Effect of Acid Additives on the Reaction of Stimulating Fluids During Acidizing Treatments

Abstract

The objective of matrix acidizing treatments is to remove the skin damage from the vicinity around the wellbore and enhance the permeability and the well productivity. While this is accomplished in sandstone by using reactive fluids to dissolve the clay and the surrounding cementing materials, carbonate stimulation is successful when the reactive fluids bypass the damage by creating conductive channels or "wormholes". It is rare in both treatments that the acids are used alone without several additives. The presence of any of these additives, which is required to achieve a certain function, may impact significantly the outcome of the acid treatment either positively or negatively. The objective of this study is to examine the effect of the type and concentration of several additives, which are currently in-use in the oilfield, on the calcite dissolution rate with HCl using the rotating disk reactor. Additives such as corrosion inhibitors, synthetic polymers, mono and divalent chloride salts, mutual solvent, dissolved iron, viscoelastic surfactants, and chelating agents were investigated.The results showed that more reliable data was obtained at lower acid concentrations. Higher acid concentrations were associated with significant surface changes and inevitable source of error. The effect of corrosions inhibitors was studied by investigating three corrosion inhibitors (CI-A, CI-B, and CI-C) obtained from three different service companies. The presence of two corrosions inhibitors was associated with a reduction in the dissolution rate (between 7 and 45%), while the presence of the third one (containing formic acid) increased the rate of dissolution up to 38%. The effect of all other additives was further examined in the presence of one of the corrosion inhibitors. The presence of a synthetic polyacrylamide polymer significantly reduced the reaction rate down to 96% compared to a blank acid solution that did not contain the polymer.Monovalent ions (sodium and potassium) showed little effect on the calcite dissolution rate, the presence of divalent ions such as magnesium chloride was associated with a reduction in the rate. Calcium chloride showed an increase in the reaction rate for both cases of the presence and the absence of a corrosion inhibitor.The results also showed that mutual solvent changed the dissolution rate and a minimum was observed at 5 vol%. These results were confirmed by changing the corrosion inhibitor and the same behavior was observed at the same mutual solvent concentration. Dissolved iron reduced the rate of reaction by 17% at iron concentration up to 5000 mg/l. At 17,000 mg/l, the rate was reduced by 39% and a reddish to brown precipitate of ferric hydroxide was observed on the rock samples after the reaction, indicating a ferric precipitate. The reaction of VES-based acid showed a minimum at 125°F, which matched the maximum viscosity at low shear rate. The presence of 5 wt% chelating agents increased the reaction rate of 0.1 N HCl by 12.7 and 25%, when the reactions were conducted with no ...

A systematic rheological study of alkyl amine surfactants for fluid mobility control in hydrocarbon reservoirs

“…Similar temperature effects are reported for other aminebased surfactants where wormlike micelles can spontaneously form at ambient temperatures based on the addition of salts, counterions, cosurfactants, surfactant mixtures, block copolymers, and/or organic solvents to the solution (Berret 2006;Hu and Lips 2005;Li et al 2011;Rabie and Nasr-El-Din 2015;Shashkina et al 2005;Wang et al 2012). In particular, as temperature increases, the viscosity initially rises to an inflection point then begins degrading afterward and this process can repeat at higher temperatures (Rabie and Nasr-El-Din 2015).…”

“…In particular, as temperature increases, the viscosity initially rises to an inflection point then begins degrading afterward and this process can repeat at higher temperatures (Rabie and Nasr-El-Din 2015). This viscosity ''enhancement'' suggests that not all of the micelles entangled to form wormlike micelles at low temperatures (Raghavan and Kaler 2001).…”

Formation Damage due to Drilling and Fracturing Fluids and Its Solution for Tight Naturally Fractured Sandstone Reservoirs

“…However, it has drawbacks including clay sensitivity, high corrosion rate and thus high acidconsumption rate for the target reservoir rock. To overcome such drawbacks, an organic acid (i.e., formic acid) is mixed with mud acid because of its retarded nature, low corrosion rate and thermal stability [41]; other additives are also applied for multiple purposes as their names suggested, such as preventing the wellbore corrosion, minimizing the potential formation of sludge and emulsions, and stabilizing the clay minerals [42,43]. In this study, the optimized formulation of the acidic treating fluid contains 9 wt.% hydrochloric acid, 3 wt.% formic acid, 2 wt.% hydrofluoric acid, 2 wt.% clay stabilizer, 4 wt.% corrosion inhibitor, 1 wt.% flow-back surfactant, 0.3 wt.% friction reducer, and 1 wt.% demulsifier.…”

Sandstone matrix acidizing knowledge and future development

“…For example, stimulation process is not affected by the addition of certain additives such as surfactants and corrosion inhibitors. These additives are added to minimize other problems like corrosion and incompatibility (Rabie and Nasr-El-Din 2015). Incompatibility problems can be minimized using surfactant additives in the main acid and after-flush stages.…”