Approaches to the Selection of Effective Inhibitors of Gas Hydrate Formation

Abstract

Hydrocarbons production in gas-lift wells of the Eastern section of the Orenburg oil and gas condensate field (ESOOGCF) is complicated by gas hydrates formation in oilwell tubing, shutoff-opening and control valves and gas lift system. In order to prevent hydrate formation, continuous supply of methanol is used, causing additional economic costs and environmental risks. Therefore, it is important to search for new more effective reagents to remove and prevent gas hydrate formation. The aim of this work was to choose the most effective inhibitors of hydrate formation for ESOOGCF conditions. The study was carried out among thermodynamic and kinetic inhibitors for gas hydrates formation. Due to different mechanism of inhibitors action, various approaches were used to evaluate their effectiveness. Experimental conditions were as close as possible to the field ones: the model gas-liquid mixture was used, the appropriate temperature and pressure conditions were determined. Thermodynamic inhibitors which reduce hydrate formation temperature were kept at a constant temperature in the GHA 350 autoclave under continuous stirring: temperature T=2°C and initial pressure 50 atm. during 12 hours. The study of kinetic inhibitors that slow down the process of hydrate formation due to adsorption on hydrate crystals was carried out by polythermic method in the temperature range from 8°C to −15°C using the RCS6 equipment with initial pressure 30 bar. The effectiveness of inhibitors was evaluated by initial temperature of absorption of hydrate-forming gas due to hydrate formation. It was proved by pressure drop in the system. In the process of studying of thermodynamic inhibitors, the formation of hydrates in the system could also be recorded visually. As a result of the experiments it was found that thermodynamic inhibitors better prevent hydrate formation in the conditions of ESOOGCF at concentrations of 15% or 20% by volume in produced water as almost all of the reagents studied showed high efficiency. Among kinetic inhibitors, only two reagents showed positive results in hydrate formation reduce at volume concentrations of 2.5% and 5% of the amount of produced water. All manufacturers whose reagents successfully passed laboratory tests were invited to participate in field tests. For today field tests of two reagents of different types of action have been carried out. During these tests the minimum effective concentration of a thermodynamic inhibitor was determined - 164 L/day. For comparison, methanol consumption before the field tests was 500 L/day despite the fact that the reagent is not inferior to him in technical terms. The minimum effective dosage of the kinetic inhibitor of hydrate formation according to the results of field tests was 50 L/day. Thus, the application of thermodynamic and kinetic inhibitors of hydrate formation is economically profitable under the same technical parameters of the base reagent. The conditions of each individual object require an individual inhibitors selection which can show the best efficiency in these conditions. Currently, effective dosages of hydrate inhibitors are determined during field tests, which lead to high economic costs and technological risks. This paper proposes an assessment of inhibitors' effectiveness in laboratory, which reduces the cost of reagents selection and minimizes technological risks. The paper presents economic benefits of using low-dose inhibitors in front of the basic reagent - methanol. This article focuses on different approaches to the selection of effective inhibitors of hydrate formation. Research objects are hydrate-formation inhibitors for conditions of the Eastern section of the Orenburg oil and gas condensate field. Nowadays continuous supply of methanol is used to prevent hydrate formation. Due to the need for more efficient and cost-effective solutions, searches are being conducted for new ways to reduce hydrate formation.