BAKER HUGHES - Drilling Fluids Reference Manual

PRESSURE PREDICTION AND CONTROL
Chloride Trends
Changes in the chloride ion content of the drilling fluid are a valid pressure indicator, but
changes are difficult to establish unless there is close control and analysis of fluid properties.
Most methods currently available to make routine chloride ion tests are inadequate to show
subtle changes. An alternative to actually measuring the chloride content of the filtrate is
continuous monitoring of the resistivity of the fluid both into and out of the hole.
Paleo Information
Abnormally high pore pressures are frequently related to certain environmental conditions
within a given geologic time period. This depositional environment is marked by the presence
of certain fossils. Should examination of cuttings reveal these fossils, then the operator should
be alerted to the potential problem of encountering abnormally high pore pressures.
CONTROLLING FORMATION PRESSURE
Control of formation pressure is one of the primary functions of drilling fluids. The hydrostatic
pressure exerted by the fluid column is the most important method of controlling formation
pressure. Whenever formation pressure exceeds the total amount of pressure exerted on the
formation, formation fluids may enter the wellbore causing a kick. A kick is defined as any
unscheduled entry of formation fluids into the wellbore. Early recognition of a kick and prompt
initiation of control procedures are the keys to successful well control. If kicks are not detected
early enough or controlled properly when detected, a blowout can occur.
Preplanning to Prevent or to Handle Kicks Safely
The cornerstone of a safe, efficient drilling program is prediction of pressure gradient, fracture
gradient, and fluid densities based on drilling, geological, and physical experience in the area.
This has been discussed in the first part of this chapter.
On exploratory wells, or in areas where little information is available, it is necessary to focus
on drilling parameters such as penetration rate, modified “d” exponent, gas readings and trends,
fluid temperature, fluid conductivity, etc., and to run confirmation logs when drilling
parameters indicate changes in pressure gradient. In fact, these drilling parameters should be
monitored even in areas where information is available. The preliminary drilling plan is merely
a guideline and does not eliminate the possibility of unexpected changes in pressure gradient.
Blowout frequency for exploratory drilling is about double that of the average for all drilling
operations.
Preplanning on the rig should give consideration to the following aspects of the operation.
• Assignment of responsibilities. Each crew member should know who will perform various
surveillance tasks, coordinate well kill procedures, and operate the choke.
• Periodic inspection and testing of well control and detection equipment to insure kicks can be
detected and contained.
• Pit drills should be conducted on a regular basis by all crew members to condition the crew to
execute proper kick control procedures.
BAKER HUGHES DRILLING FLUIDS
REFERENCE MANUAL
REVISION 2006 12-16