Selecting Chemicals Applied to Recoverable MEG Used for Hydrate Protection

Abstract

Hydrate protection of gas condensate production can be achieved by injection of monoethylene glycol (MEG) thermodynamic hydrate inhibitor. After mixing with produced fluids, the MEG is recovered and reused by regeneration to reduce the water content, and/or reclamation to reduce highly soluble monovalent salts. These systems come in a variety of configurations and may also include a pre-treatment stage whereby divalent cations in the produced MEG containing fluids are reduced. Regeneration units may operate up to 160°C and reclamation units up to 135°C. The process is cyclical as the recovered MEG is pumped back to the producing wells for hydrate inhibition. As with any production system, chemical additives are injected to aid corrosion inhibition, scale inhibition, demulsification, wax inhibition, foaming, water clarification and so on. These chemical additives may be injected upstream or within a MEG recovery process and as such their components are present under severe cyclical regeneration and reclamation processing conditions. The components within these chemical additives may build-up in the MEG and cause fouling, alternatively referred to as gunk. Gunk may cause operational issues that cannot be easily remediated by normal clean in place operations. Hence, prior to the introduction of a new chemical additive in the field a laboratory gunking assessment needs to be conducted. In this paper, two methods to assess chemical additive gunking are described along with the results of testing. The first method is a mud bomb test where MEG fluids containing chemical additives are placed in pressurized vessels at regeneration system temperature under pressure for 24 hours. Results are then assessed by visual observation, turbidity, total suspended solids, and oil in water measurement. This method proved to be a quick method to rapidly screen various fluid compositions and chemical additives. The second method is a rotary evaporator – reflux test to simulate regeneration and reclamation conditions. This is a more intensive technique that should be conducted as a confirmation test whenever a new chemical additive is introduced into a process. Again, results were assessed by visual observation, turbidity, total suspended solids, and oil in water measurement. Finally, a novel dispersion test is described which proved valuable to further qualitatively assess if a chemical additive gunked. Most chemical additives tested in our laboratory by both methods tend not to gunk. However, a cationic acrylamide copolymer chemical additive that was being assessed to aid divalent cation solid agglomeration did gunk. This test as well as being a valuable reference to future chemical additive gunking assessments also showed how visual observation is the best indicator of chemical additive gunking. The laboratory gunking assessment methodologies and results presented here is how the authors establish if a chemical additive is likely to gunk in a particular gas condensate production process with a MEG system. There are other methods used in the industry, but a lack of published literature is available. We hope that this paper will invoke others to publish how they assess chemical additive gunking with the aim to eventually have a standard practice established within the oil and gas industry.