Investigation of Acid-Induced Emulsion and Asphaltene Precipitation in Low Permeability Carbonate Reservoirs

Abstract

Abstract The increasing demand for energy has extended the development horizon towards relatively tighter formations all over the world. In Saudi Arabia, hydrochloric and organic acids have been extensively used to enhance well productivity or injectivity in low permeability formations. However, the use of these acids was associated with severe formation damage, which is attributed to acid/oil emulsions and/or asphaltene precipitation in some of the low permeability carbonate reservoirs. Consequently, a detailed study on different factors that influence the acid/oil emulsion and asphaltene precipitation mechanism was carried out for these reservoirs. Several compatibility studies were conducted using representative crude samples and different acid systems such as HCl and formic acid. The experiments were conducted at various temperatures up to 240°F using HP/HT aging cell for both live and spent acid samples, where some of the experiments included anti-sludge, iron control and demulsifier chemical additives. In addition, another set of experiments was performed in the presence of ferric ions (Fe3+). The total iron concentration in these experiments varied between 0-1,000 ppm. The results obtained from this study have revealed that the acid systems were not compatible with several representative oil field samples. The amount of asphaltene precipitation and the stability of formed emulsions increased significantly in the presence of ferric ions. Several wells have already been acidized and damaged prior to initiating this study. This paper discusses different tests conducted to identify, quantify and treat acid-oil emulsions/asphaltene precipitation in tight carbonate reservoirs. It also provides details of a special solvent treatment fluid recommended to revive dead wells which were damaged by acid-induced emulsion and asphaltene precipitation.