Page 454 - Handbook Of Multiphase Flow Assurance

454 13. Risk analysis

Modeling dynamic behavior

Probabilities of individual flow assurance issues should be tabulated along with the im-
pact of such an event. Individual risks should be integrated in a dynamic field development
model to evaluate a range of probabilistic scenarios for reaching the target profitability per-
formance for the field.
Time-dependent events such as aquifer water breakthrough or injection water break-
through should be reflected by the increased risk to project performance.
After the project starts, with time, more understanding of the relative weights and conse-
quences for individual flow assurance risks becomes available. Risk based model should be
kept updated to both optimize the risk evaluation for the existing field and to serve as prob-
ability basis for the future fields.

Integration of various precipitation phenomena

All flow assurance and production chemistry issues should be evaluated simultaneously.
The likelihood of one issue may increase the probability of a different issue. An example from
a West African subsea tieback operation shows that a wax deposition risk was not managed
and wax was allowed to deposit and remain in the pipe as it was not causing a significant
hydraulic resistance to flow. A hydrate plug then formed, became solid. During pressure
changes attempting to resolve the blockage, the hydrate plug became mobile and scraped
wax off the pipe wall like a pig, compacting it into a secondary blockage. While hydrate could
be dissociated by depressurization, the paraffin blockage could not. This caused a significant
downtime to gradually dissolve the paraffin blockage with a solvent.
A similar example from USA deepwater shows a flowline where asphaltene was allowed
to deposit, which provided local restrictions in the pipe cross-section and promoted hydrate
accumulation and blockage.

Impact on overall planning

The combined field development plan should be prepared with input from and interaction
with flow assurance and production chemistry specialists, as well as corrosion engineers.
A systematic approach to risk analysis of the individual flow assurance issues and their
integration in a field development model can be used to support investment decisions.