Case Study Southern Oil Field Oman: Novel Approach in Optimizing Dispersed Acid System for Matrix Stimulation in Water Injectors to Improve Injectivity

Abstract The injectivity declines in water injector wells is one of challenges in water flooding fields located in Southern Sultanate of Oman. The main root cause of the injection rate decline in these injectors due to scale or damage formation in the well bore or at the sand face. This scale is mainly inorganic scale like calcium carbonate but recently it has been found that a combination of inorganic and organic scales are formed together at the same well making the clean out operation costly and sometime not very effective. Initially downhole samples were collected from water injector wells for analysis. Lab testing showed the sample is partially dissolved in an aromatic solvent and partially in hydrochloric acid (HCl). Produced water is utilized as source for injector wells which has a lack of treatment process including high Oil-in-water (OIW) and Total Dissolved Solids (TDS) resulting in precipitations of commingle scale of organic and inorganic. The conventional way to treat both scales separately increases the operation time, foot print, cost of the intervention & complicates the operation. Hence, a system that tackles both damages simultaneously was used upon series of enhancement and lab tests. This system has been selected for the next well interventions. Several dispersed acid systems were evaluated at both lap and field stages. The successful dispersed system selected was implemented in a number of field trials. The treated wells showed a good success and injectivity were restored. The injectivity index increased significantly, from 17% to more than 200%. Furthermore, the injectivity has been sustained for more than six months so far, indicating the effectiveness and durability of the treatment. The same stimulation fluids replicated across the water injector wells in the same field. The paper highlights the importance of conducting laboratory studies to select the optimum tailored dispersed acid system that is effective in treating specific formation damage, which can be useful for other oil and gas production fields facing similar challenges in injectivity decline. The new approach can be replicated across other fields in comparison with the conventional acid system.