| Oil well scale formation and deposition is an expensive problem and could be a nightmare for any production engineer if the rate of deposition is rapid as in the case of North Sea oil fields. Inorganic scales accumulate in surface and subsurface equipment causing a reduction in oil production and severe damage for production equipment. The major components of most oil field scale deposits are BaSO4, CaSO4 and SrSO4, which are formed due to incompatible mixing of reservoir formation water and sea water flooded in secondary enhanced oil recovery (EOR) processes. This work focuses on BaSO4 scale as it is one of the toughest scale components to be removed either by chemical means or mechanical means. Scale control methods usually involve complicated treatment using chemical dissolution methods as primary attempt and mechanical scrapping or jetting methods in case of failure of the chemical means. In this work, we devised a novel in-situ scale control method benefiting from the application of direct current (DC) which involves some of the electrokinetic (EK) phenomena. The applications of EK has been proved in our laboratories yielding high efficiency in capturing barium and separating it from sulfate before reaching the production well, thus preventing deposition in the production wellbore or wellbore formation.;This objective was evaluated in our lab designed EK apparatus in three parts. In part-1, an 18.5 cm unconsolidated sand core was used which produced inconsistent results. This problem was overcome in part-2, where the porous media involved 46 cm consolidated sandcore. This also partly fulfilled the purpose of upscaling. In part-3, the porous media was extended to a 100 cm spatial distance between the injection and production wells. For all the experiments the reservoir models were made of 125 microm uniform sand particles and followed a final consolidation pressure of 30 psi. The EK-reservoir model contains 2 basic junctions; one of them injecting a 500 ppm SO4 2- solution, representing sulfate rich sea water and the other injecting a 500 ppm Ba2+ solution representing divalent cations rich in formation water and an outlet for water production. In part-1, there were 4 locations for the electrodes, while in part-2 and part-3 there were 5 electrode locations distributed along the spatial distance. Salinity of injection and formation water was varied within a range of 0 to 40,000 ppm. The flow rates of injection and formation water were constant throughout each experiment. In part-1 experiments, the flow rate was 1 ml/min, in part-2 this was increased to 2 ml/min, finally in part-3 this was further increased to 4.3 ml/min. 2 V/cm voltage gradient was applied for all of the experiments. On a real time basis the current, pressure, temperature, and pH of production water were all monitored. Finally, solid samples with scale deposits within were collected from different locations of the flow tubes. To be analyzed using an ICP-MS.;The results have demonstrated up to 90% scale mitigation by the application of EK. In addition, there was pressure reduction in the flow tube, which could be justified due to chlorine gas generation at the locations sides creating a stimulation effect due to increased acidity. The observations from this study concluded that the application of EK will attribute to the production efficiency due to less scaling and reducing corrosion of surface equipment. This will attempt to demonstrate the world's first promising technique that could be used to replace expensive solutions which require well closure and incur production interruption loss. However, it is recommended that further extensive studies need to be done to confirm the results and finally design a pilot scale project to validate the lab work. |
