Oilfield scale inhibition
[1][2] Oilfield scaling is the precipitation and accumulation of insoluble crystals (salts) from a mixture of incompatible aqueous phases in oil processing systems.
[2] Scale is a common term in the oil industry used to describe solid deposits that grow over time, blocking and hindering fluid flow through pipelines, valves, pumps etc.
As the reservoir fluids are pumped from the ground, changes in temperature, pressure and chemical composition shift the equilibria and cause precipitation and deposition of sparingly soluble salts that build up over time with the potential of blocking vital assets in the oil production setups.
[5] Scaling can occur at all stages of oil/gas production systems (upstream, midstream and downstream) and causes blockages of well-bore perforations, casing, pipelines, pumps, valves etc.
[4] The scaling-tendency of an oil-well can be predicted based on the prevailing conditions such as pH, temperature, pressure, ionic strength and the mole fraction of CO2 in the vapor and aqueous phases.
For instance, to bind positively charged ions in the water, anions must be present in the inhibitor molecular backbone structure and vice versa.
[18] Generally, the environmental impacts of SIs are complicated further by combination of other chemicals applied through exploratory, drilling, well-completion and start-up operations.
Produced fluids, and other wastes from oil and gas operations with high content of different toxic compounds are hazardous and harmful to human health, water supplies, marine and freshwater organisms.
[19][20] For instance trails of increased turbidity resulting from oil and gas exploratory activities on the eastern shelf of Sakhalin in Russia have been reported with consequential adverse effects on salmon, cod and littoral amphipods.
[4][22][23] Phosphate ester SIs, commonly employed for treating calcium carbonate scales are known to be environmentally friendly but poor inhibition efficiency.
[23] Release of SIs containing Nitrogen and Phosphorus distorts the natural equilibrium of the immediate water body with adverse effects on aquatic life.
[23] Another alternative, polysaccharide SIs meet the requirements for environmentally friendly materials; they contain no Phosphorus or Nitrogen and are noted for their non-toxic, renewable, and biodegradable properties.
[24][25] Carboxymethyl inulin (CMI), which is isolated from the roots of Inula helenium has been used in oil exploration and its very low toxicity[26] and crystal growth inhibition power[27] has been reported for treating calcite scales.
[21] Another modern alternative to SI use for environmental protection is the development of materials or coatings that intrinsically resist formation of inorganic scale to begin with.
