Low-Dosage, High-Efficiency, and Environment-Friendly Inhibitors: A New Horizon in Gas Hydrates Mitigation in Production Systems

Abstract

Abstract Presently, gas hydrates formation pose problems, causing flow restrictions, in gas and oil industry including drilling operations (particularly in deep water), production process, well workovers where gas and water come into contact at equilibrium conditions. Traditional hydrate control methods of insulation and/or thermodynamic or chemical inhibition may not provide the desired level of hydrate protection at an economic price. Low-Dosage Hydrate Inhibitors (LDHIs) are a proven technology to control hydrates in numerous applications and are instrumental in reducing the total cost of operations. Low dosage Inhibitors are either kinetic, thermodynamic inhibitors or anti- aglomerants, which either prevent hydrate formation or remove the hydrates that are already formed respectively. Therefore, this paper focuses on introduction to such low dosage inhibitor which can perform all the functions like prevention of formation of hydrate nuclei (like kinetic or thermodynamic inhibitors) and dispersing the already formed ones in flowlines (like anti- agglomerants). This paper proposes the use of Cationic polymers like cationic starch (from a high amylose carbohydrate source) in low concentration with addition of Polyethylene Oxide (PEO) as a new Gas Hydrates inhibitor. The polymer with PEO, dissolved in water, can be introduced in petroleum fluid using mechanical equipment or utilized in treating fluid prior to substantial formation of the hydrates. As observed from an experimental analysis, these positively charged polymers interfere with nucleation of hydrates, increase induction time of gas hydrate nucleation, suppress memory effect, and act as antifreeze and thereby controlling hydrates. With reference to these polymers, their abundant availability, easy application techniques and simple cationization procedure all contribute to its inexpensive and environment friendly usage as gas hydrate inhibitor. This paper provides systematic approach and relevant theoretical explanation for the proposed technique. Introduction Gas hydrates form when water molecules crystallize around guest molecules such as light hydrocarbons, methane to heptane, nitrogen, carbon dioxide and hydrogen sulphide. To varying degrees, the extracted oil and gas mixture contains water. In the presence of water, and under a fixed range of pressure and temperature conditions (greater than 80°F), specific to each hydrocarbon mixture, hydrates of the light gases can form. Hydrates, which have a crystalline structure analogous to that of ice, form solid plugs and block the flow. Clearly, inhibition of hydrate formation is of utmost interest to industry. Formation of gas hydrates can be inhibited by several methods. The principle of these methods is to control or eliminate one of the four essential elements necessary for hydrate formation. The four essential elements are: the presence of hydrate-forming components in natural gas (e.g., methane), the presence of water, conditions of low temperature and high pressure. The absence of any of these four elements would make hydrate formation impossible. Depressurization i.e. reducing pressures at both side of hydrate plugs helps in hydrate control. Transmission lines heating and insulating is a common mechanical solution to hydrate problems encountered in a long sub sea pipelines. Hydrates will never form if the gas/water is kept above hydrate formation temperature. Preheating of the well bore in exploratory wells during well testing is also one of the methods employed. However, in practical field operation, water can be economically removed to a certain vapour pressure only and residual water vapours are always present in dry gas. Removal of water and providing insulation is beyond economical limits. Preheating well bore too adds to tremendous energy loss.