Fractured Reservoirs - Elective I
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Questions and Answers

What are three-dimensional features that have a distribution that is generally heterogeneous?

Fractures

What can be analyzed to determine the aperture and probable production rates of fractures?

Fractures seen in the wellbore

What is the kind of study that is most successful where the reservoir is formed almost entirely of fracture porosity?

Borehole micro-scanners

Fractures are important because of their influence on tight reservoirs due to their actual oil storage capability.

<p>False (B)</p> Signup and view all the answers

Fracture volume is usually small compared to the total reservoir volume.

<p>True (A)</p> Signup and view all the answers

What does a fracture provide that is much larger than the borehole?

<p>An interface with the matrix</p> Signup and view all the answers

What factors control the occurrence of natural, open, permeable fractures? (Select all that apply)

<p>In-situ stresses (A), Nature and degree of folding and/or faulting (C), Changes in rock properties such as porosity and bedding (D)</p> Signup and view all the answers

When are fractures usually formed?

<p>During folding or doming of a reservoir</p> Signup and view all the answers

Fractures are critical to productivity in areas where reservoirs have little or no matrix permeability.

<p>True (A)</p> Signup and view all the answers

What types of rocks are fractures more common in? (Select all that apply)

<p>Igneous (A), Metamorphic (B), Carbonates (C)</p> Signup and view all the answers

What type of fractures are usually long straight cracks in an axial position on opposite sides of the borehole?

<p>Large fractures induced from drilling conditions perpendicular to the direction of borehole enlargement</p> Signup and view all the answers

Induced cracks are extensional fractures that form and are propagated in front of the bit during drilling.

<p>True (A)</p> Signup and view all the answers

How are fractures often detected while drilling? (Select all that apply)

<p>Drilling breaks (A), Massive lost circulation (B), Sudden pressure kicks (D)</p> Signup and view all the answers

What type of logs are the best means of describing the fracture geometry?

<p>High-resolution logs, ideally electrical imaging logs such as the Formation Micro-Scanner or FMI tool</p> Signup and view all the answers

What can be determined directly from inspection of the images?

<p>The fracture inclination and spacing</p> Signup and view all the answers

Electrical images and acoustic images have the same resolution and depth of investigation.

<p>False (B)</p> Signup and view all the answers

What do fractured reservoirs consist of?

<p>Fractured reservoirs are essentially reservoirs where the porosity is primarily due to the presence of fractures.</p> Signup and view all the answers

What tools are used in detecting fractures?

<p>The tools used in detecting fractures include borehole imaging logs, 3D seismic surveys, and horizontal wells.</p> Signup and view all the answers

What are the important of fractures?

<p>Fractures are important because they allow fluids to flow through the reservoir, even if the matrix has very little porosity. They are particularly important in tight reservoirs, which have very low permeability.</p> Signup and view all the answers

What is the fracture intensity?

<p>Fracture intensity is defined as the number of fractures per unit length inside an interval of a defined height.</p> Signup and view all the answers

What is the most common type of rock in which fractures exist?

<p>The most common fractures are exist in lithology.</p> Signup and view all the answers

Fractures related to faults are more abundant than fractures related to folding.

<p>False (B)</p> Signup and view all the answers

Fractures induced during drilling are horizontal to the bit drilling borehole.

<p>False (B)</p> Signup and view all the answers

Mud circulation cannot detect fractures.

<p>False (B)</p> Signup and view all the answers

Explain why mud circulation cannot always detect fractures.

<p>Mud circulation cannot always detect fractures because the fractures might be small or filled with fluids that are not permeable to the mud.</p> Signup and view all the answers

Flashcards

Fractured Reservoirs

Reservoirs containing interconnected fracture systems that influence fluid flow and production.

Fracture Distribution

The uneven and 3-dimensional pattern of fractures within a reservoir.

Fracture Aperture

The open space between fracture surfaces; a measure of fracture size.

Production Rate Determination

Estimating oil or gas production from a fractured reservoir based on wellbore observations.

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Imaging Logs

Borehole logs used to visualize subsurface formations, especially fractures.

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Formation Micro-Scanner (FMI)

A type of imaging log useful for identifying fractures in a reservoir.

