 Frontier Exploration – a term used to describe Terms of the license:

the first episode of exploration in basin i. Time of exploration before the

license reverts or partially
TWO FACTORS THAT CONTROLS THE TIME A BASIN reverts to the govt. (process
SPENDS IN THE FRONTIER EXPLORATION termed as relinquishment)
1. Technical factors ii. Process in which it can be
 Hostile climate appraised and developed
 Difficult terrain Once exploration success is
 Deep water declared in a new area, the
 Impenetrable jungle competition for new acreage
2. Political factors will increase, encouraging the
 Border disputes licensing authorities to make
 Financial constraints of the oil the license fees tougher, which
companies will have an impact on license
 Strict licensing policy imposed by the fees and access costs.
licensing authorities  Tax Relief – a common tool
GEOLOGICAL FACTORS THAT ARE CONSIDERED IN used by the licensing
CATEGORIZING A BASIN FOR FRONTIER authorities to encourage
EXPLORATION companies to explore
 Type of Basin - means that a company
 Source Rocks in the Basin will need to explore,
o If it’s mature for petroleum generation discover, appraise and
o Oil prone/ Gas prone develop a field before it
can obtain tax concession
 Statigraphy of the Basin
against new exploration
o Location of Source Rocks, reservoirs,
3. License Areas
and seals
o History of the Basin  May be bounded by geographic
features, settlements or old petroleum
TECHNICAL ACTIVITIES DONE DURING A CONDUCT concessions, or tied to an arbitrary
OF FRONTIER EXPLORATION geographic grid
 Offshore license tends to be much more
I. ACQUISITION OF ACREAGE
simply defined using latitude and
1. Early access to acreage
longitude.
- Obtaining a high-quality exploration
 Deviations:
acreage ahead of the competition is
i. Numerical/alpha-numerical
important
hierarchical coding system
- Having discovered the petroleum, the
ii. Quadrant system
companies will need to build production
 New license rounds commonly offer
and transportation facilities to move the
part blocks or amalgamations of part
petroleum to market
blocks into single licenses.
2 WAYS OF ACQUIRING ACREAGE - those areas can be licensed,
1. Negotiation with the land or offshore unsuccessfully explored,
rights holders relinquished, relicensed and
2. Bid process (much common) reexplored showing the complexity
of petroleum exploration
2. The Licensing Process 4. Farm ins, farm-outs, and other deals
- License rounds are tend to be  The company that discovers an oil or
organized by ministries for energy or gasfield may not the company that
state oil companies abandons it. The ownership may change
- Terms of license are defined before the throughout the life of a field.
bid round takes place.  Companies obtain a license that might
or might not have drilling commitments
2 WAYS IN ORGANIZING A LICENSE  If drilling is too risky to execute, the
1. Financial Bid for a piece of acreage company will invite other companies to
2. Technical bid to understand the piece of farm into its acreage
acreage by collection of data (seismic and  Farm-in exchange of equity for the cost
drilling wells) of drilling a well with the so called
“promote”
II. IDENTIFICATION & ANALYSIS OF DIRECT TWO TYPES OF SEAL FAILURE
PETROLEUM INDICATORS
1. Capillary failure – due to
There are two broad methods whereby the presence hydrostatic and overpressure
of petroleum in a basin may be proven ahead of conditions
acreage acquisition and drilling. (shortcuts to 2. Fracture Failure – high –
petroleum success!) overpressure situations

More advantageous if done before acquisition of

acreage TYPES OF SEEPAGES

I. Petroleum leakage and seepage 1. Widespread pervasive but low

The importance of reviewing the three density
stages of seepage process is to know its
2. Pervasive in small area but low
relationship with the spatial patterns of
intensity
seepage and phase (gas vs liquid) which
are influenced by all these 3 stages:

3 STAGES OF SEEPAGE PROCESS

1. Seal Failure – mainly due to the forces
that acts upon it
1. Buoyancy – the
density contrast
between petroleum
and subsurface brine
2. Capillary resistance –
the force that
opposes buoyancy.
- the smaller and
narrower pore throats
are, the more
effective the seal is
- the seal may fail if
the driving force is
enough to fracture the
rock

