passes inside conductor, surface casing and intermediate casing to the formation pay zone or below it.
4. The first and the smallest in diameter casing string is called conductor.
5. Christmas tree required for field operations includes: wellhead, valves 
and chokes, emergency shut down systems, blowout preventers, fluid 
tanks, separators, line heaters, dehydration equipment, gas sweetening 
equipment, compressors.
6. On wells where high formation pressure or presence of aggressive 
gases are expected, special control equipment should be installed 
above casing string or tubing spool after well completion.
7. Casing strings run in the hole have specific purposes and include: 
conductor, surface casing, intermediate casing and production casing 
always with a liner.
8. Intermediate casing strings should be run in the hole when it is feasible to drill the well to the design depth without preliminary isolation 
of problematic zones (blowouts, collapses).
9. Surface casing is the first string run in the hole and cemented.
UNIT 4. PETROLEUM DRILLING
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10. Well design can be desc
ТЕкст: Well design can be described as pipeline from the ground surface to the oil 
bearing formation. Oil comes to the surface through this pipeline. Such pipeline 
includes a number of special pipes connected between each other called a casing 
string.
Casing strings run in the hole have specific purposes and include: conductor, surface casing, intermediate casing and production casing often with a liner.
The first and the largest in diameter casing string is called conductor. This 
string can be installed in the well or driven in soil.
Surface casing is the second string run in the hole and cemented. It is installed to the depth, which is sufficient in order to protect the well from underground waters and collapse of surface soil.
Another smaller in diameter casing string can be applied. It is called intermediate casing. If the well is shallow, intermediate casing, as a rule, is not used. 
Intermediate casing strings should be run in the hole when it is not feasible to 
drill the well to the design depth without preliminary isolation of problematic 
zones (blowouts, collapses).
The last casing string called production casing is installed from the surface, 
passes inside conductor, surface casing and intermediate casing to the formation 
pay zone or below it. This is the string, in which the well is completed and controlled.
Well equipment required for field operations includes: wellhead, valves and 
chokes, emergency shut down systems, blowout preventers, fluid tanks, separators, 
line heaters, dehydration equipment, gas sweetening equipment, compressors.
On wells where high formation pressure or presence of aggressive gases are 
expected, special control equipment should be installed above casing string or 
tubing spool before well completion. A set of such control equipment including 
valves and pressure gauges controls oil and gas flow from the well and is called 
Christmas tree, which is associated with its shape and high number of branches 
with valves on the tree trunk.
Christmas tree is the main component of wellhead equipment. Christmas 
tree is attached to casing. It is designed to hold casing and tubing strings, isolate 
or seal annulus between these strings, provide fluid access to all strings, control 
processes of fluid and gas injection and production by means of valves.
Standard Christmas tree assembly includes adaptor flange, master valve, 
flanged cross, top adaptor, secondary master valve, wing valve, wing valve and 
a choke.
Pressure gauges are installed on Christmas tree to measure pressure in annulus and tubing. When pressure values under different working conditions are 
known the well can be controlled much easier.