PetE 409 - Reservoir Geomechanics - Flashcards

This set of flashcards covers essential vocabulary and concepts from the lecture notes on Reservoir Geomechanics.

Reservoir Geomechanics

Focuses on understanding the mechanical behavior of rock formations within hydrocarbon reservoirs.

Geomechanics

The study of how subsurface rocks deform or fail in response to changes of stress, pressure, and temperature.

Stress

Defined as the force acting over a given area and is a tensor that describes the density of forces acting on all surfaces passing through a given point.

Strain

Deformation that occurs when stress causes a material to change shape.

Elastic Deformation

Occurs when the rock returns to its original shape when stress is removed.

Plastic Deformation

Occurs when rock under stress does not return to its original shape when the stress is removed.

Fracture

When a rock under stress breaks.

Uniformly Dipping Beds

Layers of rock or sedimentary strata that dip at a constant angle and direction relative to the horizontal plane.

Dip

The angle that the plane makes with the horizontal plane.

Angle of Dip

The angle that the plane makes with the horizontal plane.

Folds

Rocks deforming plastically under compressive stresses.

Monocline

A simple bend in rock layers so that they are no longer horizontal.

Anticline

Folded rocks that arch upward and dip away from the center of the fold.

Dome

When rocks arch upward forming a circular structure.

Syncline

A fold that bends downward, causing the youngest rock to be at the center and the oldest on the outside.

Basin

When rock bends downward in a circular structure.

Fault-bend Folds

Formed where the dip of the fault changes.

Detachment Folds

Formed where the slip changes, and distortion is accommodated in the hanging wall.

Fault-propagation Folds

Formed where the dip and the slip change, typically where a fault tip climbs up a ramp during fault propagation.

Cylindrical Folded Surface

The shape of which can be generated by taking a straight line and moving it whilst keeping it parallel to itself.

Non-cylindrical Folding

Folds which cannot be generated by translating a straight line.

Joint

No movement on either side of a fracture.

Fault

The block of rock on one or both sides of a fracture that moves.

Slip

The distance rock moves along a fault.

Normal Faults

The fault where the hanging wall drops down relative to the foot wall.

Reverse Faults

The fault where the footwall drops down relative to the hanging wall.

Strike-slip Fault

A fault where rock blocks slide past each other; an example is California's San Andreas Fault.

Horst

A block between two normal faults that dip away from each other, where rocks stand higher.

Graben

A block between two normal faults that dip towards each other, where rocks stand lower.

Half-graben

A tilted block in a rift zone, dropped down relative to the rocks on either side, having a fault on one side.

Synthetic Faults

Faults that dip in the same direction.

Antithetic Faults

Faults that dip in the opposite direction.

Foreland Basin

An area adjacent to a thrust belt.

Klippe

An area of hanging wall entirely surrounded by footwall.

Fenster or Tectonic Window

An area of footwall entirely surrounded by hanging wall.

Ramp

The steeper portions of a fault.

Flats

The gentler portions of a fault.

Decollement

A very extensive flat, where there has been a large amount of movement.

Humber Arm Allochthon

Composed of Cambrian and Ordovician deep-water sedimentary rocks and ophiolites from the floor of the Iapetus Ocean.

Vergence

The direction in which rocks near the surface have moved relative to the rocks deeper down.

Foreland

The area towards which most of the thrusts verge.

Hinterland

the opposite side of the thrust belt, the side from which most of the thrust sheets appear to come

Imbricate Fan

Multiple listric thrust faults that branch upward from a single flat.

Branch Point

The point where one thrust fault branches from another.

Trailing Branch Point

One fault branches into two as you follow it towards the foreland.

Duplex

Imbricate thrust faults merging into flats both upward and downward.

Roof Thrust

The upper flat of a duplex.

Floor Thrust

The lower flat of a duplex.

Tectonic Wedge

A pair of opposed thrusts that meet in the subsurface.

Triangle Zone

If a third thrust cuts off a triangular section of the rock.

Dextral Riedel Shears

Shears at 15 degrees clockwise from the overall dextral strike-slip zone.

Sinistral Antithetic Riedel Shears

Shears at 75 degrees clockwise from the overall direction of dextral strike-slip.

Transtension

A combination of strike-slip motion with extension.

Pull-apart Basin

A parallelogram-shaped subsiding area.

Transpression

A combination of strike-slip motion with shortening.

Topographic Map

A type of map that represents the three-dimensional surface features of an area on a two-dimensional plane.

Geological Map

Shows the distribution of various types of bedrock in an area, usually combined with a topographic map.

Contour Line

Imaginary line which connects points of equal elevation.

Contour Value

A numerical value placed upon a contour line to denote its elevation relative to a given datum.

Contour Interval

The constant vertical distance between two consecutive contours.

Depression

Approximately concentric closed contours with increasing values towards the center, indicating hills.

U-shape

Contour lines shaped with convexity towards lower ground, indicating a ridge.

V-shaped

Contour lines shaped with convexity towards higher ground, indicating a valley.

Vertical Cliff

Indicated by contour lines meeting in some portion, showing existence of a vertical cliff.

Saddle

Depression between summits represented by four sets of contours.

Index Contour Line

The boldest lines on a topographic map, usually numbered to indicate elevation.

Intermediate Contour Lines

Finer, less bold lines between index contour lines that provide additional detail.

Supplementary Contour Lines

Dashed lines indicating minor elevation changes in very flat terrain.

Slopes

Represent the rising or falling of the land surface.

Gradient

Measured by the vertical increase relative to horizontal equivalent, indicating how steep or gentle a slope is.