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Geoscience > Unit 3 - Petroleum Play > Flashcards

Unit 3 - Petroleum Play Flashcards

1
Q

What is a petroleum play?

A
  • A model or perception of how a specific region of the Earth’s subsurface may be an appropriate target for exploration drilling
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2
Q

What are the 4 big parts of the petroleum play?

A
  • producible reservoir → rock with its connected pore or fracture system
  • Petroleum charge system → the source rock for HC and the migrations part to reservoir
  • Regional topseal (the capping rock preventing migration out of the reservoir)
  • Trap (the geological features defining the physical limits to the reservoir rock in the subsurface)

→ combine to create significant petroleum accumulations at a specific stratigraphic level.

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3
Q

What kind of data do explorationists use to identify the parts of a petroleum play?

A
  • outcrops
  • well data
  • seismic data
  • geological studies by government geological surveys or industry contractors
  • infos from discussions with other professionals
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4
Q

What is a prospect?

A

Identified trap which:

  • reasonable chance of containing connected porous rocks containing a fluid (permeable)
  • is older than the time in which oil and gas was available because oil/gas migrates from a source rock once it reaches thermal maturity
  • Is in location to which oil/gas could move (migrate)
  • Is of sufficient potential size with enough confidence (or probability) that oil will be found to warrant drilling an exploration well.
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5
Q

What is the most important task of explorationists after identifying a prospect?

A
  • Provide an estimation of technical risk
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6
Q

What are the key elements of a prospect?

A
  • Reservoir
  • Seal
  • Source Rock, Maturity and Migration Path
  • Timing
  • Trap
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7
Q

The analysis of the Petroleum Play leads to?

A

the estimation of the probability of success for a particular prospect

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8
Q

In prospect appraisal, do explorationists usually focus more on porosity or permeability ?

A

Usually more on porosity → 10% porosity often equates to a 1mD cut-off which is thought necessary for oil production

The explorationist will therefore risk the occurrence of rock that is greater than 10% porosity in order to define the reservoir

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9
Q

What are the two main elements of textural description of the rock in the petroleum play ?

A
  • grain size
  • grain sorting
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10
Q

Why do geologists use the term palaeo- ?

A

to indicate a feature in the geological record

E.g. palaeo- slope, palaeo-wind

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11
Q

Why do you want to understand the depositional processes through time?

A
  • reconstructions can be made with a certain level of accuracy → even in areas where you don’t have samples
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12
Q

Grain size and sorting are a function of ?

A

Depositional environment

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13
Q

Porosity and permeability developed in carbonate reservoirs is dominated by ?

A

Secondary processes

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14
Q

What is a seal?

A
  • a fine grained rock, which prevents oil from migrating to surface
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15
Q

What is a source rock?

A

a rock unit, that has generated oil or gas in a sufficient amount for migration and accumulation

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16
Q

What do source rocks contain?

A

biologically-derived organic matter buried as sediment → HC originate from these rocks when the pressure temperature conditions cause changes in original organic matter

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17
Q

How much organic matter do “good” source rocks contain?

A

5-20%

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18
Q

What are the four main chemical components of organic matter ?

A
  • Protein
  • Carbohydrates
  • Lipid (marine animals)
  • Lignin (land plants)
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19
Q

Why do you need anoxic conditions to preserve organic matter?

A
  • because it restricts the action of organisms, that would otherwise consume organic materials
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20
Q

What are the three main settings, where source rocks are deposited?

A
  • lakes
  • deltas
  • marine basins
21
Q

why are lakes good for the deposition of source rocks?

A
  • they usually have a poor turnover of a water column because there isn’t a strong water flow which allows the anoxic accumulation of land-derived (gas prone) or algal-derived (oil prone) organic matter
22
Q

What is a typical source rock?

A
  • Fine grained → like mudstones → become shale when compressed
23
Q

Why are source rocks often fine grained muddy sediments?

A
  • are often more likely to be impermeable → largely because of small pore sizes and efficient packing of clay particles
  • impermeability prevents oxygenated waters in overlying water column to penetrate the sediment and oxidising the organic matter deposited along with the mud particles
24
Q

What happens after the organic matter is buried and preserved?

A
  • Organic matter contains various biopolymers → are quickly condensed and converted to insoluble kerogen during diagenesis
  • Bitumen is the soluble remnant of this process
  • Kerogen has different types and properties depending on the source of organic matter: algal matter, waxy plant fragments, or woody plant fragments.
25
Q

What is headspace gas ?

A

Gas given off by drilling cutting samples, when stored in a can

26
Q

How can you use the relectivity of vitrinite?

A

The reflectivity of vitrinite to normal light under the microscope increases as the maturity of a coal increases.

27
Q

How is the vitrinite reflectance measured?

A

As a percentage of the light reflected back

28
Q

What is kerogen?

A

Lipid-rich part of organic matter which is not soluble in common organic solvents

29
Q

What happens to kerogen during the maturation process?

A
  • it is converted to bitumen, which is the extractable content
30
Q

What happens to bitumen during migration?

A
  • It turns to petroleum ( the lighter HC migrate more easily and heavier ones are left behind)
  • Petroleum is liquid organic substance recovered in wells
  • Crude oil is the naturally occurring liquid form of petroleum
31
Q

What are the most important factors of breaking down kerogen?

A
  • time
  • temperature
32
Q

How come that the composition of the HC produced by maturation processes varies ?

A

Because initial present organic matter (kerogen) differs in composition

33
Q

What does TOC stand for?

A
  • total organic carbon
34
Q

What is the necessary amount of TOC for a shale to be considered a source rock

A

greater 0.5%

35
Q

What is the source “kitchen”?

A

location where oil generation happens

36
Q

What does it mean that oil gets cracked?

A
  • it turns to gas (heat)
37
Q

What do you call primary migration?

A

migration from the source rock into the carrier bed

38
Q

What is the driver of primary migration?

A

Pressure build up caused by HC generation

39
Q

Structural traps are caused by ?

A

Tectonic, diapiric, gravitational and compactional processes

40
Q

Why is the timing for a petroleum play so important?

A

Because timing of trap development relative to the timing of HC- migration is super important

41
Q

How can you determine the timing of oil migration?

A

by basin modelling → the time period for each rock unit can be determined using biostratigraphy

42
Q

What is another word for basin modelling?

A

Geohistory analysis

43
Q

How do you do a risk analysis of a Petroleum Play ?

A

Probabilities are assigned for each of the elements (reservoir, seal, source, trap and timing) from 0 (meaning impossible), to 1 (certain or very likely)

44
Q

What can you do if one of your probabilities for the main factors is very low?

A
  • more date (e. g., shoot more seismic)
  • wait for someone else to do it for you (by drilling a well and making a discovery nearby)
  • farm-out
  • relinquish the area (thereby saving the rental costs)
45
Q

What is a conventional play?

A
  • HC are generated in source rock and move/migrate to porous and permeable reservoir rock → there they can be extracted by normal drilling
46
Q

What is an unconventional play ?

A

HC are generated in a source rock but some or all of them are trapped within source rock → they will not migrate

  • you have to drill into source rock using hydraulic fracturing of rock to provide HC present with pathways to escape into well (“shale gas/oil”)
47
Q

What is a Lead?

A

Specific locations, where traps may exist

48
Q

Play to production ? Key stages

A
  • Play concept
  • Leads
  • Prospects
  • Discovery
  • Appraisal
  • Development
49
Q
A

Geoscience (10 decks)

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