Qualification of Scale Inhibitors for Sub Sea Tie Backs with MEG Injection

Abstract

The Ormen Lange field are using continuous injection of MEG to prevent hydrate formation. The MEG is regenerated and reused, and corrosion control of the multiphase pipelines are accommodated by a combination of pH stabilised MEG and corrosion inhibitors. In order to avoid scaling if formation water is produced a scale inhibitor will be added to the lean MEG.A comprehensive scale inhibitor qualification program was carried out, and the goal was to qualify one or more scale inhibitors for scale prevention downstream the MEG injection point at subsea wellhead for fully and partial pH stabilisation. 5 suppliers were invited to supply inhibitors to be included in the qualification programme and the suppliers submitted a total of 10 inhibitors. The qualification program included environmental properties, solubility in lean MEG, scale inhibitor screening tests, scale inhibitor dynamic tests, compatibility of chemicals, emulsion and foaming, partitioning, effect on particles formation and settling onshore, consumption/loss of scale inhibitor in the MEG process and stability in MEG regeneration reboiler.The different tests are described and the results are displayed. The results from the qualification program demonstrated that only few inhibitors satisfied all requirements, the chemicals affect the formation and precipitation behaviour of calcium and iron carbonate and that only one combination of scale and corrosion fulfilled all the requirements. If a scale inhibitor has to be used in combination with a corrosion inhibitor compatibility testing is required. Incompatibility between corrosion and scale inhibitor will cause gunking and scaling. A successful combination of corrosion and scale inhibitor will not increase the corrosivity and simultaneously prevent scaling. It has been observed that such combination of chemicals does not prevent formation of particles but prevents the particles to stick to the surface.The scale qualification program demonstrates the complexity in qualifying chemicals and the need for a good dialogue between the involved disciplines.

The influence of magnetic fields on calcium carbonate scale formation within monoethylene glycol solutions at regeneration conditions

“…However, in such applications, several problems may arise following the breakthrough of formation water and subsequent introduction of mineral salts into the regeneration loop 15,18 . The introduction of divalent cations including calcium, magnesium, and barium, pose a scaling risk within critical systems including subsea pipelines, and MEG injection points 20 as well as within MEG regeneration systems operating at a higher temperature such as reboilers 17,21 . Scaling within the MEG loop and associated systems can be controlled by careful control of system pH or by injection of suitable scaling inhibitors [21][22] .…”

Experimental investigation and kinetic modeling of nanocrystal growth for scale reduction in mono-ethylene glycol regeneration unit

“…Using the optimized values of adjustable parameters, the growth models of crystallization deposition in a MEG solution without and with silica nanoparticles can be expressed by Eqs. (15) and 16…”

“…Crystal growth of CaCO 3 in mixed MEG water solvent was studied by Flaten et al [12], and its impact on the performance of re-boilers was tested by Kananeh et al [13]. Moreover, the impact of using different kinds of inhibitors like hydrate, scale, and corrosion inhibitors on scaling under oilfield condition was discussed, as an inappropriate selection of these chemicals can lead to severe fouling, foaming, and emulsion issue in the facilities of MEG line [6,[14][15][16][17][18].…”

“…Also, such inhibitors are sensitive to equilibrium changes. This can be a reason why a particular inhibitor loses its effectiveness after a while, and scale forms even more aggressively [15,20,23]. Particularly, the ion-exchange softening unit used to remove cations and anions from MEG solution may not operate efficiently due to leakage and many other maintenance issues in its hydrochloric acid equipment.…”

Hydrate Phase Equilibria of Phosphonate Scale Inhibitors, Amines, and Ethylene Glycol

“…Scaling can cause serious complications in pumps, valves, and other production equipment while increasing inner surface roughness, decreasing the pipeline diameter thus causing a pressure drop or complete flow blockage leading to loss in production time. , Typical scales that occur in oilfield production are calcium sulfate (CaSO 4 ), barium sulfate (BaSO 4 ), strontium sulfate (SrSO 4 ), and calcium carbonate (CaCO 3 ). , Scales of the sulfate type occur due to the mingling of different waters that are chemically incompatible such as formation water, seawater, or injection water as given in eq , while carbonate scales have a tendency to form due to pressure reduction or an increase in pH caused by escaping CO 2 . , In some fields, formation of water production occurs later in the life of the field, thus increasing the risk of scale formation. At this time, the use of amines such as methyldiethanolamine (MDEA) for corrosion control via the pH stabilization method can no longer be employed because of the high risk of scale formation. , Thus, there is a change in the corrosion control method, whereby a film-forming corrosion inhibitor is utilized, while the use of a scale inhibitor (typically phosphonates) becomes incumbent to protect the system and to prevent/reduce scale formation in pipelines. , …”