Effect of temperature on sandstone acidizing using non-Newtonian fluids

Abstract

Rock formation is subjected to acid stimulation to increase oil reservoirs productivity. Acidizing of sandstone rocks is a common method to remove damage and recover the oil flow to the wellbore. A matrix acid stimulation will always require additives depending on mud acid (HF/HCl) components, which cause non-Newtonian fluid behavior. In this study, the 3-D mathematical model of sandstone matrix acidizing in radial flow has been presented by a modified two-parameter model to consider non-Newtonian fluids and temperature effects. To this end, the Carreau-Yasuda equation has been employed to predict dissolution patterns created by non-Newtonian reactive fluids in sandstone formations. Meanwhile, the energy equation has been solved in the porous media to estimate the temperature in each time step, which affects the dissolution patterns in matrix acidizing. Three main phenomena are involved in dissolution patterns: surface reaction, diffusion and convection. Acidizing simulation indicates the acid-rock reaction constant in the formation network is temperature sensitive, and increases exponentially by increasing the reservoir temperature. In this work, the effects of various heterogeneity magnitude and porosity in the porous media, injection rate, reaction rate constant, power-law index (n) and temperature are considered by the various presented dissolution patterns of sandstone acidizing. The results show that, to reach a certain penetration length, the pore volume (PV) of injected acid decreases sharply with reservoir temperature, but after the critical temperature, it decreases slowly. The model discretized the Darcy, mass and energy balance equations by finite difference method and pore evaluation by Karman-Cozney correlations, and then employed the Tri-Diagonal matrix algorithm (TDMA) method to achieve the solution of the model and analysis of dissolution patterns in various acidizing regimes and rheological properties. All mathematical estimations including Darcy correlations, mass and energy balance and pore evaluation have been solved in FORTRAN program by parallel processing to accelerate 3-D calculations.