Traditionally, phosphonate based scale inhibitors have dominated the global squeeze treatment market and for very good reasons: they combine high performance with ease of measurement. However, increasingly stringent environmental legislation has resulted in the development of new, enhanced polymeric scale inhibitors that contain low levels of phosphorus, such as phosphonate end-capped polymers. These polymers are highly effective with particularly low MIC (minimum inhibition concentration) values, but this creates analytical problems as they can't currently be easily measured at these low levels. Therefore, to realise the full performance and environmental benefits of such polymers it is necessary to be able to readily and easily measure them at low concentrations in a variety of brine chemistries.
A novel separation and pre-concentration procedure has been developed that can be combined with industry standard analytical methods (e.g. Hyamine) to detect such scale inhibitors. It is simple to use, flexible, requires no specialist knowledge or equipment and can measure sub-ppm levels of inhibitor reliably and accurately in even the most concentrated brines.
Secondary oil recovery operations typically involve the continuous injection of large volumes of water into the petroleum bearing reservoir (water-flooding) to help maintain reservoir pressure and optimise oil recovery. Whilst this is beneficial in terms of oil production, it does introduce water related process problems such as corrosion, microbial activity and mineral scale deposition.
The traditional options for controlling mineral scale in production wells are continuous injection of scale inhibitors down a capillary line (macaroni string), which is commonly deployed in wells where calcium carbonate formation, due to depressurisation, is the primary scale potential, or squeeze treatment (batch injection of scale inhibitors down the production well) to control all types of mineral scale both within the production well tubing and immediate production well bore.
Squeeze treatment applications require the production well to be shut down for 12- 24 hours while a squeeze treatment process is carried out: this results in costly deferred oil production and so it is advantageous to optimise treatment programmes to maximise the length of the treatment (maximise squeeze treatment lifetime) to reduce the total number of production interventions.
Typically a squeeze treatment lifetime is controlled by the properties of the scale inhibitor, both in terms of its ability to control scale and its ability to interact with the reservoir rock matrix/water chemistry to produce a controlled release of the scale inhibitor back into the production well. Long squeeze lifetimes are produced by low scale inhibitor minimum inhibition concentrations (MIC's) against the targeted scaling environments, and controlled desorption from the reservoir rock or dissolution of a precipitated calcium inhibitor salt. However, a third vitally important parameter of the scale inhibitor is detectability: the ability to accurately and reliably detect the scale inhibitor in produced waters at MIC values, which could be just a few parts per million (ppm) in high total dissolved solids (TDS) brines.
Traditionally phosphonates, such as diethylenetriamine pentakis(methylene phosphonic acid) , DETA phosphonate, have been deployed as squeeze treatment scale inhibitors due to their excellent scale inhibition properties and excellent adsorption/desorption profile on reservoir rock.
