Wax Operating Envelopes
In a recent study conducted we performed a study on a gas condensate network which had just drilled an oil well with a high WAT (~60°C). The Operator wanted to examine different options for producing this well through the existing (uninsulated) gas condensate network. Numerous mitigation / remediation strategies were to be considered, such as:
· Chemical injection;
· Pigging;
· Blending i.e. ramp-down oil well; and
· Combinations of the above
An important part of this study was examining the current operation and only then developing wax operating envelopes with the oil well producing. Unbeknown to the Operator was just how close they were already operating to the WAT (and slightly inside in one part of the network).
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So utilizing the existing gas condensate for blending wasn’t really an option given there was already no margin to play with and blending isn’t a very efficient way of reducing the WAT either. The below plot shows that the inclusion of the oil well increases the WAT of the combined fluid and we are operating far inside it.
Although operation below WAT is not the preferred option, significant wax deposition would only occur at temperatures below WAT. Therefore a wax deposition study was performed to determine if the wax deposition rate would be significant and if operational pigging could be utilised instead. Although the deposition rates were relatively minor the pressure requirement needed to remove the wax every 30 days was too large.
Chemical testing was also performed to establish how much mitigation could be obtained. It was noted that some wax deposition was likely to occur still, but that this could be managed with pigging then. Chemical testing and later field trials are still being performed to determine the correct chemical and pigging strategy.
The key takeaway from this was that the current operating envelopes were unknown and the operation was already close to a wax risk. Understanding current operation is essential to understanding future operation (not just with wax!)
Thanks for sharing this interesting case study. Nice work. Do you have any thoughts or comments regarding the differences seen between the Matzain and RRR wax deposition models you shown in the last plot? The way I read this plot, there is no/minimal wax deposition for the first 2,500 meters of the pipeline. From there on, pigs move at different speeds and there is a significant difference in the pressure required to drive the pig forward. I would assume this is primarily due to differences in wax deposition thickness, or is this also impacted by differences in, e.g., breaking force? Can you elaborate on the differences, what can be expected from different wax deposition models out-of-the-box, and what would be recommended approaches if operational data was available?
Great summary Christopher Cooper. How long could we prolong pigging from 30 days, after the introduction of chemical injection? That would be interesting 🙏🏻. Will Pigging take away the Wax or supplemental Hot Diesel required to melt the Wax deposited in the case study. It's a complex operation for sure.
Great summary chris! Maybe just to add 🙈 in order to come to this conclusion, i believe we simulated hundreds of fluid blends (i think i got cross eyed for awhile 😵💫😅) considering current and future production tie-ins in order to find an optimum production ratio. But was not feasible.