One of the methods to stimulate a carbonate formation involves injecting acid into the matrix under fracturing pressure and dissolving near wellbore damage. The reaction of acid with the soluble carbonate matrix results in the formation of dissolution structures that depend on several factors like injection rate, formation mineralogy, reaction chemistry of the acid, temperature conditions, etc. The effect of temperature on carbonate dissolution has been illustrated in the past by conducting laboratory experiments at different temperatures. It has been shown that depending on the reaction kinetics for a given fluid and formation, the effect of temperature on wormhole formation varies. For instance, in hydrochloric (HCl) acid-limestone system, the acid volume required to achieve a given permeability increase or skin decrease has been shown to increase as the temperature is increased. On the contrary, in HCl-dolomite system, the effect of temperature is more complex and depends on the injection rate. A clear understanding of the effect of temperature on different types of formations and injection fluids is still not available.
In this work, a mathematical model is used to investigate the effect of temperature on carbonate matrix acidizing. It is shown that an optimum in temperature occurs in terms of minimum acid volume and optimum injection rate. In particular, fluid temperature has been identified as a design parameter and its importance is illustrated by simulating injection of acid at a temperature different from the formation.
Considerable number of current carbonate reservoirs are high temperature, making it imperative to understand the effect of temperature on acidizing design. The results from this work translate directly into recommendations on using temperature as a design parameter in matrix acidizing for varying formation and fluid conditions.