1 -Geology and Rock Properties

1- Geology and Rock Properties

Geology and Rock Properties

1- Geology and Rock Properties Page-2

1- Geology and Rock PropertiesContents

1- Reservoir Geology

a. Tectonics & Sedimentationsb. Source Rocksc. Hydrocarbon Migrationd. Reservoirse. Cap Rocks/Traps/Sealsf. Timing Sequence

2- Reservoir Rock Characteristicsa. Carbonatesb. Sandstonesc. Porosityd. Permeability



ObjectivesUnderstanding the following:

Petroleum entrapment. Sedimentary basins. Hydrocarbon generation and migration. Trapping configurations. Key characteristics of source rocks, reservoir rocks and seals.Understand key reservoir properties of Lithology, porosity and permeability



Tectonics and Sedimentations



OverviewThe story of oil and natural gas begins far back in time as long as 500 million years ago. Over the 4.5 billion years of it's lifetime the earth has been in an extremely slow but constant process of change.




1- Geology and Rock PropertiesTectonic Plates

OverviewPresent day continents were once joined together in a super-continent called Pangaea and have been drifting apart over the past 150 million years. Explained by a theory called plate tectonics -states that the continents are on enormous moving plates. As these plates move in response to stresses in the earth's mantle they collide or spread apart or slide past each other.



Present Day

CRETACEOUS65 Million Years agoJURASIC

135 Million Years ago

TRIASSIC200 Million Years ago

PERMIAN225 Million Years ago



OverviewAs these plates move over the surface of the earth, in response to stresses in the earth's mantle they collide or spread apart or slide past each other. Mountains are often formed where plates collide. And more important to the industry these deformations of the earth's crust also form the basins, traps, and fluid movement that make petroleum possible.





Generation: Sedimentary BasinsThere are about 600 major sedimentary basins in the world today. These are depressed areas of the earth's crust where sedimentary rock has built up over time to thicknesses up to 15,000 meters. Basins are often created when land masses pull apart, and the area between them sinks, creating a bowl-shaped depression which fills with water, and subsequently sediments.



Distribution of the various types of Carbonate Rocks



Reservoir Geology:

Source RocksMigrationsReservoir RocksTrapsTiming



OverviewIn the petroleum industry you will hear oil described as found in the late Cretaceous or the late Jurassic. These terms refer to the time on geologic time scale when these layers were deposited. Over the course of millions of years a fortunate timing of geological events can bring the right elements together at the right time in order to produce economic accumulations of oil.



Overview The Petroleum Systems approach has four elements:Biological origin of petroleum from organically rich source rocksMigration of oil and gas from source to trapReservoir rocks that hold the gas or oilTraps and seals that allow accumulation and concentration.


1- Geology and Rock PropertiesOverview: Generation, Migration, and Trapping of Hydrocarbons

SealReservoir

rock

SealMigration route

Oil/watercontact (OWC)

Hydrocarbonaccumulation

in thereservoir rock

Top of maturity

Source rock

Fault(impermeable)

Seal



Generation: Sedimentary BasinsSedimentary basins are often bounded on the bottom by basementrock, and on the top by overburden material. It is estimated that more than 90% of the world's oil and gas occurs in sedimentary basins. Examples of important oil producing basins are the Gulf of Mexico and the Gulf of Suez

Generation: Sedimentary BasinsSedimentary basins are often bounded on the bottom by basementrock, and on the top by overburden material. It is estimated that more than 90% of the world's oil and gas occurs in sedimentary basins. Examples of important oil producing basins are the Gulf of Mexico and the Gulf of Suez



1- Generation: Source Rocks and MaturationAs sedimentary layers accumulate in basins the stage is set for the generation of hydrocarbons.



1- Generation: Source Rocks and MaturationWhen sediments are deposited, they often include carbon-rich remains of many different organisms including plants and algae. This material is referred to as organic.


1- Geology and Rock Properties1- Generation: Source Rocks and MaturationLayers accumulate and in time the overburden weight compresses the sediments. Temperature increases with depth and the combination of pressure and heat begins a slow transformation of the organic material into petroleum. Organic material is changed into intermediate kerogens, and then into oil and gas in a process called maturation.


1- Geology and Rock Properties1- Generation: Source Rocks and MaturationAt about 2100 meters below the surface, the minimum temperature for the formation of oil (65 degrees Celsius) is reached. At even deeper levels, where temperatures rise above 150 degrees Celsius, organic matter will be transformed instead to natural gas.





