Seyed Alireza Mostafavi

In order to reach sustainable and environmentally friendly operations; it is critical to have an effective management of produced water in oil production wells. In this research, compatibility of re-injection of produced water (PWRI) into an offshore reservoir for the purpose of reducing injectivity loss caused by inorganic scaling deposition is examined. The study compares results from both laboratory compatibility tests and geochemical simulators - Oli ScaleChem and PHREEQC- under reservoir conditions to check their predictability for scaling deposition tendency.

The research is conducted on a south-west Iranian mature oil field with water production of almost 7,000 barrels per day. The produced water and formation brine were mixed in various ratios and re-injected into another reservoir. Compatibility tests were performed by conducting equilibrium experiments, scale separation and SEM-EDX analysis. The total scale measured in experimental study was 134 mg/L and the main minerals identified were Sodium Chloride, Iron Oxide and Silicon Oxide. On another hand, the geochemical simulators predicted precipitation of different types and amounts of scales with high deviation from laboratory experiments for Iron Oxide, Calcium Chloride and Sodium Chloride scales. 

The research concludes that although the simulations are quick and cheap, they only consider super-saturation as the main and only reason for scale formation without considering nucleation and crystal growth processes and the predictive geochemical simulators need deep refinements. On another hand, even though laboratory experiments are generally time-consuming and expensive, they give more accurate and elaborate information regarding the scale formation. Accordingly, the combination of experimental methods with advanced simulations may better optimize water management strategies, reduce environmental impact and increase hydrocarbon production sustainability.