Casing & Cementing
Casing & Cementing
Casing & Cementing
• An oil and gas well is drilled in sections from the surface to the production zone.
• It is not possible to drill the well in one section due to the difference in formations
properties.
• Each section of formation, after being drilled, has to be sealed off by running a steel pipe
called casing. The annular space between the casing and the borehole is filled with
cement .
CASING FUNCTIONS
Casing has many functions and can be summarized as follows.
Provide a support for fractured, weak and vulnerable formations.
Prevent contamination of fresh water zones.
Isolate abnormal pressure zones and also lost circulation zones
Provide passage for production fluids. In general, production operations are
performed through tubing which is run inside the casing.
Provide support for surface equipment (blow out preventer and production
tree)
Allow an adequate means for installing artificial lift equipment for production
Offer a known borehole diameter in order to perform further operations
TYPES OF CASING
THE CONDUCTOR CASING
• It is the first and largest casing to be run. It is generally set at 100 ft below the
ground level.
• The main function of setting the conductor pipe is sealing off the unconsolidated
formations which are near the surface. These formations can be easily washed out
with continuous mud circulation; also they are characterized with low fracture
gradient which can be exceeded by the hydrostatic pressure generated by the
drilling fluids.
•
SURFACE CASING
• The function of this type of casing is sealing off the fresh water zones and
providing a support for the blowout preventer (BOP). The setting depth of this
casing has to be accurately designed in areas where high pressure is expected.
• If the surface casing is set higher than planned or the setting depth is
underestimated, the formation at casing shoe cannot resist to the pressure
exerted while circulating gas influx which can occurs during drilling the next
section
INTERMEDIATE CASING
• There are many reasons for pumping cement slurry while drilling
operations, the most important functions are:
• Preventing fluids flow from one formation to another or to the surface.
The fluids can flow between the casing and the formation.
• - Bonding the casing to the formation
• - Supporting the casing string
• - Protecting the casing from the corrosion caused by formation fluids
• - Sealing off the troublesome zones
•