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Unit 5 casing. Cementing

It is generally not possible to drill a well through all of the formations from surface to the target depth in one hole section. The well is therefore drilled in sections, with each section of the well being sealed of by lining the inside of the borehole with steel pipes, known as casing and filling the annular space between this casing string and the borehole with cement, before drilling the subsequent hole section.

Lead in

Make comments about reasons for casing off formations.

u

Casing off

nstable formation high pore pressure zones

w ell formation lost circulation zone

selective access structural support

    1. Pay special attention to the pronunciation and stress of the following words.

conduit [΄kondjuıt, ΄konduıt] threaded anticipated liner

subsequent [΄sλbsıkwənt] hydraulically

    1. Read the following texts and match them with casing types.

Casing types: 1. Conductor casing; 2. Surface casing; 3. Intermediate casing; 4. Production casing; 5. Liner

a)

It either runs through the pay zone or sets just above the pay zone. The main function of this casing is to isolate the production interval from other formations. It also provides protection for the environment in the event of failure of the tubing string during production operations and permits the production tubing to be replaced or repaired later in the life of the well.

b)

It generally sets at approximately 1000-1500ft. below the ground level. The main functions: prevents cave-in of unconsolidated, weaker, near-surface sediments and protects the shallow fresh water sands from contamination; supports and protects from corrosion any subsequent casing strings run in the well; supports the wellhead and BOP equipment (in case of kick, surface casing generally allows the flow to be contained by closing the BOPs )

c)

It is a short casing string which is suspended from the inside of the previous casing string by a special device known as ......... This device is attached to the top joint of the casing in the string. The collar and slips support its weight. The overlap with the previous casing is usually 200ft. – 400ft.

d)

It is the largest casing. It is generally set at approximately 100ft, below the ground level. Its function is to seal off unconsolidated formations shallow depths. It protects the subsequent casing strings from corrosion and may be used to support structurally some of the wellhead load.

e)

A heavy, flanged steel fitting connected to the first string of casing. It provides a housing for slips and packing assemblies, allows suspension of intermediate and production strings of casing, and supplies the means for the annulus to be sealed off.

f)

It is used to isolate troublesome formations including unstable shales, lost circulation zones, abnormally pressured zones and squeezing salts. When abnormal formation pore pressures are present in the deeper portions of a well, this casing is needed to protect formations from the pressures created by the required high-drilling-fluid density.

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