Page 201 - Handbook Of Multiphase Flow Assurance

198 6. Production chemistry and fluid quality

Calcium naphthenate is a calcium soap of naphthenic acids in crude oil, and appears as a
light brown gel.
Sodium naphthenate looks like white gel or clear dark brown liquid. Sodium naphthenate
behaves as an emulsifier and as a mild detergent.
Naphthenic acids molecular weight ranges from 120 to over 700 g/mol. Naphthenic acids
may be present in immature heavy oils. Paraffinic crudes usually have low acid content.
Naphthenate potential can be evaluated with laboratory measurements of oil and water
samples collected under pressure and properly preserved as needed upon depressurization.
ARN-acid is the naphthenate of concern for the calcium naphthenate issue.
The naphthenate potential is analyzed based on the total acid number (TAN), the CO 2 con-
−
tent in the reservoir oil and bicarbonate ion HCO 3 in reservoir brine. Total acid number can
be determined by thermometric titration.
Naphthenate restriction may be controlled by chemical or physical means. Physical means in-
clude avoiding incompatible fluids commingling, if it is practical to have segregation with a slid-
ing sleeve completion or having separate wells and flowlines for different incompatible reservoirs.
Technologies which could be considered for management of naphthenates in produced
fluids include:
• Naphthenate inhibitor chemical
• Preventing exposure of oil to calcium-rich water
• Acetic acid chemical
• Selection of a different emulsion breaker chemical to remedy separation threats

Heavy oil management

Heavy oil increases the backpressure on reservoir which reduces production by high
density.
Technologies which could be considered for management of heavy oil in produced fluids
include:
• Artificial lift
• Preliminary water knock-out or subsea water separation
• Multiphase pumping.

Viscous oil management

Viscous oils increase the backpressure on reservoir which reduces production by high vis-
cosity. In some countries the oil is considered to be viscous when its viscosity at reservoir
conditions exceeds 200 cP.
Technologies which could be considered for management of viscous oil in produced fluids
include:
• Multiphase pumping
• Drag reducing agent chemical