2. Tertiary Migration – Movement of

petroleum from the trap to the surface
- almost the same with secondary
migration, but the rate of supply of
tertiary migration is much higher when
a seal fails due to buoyancy assisted by
over pressure gradients
- other signs of a seep other than live
petroleum are pock marks (shallow
depressions formed by the catastrophic
release of gas) and mud
volcanoes/diapirs (rise when mud
reduced density moves vertically
upward)
i. Lateral Migration
ii. Vertical Migration
iii. Effects of fractures and Faults
iv. Effects of Salt
 3. Dissipation – separating of gas from the TWO MAIN MECHANISMS W/C CREATES
oil as the petroleum reaches the water EXTENSIONAL BASINS
table.
1. Active rifting – when a thermal plume or
- the released gas may also dissolve in
sheet impinges on the base of the
the water
lithosphere
II. Seismic Data
2. Passive rifting - continental stretching
 Petroleum products can be detected if the
and thinning.
acoustic properties are large or if the
 Failed rift basin – differences between
architecture of the affected volume is
basins caused by the cooling of crusts
distinctive
making it denser produced by tension of
 In the subsurface, the presence of petroleum
the faults and subsidence
and seepage can create topographic effects
2. Basins generated during convergent plate
that are possible on seismic data.
motion
 High resolution seismic survey data and
 Compressional; but both
conventional seismic data can be used for
inhomogenous stress distribution
the identification of gas in shallow
and thermal effects similar
reservoirs, as plumes and as gas hydrate
produces areas of extension. Thus,
mounds.
both compressional and
 “Clathrates” – gas hydrates that are
extensional basins can develop
crystalline compounds of gas and water that
a. Arc Systems – characterized by 6
produces huge amplitude effect that
components:
manifest on seismic data sometimes in
i. Outer rise on the oceanic
multiples
plate. This occurs as an
 Direct Hydrocarbon Indicator (DHI) –
arch on the abyssal plain,
generated by gas and on occasion oil, in situ
as a forebulge on oceanic
in the reservoir
plate
ii. A trench. Generated from
BASIN TYPES subduction of oceanic
 Basins are generated by plate tectonics, the plate. Not prospective for
process responsible for continental drift exploration.
 Plates which were formed may be stretched, iii. A subduction complex.
broken, pushed, rotate past each other that Comprises of stacked
leads to the formation of basins fragments of oceanic crust
o Divergence – extension and its pelagic cover,
o Convergence – Compression and together with material
extension derived from the arc.
o Strike-slip – wrench iv. A fore-arc basin. Lies
between subduction zone
TYPES OF BASINS and volcanic arc. Rare
1. Extensional Basins, generated by divergent source of petroleum.
plate motion v. Volcanic (magmatic) arc.
a. Intracratonic basins: sags – broadly Generated from partial
oval; the sediment infill package melting of the overriding
increases from edge to center. and possibly subducting
b. Rift basins – location of rifts follows plates.
old lines of weak spots or form vi. Back-arc region. Floored
above mantle hotspots. - The by either oceanic or
degree of uplift and the rate of continental lithosphere.
rifting are controlled by the May or may not develop
magnitude of thermal disturbance basins.
and stresses applied to the plate. b. Foreland Basins – outranks other
c. Passive Margins – a point where basins generated by the convergent
the fault ends since extensions can plate motions because of its wide
no longer accommodate by the and deep structure.
fault block rotation alone forming FACTORS THAT AFFECT THE
oceanic crust at the midpoint of the DEVELOPMENT OF THE STYLE OF
rift system BASIN
1. Types of crust undergoing
convergence (continental-
 continental, oceanic-  The type of sediment depends on the
oceanic, oceanic – climate and nature of the sediment
continental) supply
2. Age of oceanic crust – as  Rift Basins. After the movement of
