Lecture 2 - Exploration: Part 1 Flashcards
What is a ‘jack-up?’
Self-contained combination drilling rig and floating barge.
Fitted with long support legs that can be raised or lowered independently of each other.
How is the jack up towed to location?
With legs up and the barge section floating on the water
What is a semi-submersible?
Floating drill unit with platoons and columns that, when flooded with seawater, cause the pontoons to submerge to predetermined depth
Why is the semi-submersible the preferred choice for exploration?
Very stage installation, large proportion submerged and has 8 huge mooring anchors
Why are anchor handling boats less favourable for exploration?
Expensive
Dangerous operation
Describe the structure of a platform
Immobile, built from concrete or steel, rests on sea bed
When is a platform constructed and what is it used for?
When oil or gas is located
Platform constructed to drill further wells at site and produce hydrocarbons
Give three advantages of drill ships and one major disadvantage
Advantages: Do not require anchors Global positioning Deep water capability (3000m) Disadvantages: VERY expensive ($500K+/day to run)
Name three methods of offshore transport
Helicopter
Stand-off vessel
Supply vessel
What is the purpose of the riser when drilling a well?
Protects/isolates drill from sea
Runs from below the rotary table to the sea bed
What is a blow out preventer (BOP)?
Sophisticated safety valve on sea bed
Name the three different drill bits
Roller cone: tri-cone
Polycrystalline diamond compact (PDC)
Turbines
What are the advantages of PDC drill bit?
Excellent wearability
Impact toughness
What are turbines used for?
All the tough stuff
What does a shaker table allow?
Separation of cuttings (ground up rock) from the drilling mud allowing lithological analysis
Explain the circulation system when drilling a well
Pumps drilling mud under pressure through the kelly, rotary table, drill pipes and drill collars
What is a kelly?
Four or six sided steel pipe that transfers rotary motion to the turntable and drill string
Why is casing used? How is it effected by drilling deeper?
Inserted to stabilise well and stop ingress of fluids or hole collapse
Decreasing size with depth, left in hole when done
What is drilling mud composed of?
Mixture of water, clay, weighting material and chemicals
Oil or water based
What is drilling mud used for? (3 things)
Lift rock cuttings from drill bit to surface
Lubricate drill bit
Prevent invasion of formation fluids
How are ditch cuttings recovered and what are they used for?
Come up with mud, collected from shakers by mud catcher, washed and dried
Used to determine Lithology, palaeontology/ biostratigraphy
What are side wall cores (SWC) used for?
Determine Lithology where core has not been taken
When would you recover a core?
Known/anticipated reservoir intervals, very expensive
Why is core brought to surface slowly?
Allow reservoir gases to dissipate
