BAKER HUGHES - Drilling Fluids Reference Manual

RESERVOIR APPLICATION FLUIDS
• swelling of expandable clays in the producing formation is caused by the invading fluid
• there is particle movement within the sandstone
• the fluid lost to the formation forms a viscous emulsion with formation fluids or changes the
interfacial tension resulting in reduced production
• enough fluid is lost to the formation to flush the hydrocarbons away from the wellbore, thus
allowing water from a water drive to enter the wellbore
For a well to return to full production after workover operations, the fluid lost to the formation
during workover should be minimized and the solids and chemicals lost to the formation must be
removed.
Simply producing the well may be sufficient to flush these solids from the formation face. The
smaller clay and barite particles, however, are carried deep into the formation where they lodge and
cannot be flushed out, thus permanently impairing the productivity of the well.
Heavy Brines
Many of these problems can be avoided by using solids-free workover fluids. By using diesel oil (a
fire hazard) or various brines (sodium chloride, calcium chloride, calcium bromide, or zinc
bromide), it is possible to have solids-free workover systems with a density range of 7.0 to 19.2
lb m /gal. The maximum operational densities in pounds per gallon which may be achieved with
various salts are shown in the tables above. The use of these brines as workover and completion
fluids has increased dramatically over recent years due to their non-damaging characteristics. In
addition to heavy brines being used as workover fluids, they are also used as packer fluids,
perforating fluids, and gravel pack fluids.
Calcium chloride has a greater solubility than sodium chloride and, at higher concentrations of
these mixed salts, the sodium chloride can come out of solution. As much sodium chloride as
possible should be used for a given weight to reduce cost when these two salts are used.
The properties of calcium chloride solutions can be found in the preceding tables. The material
requirements for preparing chloride and bromide solutions are also found in the preceding tables.
The solubility of calcium bromide increases with temperature, and much of it may precipitate from
higher density solutions if the solution is allowed to cool. Requirements of a calcium chloride and
calcium bromide solution can be found in the preceding tables.
Unfortunately, solids-free workover fluids cannot do everything that is required of a workover
fluid. They do not have the carrying capacity needed to clean the hole, and they have no filtration
control or means of controlling lost returns. In addition, when calcium bromide or zinc bromide is
needed for density requirements, these fluids can be very expensive.
BAKER HUGHES DRILLING FLUIDS
REFERENCE MANUAL
REVISION 2006 6-75