the crust cools, it thickens, faults and subsidence, coarse, non-
which tends to subduct marine, fluvial and alluvial sediments
3. Strike-slip basins are deposited. When stagnant and cut
 Occurs where sections of crust from the water forms, it promotes
move laterally with respect to each formation of sediments that are rich in
other. organic matter and can be a source of
 Commonly involve oblique petroleum.
movement of plates on either sides  Foreland Basins. Sedimentation rate is
this having some parts which are in slower than the subsidence rate, which
tension and other in compression. will be exceeded by the sedimentation
rate in the later stage which leads to the
major upward coarsening of sediments.
BASIN HISTORIES  Flysh – a sequence of sediments
containing deep water muds and
FACTORS THAT AFFECT THE SEQUENCE OF ROCKS interbedded turbidite sandstones which
implies that as the amount of sediment
 Tectonic Subsidence
increases and become coarser as it
 Compression and Inversion tectonic forces nears the basement and foreland wedge
 Changes in Temperature of the base of the of sediments.
lithosphere
 Molasse - a sequence of deep water to
 Lithospheric flexure shallow clastic rocks followed by coarse
 Vertical sequence of rocks unravel the history of clastic rocks in fluvial or alluvial
basin which is discovered by drilling a borehole conditions
FACTORS THAT HELP IN DETERMINING THE QUALITY 3. Burial History
OF RESERVOIR  In a vertical sequence, it is
reconstructed from age (rock chippings,
1. Subsidence outcrop, and core and any correlation
 Two main controls of subsidence with other rocks with known age) and
i. Tectonic; Due to compressional depth information (drilling and logging
and extensional forces in the of boreholes)
lithosphere  Backstripping – used to determine the
ii. Thermal; due to heat changes burial curve which reconstructs the
in the lithosphere history through taking of the thickness
 Sag Basins. Have an early history of of the overlying rocks sequentially, with
erosion which is maximized at the new age assigned by the known
center, which also means that the boundary ages
subsidence is greatest at the center  Mechanical Compaction - used to
 Rift Basins. The subsidence exceeds the determine the progressive loss of
level of the thermal uplift when the porosity due to imposed stresses and
crust is greater than 18km. Also the leads to a reduction of thickness of the
subsidence creates space for the original sedimentary unit as water is
sediments to be deposited. driven out f the bulk rock
 Foreland Basins. Subsidence is created 4. Thermal History
due to thermal loading.  Determined by the boundary conditions
 Strike-slip Basins. Created by hybrid of of the surface temperature ( cold in
tectonic and thermal forces. polar and hot in equatorial regions) and
 En echelon – flower like structures that the basement heat flow.
is resulted from the strike slip tectonics  Thermal conductivities of the sediments
where high heat flow creates uplift control the temperature at points which
followed by subsidence. can be used to determine the heat flow
2. Sediment Supply using this equation
 The rate at which the space (created by 𝒅𝑻
𝑸 = −𝑲.
the thermal and tectonic forces) is filled 𝒅𝒁
depends on the availability of the  Heat transport is governed by the
sediment thermal conductivity of the rocks, which
 varies for each lithology and porous software which includes, direct pressure
sediments due to the fluid contained in measurement from reservoir units, as
the rocks well as matching to any porosity and or
 The boundary conditions of surface permeability data that are available
temp and basement heat flow vary today
through time during the evolution of a
Integrated Basin Modelling
sedimentary basin.
 Arrhenius Equation – used to asses the  Models the timing of maturation of
cumulative effect of changing temp source rocks and later to couple this
through time in maturation geochemical modeling with fluid flow
5. Uplift modeling
 A sedimentary section raised above  Input for the models include parameters
