INORGANIC SCALING POTENTIAL OF INJECTION AND FORMATION WATER IN THE PRESENCE OF POLYMER BASED INHIBITOR

Production of oil and gas from oil fields are sometimes plagued by the formation of scales, which is precipitation of organic or inorganic materials in tubings, down hole equipment or sub-sea flow lines that block the flow of reservoir fluids in the production system. Formation of scales could cause operational problems, reduction in the oil and gas production in addition to expensive cost in cleaning the affected locations in the production system. The present study investigates the scaling potential of the seawater, used as the injection water, and the formation water in the Angsi Field, offshore Peninsular Malaysia. The objective of the study is to predict the scaling potential over a range of temperature and pressure of injected water prepared from various ratios of sea and formation waters. Besides, the study also evaluates the effectiveness of a scale inhibitor being used in the field to prevent the formation of scales. Water compositional analysis was performed on the sea and formation waters to provide data for the baseline simulation case and for treated waters. NACE Standard TM0374-09 was referred as the standard to test the effectiveness of the polymer based scale inhibitor. Changes in the water composition due to the action of the inhibitor were then used as inputs to the geochemical modeling software, Solmineq88 to predict the scale potential of various samples of mixed sea – formation waters. Results from the simulation work, which is based on the equilibrium thermodynamics for water-rock interaction indicate that both sea and formation waters have the potential to form scales in the form of barite, calcite, dolomite, siderite, huntite and magnesite. In fact, the mixture of both waters at 0 to 100 % ratios seems to suggest that the formation of scales in the form of calcite and dolomite would be exacerbated. Even though the scale inhibitor at 5 to 20 ppm dosage could minimize the calcite scaling in the seawater alone, the polymer based inhibitor becomes inactive in the presence of the formation water. Keywords: inorganic scales, flow assurance, scaling potential, dolomites