Important Definitions For Petroleum Geoscience Exam

Half of the Petroleum Geoscience exam in the Msc Petroleum Engineering degree with Heriot Watt University is comprised of part A questions that ask you for definitions to different terminologies. That’s 50 marks. While it is difficult to know exactly what might be on the exam, the following is a list of what I think are indispensable definitions that you should have mastered before heading in. I found a great way to study for these is to print out several sheets of paper with the terminologies listed and draw mind maps out from the center of term. Begin by first reading through the answers and then trying to complete it on your own. Each time you finish, review your answers and compare with the solutions noting any differences or gaps in your knowledge. After a few attempts you’ll have the definitions word for word. I think many of the questions also look for around four dot points as they generally award 0.5 marks for each unique component of your answer. I’ve attached my document so you can download.

1. Reasonable Range of Recovery Factors

In an oil well we have:

  • Gas Solution Drive: 5-30%
  • Gravity Drainage: 5-30%
  • Gas Cap Drive: 20-40%
  • Water Drive: 35-75%

In a gas well we have:

  • Mobile aquifer drive: 55-75%
  • No aquifer: 80-90%

2. Strike and Dip 

  • Method for describing the orientation of a planar surface
  • Usually with regards to a fault or fracture
  • The horizontal line on the surface gives the orientation of strike
  • Dip is the angle between a horizontal plane and the planar surface

3. Basin

  • Large low lying area
  • Collects depositional sediment
  • Undergoes subsidence to continually allow the addition of new sediment
  • Found in a range of tectonic environments (divergent, transform etc)

For reserves and proven reserves definition follow the link here

4. Fractures

  • Break in structure of rocks
  • No relative movement between surfaces
  • Can have open fractures that create secondary porosity and permeability
  • Can also have closed fractures that are infilled by finer sediments

5. Trough Cross-bedding

  • Trough cross-bedding is a sedimentary process
  • Caused by the migration of mega ripples or migrating dunes with curved crests
  • Usually greater than 5cm in thickness
  • Cross-bedding erosional boundaries in the system are curved

6. Turbidites

  • Result from turbidite flow
  • Can be found in submarine fan environment or on the basin floor
  • Remember the BOUMA sequence
  • High energy erosional process
  • Results in coarse sediments fining upwards

7. Secondary Sedimentary Structures

  • These occur after the primary sedimentation process has taken place
  • Deformation – with mechanical failure of a strata will cause new secondary sedimentary structure (pillows are one example)
  • Bioturbation – the movement and disturbance of primary sedimentation by marine or aquatic life burrowing and digging.
  • Rain drop patterns

8. Crust and Lithosphere

  • Crust is comprised of both ocean crust and continental crust
  • Lithosphere comprises of both the earth’s crust and the outermost solid and hard mantle of the earth
  • Lithosphere formed by plates and is able to move around on top of the more ductile and soft layer below it

9. Plate Margin

  • The interface between two different lithospheres
  • Move in three different manners relative to each other
  • Transform side/slip
  • Convergent is compressional, causes volcanoes and mountains
  • Divergent is tensile, moving away from each other. Causes subsidence.

10. Gross Rock Volume

This is a hard one to get out more than one point without waffling on

  • From the Oil Water Contact (OWC) to the top of the hydrocarbon bearing formation

11. Biostratigraphy

  • Grouping or exclusion of stratigraphic sections based on the presence or absence of fossils
  • Fossils are left behind from animal remains or plant material
  • For it to be useful need to have animal or plant life form that had a widespread presence

12. Walther’s Law

  • States that facies that are stacked in a vertical conformable succession must have been deposited in adjacent sedimentary environments at the same time
  • The movement of depositional environments over time causes the facies to stack atop each other
  • If there are two facies stacked in vertical succession that could not have been deposited at the same time then there must be an unconformity.

13. Triangulation

  • Technique to create a contour on surface or thickness maps
  • Links data points to form triangles. No lines cross though.
  • Removes the human element of subjectivity, good if geologists have differing opinions
  • Should be the same no matter who draws it

14. Seismic Resolution

  • The smallest thickness of a bed such that the top and bottom surface can be picked up by seismic energy
  • Usually around 1/4 wavelength of the seismic pulse (8-60m)

15.  Isopach

  • True stratigraphic thickness
  • Measured perpendicular to the surface of the bed

Click on the link below to download the pdf with terminologies.

List of Definitions

 

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