Effects of PRESSURE and TEMPERATURE on the GAS and LIQUID Phase transition



C1H4 (methane)

C3H8

C3H8C6H14

C8H18 (Octane)

1- Generation: Source Rocks and MaturationAll of these substances are called hydrocarbons, because they consist mainly of the elements hydrogen and carbon in various combinations.


1- Geology and Rock Properties1- Generation: Source Rocks and MaturationThe organically rich sedimentary rocks from which oil and gas form are called mature source rocks.



1- Generation: Source Rocks and MaturationSource rocks that have generated oil or gas sometime in the geological past are considered one of the four main requirements of an economic petroleum accumulation. Shale is a common source rock.

1- Generation: Source Rocks and MaturationSource rocks that have generated oil or gas sometime in the geological past are considered one of the four main requirements of an economic petroleum accumulation. Shale is a common source rock.



2- Expulsion and Migration:

This process is called primary migration, or expulsion.


1- Geology and Rock Properties 2- Expulsion and Migration: After oil or gas is generated in a source rock, increasing pressure may cause microfractures that allow hydrocarbons to escape.



2- Expulsion and Migration: Because oil and gas are less dense than water, buoyant forces cause them to flow up along the path of least resistance toward the surface. The paths newly generated hydrocarbons take can be along faults or fractures, or directly through other permeable rock layers, called carrier beds. This is known as secondary migration.


1- Geology and Rock PropertiesMicroscopic View

2 mm

HC

H2O

2- Expulsion and Migration: Fluids are able to flow through certain rock beds, such as sandstones and carbonates, due to their high permeability. This flow process may be slow, but on a geological scale this is short.


1- Geology and Rock Properties2- Expulsion and Migration:

At this point, most of the migrating hydrocarbons can either trapped downhole.

Or find their way to the surface and create seeps



Surface Oil Seepage2- Expulsion and Migration

Surface oil lakes were very common in Persia and Iraq. This oil was used for a variety of applications dating back thousands of years.

Surface oil lakes were very common in Persia and Iraq. This oil was used for a variety of applications dating back thousands of years.



The Construction of Babylon2- Expulsion and Migration

The bricks used in the construction of Babylon were cemented together using seepage oil. This can still be seen on the excavated site.

The bricks used in the construction of Babylon were cemented together using seepage oil. This can still be seen on the excavated site.


1- Geology and Rock PropertiesBoats on the Tigris2- Expulsion and Migration

This congregation of boats was a common sight on the Tigris River in the 19th

Century. These boats were constructed from wood and bamboo. They were made water proof by using the seepage oil to bind the wood and bamboo.

This congregation of boats was a common sight on the Tigris River in the 19th

Century. These boats were constructed from wood and bamboo. They were made water proof by using the seepage oil to bind the wood and bamboo.



2- Expulsion and Migration:Some of the hydrocarbon can become trapped in porous reservoir rock - another of the main requirements of an economic petroleum accumulation. Because of migration, oil and gas can end up accumulating far from their source.



3- Reservoir RockA reservoir rock is any rock that has enough porosity and permeability to both store and allow the production of hydrocarbons.



3- Reservoirs:

Migration, under the right environment, will create accumulation and entrapment of petroleum in reservoir rock.



3- Reservoir RockPermeability can be defined as the measure of ease with which fluid flows through a rock. This is necessary so that hydrocarbons can initially enter the reservoir, and then later be produced through a well.



3- Reservoir RockA good reservoir rock must also have sufficient porosity to hold an economic volume of oil or gas.



4- Trapping and SealsThe opposite of a reservoir rock, but a rock just as necessary for the formation of an economic petroleum accumulation is a seal.



4- Trapping and SealsSeals can be any rock with a low permeability to hydrocarbons. Seals can also be the result of a barrier to flow such as a fault. Some rocks commonly found acting as seals are shales and salts.



4- Trapping & SealsIf there is no seal, or cap rock present, hydrocarbons will continue to migrate to the surface and never become trapped.


1- Geology and Rock Properties4- Trapping & Seals: Trapping StructuresAs oil and gas migrate through the reservoir rock and carrier beds, they may encounter a high point, barrier, or seal where the fluids stop and accumulate. These structures are called traps and they are the third required element of an economic petroleum accumulation. There are two main types of traps-structural and stratigraphic.



