Flow assurance of hydrocarbon streams in subsea systems, such as pipelines, is a very important subject in the oil and gas industry. It is diverse and encompasses many branches of engineering disciplines. Flow assurance involves handling many solids deposits from hydrocarbon fluid streams that can form in subsea flow lines. Some of the flow assurance risks in subsea pipelines include gas hydrates, slugging, corrosion, reservoir souring, wax, scales etc. Among these flow assurance risks, hydrate formation is of major concern in the oil and gas industry. Hydrates are solid-crystalline compounds formed when water come into contact with light hydrocarbons such as methane, ethane and propane under thermodynamically, usually high pressure and low temperature. Hence, hydrate readily form in flow lines transporting hydrocarbon streams along with produced water often lead to pressure drop in flow lines and eventually plug flow.
Nowadays, offshore oil and gas projects have been moving further into the deeper sea where hydrates are significant problems due to favourable high pressure and low temperature conditions. As a result, deep water flow assurance has become an increasingly major concern for oil and gas industry. The potential formation of hydrates in gas production is of great importance in connection with pipeline transportation of hydrocarbon liquids and with the production of fluids from natural gas or gas condensate reservoirs. Hydrate formation during oil and gas production can plug production facilities and cause a long-term problem to oil and gas project. According to Dholabhal et al. (1993), the accumulation of hydrates is common in the horizontal sections and around fittings could lead to disastrous pipeline blockage.
Hydrates are significant problems in upstream oil and gas production because the deep sea operating temperature and pressure conditions suit the formation of hydrate (Chen et al., 2008; Song et al., 2009). Plugging of subsea flow lines, valves, instrumentation can lead to explosion, in addition to pipeline rupture can lead to spills of containment, environmental disaster and high cost of repair and maintenance. For instance, the worldwide methanol costs for hydrate inhibition are estimated at US$740,000 daily in Creek et al. (2011). Additionally in Jassim et al. (2008), offshore operations employ approximately $1 million per mile for insulation of subsea pipelines to prevent hydrates, while Lysne (1995) reported three incidents in which hydrate projectiles broke through pipelines at elbows and caused loss of personnel lives and over $7 million (US ) in capital costs.
Petrochemical industry has shown considerable interest in the conditions under which hydrates will form, predominantly in areas where light hydrocarbons and related materials are being handled, stored and processed (NG and Robinson, 1977). Many experimental and theoretical studies have been completed on hydrate formation in system containing...