PDF: PROBLEM DETECTION DURING TRIPPING OPERATIONS IN
HORIZONTAL AND DIRECTIONAL WELLS
1. Hook loade: The total force pulling down on the hook. This total force
includes the weight of the drillstring in air, the drill collars and any ancillary
equipment, reduced by any force that tends to reduce that weight. Some
forces that might reduce the weight include friction along the wellbore wall
(especially in deviated wells) and, importantly, buoyant forces on the
drillstring caused by its immersion in drilling fluid.
2. Borehole: The wellbore itself, including the openhole or uncased portion
of the well. Borehole may refer to the inside diameter of the wellbore wall,
the rock face that bounds the drilled hole.
3. Tripping: The act of pulling the drillstring out of the hole or replacing it in
the hole. A pipe trip is usually done because the bit has dulled or has
otherwise ceased to drill efficiently and must be replaced.
4. Raw: Crude oil direct from the wellbore, before it is treated in a gas
separation plant. It usually contains nonhydrocarbon contaminants.
5. Drillstring: The combination of the drillpipe, the bottomhole assembly and
any other tools used to make the drill bit turn at the bottom of the wellbore.
6. Tool joint: The enlarged and threaded ends of joints of drillpipe. These
components are fabricated separately from the pipe body and welded onto
the pipe at a manufacturing facility. The tool joints provide high-strength,
high-pressure threaded connections that are sufficiently robust to survive
the rigors of drilling and numerous cycles of tightening and loosening at
threads.
7. Mud cake: The residue deposited on a permeable medium when a slurry,
such as a drilling fluid, is forced against the medium under a pressure.
Filtrate is the liquid that passes through the medium, leaving the cake on
the medium. Drilling muds are tested to determine filtration rate and filter-
cake properties.
8. Cutting bed: Small pieces of rock that break away due to the action of the
bit teeth. Cuttings are screened out of the liquid mud system at the shale
shakers and are monitored for composition, size, shape, color, texture,
hydrocarbon content and other properties by the mud engineer, the mud
logger and other on-site personnel.
9. Bridges: To intentionally or accidentally plug off pore spaces or fluid paths
in a rock formation, or to make a restriction in a wellbore or annulus. A
bridge may be partial or total, and is usually caused by solids (drilled
solids, cuttings, cavings or junk) becoming lodged together in a narrow
spot or geometry change in the wellbore.
10. Buoyancy: The upward force acting on an object placed in a fluid. The
buoyancy force is equal to the weight of fluid displaced by the object.
Buoyancy can have significant effects over a wide range of completion and
workover activities, especially in cases in which the wellbore and tubing
string contain liquid and gas. Any change in the relative volumes or fluid
levels will change the buoyancy forces.
11. Differencial sticking: A condition whereby the drillstring cannot be moved
(rotated or reciprocated) along the axis of the wellbore. Differential sticking
typically occurs when high-contact forces caused by low reservoir
pressures, high wellbore pressures, or both, are exerted over a sufficiently
large area of the drillstring. It is important to note that the sticking force is
a product of the differential pressure between the wellbore and the
reservoir and the area that the differential pressure is acting upon.
12. Keyseats: A small-diameter channel worn into the side of a larger
diameter wellbore. This can be the result of a sharp change in direction of
the wellbore (a dogleg), or if a hard formation ledge is left between softer
formations that enlarge over time.
