Transcript Coastal and Marine Resources Management

TEKNOLOGI PEMROSESAN
HIDROKARBON
K02
The Origin of Oil and Gas
Dr. Wahyudi
Dept. Ocean Engineering, ITS
Surabaya
Petroleum Exploration
• Surface and subsurface geological studies
• Seismic surveys
• Gravity and magnetic surveys
• Horizontal magnetic gradient
• Helium content of soils
Surface and Subsurface Geology
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Stratigraphy
Structure
Paleontology
Geochemistry
Seismic Surveys
• Create an artificial shock wave
• Record the arrival of the shock waves at
groups of vibration detectors
• Move vibration detectors and repeat
• A profile is constructed by plotting the
arrival times of the waves at the detectors
Other Types of Surveys
• Horizontal Magnetic
Gradient
– Measures small
changes in the
horizontal gradient of
the Earth’s magnetic
field that are related to
magnetic minerals
formed when by
petroleum
microseepages
• Helium Content of
Soils
– Analyze near-surface
borehole samples for
helium that is a byproduct of radioactive
decay associated with
petroleum
The Origin of Petroleum
Hydrocarbons
• Theories of inorganic origin
1.
2.
3.

(at high T) metallic carbides + water  acetylene
Volcanic emanation  acetylene
high T alkaline + carbonatite  hydrocarbon
failed
• Theories of organic origin
it had been believed (before WW II) that
hydrocarbon originally from organic
matter
How organic matter accumulates
• High surface productivity
• Reductive environment
• High sedimentation rates
• Low water circulation
• Close basin
Where and how
oil and gas accumulate
•Source rocks
•Oil & gas migration
•Oil & gas reservoir
•Reservoir rock
•Cap rock
•Oil traps
The 5 main components
of an oil accumulation
1. Must be an organic-rich source rock to generate the oil/gas
2. The source rock must have been heated sufficiently to yield
its petroleum
3. There must be a reservoir to contain the expelled
hydrocarbons. This must have:
a.
b.
Porosity, to hold the hydrocarbons
Permeability, to allow fluid flow
4. The reservoir must be sealed by an impermeable Cap
Rock to prevent upwards escape of the hydrocarbons to the
earth’s surface
5. Source, reservoir and seal must be arranged in such a way
that the petroleum is Trapped
Formation of an oil accumulation
1. Burial of adequate organic source material.
 most petroleum is derived from the accumulation of trillions of individual microorganisms.
2. Burial to the appropriate depths.
 depths of 2-6 km and temperatures of 60-160º C.
3. Presence of a reservoir-quality rock.
1. a porous storage space. Sandstone and limestones are the most common
reservoir rocks. To be a reservoir they must have:
 Porosity, to hold the hydrocarbons
 Permeability, to allow fluid flow
4. Presence of an adequate seal
 A seal is an impermeable bed (such as a shale or a bed of salt) that sits on top of
the trap and prevents the hydrocarbons rising any further.
5. Presence of a trap
 In order to prevent the hydrocarbons rising to the surface and escaping they
must be caught in a confined space, termed a trap. i.e. the source, reservoir and
seal must be arranged in such a way that the petroleum is trapped.
The Petroleum System
In addition to the 5 components,
a further two events are essential:
– Timing: no trapping unless the traps are present
when migration is occurring
– Maturation: no petroleum if the source rock OM
does not mature
– Migration: no accumulation if the petroleum doesn’t
migrate
Source rocks
• Definitions:
– A rock capable of generating significant amounts of
oil or gas
• Characteristics:
– Blackish, black fine grain sedimentary rocks
– Shale
• Sedimentary rocks rich enough in organic matter
– 0.5-2 weight percent organic matter
• Can be land or water based material
• Type of organic material can determine the type of
petroleum generated
The Source Rock
• This shale typically contains >1% of organic carbon, by weight. The
shale is very widespread, underlying much of Britain and most of the
North Sea, and is by far the most important source rock for the oil that
has been found in the North Sea Basin.
When does an OM rich rock become a
source rock?
• Determined by:
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–
–
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Richness of source rock
Maturity history
Geological framework in which it exists
Current economics and politics of exploitation
Source Rocks Can Be:
• Immature (potential sources)
• Mature (active): generation has begun
• Over-mature (cooked): generation has been
completed
• NB even immature source rocks contain
hydrocarbons (waxes etc inherited from the
living biomass)
How does OM become Oil?
2 stages:
Conversion of OM to kerogen
Conversion of Kerogen to petroleum and gas
The Transformation of
Organic Matter
Kerogen Formation
• 2 stage:
• Polymerization: Conversion of
geomonomers to geopolymers (onset
rapid, short period: 100’s – 1000’s years.
Temperatures up to 50°C
• Rearrangement of the geopolymers
What Is Kerogen?
• Precursor to oil and gas
• Insoluble in organic solvents
• Complex mixture of high molecular weight organic
materials
• Bulk composition determined by source and
environment
• General composition may be described as:
• (C12H12ON0.16)x
Kerogen Type
• It is important to identify the type of
kerogen in a source rock
– Determines the type of hydrocarbon
produced, if at all
Trapping Mechanisms
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