Page 187 - Handbook Of Multiphase Flow Assurance

Seven suggestions from operations in deepwater and onshore 183

‐ Mechanical movement; hydrate plugs have been known to move and scrape wax
deposit from a pipe wall into a solid wax blockage, which could not be removed by
depressurization.
‐ Mechanical expansion; hydrate expands more than ice relative to liquid water upon
freezing; hydrate formed downhole has been known to crush well tubing. Mechanical
expansion also affects rock consolidation in natural environments as hydrate formation
and dissociation over geologic times affected sediment strength.
‐ Hydrate formation introduces solid particles, which may lead to increased
erosion-corrosion.
‐ Hydrates are water-based compounds and remove water from produced stream;
removal of water may cause other water-dissolved materials to precipitate; It was
confirmed experimentally (Hu et al., 2018) that solid halite scale does precipitate out of
water solution after hydrate formation consumes some water. It is also hypothesized
that chemical inhibitors formulated in water may precipitate out of solution as water
molecules are removed into hydrate.
‐ Hydrates consume light hydrocarbons and sour gases. Change in the amount of
dissolved methane may affect asphaltene stability; change in CO 2 content may affect
carbonate scale stability; change in H 2 S content may affect corrosion.
‐ If dissociated in Arctic or other sub-zero environments by depressurization, hydrate will
convert to an ice plug and remain as ice until the warm season; in Arctic subsea with
−2 °C seawater temperature time to a warm season may take a while.

Seven suggestions from operations in deepwater and onshore

FA is prediction and management of physical and chemical behavior of produced fluids to
ensure uninterrupted operation. The following are suggested as seven rules of a successful
flow assurance engineer (both multiphase and production chemistry).
1. Keep track of your fluids.
Double check what's being injected and whether it's compatible with the fluids and ma-
terials in place. Chemical tanks may get re-badged or de-badged en-route or at the blending
plant.
2. No inhibitor gives 100%.
Even after passing lab tests for one set of fluids, inhibitors may underperform in changed
fluids.
3. Displace while you still can.
Use a proven method to safe-out systems from hydrate even if another issue (scale etc.) is
suspect.
4. All models approximate.
A recent comparison across commercial and in-house software packages brought up dis-
similarities and gaps in inhibition prediction for brines+MEG.
5. Unplug from downstream.
In a short system (a jumper) a solid month-old hydrate blockage was unplugged after
methanol was injected in reverse to the original flow.