BAKER HUGHES - Drilling Fluids Reference Manual

RESERVOIR APPLICATION FLUIDS
PACKER FLUIDS
Packer fluids are fluids, either clay-laden or without solids, which are left in the annular space
between the tubing and casing.
Packer fluids for the most part have been drilling fluids conditioned to be left in the hole on
completion of the well. Under normal situations of low temperatures and normal pressures, this
approach has usually been satisfactory. Not until the advent of lime fluid in the late 1940s and early
1950s did packer fluids attain industry attention. Lime fluids, when exposed for prolonged periods
of time to high temperature, may set to a non-pumpable solid state from the chemical reaction of
clays, silica, lime, and caustic soda, which forms the cement-like substance tobermorite. This
condition becomes severe at about 250°F. Such fluids prevent unseating of the tubing from the
packer and pulling of the tubing during workover operations. Literally, these “set” fluids have to be
drilled out.
The problem of lime fluids focused considerable attention on packer fluid requirements. Since then,
a number of approaches to the design of packer fluids have evolved.
Requirements of a Good Packer Fluid
The primary purpose of packer fluids is to provide sufficient hydrostatic pressure to protect the
casing from excess formation pressures. Hydrostatic pressure is obtained by using soluble salts
such as NaCl, CaCl 2 , CaBr 2 , ZnBr 2 , and insoluble materials such as barite and calcium carbonate.
A packer fluid should be thermally stable at bottomhole temperatures. It should have sufficient
gel properties for adequate suspension of barite in weighted systems, but be easily sheared down
during pumping or pulling operations.
The packer fluid should be non-corrosive. It should not form scales or produce gaseous byproducts
such as H 2 S or CO 2 . It should not react with metal to produce inter-granular crystallization
or changes in the metallurgical structure of the steel.
A packer fluid should be free of solids settling on the packer. Gel properties in solids systems
must be controlled to prevent sedimentation. Salt solutions must not form scales or produce
insoluble sediments which could settle on the packer.
Types of Packer Fluids
Clear Brines
Brine solutions are sometimes used as completion and packer fluids instead of conventional drilling
fluid systems. There are two primary advantages to salt brines.
1. A clean, particle-free medium minimizes formation damage during completion
operations (cleaner perforations, good sand control, more successful plastic squeeze
jobs, etc.).
2. Fluids do not settle or solidify in the tubing-casing annulus to complicate workover
jobs. Also, a reliable circulating fluid capable of retaining any formation pressures in the
BAKER HUGHES DRILLING FLUIDS
REFERENCE MANUAL
REVISION 2006 6-101