General

Question 1

Functions of drilling mud

Answer 1

Lubrication and cooling of the drill string
Removal of cuttings from the hole
Assistance in the interpretation of hole behaviour

Question 2

Define and describe the purpose of a conductor casing

Answer 2

Large, thick-walled pipe driven into the ground (typically 36” OD).
Is used from the surface to some shallow depth.
Protect near-surface unconsolidated formations and prevent washout.
Seal off shallow water zones.
Supports a diverter to provide protection against gas flows from shallow gas formations.
Provide a circuit for the drilling mud to protect the foundations of the platform.
BOPs may be installed on this casing.

Question 3

Define and describe the purpose of a surface casing

Answer 3

First real string of casing pipe.
Secures formations near the surface to prevent them from caving in.
Seals off surface fresh water to stop it being contaminated with drill mud.
Provides an anchor point for BOPs and hangers for further casing strings.
Cemented right up to the surface.
Lengths of string may vary from 10s to 100s of metres depending on local conditions.

Question 4

Define and describe the purpose of an intermediate casing

Answer 4

Below the surface casing and cemented in place before penetrating the reservoir.
A deeper casing gives increased strength at the shoe because rocks that are buried deeper are usually stronger than those higher up.
Allows higher blowout protection as set in more competent formations than surface casings.
Protects the well that was already drilled as the well is deepened further.
Used in transition zones (below/above high pressure zones) to seal off a severe loss zone and protect against problematic formations (i.e. salt sections).

Question 5

Define and describe the purpose of a production casing

Answer 5

Last casing, used to isolate production zones, provide reservoir fluid control and permit selective production in multi-zone production.
String through which the well will be completed.

Question 6

Define a non-newtonian fluid

Answer 6

There is no linear relationship between shear stress and shear strain, so the viscosity varies.
Three types: Bingham plastic (time independent), Power law (time independent), time dependent (viscosity changes with the duration of the shear).

Question 7

Define the yield point of a Bingham plastic fluid

Answer 7

Minimum shear stress at which deformation takes place

Question 8

Define the plastic viscosity of a Bingham plastic fluid

Answer 8

The constant viscosity occurring after the yield point has been reached.

Question 9

How are seismic surveys conducted onshore?

Answer 9

Acoustic source provided by explosives or dropping a weight off the back of a lorry, or vibrating a metal plate on the ground (vibroseis).
Returning acoustic waves recorded by lines or arrays of geophones.

Question 10

How are seismic surveys conducted offshore?

Answer 10

Air gun behind ship transmits sound into water column and subsurface.
Hydrophones towed behind the vessel record the reflected waves.
Simpler, faster, higher quality and cheaper than onshore acquisition.
One boat can operate several energy sources.

Question 11

Description of liners and advatages/disadvantages

Answer 11

Hung on the intermediate casing (doesn’t reach the surface).
Can also be used as production strings.
Advantages:
Total costs of string are reduced
Running and cementing times reduced
Length of reduced diameter reduced, allowing completion with adequate size tubings
Disadvantages:
Casing and cementation processes are more complex
Possible leaks across liner hanger