pab 1023 petroleum geoscience1 basin analysis & petroleum system qab3033 petroleum system assoc....

PAB 1023 Petroleum Geoscience 1

Basin Analysis & Petroleum SystemQAB3033

Petroleum System

Assoc. Prof. Dr. Swapan Kumar BhattacharyaGeoscience & Petroleum Engineering Department

Petroleum System

• This Week• Fundamentals of Petroleum Geology

Source Rock Generation

Elements Reservoir Rock Processes Migration Seal Rock Accumulation Overburden Rock

• Prospect & Play Analysis

Prospect & Play

• Prospect - a lead which has been fully evaluated and is ready to drill.

• Play - A particular combination of reservoir, seal, source and trap associated with proven hydrocarbon accumulations.

Source Rock

Source Rock is defined as the rock having efficienthydrocarbon generation and expulsion capacities.

Characteristically, these are fine grained sedimentary rocks with high total organic carbon (TOC), high molarH/C ratio.

Their thermal maturity (Vro) need to be sufficient so that at least they cross oil or gas Window for specific oil or gas generation.

Reservoir Rock Reservoir Rock is defined as the rock having

appreciable porosity to trap the hydrocarbons and sufficient permeability for the oil to flow during

migration and production.

Characteristically, these are coarse grained clastic sedimentary rocks or porous limestones or fractured igneous or metamorphic rocks.

Hydrocarbon Traps Hydrocarbon Traps are:

(1)Structural: If trapping is exclusively due to structural style, or

(2)Stratigraphic: If trapping is exclusively due to stratigraphic disposition, or

(3)Combination: If trapping is due to both structure & stratigraphic disposition.

Structural Traps: Folds, FaultsStratigraphic Traps: Lenticular Sands, Channel fillsCombination Traps: Up-dip pinchouts


Structural Traps• Structural traps are those where entrapment of

hydrocarbon takes place due to structural configuration only. Structural traps form usually by tectonic forces.

– An anticline is where rocks are folded or bent upwards. Hydrocarbons migrate up the flanks of the anticline and are trapped in the crest.

– Faults occur where there is movement along a joint or fracture. Offset of the beds could result in an impermeable layer being on top of a permeable layer.


Structural Traps

:


Structural Traps Terminology


Six trapping and two non-trapping configurations against a fault, depending on whether the fault is normal or reverse, on the direction of dip of the beds relative to the fault plane, and on the amount of displacement of the reservoir.


Sealing Faults• An investigation into the sealing qualities of faults affecting

roll-over anticlines in the Niger Delta, where the reservoirs overlie overpressured shales (bulging).

• Where a reservoir is full to spill-point against a fault, and where an oil-water contact is continuous across a fault, it is presumed that the fault is non-sealing; elsewhere it appears to form a trap. The difference is believed to be due to clay being smeared into the fault plane, where there is enough of it in the section, as the fault moved


Sealing Faults


Stratigraphic Traps• Stratigraphic traps are those where

entrapment of hydrocarbon takes place due to stratigraphic disposition only.

• Rock layers changing from a good reservoir to non-reservoir due to change in rock type (pinch-out), reservoir quality (diagenesis), or removal (erosional unconformity)


Pinch Out• Sometimes due to a lateral

change in the environment of deposition a lens of permeable sand is surrounded by less permeable siltstones and shales, forming a pinch out trap.

• This commonly happens in stream environments where sand is deposited along the stream channel which is surrounded by a flood plain characterized by finer grained sediments.


Channel Trap


Unconformity• Unconformities are another

type of stratigraphic trap. – They represent a gap in the

geologic record, in other words a period of erosion and/or nondeposition.

• They can result in a permeable reservoir rock being truncated and overlain by an impermeable unit.


Hydrodynamic trap

• Oil, attempting to escape to surface up a reservoir, is held against an unevenness of its upper surface by water flowing in the opposite direction. There is no structural or stratigraphic closure. – Note that the oil-water

contact is tilted down in the direction of water flow.


Diapiric Traps

• Caused by upward movement of sediments that are less dense than those overlying them– Salt– Clay


Salt Dome Associated Traps


Seal

• A seal is a fine-grained rock that prevents the oil migrating to the surface @ vertical migration (which happens in many parts of the world - leading to natural oil seeps).

• The seal is an important component in a prospect.


SEAL

• Common seals include – salt evaporites, chalks provides an effective seal,

but – Muddy @ clay-rich rocks @ mudrock, shale

represent most seals. – Siltstones (very fine-grained)


HOW WE QUANTIFY SEAL?

• Analysis of seals involves assessment of their thickness and extent, such that their effectiveness can be quantified.

• Knowledge of sequence stratigraphy is crucial for better understanding of seal.

Petroleum SystemA petroleum system includes all those geological elements & processes that are essential for an oildeposit to exist in nature. (Magoon, 1988)

These basic elements are:1. Petroleum Source rocks2. Reservoir Rocks3. Seals4.Migration Paths5. TrapsAnd the geological processes that created each of them

Source RockSource RockMigration RouteMigration RouteReservoir RockReservoir RockSeal RockSeal RockTrapTrap

GenerationGenerationMigrationMigrationAccumulationAccumulationPreservationPreservation

Petroleum System ProcessesPetroleum System Processes

24803

Petroleum System ElementsPetroleum System Elements

120° F120° F

350° F350° FGenerationGeneration

MigrationMigration

Seal RockSeal Rock

Reservoir RockReservoir Rock

OilOil

WaterWater

Gas CapGas Cap

EntrapmentEntrapmentAccumulationAccumulation

Source Source RockRock

Petroleum SystemThe term petroleum includes high concentrations of either thermal or biogenic gas, condensates, crude oils, natural waxes, or asphalts found in both conventional & in tight reservoirs, fractured shales, gas hydrates, coal beds and bituminous sandstones.

