Page 15 - Handbook Of Multiphase Flow Assurance

Examples of flow assurance problems 9

Fig. 1.8 Solid salt scale plug in an Orenburg gas-condensate well, 100 mm diameter. Photo by Yuri F.
Makogon, Originally published by PennWell Corporation in Hydrates of Hydrocarbons, 1997 and reprinted with permission.

saturation. As water flows from the reservoir with the produced gas or oil, its pressure and
temperature change, which affects the solubility of dissolved ions in water. Saturation limit
for some ions may also be reached because water composition changes if the water table rises
to the produced zone from another zone. Similarly, waters saturated with different ions from
different zones mix, some ions combine and solid scale may form and restrict the pores in
reservoir rock or in well tubing, thus limiting the productivity.
Saturation limit for salt ions in water may also be reached because water molecules get
consumed to form a hydrate leading to a concentrated brine, or because of the change of
pressure or temperature.
Hydrate formation can also lead to precipitation of solid salt scale in small-volume closed
systems (Hu et al. 2017a,b, 2018)
Petroleum industry access to ultra deep reservoirs often has to deal with high-pressure
and high-salinity fluids. Reservoirs with fluid pressure over 180 MPa are in appraisal and
development. Fluids in the reservoir may also be nearly saturated with salt in pre-salt
deposits located under salt domes and diapirs. This combination of high pressure and
high salinity of such fluids presents a unique set of challenges for wellwork and produc-
tion engineers because in order to complete a well or to produce such fluids, formation of
solid phases must be avoided. Solid phases may include gas hydrates or scales such as ha-
lite. During well completion, heavy brines are used to offset by their hydrostatic pressure
the high pressure of reservoir fluids in order to avoid a well blowout. At the same time,