Causes and Removal Methods of Crude Oil Pipeline Scale Deposition. Case Study of Diffra Oilfield - Sudan

Abstract

The deposition of scale on surface and subsurface of production equipment causes a major operation problem. The problem becomes more acute as oil and gas reserve is depleted and water production increases. This work investigated the causes of scale formation on crude oil pipeline. The work also studied the mechanical and chemical scale removal methods. The scaling problem is experienced in some Sudanese oil reservoirs especially Block-04 fields namely Diffra and Neem. Diffra oil field (Muglad basin) is taken as a case study. The study based on well and pipe line historical data of the last three years. The data included well production, well parameters, oil and water qualities and physical inspection of the formed deposits. The study revealed that the main cause of scale formation is the presence of calcium in produced water; it contains a hardness of 20 ppm. The scale contains 78% calcium carbonate, 12 % magnesium carbonate and 10% wax. The rate of deposition increases with the increase of water cut. The study of removal methods indicated that the currently employed chemical removal method is effective; however the down time is high making significant production cut. A method to reduce the cleaning down time is proposed. For the case of uniform pipe cross-section the standard pigging technology is recommended rather than chemical cleaning. For the section of the pipeline where the cross-section is non uniform due to presence of valves, reducers, etc, the chemical cleaning is recommended, however a bypass line is to be installed to reduce the down time.