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Questions and Answers
What is the main characteristic of primary stratigraphic traps?
What is the name of the trap that results from a combination of tectonic processes and changes in lithology?
What is the primary purpose of understanding driving mechanisms in oil recovery?
What happens to the reservoir pressure in an under saturated oil reservoir?
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What are the two factors that contribute to reservoir rock compressibility?
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What is the typical recovery percentage for rock and liquid expansion drive mechanism?
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What is another name for the depletion drive mechanism?
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How many driving mechanisms are necessary for oil recovery?
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What is the primary component of sandstone reservoir rocks?
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What is the purpose of the cap rock in an oil and gas trap?
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What is the term for the general physical characteristics of a rock?
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Which type of trap is formed during the sedimentation process?
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What is the effect of swelling clays on reservoir quality?
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What is an example of a structural trap?
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What is the term for the arrangement of rock layers that contains an accumulation of hydrocarbons?
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What is the term for the pore space in carbonate reservoir rocks?
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What is the primary source of energy in an internal gas drive reservoir?
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What is a characteristic of a gas-cap-drive reservoir?
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What is the primary driving force in a water-drive mechanism?
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What occurs when the reservoir pressure falls below the bubble-point pressure?
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What is a result of the differences in densities of the reservoir fluids in a gravity-drainage-drive mechanism?
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What is the combination-drive mechanism?
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What is the purpose of the example of placing crude oil and water in a jar and agitating the contents?
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What is the assumption about the reservoir fluids in a gravity-drainage-drive mechanism?
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Study Notes
Production System
- An oil and gas field involves oil and gas reservoirs (G & O Accumulation)
Lithology of Petroleum Reservoirs
- Lithology refers to the general physical characteristics of a rock
- Reservoir rocks can be divided into two types: sandstone and carbonates
- Sandstone: usually composed of silica grains (mainly quartz) and some feldspar, can be consolidated or loosely consolidated, may contain swelling clays
- Carbonates: two major types are limestone (CaCO3) and dolomite (CaMg(CO3)2), pore space consists of inter- or intragranular porosity as well as areas of dissolution (vugs) and fractures
Petroleum Traps
- An oil and gas trap is an arrangement of rock layers that contains an accumulation of hydrocarbons, covered by a cap rock to prevent them from rising to the surface
- Traps can be classified into three types: structural, stratigraphic, and combination traps
- Structural traps result from a local deformation of the reservoir formation, such as folding and/or faulting of the rock layers
- The most common types of structural traps are:
- Anticline traps: formed by folding of rock
- Fault traps: formed when reservoir rock is split along a fault line
- Stratigraphic traps are formed during the sedimentation process, and can be primary or secondary
- Combination traps result from a combination of tectonic processes and changes in lithology
Primary Recovery Mechanisms
- There are six driving mechanisms that provide the natural energy necessary for oil recovery:
- Rock and liquid expansion drive
- Depletion drive
- Gas cap drive
- Water drive
- Gravity drainage drive
- Combination drive
Rock and Liquid Expansion Drive
- Occurs when an oil reservoir initially exists at a pressure higher than its bubble-point pressure
- As the reservoir pressure declines, the rock and fluids expand due to their individual compressibilities
- This type of reservoir is considered the least efficient driving force and usually results in the recovery of only a small percentage of the total oil in place (3-5%)
Depletion Drive Mechanism
- Also referred to as solution gas drive, dissolved gas drive, or internal gas drive
- The principal source of energy is the gas liberation from the crude oil and the subsequent expansion of the solution gas as the reservoir pressure is reduced
Gas Cap Drive
- Gas-cap-drive reservoirs can be identified by the presence of a gas cap with little or no water drive
- The natural energy available to produce the crude oil comes from the expansion of the gas cap and the solution gas as it is liberated
Water Drive Mechanism
- Common types are edge water or bottom water in the water influx into a reservoir
- Bottom water occurs directly beneath the oil and edge water occurs off the flanks of the structure at the edge of the oil
Gravity-Drainage-Drive Mechanism
- Occurs due to differences in densities of the reservoir fluids
- Gravitational forces can be illustrated by placing a quantity of crude oil and a quantity of water in a jar and agitating the contents
Combination-Drive Mechanism
- A combination of driving forces resulting from the presence of a gas-cap and an aquifer
- Two combinations of driving forces resulting from the presence of a gas-cap and an aquifer
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Description
This quiz covers the basics of petroleum engineering, including the definition of oil and gas fields, lithology of petroleum reservoirs, and characteristics of sandstone and carbonate reservoir rocks.
