Lecture 2 - Exploration: Part 2

Question 1

What is used to control mud viscosity?

Answer 1

Bentonite

Question 2

What is used to control mud density?

Answer 2

Baryte

Question 3

How is mud lost?

Answer 3

Mud penetrating rock formation and subsequent loss

Question 4

What is the consequence of ‘formation kicks’?

Answer 4

Could lead to a blowout

Penetration of formation fluids into mud

Question 5

What are mud samples analysed for? How?

Answer 5

Hydrocarbon gases using gas chromatography

Question 6

Why is drill-stem testing done?

Answer 6

Good indication of reservoir characteristics (poroperm, nature of gases) from analysis of flow rate, amount of formation fluid recovered in drill string and the formation pressures recorded.

Question 7

What is LWD?

Answer 7

Logging while drilling

- logging after each section is drilled usually prior to inserting casing

Question 8

What are gamma rays?

Answer 8

High-energy electromagnetic waves which are emitted by atomic nuclei as a form of radiation

Question 9

What does a gamma ray log measure? Where does the radiation come from?

Answer 9

Measurement of natural radioactivity in formation versus depth
Radiation from element such as U, Th and K

Question 10

What does the spontaneous potential (SP) curve record?

Answer 10

The natural occurring electrical potential produced by the interaction of formation connate water, conductive drilling fluid and shale

Question 11

What does the spontaneous potential (SP) curve reflect?

Answer 11

The difference in electrical potential between a moveable electrode in the borehole and a fixed reference electrode at the surface

Question 12

The spontaneous potential is primarily used as a Lithology indicator. What else can it be used for?

Answer 12

Permeability indicator
Shale volume indicator
Porosity indicator
Measurement of Rw (hence formation water salinity)

Question 13

What is the neutron log used for?

Answer 13

Evaluating formation porosity (although it is essentially just a hydrogen detector)

Question 14

What does the capture of hydrogen atoms result in?

Answer 14

Emission of a secondary gamma ray

Question 15

What is the formation density log used to measure?

Answer 15

Porosity log measuring the electron density of a formation

Question 16

How do dense and low density formations compare in a formation density log?

Answer 16

Dense formations absorb many gamma rays so have low count rates
Low density formations absorb fewer gamma rays so have high count rates

Question 17

What does resistivity measure?

Answer 17

Electrical properties of the rock

Question 18

What three factors affect the ability of a material to conduct an electric current?

Answer 18

Volume of water
Temperature of formation
Salinity of formation

Question 19

What do resistivity logs measure?

Answer 19

Ability of rocks to conduct electrical current

Question 20

What do acoustic tools measure?

Answer 20

Speed of soundwaves in subsurface formations

Question 21

How do acoustic logs indicate Lithology?

Answer 21

Using the ratio of compressional velocity over shear velocity

Question 22

Name two types of image logs and the companies that use them

Answer 22

FMI (Schlumberger)
STAR Imager (Baker)

Question 23

What are image logs based on and what do they show?

Answer 23

Based upon electrical resistivity/conductivity of units

Shows up internal character of units e.g. bedding, fractures

Question 24

How do high resistivity units appear on image logs? Give examples of these

Answer 24

Show up as bright

E.g. lava and sills

Question 25

What does STAR Imager provide?

Answer 25

High-resolution resistivity formation images in conductive mud systems

Question 26

What does abandonment mean?

Answer 26

Converting a well to a state that can be left indefinitely, will not damage water supplies, potential hydrocarbon or the environment

Question 27

What two methods of abandonment are there?

Answer 27

P + A: Plugged (cement plug) and abandoned

Suspended: left in state with sealed well head cover for later activity