Lecture 1 - The reservoir

Question 1

What do GOC and OWC stand for?

Answer 1

GOC - Gas-oil contact

OWC - Oil-water contact

Question 2

What is the formation volume factor?

Answer 2

As hydrocarbons come to the surface of the Earth their T+P reduce, leading to shrinkage - gas exsolution and less heat

Question 3

What is the formation volume factor ratio?

Answer 3

V in place/V surface

Question 4

What does ‘NTG’ mean?

Answer 4

Net-to-gross: % of reservoir that is productive

I.e. net productive sand in a siliciclastic system

Question 5

What is primary porosity and secondary porosity?

Answer 5

Primary porosity: pore spaces

Secondary porosity: e.g. dissolution of grains or sediments

Question 6

What is the ratio of recoverable hydrocarbons between dolomite and limestone? What creates best carbonate reservoirs?

Answer 6

80% dolomite
20% limestone
dolomitisation and karstification can create excellent reservoirs

Question 7

What is the key influence on NTG? What is it measured in? What is the NTG typically in light oil and in gas?

Answer 7

Permeability
Measured in mD
Typically > 10mD for light oil and > 1mD for gas

Question 8

How does sorting affect porosity in gravel?

Answer 8

Well sorted = high porosity

Poorly sorted = low porosity

Question 9

Which of the following has high porosity:
Cemented sandstones
Clay
Limestone
Shale?

Answer 9

Clay

Question 10

What is permeability? What unit is used?

Answer 10

A measure of the ability of a fluid to flow

Milli-darcies (mD) are used to measure

Question 11

Where in the world are limestones important?

Answer 11

Middle-east

Question 12

What makes the best reservoir sands?

Answer 12

Coarse
Least cement
More permeable