Porosity & Reserves

Question 1

[Q] What does porosity tell us?

Answer 1

Gives us a feel for storage capacity of the formation.

Question 2

[T/F] Size of pore space is not the same as porosity

Answer 2

True

Question 3

[Q] What is absolute porosity?

Answer 3

Total porosity regardless of connectivity.

Question 4

[Q] What is the effective porosity?

Answer 4

Porosity based on interconnected pores.

Question 5

[Q] What is dead-end porosity?

Answer 5

Porosity based on interconnected pores that do not contribute to the flow, similar to cul-de-sacs.

Question 6

[Q} What is the porosity of cubic packing?

Answer 6

47.6%

Question 7

[Q} What is the porosity of hexagonal packing?

Answer 7

39.5%

Question 8

[Q} What is the porosity of rhombohedral packing?

Answer 8

25.9%

Question 9

[Q] What is primary/intergranular porosity?

Answer 9

Porosity due to sediment deposition (pore spaces are those between individual grains of sediment).

Question 10

[Q] What is an example of primary porosity?

Answer 10

Sandstone porosity

Question 11

[Q] What is secondary porosity?

Answer 11

Porosity due to voids formed after the original sediments were deposited. It is also more difficult to estimate.

Question 12

[Q] What are examples of secondary porosity?

Answer 12

Fractures, fissures, and dolomitization.

Question 13

[Q] What is dual porosity?

Answer 13

Both primary and secondary porosity existing in the same formation.

Question 14

[Q] What does a fractured reservoir usually refer to?

Answer 14

A reservoir that has dual porosity.

Question 15

[Q] What is a non-fractured formation called?

Answer 15

A matrix.

Question 16

[Q] What is the conceptual approach to estimating porosity?

Answer 16

1 - Draw air from the rock by creating a vacuum
2 - Imbibe the fluid into the rock
3 - Volume of fluid imbibed in the porosity

Question 17

[Q] What does a density log do?

Answer 17

Measures the electron density of a formation (relating it to the formation’s bulk density).

Question 18

[Q] What does a neutron log do?

Answer 18

Measures the hydrogen ion concentration in a formation.

Question 19

[Q] What does a sonic log do?

Answer 19

Measures the interval transit time of a compressional sound wave.

Question 20

[FITB] Density & Neutron tools measure ____

Answer 20

Total porosity

Question 21

[FITB] Sonic tools measure ____

Answer 21

Effective porosity

Question 22

[Q] What is the Sonic Response (Wyllie Linear Relationship) valid for?

Answer 22

• Uniform inter-angular porosity
• Water-bearing formation
• Clean formation (no shale)
• Compacted formation

Question 23

[Q] What factors affect logging measurements?

Answer 23

• Compaction
• Shaliness
• Hydrocarbon
• Fractures
• Borehole Effects

Question 24

Compare the pros and cons of logs vs cores:

Answer 24

Logs (pros):
- Less expensive
- Can be done while drilling
- Can cover the entire section of the well
- Does not degrade with time
Logs (cons):
- Less precise
- Less resolution than core measurements
Cores (pros):
- More precise
- Higher resolution with logs
Cores (cons):
- More expensive
- Time consuming
- Does not cover the entire section of the well
- Degrades with time

Question 25

[Q] What is the effect of grain size on porosity and permeability?

Answer 25

``` Large regular grains: -High porosity - High K Smaller regular grains: - High porosity - Low K ```

Question 26

[Q] What is the effect of connate water on porosity and permeability?

Answer 26

``` In large regular grains: - Low Swc - High porosity - High K In small regular grains: - Increased Swc - High porosity - Moderate K ```

Question 27

[Q] What is the effect of Clay/cement on porosity and permeability?

Answer 27

``` No clay/cement: - High porosity - High K Clay + Bound Water: - Moderate porosity - Low K ```

Question 28

[FITB] Capillary pressure always results in ____

Answer 28

a transition zone

Question 29

[T/F] Capillary force tends to trap oil

Answer 29

True

Question 30

[T/F] Gas is always the wetting phase

Answer 30

True

Question 31

[Q] What is wettability?

Answer 31

Wettability is the tendency for one fluid to preferentially spread/adhere to a solid surface in the presence of other immiscible fluids.

Question 32

[T/F] A contact angle less than 90 degrees implies the solid is oil-wet

Answer 32

False (it is water-wet)

Question 33

[Q] What are the 3 forces that govern all Petroleum Engineering? What is the one we can control?

Answer 33

Viscous forces, capillary pressure, and gravity. | Viscous forces are the only ones we can control.

Question 34

[FITB] The oil extracted will have ____ volume on the surface than the reservoir. [Q] Why?

Answer 34

Less | Due to changes in temperature and pressure.

Question 35

[Q] What is a resource in Petroleum Engineering?

Answer 35

The hydrocarbons in place (HCIP)

Question 36

[Q] What is a reserve in Petroleum Engineering?

Answer 36

The volume of hydrocarbons that can be viably extracted under current well, environmental, & political conditions.

Question 37

[T/F] Reserve applies to both refined & non-refined hydrocarbons.

Answer 37

False | Only non-refined.

Question 38

[Q] What is overburden pressure?

Answer 38

It is the pressure exerted on a layer of rock by the overlying formation.

Question 39

[Q] What are static and dynamic methods in estimation?

Answer 39

Static is based on geological/engineering data before production. Dynamic is based on static methods + pressure profiles, economic analysis, etc...

Question 40

[T/F] A P90 probability will yield less oil than P10.

Answer 40

True

Question 41

[Q] What are proven reserves? What are their types?

Answer 41

Reserves that have a reasonable certainty to be commercially recoverable. They can be classified as either producing or non-producing.

Question 42

[FITB] P1, P2, & P3 respectively refer to ____

Answer 42

Proved, probable, & possible reserves.

Question 43

[Q] What is an advantage of under-balanced drilling?

Answer 43

Makes cleaning the well easier.

Question 44

[FITB] Over-pressure = ____

Answer 44

Fluid-pressure + Grain-pressure

Question 45

[FITB] Drainage is the injection of the ____ phase while imbibition is the injection of the ____ phase.

Answer 45

non-wetting | wetting

Question 46

[Q] What is the difference between under-balanced & over-balanced drilling?

Answer 46

Under-balanced drilling is when the well-bore pressure during drilling is kept below the formation pressure, the formation fluid will begin to flow into the well-bore. Over-balanced drilling is when the well-bore pressure during drilling is kept above the formation pressure, this formation fluid will remain in the formation and the drilling fluid will begin to flow into the formation. If not careful, the formation can begin to crack.