Laboratory Optimization of an Emulsified Acid Blend for Stimulation of High-Temperature Carbonate Reservoirs

Abstract

Emulsified hydrochloric (HCl) acid has been used in both fracture and matrix acidizing of carbonate reservoirs to help penetrate deeper into the reservoir before spending. The emulsion stability and adequate corrosion inhibition are critical requirements of this blend, which are challenging to accomplish using emulsified acids of high HCl acid concentration (>26%) at high temperatures (>250°F) because many corrosion inhibitors used in the industry can severely affect emulsion stability by interacting with the emulsifier. The requirement of other additives, such as iron-control additives, surfactants other than the emulsifier, H2S scavengers, etc., can further add to the challenges. This work presents the laboratory optimization of 26% emulsified HCl-acid blends for use at temperature ranges between 250 and 300°F. Quaternary ammonium salt based Inhibitor I-C and a propargyl alcohol based Inhibitor I-N were used in this study. One inorganic halide based (IN-H) and one organic acid based (IN-O) intensifier were used to achieve adequate corrosion inhibition. A single commercial blend of surfactants was used for all the tests. Based on the high-pressure high-temperature (HPHT) static corrosion tests, Inhibitor I-C performed better than Inhibitor I-N at 275°F. However, Inhibitor I-C was found more damaging to emulsion stability than Inhibitor I-N. At 250°F, the performances of both inhibitors were comparable. A common misconception that prevails in the industry is that a stable emulsified acid can ensure a successful acid job without (or with a very little amount of) corrosion inhibitor. It was clearly evidenced during this study that the emulsion stability alone does not ensure the protection of alloys from corrosion. Using a suitable corrosion inhibitor in appropriate concentration is as equally important as emulsion stability for successful completion of an emulsified acid job without encountering severe corrosion problems.

Influence of Surfactant Structure on the Stability of Water-in-Oil Emulsions under High-Temperature High-Salinity Conditions

“…It is reported that both the addition rate of the dispersed phase and mixing intensity govern the type of emulsion; a coarse emulsion will be the result of adding the dispersed phase to the continuous phase in one step without intensive mixing. However, a fine emulsion can be produced by adding the dispersed phase in atomized form coupled with intensive mixing [20,38].…”

A Review on Use of Emulsified Acids for Matrix Acidizing in Carbonate Reservoirs

“…Water in oil emulsions provide better retardation due to the low diffusivity created by the oil phase around acid droplets, which allows for minimum acid volume contact with t h e r o c k − t u b u l a r s u r f a c e . T h u s , m o s t r esearch 18,26,[29][30][31][32][33][34][35][36][37]39,40,[42][43][44][45][46][47][48][49][50][51]53 has adapted W/O emulsions due to their desirable retardation effect and corrosion inhibition in comparison to O/W emulsions, 27,28 as depicted in Figure 5.…”

“…Additives such as corrosion inhibitors and emulsifiers can be adsorbed and lost on to the rock surface, resulting in emulsion destabilization, increased chances of formation damage, and unwanted corrosion scale generation. 37,43 5.3. Emulsifier Concentration.…”

Application of emulsified acids on sandstone formation at elevated temperature conditions: an experimental study

“…Hence, the delayed nature of emulsified acid has attracted the attention of the oil and gas industry as it could decrease the reaction rate, reduce the contact between acid and well tabular and minimise corrosion issues that is related to well integrity, cost and above all issue associated with safety and environment. In carbonate matrix acidizing using emulsified acid, longer conductive flow paths or "wormholes" are induced, thus improving the permeability and productivity of the reservoir (Sabhapondit et al 2012;Al-Zahrani 2013;Fattah and Nasr-El-Din 2008). Experimental studies and real field application has indicated that emulsified acid can improve carbonate porosity and permeability while minimizing corrosion issues (Sayed et al 2013;Zakaria et al 2012;Navarrete et al 1998;Al-Anazi et al 1998).…”