Abstract

The paper describes the development of the first readily biodegradable - in seawater - phosphonated amino acid chemistry (PHAAC), which is able to control calcite and calcium sulphate scale under unconventional HTHP1 conditions (simulated Shearwater field conditions and T/P up to 250°C/1,000bar). This novel chemistry is aimed to support unconventional and ultra HTHP productions in a cost-wise sustainable manner.

The chemistry development is described from the selection of the suitable chemical functionalities through the evaluation of the "must have" properties – brine compatibility, thermal resistance, eco-toxicity profile – to the assessment of performance for calcite, calcium and barium sulphate by dynamic and static scale inhibition tests under uniquely severe conditions (T= 55°C-250°C, salinity = max. 250,000ppm, Calcium = max. 18,960ppm). Successful squeeze simulation was tested at high temperature with a high Ca connate water. Software simulations - Pitzer electrolyte theory - were used to preliminary screen out and define conditions.

The novel chemistry, when compared to industry benchmark inhibitors from low (55°C) to ultra high temperature (250°C), showed an extremely positive overall performance gap. The product thermal resistance evaluation and its impact on chemical stability, properties and performance, is presented showing that stability of the chemical structure - only 1.3% degradation after 7 days at 160°C - eliminates the performance drop when conditions get severe. Minimum inhibitor concentration of the novelty chemistry is up to 10 folds less than conventional chemistries in dynamic scale rig tests and squeeze life is excellent, allowing remarkable cost saving in treating scale in extreme conditions. Detrimental effect of Fe++ on performance and chemical compatibilities are also assessed. Negligible toxicity against marine species and readily biodegradability in seawater makes the chemistry suitable for offshore operations in OSPAR countries. Presented results coupled to ease of detection proof that the new experimental environmentally friendly scale inhibitor can be successfully deployed in HTHP applications for the control of calcium carbonate and calcium sulphate under extremely severe regimes.

The novel chemistry is the first readily biodegradable (OECD306) phosphonate for scale inhibitor applications in HTHP unconventional conditions. It sets new levels of performance in the control of frequently encountered scale types in O&G. The documented inhibitor properties and performance, confirm that it can be a game changer for flow assurance strategies in unconventional productions.

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