Pushing Conventional Boundaries of Hydrate Management in a Dry Tree Facility

摘要

In the oil and gas production industry, it is well known that formation of hydrate blockages can causernsubstantial economic impact in terms of deferred production and the costs of remediation. Considering thesernfinancial implications and to avoid any potential safety concerns during a hydrate remediation, most oftenrnoperating companies design and operate fields on a hydrate management philosophy of complete avoidancernof hydrate formation. In the last few years, however, a shift in the hydrate management philosophy is beingrnobserved as discussed in the publications of Creek et al., 2011 and Kinnari et al., 2015, to cite a few. Due tornthe developments shifting towards more extreme environments, hydrate management philosophy is shiftingrnfrom complete avoidance to risk management.rnThis paper discusses the evolution of hydrate management philosophy of a dry tree facility in the Gulf ofrnMexico. During steady state production, the fluids flow at temperatures outside the hydrate envelope. Thernhydrate management strategy following a shutdown is to displace (bullhead) the riser tubing with dead oilrnwithin the cooldown time (time required for the fluids to enter hydrate forming conditions after a shutdown).rnHowever, due to the dry tree configuration, low liquid rates and insulation performance, the cooldown timernis short for these high water cut wells. Using gas lift to boost production further decreases the predictedrncooldown time to less than an hour making it operationally difficult to complete hydrate safe out measuresrnwithin the design cooldown time. A few tests conducted in the field to identify a realistic time availablernafter shutdown, along with a few historical instances during which the hydrate safe out measures couldrnnot be completed within the cooldown time, have indicated that there exists a range of water cut (WC)rnand GOR (Gas to oil ratio) within which the system was restarted without a hydrate blockage. This paperrndescribes how a combination of industry standard predictive tools coupled with field observations is shapingrnthe hydrate management philosophy of this field, by operating within conditions that can form hydrates butrndo not lead to blockage. The paper also describes two hydrate blockage instances that occurred when thernoperating conditions were outside the identified hydrate blockage limit reinforcing that the WC and GORrnof the fluids have a strong influence on the hydrate blockage risk.