base level caused by compressional and for each of the main lithologies:
lithospheric forces i. Initial porosity
 Thermal parameters used to determine ii. Bulk rock and fluid
a history of uplift: compressibility
i. Vitrinite Reflectance iii. Thermal capacity and
ii. Illite to smectite ratios conductivity
iii. Fluid inclusions iv. Organic richness
iv. Fission tracks
 When uplift and erosion take place, the SOURCE ROCKS
overburden is gradually reduced,
Origin of Petroleum
decreasing the vertical stress imposed
on the sediments (compaction).  Came from living organisms (Organic
Because compaction is an irreversible Matter)
process, uplift only leads to very small  Organic Matter:
increase in porosity as the elastic o Proteins – found mostly in animal
component is recovered. tissues; built from amino acids
6. Pressure History o Carbohydrates – principal source of
 The pressure of pore fluids is controlled energy in living organisms
by the depth, the fluid gradient (a o Lipids – fatty organic compounds,
function of the density of the fluid), and insoluble in water, and found
stresses. mostly in algae, pollen and spores.
 Where pore pressures are between - rich in hydrogen, hence
hydrostatic and lithostatic, the yield high volumes of HC
sediments have overpressure and molecules in maturation
underpressure - contains special group of
 Underpressure - used to describe compounds called
sediments with pore pressures below isoprenoids (found in
hydrostatic chlorophyll) and include
 Overpressure – pore pressure in excess pristane & phytane
of hydrostatic (indicators of depositional
- Disequilibrium compaction – environment)
rapid loading of sediments in o Lignins – highly polymerized
which the fine-grained rocks material found in woods that can be
cannot dewater fast enough to used as a drilling fluid and also a
remain in equilibrium with the potential replacement for crude oil
vertical stress of the
overburden Preservation of Organic Matter
 Pressure transition zones – pressure Two Basic Requirements for the generation &
gradients in excess of hydrostatic that preservation of petroleum:
indicates low permeability rocks
o Pressure seals - low 1. High Productivity
permeability rocks that Environments with high organic productivity:
i. Continental margins
prevent equilibration of
ii. Lagoons and restricted seas
pressures between the
iii. Deltas in high latitudes
successive permeable units. iv. Lakes
 Pressure histories are estimated using
fluid flow simulation in basin modeling
 2. Oxygen Deficiency of the Water Column microorganisms in
and Sea Bed (Anoxic) marine sediments
 In the sea bed wherein there is o Fluoresces under UV
oxygen deficiency, OM’s are light
preserved, since there is a relative o Most abundant
scarcity of organisms there to o Type II – S Kerogen –
scavenge the debris. subtype which has a
high proportion of
Two Components of Organic Matter Sulfur which
1. Bitumen – composed of compounds that are influences the timing
soluble in organic solvents and rate of
2. Kerogen – insoluble component maturation of
Kerogen type (on the basis of maceral Kerogen Maturation
content – organic source material) iii. Vitrinite (Type III)
 Useful in petroleum geology to be o Low ratio of H-C and
able to identify the depositional high ratio of O-C
environment of the source rock for o Low yield kerogen,
these reasons: principally generating
o Kerogen type is dependent gas
on the types of organic o Mostly from higher
material preserved in each plant debris found in
sed. Environment coals
o Each kerogen type o Does not fluoresce in
matures under different UV light; but very
burial conditions, reflective at higher
controlling of petroleum levels
generation and expulsion iv. Inertinite (Type IV)
from the source rock o Non – fluorescing
o Each kerogen produces product
contrasting petroleum o High in C and very low
products in differing yields in H; “dead carbon”
 Recognized on optical properties o No potential to yield
such as color, fluorescence oil and gas
