A Novel Emulsified Acid for Deep Wells Stimulation: Rheology, Stability, and Coreflood Study

Abstract

Abstract The main objective of matrix acidizing is to create deep channels(wormholes) that bypass the damaged zone around the wellbore, which eventually, will increase the productivity or injectivity of the well. HCl-diesel emulsified acid is used to achieve that goal as well as other objectives such as prevention of tubing corrosion. The cost of HCl-emulsified acid could be lower by reducing the cost of either the surfactant (emulsifier) or the continuous phase (diesel). Hence, in this study, a low-cost, more efficient emulsified acid is proposed, with cheaper solid stabilizer (nanoparticle) instead of surfactant, and less expensive continuous phase; waste oil instead of diesel. Rheology, stability and coreflooding experiments were performed at high-pressure high-temperature (HPHT) of a typical reservoir conditions in the Middle East. This study addresses the feasibility of a novel waste oil emulsified acid system in acid stimulation treatment. In particular, rheology and stability of the emulsion and reactivity with limestone reservoir rock at HPHT were investigated. The reactivity was carried out through a series of core flow experiments at HPHT and compared with the conventional diesel emulsified acid. Stability experiments were conducted at 375 °F. Coreflood experiments were conducted using Indiana limestone 12″ cores and 1.5 in diameter. The initial permeability of the cores was in the range of 2-4 md. The pressure and temperature were 3000 psi and 275 °F, respectively. Four injection rates were used 0.5, 2, 5, and 10 ml/min. For better comprehension for resulted wormhole characteristic from both stimulation fluids under investigation, the CT-scan image for the Indiana limestone cores after injection of both waste oil and diesel emulsified acids were performed and analyzed through a high resolution imaging and visualization software. From the laboratory results, the novel waste oil emulsified acid system showed a good potential as a stimulation fluid. For instance, it achieved lower pore volume of acid to break through (PVBT) compared to both conventional diesel emulsified acid and plain HCl. Moreover, diesel emulsion presented a better performance at lower injection rates whereas waste oil emulsion performed superiorly at higher rates. Thisindicates that, diesel emulsion is still better in terms of stimulation efficiency, however, waste oil emulsified acid still could be recommended in acid stimulation since it has low cost and acceptable performance. Furthermore, CT scan analysis shows that waste oil emulsified acid was capable of achieving narrow, branch-free, and deep wormhole which are the desired characteristic for any potential stimulation fluid. The novelty of this work comes from the fact that waste oil emulsified acid performance for carbonate acid stimulation has not been addressed before and hence this work to fill in the gap.