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Fracture Porosity

Porosity in a reservoir that is primarily a result of fractures.

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Importance of Fractures (In Reservoirs)

Fractures influence Tight Reservoir flow, not primary storage.

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Fracture Volume

The total amount of space occupied by fractures.

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Matrix

The solid rock between fractures.

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Folding/Faulting

Geological processes causing deformation in rock layers.

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In-situ Stresses

Stresses acting on the rock in its natural state below the surface.

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Porosity & Bedding

Rock properties influencing fracture formation.

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Fracture Intensity

Number of fractures per unit length within a certain interval.

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Fracture Orientation

The direction of fractures with respect to geological features like faults.

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Tectonic Stresses

Forces causing large-scale movements of the earth's crust.

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Faults

Fractures in the earth's crust along which rocks have moved.

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Induced Fractures

Fractures formed due to drilling procedures.

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Lost Circulation

Drilling problem where drilling fluid leaks into the formation.

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Pressure Kicks

Drilling occurrences where drilling fluid pressure suddenly increases.

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Drilling Breaks

Sudden stops in drilling.

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Electrical Imaging Logs

Borehole logs that visualize fractures in detail.

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Fracture Inclination

The angle of a fracture to a horizontal plane.

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Fracture Spacing

The distance between fractures.

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Fracture Aperture

The open space between fracture surfaces.

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Fracture Geometry

The shape and arrangement of fractures in a reservoir.

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Study Notes

Fractured Reservoirs - Elective I

  • Fractures are 3-dimensional, heterogeneous features
  • Fracture distribution in wellbores can be analyzed to determine aperture and production rates
  • Well logs (e.g., borehole micro-scanners) are valuable for studying fracture porosity, especially in reservoirs formed primarily of fractures
  • Fractures are significant in tight reservoirs, influencing how well oil is extracted, but aren't major oil storage areas
  • Fracture volume, though small compared to overall reservoir volume, creates a large interface with the surrounding rock matrix
  • Factors influencing fracture presence include folding, faulting, stress states, and rock properties (porosity, bedding)
  • Fractures often form during folding and doming, concentrating in low-porosity rocks
  • In reservoirs with low matrix permeability, fractures are crucial for productivity, particularly in basement reservoirs
  • Borehole imaging and 3D seismic surveys improve fault mapping and understanding fracturing associated with reservoir faults
  • Fracturing often occurs parallel or perpendicular to faults. Oblique orientations are related to wrench or shear movements
  • Fracture density is the number of fractures per unit length within a defined interval
  • Fracture density needs correction for variations in fracture plane angle and borehole axis
  • Fracture orientations can relate to geological parameters and structural events
  • Fault-related fractures are less common than those from folding, but can lead to significant fluid flow through fault systems
  • Recognizing faults depends on detecting bedding planes above and below the fault
  • Fractures are commonly created by tectonic stresses, more common in brittle rocks (carbonates, igneous, metamorphic) than sandstones, and typically occur in specific directions dictated by regional stresses
  • Drilling can induce fractures, creating long, straight fractures on opposite sides of the borehole. These are extensional
  • Fractures are often signaled by massive lost circulation events, sudden pressure changes during drilling
  • High-resolution logs (like FMI tools) are best for describing fracture geometry
  • Fracture inclination, spacing, and opening can be determined from log inspections
  • Electrical imaging logs have a higher vertical resolution than acoustic images
  • Key problems related to fractured reservoirs include defining fractured reservoirs, tools for detecting fractures, the importance of fractures, types of fractures, diagnosing fracture intensity, and common fracture lithologies.
  • True or False: Fracture related to faults is more abundant than folding (False)
  • True or False: Induced fractures are horizontal to the bit drilling borehole (False)
  • True or False: Mud circulation cannot detect fractures (True, and explain why)

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Fractured Reservoirs Elective I PDF

Description

Explore the roles and characteristics of fractures in reservoir engineering. This quiz delves into how fractures affect oil extraction, the significance of fracture distribution in wellbores, and the methods used to study them. Test your knowledge on factors influencing fracture presence and their impact on reservoir productivity.

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