Formation damage analysis of matrix acidizing: effect of emulsion formation, asphaltene sludge, and iron precipitation

Matrix acidizing, a vital well stimulation technique, can be severely impaired by formation damage resulting from acid-crude oil emulsions, asphaltene sludge, and ferric ion precipitation. This study presents a systematic investigation into the simultaneous prevention of these issues through the evaluation and optimization of various acidizing additives under simulated reservoir conditions (366.5 K). Employing a Middle Eastern crude oil sample, laboratory tests were conducted to assess sludge formation (quantified by mass and a newly introduced average particle size metric), emulsion stability, corrosion rates on N80 steel, iron precipitation, and additive compatibility. The novelty of this work lies in its comprehensive analysis of the combined effects of multiple additives on sludge formation, beyond conventional anti-emulsion and anti-sludge agents, and the introduction of average sludge particle size as a critical indicator of formation damage. The findings reveal that while individual additives (corrosion inhibitor, corrosion inhibitor intensifier, iron control agents, non-ionic surfactant, and anti-emulsion agent) offer varying degrees of sludge reduction, their synergistic combination in 15 wt.% HCl significantly decreased sludge particle mass by 52% and average particle size by 87%. Notably, ferric ions exhibited the most detrimental impact, increasing sludge mass over twofold and average size tenfold. The optimized acidizing fluid, comprising 2 v./v.% corrosion inhibitor and 1.5 v./v.% corrosion inhibitor intensifier, effectively prevented ferric ion precipitation and minimized emulsion and sludge formation, achieving a remarkably low corrosion rate of 0.001 mg/cm², well below the critical limit. However, achieving consistently complete sludge prevention proved complex and often necessitated the inclusion of a particularly effective anti-sludge agent. This research establishes a comprehensive methodology for designing effective and compatible acidizing fluids to mitigate multiple formation damage mechanisms, with the average sludge particle size providing a novel and sensitive parameter for evaluation. Acid concentration, ferric ions & acidizing additives effect on asphaltene sludge. The mass and size of asphaltene sludge particles are directly related to each other. Acidizing fluid was optimized to prevent emulsion/sludge formation and ferric precipitation. All acidizing fluid additives have an acceptable effect on sludge reduction. Non-emulsifier concentration higher than the optimal value increased sludge formation.