga et al (2005) considered only well-connected porous media (i.e., the entire PV is accessible). The porosity in their model is randomly distributed.…”

“…The wormhole pattern is governed by a competition of axial convection, transverse diffusion, and reaction mechanisms. At low injection rates, the movement of the reaction front is suppressed by the transverse dispersion, and face dissolution occurs (Panga et al 2005). As the injection rate increases, the dissolution pattern changes from face dissolution to wormhole.…”

Parallel simulation of wormhole propagation with the Darcy–Brinkman–Forchheimer framework

“…Different from much of the two-scale model study that has only 2D simulation, Maheshwari et al [33] extended the 2D continuum model to the 3D case. Based on the 3D case, they studied the effect of the acid-injection rate on the amount of acid required to break through.…”