Page 30 - Handbook Of Multiphase Flow Assurance

24 1. Introduction

Threats to flow are normally attributed to flow assurance
Flow assurance aims to achieve an economic balance between prevention and mitigation
of mechanical or hydraulic restriction threats to flow such as hydrate plugs, scale plugs, se-
vere slugs, liquids holdup, wax plugs, asphaltene plugs, without reaching the costly reme-
diation stage. The detailed risk analysis of each threat compares the probability or frequency
of it happening during the life of field and the cost of the consequence against the cost limit
acceptable to each specific operator. Some operators may have a company policy that no
risk of blockage is acceptable because the contractual cost of a disruption to production can
be very high while others rely on their own experience and laboratory verification to accept
some amount of risk. However, risk analysis performed by specialists, who may soon retire,
should be viewed with additional independent verification.
A detailed understanding of the flow system and fluid properties are required in order to
develop a coherent design for field development.

Threats to product value or process safety (asset integrity)

Asset integrity or product value also get affected in some cases, such as severe slugging
in an un-braced flowline or jumper, a hydrate projectile movement during depressurization,
erosion by sand or treatment with methanol.
Production chemistry deals with prevention and mitigation of fluid composition threats to
product value or process safety (asset integrity) such as water in oil, oil in water, salt in oil,
oxygen in water, mercury in fluids, H 2 S in gas, corrosivity, and/or bacteria.

Hardware cost

The cost of hardware keeps continually increasing. The cost of subsea tiebacks has been
getting more expensive in the past two decades well outpacing the inflation.

Cost of subsea hardware related to flow assurance
It is prohibitively expensive to place a floating host facility with separation and processing
of produced fluids over each drill center. Such platforms, like Pompano, do exist in deepwa-
ter and use dry trees to produce fluids. It is more economic to use subsea tiebacks to produce
hydrocarbons from several drill centers or several neighboring fields to the same host facility.
Infrastructure-led exploration (ILX), or looking for more hydrocarbons near the existing fa-
cility, is key to deepwater profitability. Not only this allows to tie in new fields to the existing
facility, but it also allows export of separated hydrocarbons via existing export lines, which
improves project economics.
The highest net present value (NPV) deepwater project to-date is Na-Kika (Riazi, 2016) de-
signed by Shell and operated by BP in the US Gulf of Mexico with multiple subsea tie-backs.
Na Kika translates as octopus (Encyclopedia Mythica). ILX means that several commercially
producible average sized fields must exist within a 10–20 km radius which can be tied back to
the common host facility. Production of petroleum from these fields may then be scheduled
in phases, allowing less risk in capital investment.