[h=Transient Flow]1[/h] [h=Shut-in and Start-up]2[/h] Start-up
Hydrate inhibitor should generally be injected downhole and at the tree during start-up. When the start-up rate is high, inhibitor is not required downhole, but the hydrocarbon flow should be treated with inhibitors at the tree. Otherwise, the hydrocarbon flow is required to be treated with inhibitors downhole. Once the tree is outside the hydrate region, hydrate inhibitor can be injected at the tree and the flow rate increased to achieve system warm-up. The Start-up scenario is different for the combination of cold well with cold flowline and hot flowline (commingling production with that from other wells).
Planned Shut-in
Unplanned Shut-in
If the system is shutdown from a steady state,
- The first step is to see if the system can be restarted within 2 hours. If so, startup should begin.
- If not, one option for hydrate control is that the riser will be bullheaded with MeOH (if MeOH is chosen as a hydrate inhibitor) to ensure no hydrates are forming in the base of the riser where fluids are collecting.
- Next the tree piping will be dosed with methanol.
- After that, the fluid in the flowline will begin to be fully treated with methanol.
- Once 8 hours has been reached, operations must determine if the system can be started up or not. If it can be started, they will proceed to the startup procedure outlined previously.
- If it cannot be started up, the flowlines will be depressurized. The intention with depressurization is to reduce the hydrate dissociation temperature to below the ambient sea temperature.
- Once the flowlines are depressurized, the flowlines, jumpers, trees are in a safe state.
- If the wells have been shut in for two days without the system starting back up, then the wellbores need to be bullheaded with MeOH to fill the volume of the wellbore down to the SCSSV.
Once these steps have been taken, the entire system is safe.
[h=Blow-down]2[/h] [h=Turn Down and Ramp-up]2[/h] [h=Pigging and Slugging]2[/h]
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