Page 41 - Handbook Of Multiphase Flow Assurance

36 2. Initial diagnosis and solution of flow assurance production problems in operations

The most common differential pressure increase or no flow during a restart of a shut-in
system can be caused by a hydrate formed after MEG supply failure, scale after water break-
through, by a wax or asphaltene partial restriction cemented by a hydrate, a waxy gel, or by
a closed valve.
Other types of pressure behavior on a relative timescale with possible causes are described
below.
Restriction may be partial or complete. If there is pressure communication through a restric-
tion, solvent should be injected if safe to do so, in order to retain the pressure communication.
Below is provided a short summary of the general characteristics of each type of flow as-
surance issues, deposits or flow restrictions. Additional characteristics of the flow assurance
problem may be obtained from deposits collected at a separator inlet screen, or from the
observation of system behavior. Some general characteristics listed below may be used to
confirm the possible cause.
Asphaltene—hard and dark in color, heavier than water. Occurs in both light and heavy
oils. Common locations are in reservoir, in well production tubing, at subsurface safety
valve, in tree and in flowline.
Bacterial deposit—can be a soft accumulation in pipe or process equipment, or a hard
biodome inside a line pipe. Typical location is in surface water processing equipment.
Corrosion products—usually nonmagnetic. Can occur in any part of the production
system from well bottomhole to export pipeline when a chemical is present which takes

TABLE 2.1 Types of pressure behavior on a relative timescale with possible causes

Time of differential pressure change
Type of differential
pressure change Minutes to hours Hours to days Days to weeks Weeks to months
Single increase Mechanical, stuck Scale, hydrate Asphaltene, liquid Wax, liquid (water or
scraper, closed valve, plugging a gas line holdup in intrafield condensate) holdup
leak with seawater line in long export line
ingress
Multistep increase Hydrate plugs Multiple hydrate Sand in intrafield
forming in oil line plugs dissociating line
Single peak Water hammer, Injector well damage Waxy gel breaking
liquid surge with relief
Multiple oscillations Slugging, well liquid Severe or terrain Hydrate with wax Pressure buildup
loading, choke PID slugging compaction from gas hydrate
controller deposit
Single decrease Leak, hydrate plug Hydrate forming in a Scale formation Reservoir depletion
movement shut line damage
Multistep decrease Controlled
depressurization
Single trough Asphaltene
formation damage
with subsequent
relief downhole