reflectance. The quantity and quality of kerogen
 Controlled by the environment
Types of Kerogen: at the site of deposition of OM
i. Rate of deposition and
i. Liptinite (Type 1)
Burial
o High H to C ratio, low
ii. Ratio of terrestrial to
O to C ratio
marine plant input
o Oil prone, yield of (up
iii. Oxidation state of
to 80%)
depositional
o Mainly from algal
environment
source, lipid rich
iv. Amount of reworking
o Formed in lacustrine
of the sediment prior
or lagoonal
to burial
environments
 The quantity of kerogen
o Fluoresces under UV
defines its richness as a source
light
rock (defined by total organic
ii. Exinite (Type II)
carbon; TOC and weighted
o Intermediate H-C and
percentage of rock)
O-C ratios
o The richer the source rock,
o Oil and gas prone (40
the larger the volume of
– 60%)
HC generated
o Mainly from
o Higher proportion of the
membranous plant
rock that is Organic
debris (spores, pollen
material, the greater is the
cuticle) and
efficiency of migration of
phytoplankton and
HC out of the source rock
bacterial
  The quality of kerogen i. Distribution and
determines the HC yield – richness of the
volume of HC generated for kerogen in the
each volume (kg of HC/ ton of original source
rock; kgHCt-1) of source rock rock
ii. Rate of temp.
Maturation of Source Rocks: kerogen to oil to gas increase
 Kerogen is composed of large HC molecules iii. Primary
that are stable at low temperatures migration route
o But will break down into smaller efficiency
molecules of liquid and gaseous HC iv. Distribution of
compounds with progressive pressure
exposure to higher temperatures  Bitumens – pure HC with
Controls on transformation to smaller& large atomic ring
lighter compounds structures resulting from
1. Temperature – increases with the loss of H during CH4
depth production which a result
- source of heat comes of oil migrating from the
from the basement source rock that was
(center of the earth), trapped
couples with the decay of - can also be
radionuclides produced by late
-basement heat flow influx of gas
varies according to the (producing tar
thickness and nature of mats) into an oil-
the lithosphere, and filled reservoir
proximity to thermal (deasphalting) or
anomalies in the mantle by bacterial
- 430-460⁰C – Lab degradation
temperature needed to Lesser Controls
generate oil from a source
rock 3. Nature and abundance of the
- 80-150⁰C - Temperature kerogen in the source rock
in typical sedimentary 4. Pressure
basin but expressed in a THERMAL MATURATION
million of years 1. Diagenesis - occurs at shallow depths (1st 10
2. Reaction Kinetics – Strength of the -100 m and low temp)
bonds between the atoms and the - Microbial activity predominates
energy required to break those -transformation starts with:
bonds o Biochemical degradation
- a whole series of parallel o Polycondensation
reactions is under way o Insolubilization
simultaneous during 2. Catagenesis – Starts with continuous burial
source rock maturation, and the OM is exposed to increasing temp
including secondary  Microbial activity ceases
cracking of oil to gas at  Level of temp increase depends
higher temps. upon the geothermal gradient,
- Determiation of the act. which is the heat flow generated in
energy for each reaction is the earth’s interior
achieved in the lab and  Kerogen and geochemical fossils
there are now widely used undergo further chemical
kinetic models: transformation
Type I – Kerogen (Green  Wet gas, methane oil
River Shale) 3. Metagenesis – follows catagenesis as a
Type II – Kerogen result of continuation of burial and heating
(Toarcian Black Shale)  Occurs at great depths ( > 15,000ft/
Type III – Kerogen 4600m)
- the product will depend
 The kerogen starts to crystallize at
on the number of factors:
great depth
 PETROLEUM MIGRATION Capillary Entry Pressure Equation
Types of Migration
1. Primary - movement out of the fine grained
source into a more permeable conduit
(source rock to reservoir rock)
2. Secondary - movement from reservoir rock
into the reservoir
3. Tertiary – movement of any reservoired
petroleum

