Porosity & Reserves Flashcards
[Q] What does porosity tell us?
Gives us a feel for storage capacity of the formation.
[T/F] Size of pore space is not the same as porosity
True
[Q] What is absolute porosity?
Total porosity regardless of connectivity.
[Q] What is the effective porosity?
Porosity based on interconnected pores.
[Q] What is dead-end porosity?
Porosity based on interconnected pores that do not contribute to the flow, similar to cul-de-sacs.
[Q} What is the porosity of cubic packing?
47.6%
[Q} What is the porosity of hexagonal packing?
39.5%
[Q} What is the porosity of rhombohedral packing?
25.9%
[Q] What is primary/intergranular porosity?
Porosity due to sediment deposition (pore spaces are those between individual grains of sediment).
[Q] What is an example of primary porosity?
Sandstone porosity
[Q] What is secondary porosity?
Porosity due to voids formed after the original sediments were deposited. It is also more difficult to estimate.
[Q] What are examples of secondary porosity?
Fractures, fissures, and dolomitization.
[Q] What is dual porosity?
Both primary and secondary porosity existing in the same formation.
[Q] What does a fractured reservoir usually refer to?
A reservoir that has dual porosity.
[Q] What is a non-fractured formation called?
A matrix.
[Q] What is the conceptual approach to estimating porosity?
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
[Q] What does a density log do?
Measures the electron density of a formation (relating it to the formation’s bulk density).
[Q] What does a neutron log do?
Measures the hydrogen ion concentration in a formation.
[Q] What does a sonic log do?
Measures the interval transit time of a compressional sound wave.
[FITB] Density & Neutron tools measure ____
Total porosity
[FITB] Sonic tools measure ____
Effective porosity
[Q] What is the Sonic Response (Wyllie Linear Relationship) valid for?
- Uniform inter-angular porosity
- Water-bearing formation
- Clean formation (no shale)
- Compacted formation
[Q] What factors affect logging measurements?
- Compaction
- Shaliness
- Hydrocarbon
- Fractures
- Borehole Effects
Compare the pros and cons of logs vs cores:
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
[Q] What is the effect of grain size on porosity and permeability?
Large regular grains: -High porosity - High K Smaller regular grains: - High porosity - Low K
[Q] What is the effect of connate water on porosity and permeability?
In large regular grains: - Low Swc - High porosity - High K In small regular grains: - Increased Swc - High porosity - Moderate K
[Q] What is the effect of Clay/cement on porosity and permeability?
No clay/cement: - High porosity - High K Clay + Bound Water: - Moderate porosity - Low K
[FITB] Capillary pressure always results in ____
a transition zone
[T/F] Capillary force tends to trap oil
True
[T/F] Gas is always the wetting phase
True
[Q] What is wettability?
Wettability is the tendency for one fluid to preferentially spread/adhere to a solid surface in the presence of other immiscible fluids.
[T/F] A contact angle less than 90 degrees implies the solid is oil-wet
False (it is water-wet)
[Q] What are the 3 forces that govern all Petroleum Engineering? What is the one we can control?
Viscous forces, capillary pressure, and gravity.
Viscous forces are the only ones we can control.
[FITB] The oil extracted will have ____ volume on the surface than the reservoir.
[Q] Why?
Less
Due to changes in temperature and pressure.
[Q] What is a resource in Petroleum Engineering?
The hydrocarbons in place (HCIP)
[Q] What is a reserve in Petroleum Engineering?
The volume of hydrocarbons that can be viably extracted under current well, environmental, & political conditions.
[T/F] Reserve applies to both refined & non-refined hydrocarbons.
False
Only non-refined.
[Q] What is overburden pressure?
It is the pressure exerted on a layer of rock by the overlying formation.
[Q] What are static and dynamic methods in estimation?
Static is based on geological/engineering data before production.
Dynamic is based on static methods + pressure profiles, economic analysis, etc…
[T/F] A P90 probability will yield less oil than P10.
True
[Q] What are proven reserves? What are their types?
Reserves that have a reasonable certainty to be commercially recoverable.
They can be classified as either producing or non-producing.
[FITB] P1, P2, & P3 respectively refer to ____
Proved, probable, & possible reserves.
[Q] What is an advantage of under-balanced drilling?
Makes cleaning the well easier.
[FITB] Over-pressure = ____
Fluid-pressure + Grain-pressure
[FITB] Drainage is the injection of the ____ phase while imbibition is the injection of the ____ phase.
non-wetting
wetting
[Q] What is the difference between under-balanced & over-balanced drilling?
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.
