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Casing & Cementing

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CASING & CEMENTING

ENGR : BHARAT KUMAR HARANI


INTRODUCTION:

• 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

• Many troublesome formations can be encountered during drilling operations


till getting to the production zone. These troublesome formations have to be
isolated by what it is called intermediate casing.
• The number of strings run as intermediate casing depends on the faced
problems such as: lost circulation zones, unstable shale, squeezing salts and
abnormally pressured zones.
PRODUCTION CASING

• It can be set above the production zone or run through it.


• The main function is to isolate production zone from the other formation such
as water bearing sands.
• This type of casing is also used as a conduit for production tubing.
LINERS
• Contrarily to the other types of casing strings which are hanged at the surface,
the liners are suspended inside the previous casing string by the liner hangers.
The liner hangers consisted of slips which can be activated hydraulically or
mechanically. Slips grip inside the previous string in order to support the
weight of the liner.
• Running a liner has many advantages:
• - Significant cost reduction due to shorter strings
• - Drill pipe is used to run the liner which leads to less rig time
• - Liner can be rotated while cementing the hole which can improve the quality
of cement.
CEMENTATION

• The cement is used as a sealing material while


drilling an oil and gas well. Pumping cement behind
the casing provides a barrier to the fluids flow from or
into the formation, and bonds the casing to the
formation. This is called a primary cement job.
Cement is also pumped for other reasons like sealing
off perforated casing or plugging zones
FUNCTION OF CEMENTING

• 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

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