Oilfield scale formation and chemical removal: A review
In oil and gas industry operations, scale deposition on the surface and subsurface production equipment can cause different problems such as formation damage, loss in production, pressure reductions, and premature failure of down hole equipment. Due to geochemical processes between injection water, connate water and rock, the complex composition of reservoir fluids make it difficult to control the inorganic scale formation. Carbonate (calcium), sulfide (iron, zinc), and sulfate (calcium, barium, strontium) scales are more common in oilfield applications. The scale formation depends on several factors that include, but not limited to, temperature, pressures, solution saturation and hydrodynamic behaviour of the flow. This paper reviews different types of scales that are common in oil and gas production operations, their sources and formation mechanisms. The focus of this review is on the different chemicals that are used for the removal of different scales. Hydrochloric acid is one of the classical chemicals used since for most of the mineral scales are soluble in HCl. However, HCl is not environmentally-friendly and causes corrosion and could be very expensive particularly in high-temperature conditions due to the need of using many additives to reduce corrosion. This review discusses several alternatives to HCl that are more environment-friendly in removing oilfield scale deposits. These alternatives are mainly organic acids and chelating agents which have been successfully applied in different fields.