Sarvestan and Saadatabad oilfields produce more than 140 bbl/day of wastewater from oil processing. Due to environmental issues, the produced water is injected into a disposal well through an 8 inch, 5 km pipeline. Formation of inorganic scale may accelerate the need for frequent reservoir acid stimulation, restrict flow path, and generally add unpredicted costs for water injection operations.
This study presents the predicting scale tendency and scale precipitation at different pressures, temperature, and mixing ratios of injection wastewater with formation water in Sarvestan and Saadatabad oilfields. The experimentally measured chemical analysis of injection water and formation water were used to estimate the amount, type and composition of scale due to mixing and change in thermodynamic conditions.
Scale tendency values for eight types of scale (CaCO3 (Calcite), CaSO4 (Anhydrite), CaSO4. 2H2O (Gypsum), FeCO3 (Siderite), Fe(OH)2 (Amorphous), NaCl (Halite), Mg(OH)2 (Pyrochroite) and KCl (Silvite)) are investigated by commercial software packages (OLI ScaleChem and StimCADE). Results show that the main scales are CaCO3 and FeCO3 that can be formed in Sarvestan and Saadatabad oilfields. The formation of these scales can lead to serious problems, such as disrupting equipment and decrease production, thus it is necessary to predict all types of scales before formed. It allows design and planning for chemical inhibitor treatment, and prediction of injectivity problems and acid stimulation.