CPG Petroleum Geology & Reservoir Characterization 1 — Questions and Answers

Question 1: What is the primary source rock for petroleum?

Sandstone
Shale (Correct answer)
Limestone
Granite

Correct answer: Shale

Shale is widely recognized as the primary source rock for petroleum because it contains a high concentration of organic matter, primarily kerogen. Under specific conditions of heat and pressure over geological time, this organic matter matures and transforms into hydrocarbons (oil and natural gas), which can then migrate to reservoir rocks.

Question 2: What is porosity in a reservoir rock?

The density of the rock
The volume of solid material
The space available to hold fluids (Correct answer)
The permeability of the rock

Correct answer: The space available to hold fluids

Porosity in a reservoir rock refers to the percentage of the total rock volume that is made up of void spaces or pores. These interconnected pores are crucial because they are where hydrocarbons (oil and gas) and water are stored within the rock formation. High porosity is essential for a rock to be an effective reservoir, determining its storage capacity.

Question 3: Which tool is commonly used to evaluate reservoir properties?

Seismograph
Drill bit
Core barrel
Well log (Correct answer)

Correct answer: Well log

Well logs are continuous records of various physical properties of the rock formations encountered in a borehole, measured by instruments lowered into the well. They provide critical data on porosity, permeability, lithology, and fluid content, which are essential for evaluating reservoir quality and identifying hydrocarbon-bearing zones, guiding drilling and production decisions.

Question 4: What is the function of a cap rock in a petroleum trap?

To generate hydrocarbons
To store hydrocarbons
To seal the reservoir (Correct answer)
To fracture the rock

Correct answer: To seal the reservoir

A cap rock, also known as a seal rock, is an impermeable layer of rock that overlies a permeable reservoir rock. Its crucial function is to prevent the upward migration and escape of hydrocarbons from the reservoir, trapping them in place and forming a petroleum accumulation. Common cap rocks include shale, salt, and anhydrite, which create an effective seal.

Question 5: Which factor influences reservoir permeability?

Mineral composition
Pore throat size (Correct answer)
Color of the rock
Depth of burial

Correct answer: Pore throat size

Permeability is a measure of a rock's ability to allow fluids to flow through it. While porosity indicates the amount of space, pore throat size (the size of the connections between pores) dictates how easily fluids can move. Larger, well-connected pore throats result in higher permeability, which is vital for efficient hydrocarbon production from a reservoir.

Question 6: What does a structural trap rely on?

Chemical composition
Folding or faulting of rock layers (Correct answer)
Fluid density
Evaporation rates

Correct answer: Folding or faulting of rock layers

Structural traps are one of the main types of petroleum traps, formed by geological deformation of rock layers. These traps occur when the Earth's tectonic forces cause rocks to fold into anticlines or break along faults, creating configurations that prevent hydrocarbons from migrating further and instead accumulate them in a reservoir, forming an economic deposit.

Question 7: What is the main goal of reservoir characterization?

To locate surface oil seeps
To optimize reservoir management (Correct answer)
To drill faster
To test water quality

Correct answer: To optimize reservoir management

Reservoir characterization involves integrating geological, geophysical, and engineering data to create a detailed understanding of a petroleum reservoir's properties and behavior. The main goal is to build an accurate model that helps predict fluid flow, estimate reserves, and plan optimal drilling and production strategies to maximize hydrocarbon recovery over the life of the field.

Question 8: Which geophysical method helps identify potential reservoirs?

Gravity survey
Seismic reflection (Correct answer)
Magnetic survey
Soil sampling

Correct answer: Seismic reflection

Seismic reflection surveys are crucial for identifying potential reservoirs because they use sound waves to create detailed images of subsurface geological structures. These images allow geologists to map features like anticlines, faults, and stratigraphic traps, which are common configurations where hydrocarbons accumulate. By visualizing these structures, exploration teams can pinpoint promising locations for drilling.

Question 9: What type of rock is most commonly associated with reservoir rocks?

Shale
Basalt
Sandstone (Correct answer)
Marble

Correct answer: Sandstone

Sandstone is the most commonly associated reservoir rock due to its excellent petrophysical properties. It typically possesses high porosity, meaning it has abundant pore spaces where oil and gas can accumulate, and high permeability, allowing these fluids to flow through the rock. These characteristics make sandstone an ideal medium for storing and producing hydrocarbons.

CPG Petroleum Geology & Reservoir Characterization 1

What is the primary source rock for petroleum?