Petroleum Companies Exam for Geologists - Questions and Answers

1 Define
Crest culmination

It is the highest point in the trap

Spill point

It is the lowest point in the trap at which H.C. may be contained, it lies at a horizontal contour on a horizontal plane

Closure

The vertical distance from the crest to the spill point.

Bottom water

It is the zone immediately beneath the petroleum

Edge zone

It is the zone of the reservoir laterally adjacent to the trap.

The pay

It is the productive reservoir within the trap

Gross pay

It is the vertical distance from the top of the reservoir to the oil water contact.

Net pay

It is the cumulative vertical thickness of the reservoir from which H.C.S may be produced.

Trap

The place where oil or gas is barred from further movement.

Source rock: The source rock is a formation structurally and chronologically placed to provide a source of petroleum for the reservoir.
Formation:

It is the basic unit of nomenclature in stratigraphy,
It is a set of rocks that are common in distinctive features of lithology and is horizontally continuous and is large enough to be mapped.
It can be divided into members and grouped together into groups.

Mud logging (Mud logging unite)

A system that contains sophisticated computers and sensors used to operate a quick and comprehensive interpretation and evaluation of fluids, gases, and cuttings on well site.

Mud circulation

It is a process of pumping the mud down to the bit and back up it to the surface in a drilling or work over operation.
In mud circulation process the mud starts at the mud tanks, being pumped to the stand pipe through the pump, then to the rotary hose, swivel. To Kelly or top drive, the bit and takes its way to the surface again through annulus to the mud tanks.

Attic oil

It is oil above the bore hole in horizontal well.

Lag Time

It is the time between a chip being cut by the bit, and the time it reaches to the surface where it examined by the geologist or the mud logger.

Migration

Primary migration: the movement of the oil from the source rock to the reservoir rock.
Secondary: from the reservoir to the trap
Tertiary: from a trap to another, or along the reservoir.

Porosity:

is the percentage of volume of pores voids to total volume of the rock.

Effective porosity:

It is the inter-connected pore voids contribute to the flow of fluids or contribute to permeability in the reservoir.

Primary porosity:

Porosity preserved from deposition through lithification.

Secondary porosity:

It is occur by alteration due to processes like dolomitization, dissolution, and fracturing.

Permeability:

It is the ability of rock to transmit fluids.

Absolute permeability:

It is the ability of rock to transmit fluids when single fluid or phase is present.

Effective permeability:

It is the preferentially ability to transmit a single fluid, when other immiscible fluids are present in the reservoir.

Relative permeability

It is the ratio of effective permeability of a particular fluid at a particular saturation, to the absolute permeability of that fluid at total saturation.

mention 5 fields in GOS and mention the horizon of production

In kareem-rodies formations

Morgan
Belayim land
Belayim marine
Ramdan
Shoab Ali
Zeit bay

what is the major type of traps in GOS

– The fields in Gulf of Suez is mainly structural traps though some are stratigraphic

what are the favorable conditions to form oil

Mature source rock rich with organic matter
Reservoir rock with optimal characters of porosity, permeability, and lateral extension.
Good seal or cap rock to form a trap system

What do you know about miscellaneous reservoirs and what is the most famous example in Gulf of Suez?

It is reservoir formed from fragment igneous rocks that found mainly in GOS province in SUCO Company in Zeit Bay Field. ( fractured basement topped by basement wash )

How do we measure the Mud cake thickness?

Using caliper log.

How many geophysical methods are there? (Name them).
Gravity methods
Radiometric methods
Magnetic methods
Electric methods

SP methods
Resistivity
IP methods

Electromagnetic methods

Seismic methods

Seismic reflection
Seismic refraction

Well logging methods
GR log
Electric logs

SP log
Resistivity log

Porosity logs

Density log
Neutron log
Sonic log

Caliper log
Dipmeter log
Thermal log
Although shale is not regarded as a reservoir because its permeability is almost nothing, hydrocarbons might move from the source rock shale by one or more of the following causes select:

Through shale fissility.
Through micro-permeability caused by sand size fraction content.
By high pore pressure associating hydrocarbon maturity and increasing distance between grain boundaries

Porosity of shales for a geologic environment which is characterized by continuous, uninterrupted deposition and normal pore pressure:
a) Increases linearly with increasing depth.
b) Decreases linearly with increasing depth.
c) Decreases basically exponentially with increasing depth.
d) Exhibits an inversely proportional behavior to density.
e) A and D above.
f) C and D above.
The diagenesis of montmorillonite to illite and mixed-layer clays:
a) Requires only particular conditions of temperature.
b) Occurs only at depths normally exceeding 5000 ft.
c) Occurs only after most free pore water has been expelled.
d) Requires particular conditions of temperature and (somewhat) pressure and the availability of potass[=ium ions.
e) May occur at relatively shallow depths.
f) B, C and D above.
g) D and E above.
During compaction, particularly shales, free pore water is expelled:
a) Towards the depositional surface.
b) In any direction including downwards.
c) In a linear fasion.
d) In several stages.
e) A and D.
f) B and C.
The most common reservoirs are:

Sandstone and Carbonate rocks.
Shale and Sandstone rocks.
Anhydrite and Dolomite rocks.

Shale is:

Compaction processing of clay minerals.
Made of Calcium Carbonate and Sodium Sulphate.
Originated in deep marine water.

