Development of a New Model for Carbonate Matrix Acidizing to Consider the Effects of Spent Acid

Abstract

Carbonate matrix acidizing is widely used in oil fields as a simple and easy method of production enhancement. However, the dissolution pattern created due to the reaction between the acid and the carbonates is a complex phenomenon. Several experimental and modeling studies have been carried out to simplify this process and design the optimum conditions for acidizing. One approach is to develop continuum models to simulate the dissolution process in the core scale. Conventional modeling approaches typically do not consider the effects of spent acid in the models. However, there are a few studies and observations on the solubility of CO2 in the CaCl2-H2O-CO2 system, which shows the possibility of formation of a separate CO2 phase during acidizing. The presence of CO2 as a separate phase affects the dominant wormhole propagation and also the dissolution regime. Moreover, the acid/rock reaction leads to the change of physical properties of the flowing fluid. Hence, neglecting the alterations in the physical properties of the moving fluid, such as density and viscosity, affects the accuracy of the models. In this study, a basic model previously introduced in the Darcy scale is developed to consider the effect of reaction products on the overall acidizing performance. A thermodynamic model is used to estimate the CO2 solubility in the spent acid. The insoluble CO2 may change the relative permeability of the reactants and influence on the optimum conditions. Furthermore, the physical properties of the fluid are estimated and updated at each step of the modeling. Consideration of the spent acid effects in the modeling can improve the modeling accuracy. The developed model has the ability to consider the effect of pressure and temperature of the medium on the optimum conditions. In addition, the developed model has shown better predictions by considering the physical changes during the dissolution.

Modeling and analysis of the acidizing process in carbonate rocks using a two-phase thermal-hydrologic-chemical coupled model

“…The most widely used one is the two-scale continuum model (TSC) developed by Panga et al [22] as it is advantageous at predicting the dissolution patterns observed in experiments and its accurate estimation of P V BT . For this reason, the TSC model is continuously extended to take into account the factors that affect the wormhole propagation [23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46]. For example, Kalia and Balakotaiah [23], and Cohen et al [24] extended the TSC model to the 2-D radial case by using the r − θ coordinates.…”

Densities for Ternary System of CaCl2–H2O–CO2 at Elevated P-T: An Experimental and Modeling Approach

“…where ρ aq is density of electrolyte solution containing CO 2 (g/cm 3 ) and x CO 2 is mole fraction of CO 2 in the solution. We developed a new correlation based on the experimental data generated in this study (Equation (11)) to calculate density changes of CaCl 2 solution with addition of CO 2 :…”

“…In recent years, researchers have been paying attention to environmental issues such as CO 2 capture and geological storage in deep saline aquifers or depleted hydrocarbon reservoirs. However, the target depleted hydrocarbon reservoirs are mostly sandstone reservoirs [1][2][3][4][5][6]. Nevertheless, understanding thermodynamic behavior of this mixture is also important in flow enhancement, and well stimulation in petroleum production operations (i.e., matrix acidizing and acid fracturing) commonly used in carbonate reservoirs (i.e., limestone) are also a subject of great interest.…”

Effect of produced carbon dioxide on multiphase fluid flow modeling of carbonate acidizing

“…Bastami et al (2014) investigated the thermodynamic behavior of the H 2 O-CaCl 2 -CO 2 system as products of acid-rock reaction, to estimate the solubility of carbon dioxide and free gas saturation. Bastami and Pourafshary (2016) developed a continuum model considering the acid consumption and the effect of reaction products, such as free gas, on the acid flow and the wormhole propagation. Bastami et al (2018) extended this work by considering a thermodynamic model to calculate the density of the H 2 O-CaCl 2 -CO 2 system.…”