Migration Losses

𝟐𝜸 𝐜𝐨𝐬 𝜽
𝝆𝒅 =
𝑹

𝝆𝒅 = capillary entry pressure

𝜸 = interfacial tension bet.
the water and petroleum
𝜽 = contact angle
THE SEAL 𝑹 = radius of the largest pore

 Seal – Fundamental part of the trap which

prevents petroleum from migrating onward  These properties are routinely established in lab
through the rock experiments on rocks and the procedure involves
 Any lithologic unit can act as a seal injecting the pores with mercury and converting
Attributes that favor rock as a seal to a petroleum water system at in situ conditions
petroleum accumulation: using std. eqns.
i. Small pore size  The seal capacity determines the height of a
ii. High ductility petroleum column that can be trapped beneath
iii. Large thickness it, and the seal will be breached with Pb exceeds
iv. Wide lateral extent the Pd
Other Attributes (physical properties of the 2. The Hydraulic Seal - When the capillary entry
water and petroleum) pressure is extremely high then the failure of
v. Water Salinity cap-rock seal is controlled by the strength of
vi. Petroleum Density the rock, that if exceeded, creates a natural
vii. Interfacial tension between petroleum tension fracture (only happens when pore
and water pressure is greater than the minimum stress
 Most common seal is mudrock (shale), 60 – 70% and tensile strength)
of all sedimentary rocks are mudrocks 3. Faults - Can act as both conduits (migration
pathways) and seals, depending on
Types of Seal
i. hydraulic conditions
 Distinguished only in which petroleum’s ability to ii. rock properties of the
force is way through the pores faults
1. Membrane Seal – a subdivision of seal in which iii. properties of the rocks
petroleum is unable to force its way through the juxtaposed across the
largest pores faults
- when the petroleum is trapped beneath a cap-  The consideration of faults as seals
rock seal, there is Pb follows the same reasoning as for cap
𝝆𝒃 = (𝝆𝒘 − 𝝆𝒑 )𝒉 rock seals:
The maximum i. Sealing capacity of a fault
𝝆𝒃 = buoyancy pressure
𝝆𝒘 = density of water petroleum column is relating to its membrane
𝝆𝒑 = density of petroleum controlled by the strength - membrane fault
𝒉 = height capillary entry pressure seals fails when the pressure
of the petroleum into the largest pores of the exceeds the entry pressure of
seal. the largest pores along the
fault plane
 ii. Hydraulic strength - fails when petroleum from deep reservoirs or an active
the fault is opened petroleum source rock.
mechanically by high pore  The control upon the volume of petroleum
pressure that exceeds the contained in the trap is principally governed by
minimum stress the capacity of the seal coupled with the supply
 Faults can be induced to move (shear) of petroleum from its source
when the pore pressure exceeds the  Classification of traps:
shear resistance along the fault, which 1. Class 1 traps - seal strength is high
can be lower than the minimum tensile enough where there is no leakage
stress before petroleum fills to the spill point (
 Main processes that increase seal structural closure of the trap)
efficiency (reduce permeability along 2. Class 2 traps – those in w/c seal
and adjacent to fault planes) strengths to oil allows complete filling to
a. Clay smear – most effective spill but where the higher pressure
when there is a high proportion gradient of the gas cause leakage prior
of clay rich rocks within the to fill
faulted section such as deltaic 3. Class 3 traps – are those where oil and
environment of sand, silt, mud gas columns will exceed the seal
and coal strength before the trap is filled
b. Cataclasis – process of grain
size reduction due to grinding
of fault rock within the fault
plane; stress history should
also be taken into
consideration in cataclasis.
c. Cementation of authigenic
materials such as quartz and
dolomite – show indication of
episodic flow conditions,
suggesting cycles of fluid and
pressure buildup and release.
 Faults can be effective barrier to flow and
hence create lateral seals within traps, as
well as impeding migration of petroleum to
a conventional trap. (which tends to occur at
only one or two points)
 Fill up of the field depends on it continuous
supply and migration within the reservoir
and limited by the seal
 In a highly faulted trap, the distribution of a
petroleum depends on the pressures within
the evolving (growing) petroleum column
relative to seal capacity of each fault.
 Some faulted compartments may be devoid
of petroleum if the sealing of the faults is not
exceeded, even though, high quality  “fill and spill” - Oil from oil
reservoir may be present with the defined prone source rock > displace
structural closure of the field water downward from the
4. Trap Fill – crest of the trap (arrested by
