Locally Sourced, Ecofriendly Hydrate Inhibitor Effective in Simulated Offshore Environment
Authors: Carpenter Chris 
Published: September 2019

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 193439, “Gas-Hydrate Inhibition in a Simulated Offshore Environment Using a Local Inhibitor,” by E.V. Urunwo, SPE, S.S. Ikiensikimama, J.A. Ajienka, SPE, O. Akaranta, M.O. Onyekonwu, SPE, T.O. Odutola, SPE, and E.O. Okon, University of Port Harcourt, prepared for the 2018 Nigeria Annual International Conference and Exhibition, Lagos, 6–8 August. The paper has not been peer reviewed.

Gas hydrates pose a serious flow-assurance problem in offshore environments where accessibility is restricted. The complete paper investigates gas-hydrate inhibition in a simulated offshore environment using a plant extract (PE) as a local inhibitor. The work aims to identify an effective biodegradable gas-hydrate inhibitor from locally sourced materials and ascertain its effectiveness compared with the conventional hydrate inhibitor monoethylene glycol (MEG). Experiments were conducted using a mini-flow loop, and involved mitigating hydrate formation using varying weight percentages of the inhibitor (1, 2, and 3 wt%) and evaluating their effect on hydrate inhibition in the mini-flow loop. Sensitivity charts for pressure, temperature, and time for both the PE and MEG were made. In 1 and 2 wt% of the PE, better inhibitory capacity than MEG was demonstrated, while 3 wt% of the PE and MEG had a close match. Because of its ecofriendly and biodegradable nature, the PE is therefore recommended for field trial.

Introduction

Kinetic hydrate inhibitors (KHIs) are water-soluble polymeric compounds that prevent or delay hydrate formation. Antiagglomerants (AAs) function as surfactants and prevent hydrates from sticking together and clumping. The hydrate still forms, but the crystals do not plug and can be transported through pipelines. Unlike thermodynamic hydrate inhibitors (THIs) such as methanol or glycols, low-dosage hydrate inhibitors (LDHIs) do not stop hydrate from forming completely because they do not cause a hydrate-curve shift. Once hydrate forms, it cannot be eliminated by LDHIs because the operating conditions cannot be changed (lowering pressures or raising temperatures); thus, a well is still at risk when LDHIs are used. THIs must still be available on site, especially when shutting in or starting a well.

The local inhibitor is a water-soluble PE containing flavonoids, tannins, alkaloids, and saponins. Flavonoids act against inflammation and are anticoagulants. They are polyphenolic compounds found in vegetables, fruits, and beverages, acting as powerful oxidants that protect against reactive oxygen. Tannins are a heterogeneous group of high-molecular-weight polyphenolic compounds with the capacity to form reversible and irreversible complexes. They are also found in fruits, legumes, and grasses. Polyphenolics are a class of chemical compounds consisting of a hydroxyl group bonded directly to an aromatic hydrocarbon group. They are otherwise called polyhydroxylphenols and are phytochemicals. They are a structural class of mainly natural products. Condensed tannins are the most-abundant polyphenols and are found in virtually all families of plants. Alkaloids are natural products that contain heterocyclic nitrogen atoms and are basic in character. They are synthesized naturally by a large number of organisms including animals, plants, bacteria, and fungi. Saponins are a group of secondary metabolites found widely distributed in plant life. They form a stable foam in aqueous solutions such as soap. Chemically, saponins as a group include compounds that are glycosylated steroids, hypernoids, and steroid alkaloids. Saponins also prevent agglomeration and are surface-acting agents with bubbles and foams acting as barriers that provide good stability.