Page 29 - Handbook Of Multiphase Flow Assurance

Introduction to flow assurance risk analysis 23

Thermal Fluid flow Equipment

hydraulic Threats to Fluid quality Mitigation with chemistry

fluid-related Pipe integrity procedure

Fig. 1.15 Graphic of a bow-tie risk analysis for flow assurance.

The bowtie risk analysis is well suited to look at how well the protective barriers against
flow assurance threats are placed, and how well the remediation efforts can prevent the un-
desirable consequences.
Thermal threat may seem redundant as viscosity (hydraulic) and solids (fluid-related)
effects emerge as fluids cool down, but one should remember about the high temperature
aspects of HPHT. We can't flow if we can't effectively use corrosion inhibition at high tempera-
tures. Flow assurance helps with HPHT as well. An example is the 143 km long Snohvit line
in the N.Sea. Typical corrosion inhibitor chemicals may lose efficiency above 250 °F. Snohvit
field uses a cooling spool section of flowline long enough to cool the hot produced fluid with
seawater to 250 °F before switching to a carbon steel flowline. Regular corrosion-resistant
alloys (CRA), which may be used to transport corrosive fluids, also may have temperature
limitation of 85 °C.
The seven steps to flow assurance risk management include:

(1) Define data source
(2) Define objects to view
(3) Define the factors and threats
(4) Describer the mitigations and inspections
(5) Create an integrity model
(6) Calculate relative risk from threats
(7) Assign mitigations and inspections to each threat

After the mitigations and inspections are identified, the operations cycle may go into the
usual continuous improvement loop of Plan-Do-Check-Adjust to eventually achieve steady
quality. Risk analysis aims to quantify threats in order to achieve an economic balance be-
tween prevention and cure. Every field is different, and in very remote areas without devel-
oped infrastructure, the access to remediation technology for a formed blockage may take a
very long time which will significantly affect production and revenue, so less risk may lead
to a better project profitability. Conversely, in a region with abundant services, the time to
call in blockage removal specialists may be minimal so more risk may be taken and some up-
front capital and operating cost may be saved without significant additional impact to the net
value of the project.
Before one starts to analyze flow assurance risk in order to save cost and optimize budgets,
one should develop a list of relevant parameters to allow planning of our approach to solving
flow assurance challenges. As said above, the relevant parameters will be region-specific.