Lecture 2 - Exploration: Part 1

Question 1

What is a ‘jack-up?’

Answer 1

Self-contained combination drilling rig and floating barge.

Fitted with long support legs that can be raised or lowered independently of each other.

Question 2

How is the jack up towed to location?

Answer 2

With legs up and the barge section floating on the water

Question 3

What is a semi-submersible?

Answer 3

Floating drill unit with platoons and columns that, when flooded with seawater, cause the pontoons to submerge to predetermined depth

Question 4

Why is the semi-submersible the preferred choice for exploration?

Answer 4

Very stage installation, large proportion submerged and has 8 huge mooring anchors

Question 5

Why are anchor handling boats less favourable for exploration?

Answer 5

Expensive

Dangerous operation

Question 6

Describe the structure of a platform

Answer 6

Immobile, built from concrete or steel, rests on sea bed

Question 7

When is a platform constructed and what is it used for?

Answer 7

When oil or gas is located

Platform constructed to drill further wells at site and produce hydrocarbons

Question 8

Give three advantages of drill ships and one major disadvantage

Answer 8

Advantages:
Do not require anchors
Global positioning
Deep water capability (3000m)
Disadvantages:
VERY expensive ($500K+/day to run)

Question 9

Name three methods of offshore transport

Answer 9

Helicopter
Stand-off vessel
Supply vessel

Question 10

What is the purpose of the riser when drilling a well?

Answer 10

Protects/isolates drill from sea

Runs from below the rotary table to the sea bed

Question 11

What is a blow out preventer (BOP)?

Answer 11

Sophisticated safety valve on sea bed

Question 12

Name the three different drill bits

Answer 12

Roller cone: tri-cone
Polycrystalline diamond compact (PDC)
Turbines

Question 13

What are the advantages of PDC drill bit?

Answer 13

Excellent wearability

Impact toughness

Question 14

What are turbines used for?

Answer 14

All the tough stuff

Question 15

What does a shaker table allow?

Answer 15

Separation of cuttings (ground up rock) from the drilling mud allowing lithological analysis

Question 16

Explain the circulation system when drilling a well

Answer 16

Pumps drilling mud under pressure through the kelly, rotary table, drill pipes and drill collars

Question 17

What is a kelly?

Answer 17

Four or six sided steel pipe that transfers rotary motion to the turntable and drill string

Question 18

Why is casing used? How is it effected by drilling deeper?

Answer 18

Inserted to stabilise well and stop ingress of fluids or hole collapse
Decreasing size with depth, left in hole when done

Question 19

What is drilling mud composed of?

Answer 19

Mixture of water, clay, weighting material and chemicals

Oil or water based

Question 20

What is drilling mud used for? (3 things)

Answer 20

Lift rock cuttings from drill bit to surface
Lubricate drill bit
Prevent invasion of formation fluids

Question 21

How are ditch cuttings recovered and what are they used for?

Answer 21

Come up with mud, collected from shakers by mud catcher, washed and dried
Used to determine Lithology, palaeontology/ biostratigraphy

Question 22

What are side wall cores (SWC) used for?

Answer 22

Determine Lithology where core has not been taken

Question 23

When would you recover a core?

Answer 23

Known/anticipated reservoir intervals, very expensive

Question 24

Why is core brought to surface slowly?

Answer 24

Allow reservoir gases to dissipate

Question 25

What is fluid data sampled for?

Answer 25

Formation waters are sampled for hydrocarbon composition

Question 26

Why are heavy minerals sampled in sandstones?

Answer 26

To determine provenance and correlation of non-fossiliferous units

Question 27

Name 6 heavy metals analysed in sandstone samples

Answer 27

Zircon
Apatite
Rutile
Monazite
Titanite
Garnet