4- Trapping & Seals: Trapping StructuresThere are two main types of structural traps - anticlines and fault traps. Tectonic forces create these structures after sedimentation and lithification.



ANTICLINE

4- Trapping & Seals: Trapping StructuresWhen compressive forces act on a section of the crust that is ductile, or bendable, folds form. The arch-like folds are called anticlines and gently folded anticlines can provide some of the largest and most effective traps in the world. Some of the enormous hydrocarbon deposits in the Middle East are in low relief anticlines.



(modified from Bjorlykke, 1989)

Oil / WaterContact

Gas

Fold (Anticlinal) Trap

Oil/GasContact

Oil

Closure

Oil

SaltDiapirSalt

Dome

Seal

Structural Hydrocarbon Traps



GeologicFAULT

4- Trapping & Seals: Trapping StructuresOf course, when tectonic stresses act, they are sometimes greater than a rock can resist without breaking, and faults form.



4- Trapping & Seals: Trapping Structures

If these faults provide a barrier to fluid flow, they are called sealing faults, and they can trap hydrocarbons.



4- Trapping & Seals: Trapping StructuresAnother main class of trapping types are stratigraphic traps. These are traps created by the way in which sedimentary layers are deposited, and they include angular unconformities and pinchouts.

stratigraphic traps


1- Geology and Rock PropertiesAngular unconformities

4- Trapping and Seals: Trapping StructuresAngular unconformities occur when a section of sedimentary rock containing reservoir rock is tilted, and then eroded… and then covered again by seas, depositing sedimentary layers on top of the tilted beds. If the layer above the unconformity happens to be impermeable, hydrocarbons may accumulate below.

Trap

Reservoir



Pinch Out 4- Trapping & Seals: Trapping StructuresAnother stratigraphic trapping style is the up dip pinch out. These traps form when sediments are deposited with a slight dip down in the basin. A pinch out of reservoir rock into a non-permeable sediment layer such as shale will trap petroleum flowing up dip.

Reservoir

Reservoir

Trap

Trap



4- Trapping & Seals: Trapping StructuresThe last trap type we will cover is the salt dome. At great depth, salt acts like a light-weight, slow-moving liquid. Pressed by the weight of neighboring rocks, salt will flow upwards, creating domes of salt. These salt domes can push layers of rock up, forcing any reservoir rocks above into anticlines that can trap hydrocarbons.



4- Trapping & Seals: Trapping StructuresIn addition, any layers of reservoir rock that the impermeable salt dome cut through during it's emergence can become traps as well.



Trapping: TimingPetroleum accumulation requires mature source rock, migration, a reservoir rock, and a sealed trap. The timing of geologic events is critical. The formation of the trap must occur before migration. The reservoir seal must remain intact after the petroleum has been trapped.



Trapping: TimingFor these reasons, in many areas that have undergone years of exploration, only 1 in 3 wells drilled actually will find significant amounts of petroleum.





Exploration Economic Petroleum Accumulation

Review: Summary

GEOLOGY and SEDIMENTS: Geologic scale and formation of basins and accumulation of sediments

Formation of Oil and Gas in a source rock through a series of Organic material transformed by heat and pressure into kerogens, and finally into oil or gas.

Primary and secondary migration of oil and gas from source rock

Trapping: Importance of impermeable sealing rock structural & stratigraphic traps anticlines, fault traps, angular unconformities, pinch outs, and salt domes

Timing of migration and trappingRock properties: Permeability and porosity



Time and Scale Problems

If a course rock of a given volume generates 1 gm of oil per year, how many barrels would be generated in one million years?

1,000,000 gm1,000 kgm

1 Barrel = 159 litres1 Barrel = 159 * 0.85= 136 kgm

Barrels generated= 1,000/136 = 7.35 Barrels

Specific Gravity



Time and Scale Problems

If an oil droplet moves 1 cm in a year through a carrier bed, how far could it move in a million years?

= 1 * 1,000,000 = 1,000,000 cm= 1 * 1,000,000/100 = 10,000 meters= 1 * 1,000,000/100/1000= 10 kilometres

1 -Geology and Rock Properties

Documents

rock properties1 geology

rock properties page

sedimentary rock

rock propertiesdistribution

rock propertiestectonics

rock propertiesgeology

rock propertiesoverviewas

rock propertiesgeneration