1
Q
Explain the functions of drilling mud
A
- Lubrication and cooling of the drill string and drill bit
- Removal of cuttings from the hole
- Assist in the interpretation of hole behaviour
- Control the formation pressure
- Stabilise the well bore and prevent caving
- To transmit MWD (Measurement While Drilling) information
2
Q
Describe how acoustic downhole logs can be used to estimate porosity?
A
- Logging tool has a sound transmitter at the top and two sound receivers along the tool
- Impulse of sound emitted by transmitter and recorded by two receivers
- Record time taken for sound to travel from one receiver through rock to the other receiver
- Cannot be used in cased hole
- porosity = interval transit time - velocity of the rock at phi = 0 / velocity of the pore fluid - velocity of the rock at phi = 0
3
Q
Describe the action of a roller cutter drill bit for drilling rock
A
- Cones rotate on bearings when the bit is on bottom and is rotated
- crushing
4
Q
Describe how the plastic viscosity and yield points of drilling mud are measured using a multi-rate viscometer
A
- Instruments consists of two cylinders
- Instrument head immersed in sample cup containing the mud
- Rotation of rotor sleeve in mud produces torque on inner cylinder
- Movement of inner cylinder restricted by spring and deflection recorded on dial
- PV is obtained by subtracting the 300 RPM reading from the 600 rpm reading
- The yield point is the initial resistance to flow causes by electrochemical forces between the particles
- YP = viscosity at 300rpm - PV
5
Q
Describe how seismic surveys are conduction offshore
A
- 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 application
- One boat can operate several energy sources
6
Q
Describe circumstances under which shock loading can occur during drilling operations
A
Shock loading can happen when slips are set on moving drill pipe, which will create additional tensile force
Fs = 0.94Wdp
7
Q
What is the safety factor equation?
A
SF = Pa/P (Pa = maximum tensile load)