Anhydrite plays an important role as:

Reservoir potential rocks.
Good source rocks.
As ultimate scaling rocks.

The oil can be trapped in the:

Structure trap only.
Structure and stratigraphic traps.
Stratigraphic traps only.

Briefly explain two criteria to distinguish between shallow marine and deep marine environments.

Marine deposits

Life of the Sea zones:

Littoral or Tidal Zone: Difficult living conditions because of the strong wave action so organisms must be attached or buried
Neritic Zone: It is the most life area in marine, Sea in this area is lighted & there is abundance of food
Bathyal Zone: No light or very little, so plant life is rare but it has animal population which called Bottom Living Seavengers
Abyssal Zone: No light, near freezing temp. & pressure reach to Ton/inch2 (specialized creatures can live at this depth)
Marine Sediments:
Marine Shoreline Environments:

Much siliclastic sediments can be deposited in marine shoreline. Beaches & Barriers developed in areas of high wave action. Beaches are linear belts of sand along beach where Barriers are separated from land by lagoon.

Shallow Marine (Neritic Zone(

Coarser materials are deposited near shore & grade into finer deposits upward. Shallow marine sediments are made of sediments derived from land by ways of Stream, Glaciers or Aeolian Sediments may consist of remains of organisms & chemical precipitates.

Structural features: usually lenticular beds. Ripple, currents marks have great variation in trend & extension. Sea floor has steep slopes, so sediments may slump &develop crimpled & irregular bedding planes

Intermediate Seas (Bathyal deposits)

At the continental slope, & covered by fine sediments of land origin which called Blue Muds. The presence of Blue

Muds color is due to presence of organic matter & also to De]Oxided conditions of Iron. Blue Muds may cover over 20 million Km2 of the ocean basin.

Deep Marine (Abyssal Deposits)

Many types of sediment are Volcanic, pelagic & meteoric origin. Very poorly sorted, Set in motion by storms and quakes, Calcareous and siliceous oozes. In greatest depth of ocean, the bottom is covered by Fine Red Clay which composed of Calcareous to siliceous to terrestrial clay, Shells & other organic matters.

How can you explain presence of dry reservoir although there is Source rock, Reservoir rock and Trap?

Immature source rock
The hydrocarbon may seep out of the trap
The trap has been later than the migration of the H.C. s.
Migration of the H.C.s to another trap

Write briefly on the types of kerogen and the composition of generated HC from each.

composition of generated HC from each Kerogen is a mixture of organic chemical compounds that make up a portion of the organic matter in sedimentary rocks.[1] It is insoluble in normal organic solvents because of the huge molecular weight (upwards of 1,000 daltons or 1000 Da; 1Da= 1 atomic mass unit) of its component compounds. The soluble portion is known as bitumen. When heated to the right temperatures in the Earth’s crust, (oil window ca. 60–160 °C, gas window ca. 150–200 °C, both depending on how quickly the source rock is heated) some types of kerogen release crude oil or natural gas, collectively known as hydrocarbons (fossil fuels). When such kerogens are present in high concentration in rocks such as shale they form possible source…
Type I: Sapropelic: Shows great tendency to readily produce liquid hydrocarbons.
Type II: Planktonic: Tends to produce a mix of gas and oil.
Type II–sulfur Similar to Type II produce a mix of gas and oil. But high in sulfur.
Type III: Humic: Tends to produce coal and gas (Recent research has shown that type III kerogens can actually produce oil under extreme conditions
Type IV (residue) mostly decomposed organic matter in the form of polycyclic aromatic hydrocarbons. They have no potential to produce hydrocarbons.

Which of the following is not a stratigraphic oil trap?
Unconformity.
• Reef.
• Anticline.
• pinch out.
Which of the following is not a hydrocarbon:
Methane.
• Pentane.
• Acetylene.
• None of the above.
• All of the above.
The definition: “the pore spaces – connected or disconnected – resulting through alteration of a rock, commonly by processes such as dolimitization, dissolution or fracturing” belongs to:
Primary porosity.
• Permeability.
• Secondary porosity.
• Effective porosity.
Give an example of a rock with high porosity and high permeability.

Sand stone

Give an example of a rock with high porosity and low permeability.

shale

Give an example of a rock with low porosity and low permeability.

halite

Which of the following is not an evaporite rock:
Gypsum.
• Evaporite.
• Muscovite.
• Salt
Arrange the following environmental zones sea-ward
a) Bathyal. (3)
b) Neritic. (2)
c) Abyssal. (4)
d) Littoral. (1)
What are the reasons of presence of barren Trap?

– absence of organic matter in the source rock or source rock that is not mature

– the trap may have been formed later than the migration of H.C.s

Mention the main types of traps

A trap is a geometric configuration of structures and/ or strata, in which permeable rock types (the reservoir), are surrounded and confined by impermeable rock types (the seal).

In some cases, traps may be created by hydrodynamic factors, that is, by the movement of subsurface waters, but these are relatively rare.

Most traps fall into one of three categories structural, stratigraphic, or combination traps that have both structural and stratigraphic aspects.

Structural traps
Anticline

Compressional anticline (crustal shortening)
Compactional anticline (crustal tensional)

Fault traps
Stratigraphic traps
Primary stratigraphic traps

Sand lenses
Pinch out
Digenetic changes
Carbonate reefs

Secondary stratigraphic traps

Unconformities (truncation)

Petroleum Companies Exam for Geologists – Questions and Answers