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Research Papers: Petroleum Engineering

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

[+] Author and Article Information
Alireza Bastami

Institute of Petroleum Engineering,
School of Chemical Engineering,
Faculty of Engineering,
University of Tehran,
Tehran 1417466191, Iran
e-mail: Bastami@ut.ac.ir

Peyman Pourafshary

Department of Petroleum
and Chemical Engineering,
Sultan Qaboos University,
Muscat 123, Oman
e-mail: Pourafshary@squ.edu.om

1Corresponding author.

Contributed by the Petroleum Division of ASME for publication in the JOURNAL OF ENERGY RESOURCES TECHNOLOGY. Manuscript received February 22, 2015; final manuscript received January 10, 2016; published online March 10, 2016. Assoc. Editor: Reza Sadr.

J. Energy Resour. Technol 138(5), 052905 (Mar 10, 2016) (13 pages) Paper No: JERT-15-1086; doi: 10.1115/1.4032728 History: Received February 22, 2015; Revised January 10, 2016

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.

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Figures

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Fig. 1

Schematic of the porous medium and the boundary conditions

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Fig. 2

Flowchart of the basic equations and modifications of this study

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Fig. 3

The results of independency test with regard to time-step size

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Fig. 4

The results of independency test with regard to mesh size density

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Fig. 5

Comparison of the experimental data [8] with the basic equations

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Fig. 6

The effect of brine concentration

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Fig. 7

The effect of medium heterogeneity

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Fig. 8

The experimental data and model predictions of PVbt versus Qinj for 0.5 M HCl and HAc

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Fig. 9

Model predictions of PVbt versus Qinj for 0.5 M HCl, FA, and HAc

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Fig. 10

The optimum injection rate and minimum PVbt for 0.5 M HCl, FA, and HAc

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Fig. 11

Acid, CaCl2, and CO2 concentrations change along the medium

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Fig. 12

Comparison of the experimental data [6] with the results of Panga et al. [23] and the developed models

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Fig. 13

Qopt at different temperatures from the experiments by Bazin [6], Panga model [23], and the new developed model (7% HCl)

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Fig. 14

Minimum PVbt at different temperatures from the experiments by Bazin [6], Panga model [23], and the new developed model (7% HCl)

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Fig. 15

The effect of temperature

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Fig. 16

The effect of pressure

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Fig. 17

The effect of acid concentration

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