STANDARD HANDBOOK OF PETROLEUM & NATURAL GAS ...

Drilling Muds and Completion Fluids 707
Factor Considered
3. Fluid properties
Density
Solids content
Fluid loss
Rheology
Completion and Workover Fluid Considered
Ideal requirements: Fluid density should not be greater than
that which balances formation pressure.
Practical recommendation: Differential pressure should not
exceed 100-200 psi.
Ideal requirements: no solids in completion and workover
fluids.
Practical recommendation: Solids smaller than two microns
can be tolerated as well as the bridging solids. The bridging
solids should be: (1) greater than one-half of the average
fracture diameter: (2) readily flushed from the hole; acid or
solvent soluble.
Ideal requirements: no fluid loss.
Practical recommendations: Fluid loss to the formation can
be controlled by: (1) fluid-loss agents or vixcositiers such as
polymens, calcium carbonate, gilsonit, asphalt etc., (2) bridging
materials.
Ideal requirements: low viscosity with the yield point and gels
necessary for hole cleaning and solids suspension.
Practical recommendation: A compromise should be found to
minimize pressure losses and bring sand or cutting to the
surface at reasonable circulating rate.
Courtesy Baroid Drilling Fluids. Inc.
low damaging fluids are recommended and often a solids-free fluid is preferred.
This is because filter cake from a high solids fluid can completely fill a
perforation and be difficult to remove on back flowing or acidizing.
Perforating under diesel is sometimes employed. In this case, care is necessary
to ensure that good displacement of the previous denser fluid occurs, and the
completed zone remains in contact with the diesel without density swapping.
Perforating fluids used may be filtered clear brine or CaCO, type completion
fluids, oil, seawater, acetic acid, gas or mud.
Where large losses to the formation are probable, perforation under slugs
containing degradable bridging and loss control materials is advised. At least,
such materials should be on hand should the need arise. Under these conditions,
it is far better to fill perforations with good, degradable, bridging material than
the common mixture of iron and rust particles, mud solids, and excess pipe
dope. These foreign solids may be also not exhibit bridging and be injected into
the rock around the perforations, causing irreparable damage.
Clear Brines. Brine solutions are made from formation saltwater, seawater, or
bay water, as well as from prepared saltwater. They do not contain viscosifers
or weighting materials. Formation water-base fluids should be treated for
emulsion formation and for wettability problems. They should be checked on
location to ensure that they do not form a stable emulsion with the reservoir