Cause Analysis and Scale Control Practice of Water Injection Well in a Middle East Oilfield

The waterflood development was adopted in a carbonate oilfield in the Middle East to enhance oil recovery. The injection water has high salinity and high Ca²⁺ concentration, which lead to scale deposition in the wellbore of water injection wells, even plugging the tubing and seriously impairing the normal water injection production. To explore the causes for scale deposition in water injection wells, X-ray diffraction (XRD) technology was used to analyze the composition of the scale formation on the tubing of water injection wells. The injection water scale tendency was simulated to find out the main scale components and the influencing factors with a scale prediction software. The scale deposited on the surface of the tubing was mainly FeS, CaCO₃, FeOOH, and NaCl. Brine ratio, temperature, and ions concentration (Ca²⁺, Fe²⁺, etc.) have a significant effect on the scale tendency. High salinity, high Ca²⁺ concentration, the presence of Fe²⁺, and highly corrosive produced water are the main causes for the scale deposition in water injection well. The scale and corrosion issues were well controlled by the method of adding scale inhibitor, corrosion inhibitor, and oxygen remover and adopting ultra-high molecular weight polyethylene (UHMWPE) lined tubing.

Scale deposition is one of the most common problems in the petroleum industry. ^1-3 The scale problem can arise anywhere along water paths from surface equipment to the reservoir itself. The scale deposit can take place in the surface water injection facility, injection wells, formation, production wells, topside production facilities, pipelines, and disposal wells. ^4,5 It will cause severe injectivity/productivity problems. If no further timely action is taken, problems such as pipeline blockage, reservoir blockage, production decline, under-deposit corrosion, equipment damage, increased cost of pump inspection, and cleaning operation will threaten the long-term production and sustainable development of the oil field. ^6-10

Water injection is an important process to increase oil production and stabilize yields of oilfield.^11,12 When water the is being injected into the wellbore, its pressure and temperature will increase with the well depth. The changing pressure and temperature may cause the scale deposition on the tubing surface. Production water is commonly used as the injecteion water, but its salinity is usually high, which may cause scale deposition after injection. At the same time, some oxygen may be dissolved in the production water during the injection process, which may lead to oxygen corrosion in tubing and further aggravate the scaling issues.