The name of a petroleum system is a combination of the source & reservoir rock names followed by a symbol indicating the level of certainty of the source – reservoir association. The symbols are:

1.Known (!)2.Hypothetical (.) 3. Speculative (?)

e.g La Luna – Misoa (!) Marcaibo Basin, Venezuela.

Petroleum SystemPetroleum system is best described by:1. Table listing all the field names, year of

discovery, name of producing unit, depth, reservoir seal lithology, trap type, cumulative production & reserves.

2.A map showing the geographic extent of the system, matured source pod , location of fields & key wells etc.

3.A burial history chart at one or more locations.4. A geologic cross-section drawn at the critical

moment illustrating the spatial relationship of the essential elements.

5.An event chart indicating the time intervals of the essential elements & processes including preservation time & critical moment.

Petroleum System

Basement

GEOGRAPHIC EXTENT OF PETROLEUM SYSTEM Present-Day

STRATIGRAPHICEXTENT OF

PETROLEUM SYSTEM

Petroleum accumulation

Top of oil window

Bottom of oil window

Trap TrapTrap

Seal

Reservoir

Source

Underburden

Overburden

A A’

Magoon and Dow, 1994Magoon and Dow, 1994

Present-Day Petroleum SystemPresent-Day Petroleum System

Petroleum System

Petroleum System

M (g.TOC) = V (cm3) x p (g/cm3) x [TOC(wt%) /100]

R (mg HC/g TOC) = HI0(mg HC/g TOC) – HIp (mg HC/g TOC)

HCG (kg HC) = R xM x 10-6

Oil (bbl) = HCG / 131.15 (kg/bbl of 400 API oil)

Formulae to calculate hydrocarbon generation

Total Petroleum System

Reasons for carrying out oil and gas related investigations in a geologic province are :

•To decide where to explore and / or•To assess undiscovered commercial quantities of petroleum

Both can be assessed by ‘Petroleum System’

In USGS World Petroleum Assessment, 2000 the term ‘Total Petroleum System’ was introduced to evaluate undiscovered oil and Gas resources that have the potential to be added within the next 30 years

To reserves in the world.

The ‘Total Petroleum System is evaluated by dividing the world into eight (8)

regions and 937 geological provinces. Maps were prepared for each region

using GIS and each region and province is named and numbered. Each

province is characteristically hundred or even thousand square kilometers

encompassing a natural geological entity – a basin, a thrust belt, a delta or

some combination of geological entity. These provinces are then ranked by

known volume of petroleum in barrels.



The goal of ‘TPS’ investigation is to understand the geographic,

stratigraphic and temporal evolution of the system so that the resource

assessment can be based on sound geologic and geochemical concepts.

‘TPS’ ideally includes : 1.Genetically related known oil and gas accumulations, shows and seeps

2.The pod or pods of active source rocks3.Minimum geographic extent

4.Maximum geographic extent.5.The location of the TPS cross-section and

6.The location of the locality depicted in the burial history chart.


1. Discovered accumulations, shows and seeps:

Within a given TPS, the genetically related discovered oil and gas fields or petroleum accumulations originated from same pod of active source rock. The investigator starts with a map that shows the discovered oil and gas fields. The investigator then groups the oil and gas fields into one or more possible TPS based on their geographic and stratigraphic locations and the bulk and geochemical properties of the fluids in each accumulation.

2. Pod of active source rock:

The pod of active source rock is a contiguous volume of source rock that generated and expelled petroleum at the critical moment and is the provenance for a group of genetically petroleum shows, seeps and accumulations in a TPS. A pod of active source rock may be active, inactive or spent.


3. Minimum geographic extent:

The minimum geographic extent of the TPS is a line that circumscribes the pod of active source rock and includes all the discoveredPetroleum shows, seeps and accumulations that generated from this pod.This is the same line of the geographic extent of the petroleum system.

4. Maximum geographic extent:

The maximum geographic extent of the TPS is line that lies beyond or coincides with minimum geographic extent. The maximum geographic extent is mapped using geological evidence, such as the geographic extent of the reservoir rock, the indicates the possibility that oil and gas migrated beyond the minimum geographic extent but no seeps, shows or accumulationsare known.

Source Material

Non-Biogenic Origins

Biogenic (Kerogen Types)Type I – Algal (oil prone) sapropelic

Type II – MixedType III – Woody (gas prone) humic

Host rock (Shales and Coals)

2

1

2

3

4

5

6

7

89

10

1112

13

14

15

TOC VroWell

1 5.2 0.56 802 5.1 0.60 1403 5.0 0.60 1304 5.2 0.55 1505 5.2 0.58 1156 6.4 0.45 1507 4.8 0.78 1208 3.9 0.65 1109 3.0 0.50 8010 2.0 0.43 3011 0.3 0.42 5012 0.6 0.45 2513 0.8 0.5 6014 0.3 0.4 6515 0.25 0.35 20

ThicknessThese data are available with data package. Other data you have to purchase @ USD1000

You are asked to evaluateand bid for the exploration.

Kerogen TypesKerogen TypesType 1 Type 2 Type 3

pab 1023 petroleum geoscience1 basin analysis & petroleum system qab3033 petroleum system assoc....

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