Page 185 - Handbook Of Multiphase Flow Assurance

Interaction of flow assurance issues with and effects on produced fluids and flow 181

Solubility of scales in acids usually increases with temperature. Laboratory verification
of scale type and selection of the best solvent is required for efficient remediation of formed
scale deposits.
Barium sulfate scale is insoluble in water or acid and has to be removed by chelant chemi-
cal treatment, or by mechanical milling.
Scale may be controlled by optimization of operating pressure or temperature to reduce or
prevent scale precipitation, or by injection of chemical inhibitors.
Scale inhibitors are usually deployed downhole in the deepest chemical injection location.
Inhibitors may be deployed as periodic batch treatments via annulus, as continuous treat-
ment via chemical injection tubing, as periodic treatment by squeeze into reservoir rock, and
as periodic treatment with solid soluble material placed in well sump.

Scale prevention
Scale management aims to mitigate the risk of scale restriction by physical or chemical
means. Physical means include avoiding comingling of incompatible fluids from multiple
zones.
Scale potential should be evaluated based on laboratory measurements of water samples
collected under pressure and properly preserved upon depressurization. In absence of water
samples from exploration/appraisal wells, one may utilize high pressure water chemistry
from analog fields.
Technologies which could be considered for management of scale in produced fluids
include:
• Scale inhibitor chemical on topsides, at tree, or downhole
• pressure maintenance to reduce carbonate evolution
• desulphation of injection water
• preventing comingling of incompatible fluids.
Note that scale inhibitor chemical deployment downhole may be accomplished continu-
ously by injection via capillary tube, periodically by squeeze into the formation, periodically
by soluble pellets in sump, or initially by proppant pellets impregnated with chemical.
Some examples of scale inhibitor chemicals include phosphonate, polyacrylic acid, polyvi-
nylsulphonic acid or phosphinopolycarboxylic acid.
Following remediation technologies could also be considered as a back-up.
• acid or water solvent wash, depending on scale type
• coiled tubing to mill out the deposit, especially for a wellbore or a riser for insoluble
scales

Interaction of flow assurance issues with and effects on produced
fluids and flow

The issue of interaction of flow assurance issues is an interesting one, and was brought into
a separate section rather than listing the likely interactions individually for each issue.