ROBUSTNESS TESTING OF ‘COLD FLOW’

摘要

As presented earlier at the OFCS [1], a specific Cold Flow concept has been developed and tested under high-pressure laboratory conditions, building on the realisation that precipitation phenomena in multiphase production flows may be controlled through use of a recirculation seeding and cooling process, instead of being avoided at large costs. We will in this work present new experimental results from a high-pressure, temperature controlled wheel-shaped flow loop (an ‘endless’ system without a pump), showing that the proposed ‘Cold Flow’ process also seems to be rather stable with respect to perturbations. The results include data showing the hydrate slurry (from crude oil, with saline water): ? surviving temperature cycling up to and in some cases even above the hydrate stability temperature for the system in question, ? surviving injection of a large slug of warm water, and ? surviving a methanol slug injection. The oil used was a medium light North Sea oil. The oil recovered almost exactly its previous flow properties after temperature cycling to several levels within the system hydrate equilibrium limit at flowing conditions, and conditions where the cooling was done on a stagnant system. The stagnant cooling did indicate, however, that layers of water could form, and re-freeze in a ‘standard’ (non-Cold Flow) manner. In no cases were there signs of significant deposition. When the temperature was cycled up to (or even slightly beyond) the maximum equilibrium temperature for the system, the slurry was also seemingly reformed as a Cold Flow slurry upon cooling. The ‘surviving’ Cold Flow particles seemed in all cases able to dominate the hydrate formation processes when the flow was restarted cold, and to ‘pick up’ any separated water from the melting and subsequent cooling. The systems exposed to injection of hot water slugs or methanol slugs also showed good ‘survivability’. The physical and chemical processes involved in this Cold Flow process are complex enough that laboratory-size testing will always fall short of full-scale realism. However, within the limits of the experimental apparatus and procedures, we conclude that the level of robustness indicated in these tests is a strong indication that this Cold Flow process may be a good candidate for actual field implementation, and that it will probably withstand many possible system perturbations.