Under-filled trap - occur when the seal leaks seal) >gas generation under
before the structure is filled to capacity or favorable conditions> gas will
because there is an insufficient supply of migrate the trap> gas displaces
petroleum from the source the oil downward > oil spill >
- or because of mechanisms like seal leakage, gas spill when all the oil is
petroleum migration and trap filling (w/c rate displaced and the trap is filled
dependent) with gas> the oil and later gas
Over filling - result of active petroleum charging will migrate to other traps from
up a deep- seated fault that can access the sill point of original trap
5. The Pressure Seal - a seal w/c has a condition iii. Permeability – determines how a fluid
where very low flow conditions for water lead to can pass through it. Darcy (D) is the
the buildup of pore fluid pressures well. standard unit of permeability but
 Recognized where there are variations in millidarcy (1mD =10-3)
pore fluid pressures, excluding those related to  Absolute permeability - when
the density of the pore fluids. the rock is 100% saturated with
THE RESERVOIR one fluid phase.
iv. Hydrocarbon Saturation – Most
 For a rock to become a petroleum reservoir, it
commonly, reservoir contain both oil
need only to be porous to be able to hold
and water. It is rare to find a reservoir
petroleum
with pure oil or gas.
 Factors to be considered for a rock to become Reservoir Lithologies
‘economically viable petroleum reservoir’
I. Sandstone Depositional Environment
i. Permeable
a. Alluvial Fans – develops along the
ii. Volume should be sufficient
mountains. High energy streams
iii. Reservoir not to compartmentalized
lose energy as they escape from the
 Formation volume factor represents the change mountain vallets and drop their
in volume of the oil that will take place when it is sediment load as soon as they reach
lifted from the high pressure and temperature of flatter open land.
the reservoir and placed in the “stock tank” - reservoir are small unless the fans
are amalgamated along a fault front
or a large thickess of potential
reservoir rock accumulates as
faulting creates accommodation
space.
b. Aeolian Dunes - develop wthin
deserts. Cresent with the tips
pointing down wind.
- uncommon for reservoirs,
because of low preservation
potential because the sea washes
them away
- but also has excellent quality of
reservoir because of their well
sorted, rounded grains that they
can avoid cementation that such
reservoirs will be both prous and
permeable.
c. Lakes – are common features of
terrestrial sediment systems
- preservation potential is low and
 Intrinsic Properties of a potential reservoir rock: also uncommon
i. Net to gross – measure of potentially d. Fluvial Systems – has river systems
productive part of a reservoir. that connaect the sites of sediment
Commonly expressed as percentag of production (erosion) to areas of
producible (net) reservoir within the (coastal) deposition.
overall (gross) reservoir oackage. - braided rivers are very sand rich
ii. Porosity – void space in the rock, and can develop a very high net to
measured as volume percentage or a gross
fraction (as decimal) - meandering river can also form
a. Intergranular porosity - extensive sand bodies that may
between grains occur as petroleum reservoirs
b. Intragranular – created in e. Deltas – rich in sand; can form
partial dissolution of grains important petroleum reservoirs
c. Intercrystalline - the best sandstones are of
d. Intracrystalline excellent reservoir quality, but
e. Biomoldic abundant barriers ad baffles o fluid
f. Vuggy flow often complicate reservoirs
g. Fracture f. Shallow Marine System – shallow
h. Cavernous marine sandstones can form ideal
 petroleum systems. This is because STRATIGRAPHY
they can commonly accumulate in  The study of temporal and spatial
association with a source rock relationships between bodies of
which may also act as a seal. sedimentary rocks
-compared than marine and  The goal of any stratigraphic analysis is to
shallow marine are relatively establish the temporal sequence of
simple and homogenous. sedimentary rocks in the area under
g. Submarine Fans – deep water and investigation
final resting place within submarine  In frontier exploration, stratigraphic analysis
fan system. of seismic and well data is used to determine
- because of their large size, tareas the disposition and age of main subdivision
withhigher than average of sand of a basin fill
concentrations, it can be viable as a  Unconformity – is a surface that separates a
reservoirs body of older rock from a body of younger
II. Limestone and Dolomite – some of the rock. The surface is equivalent to a period of
largest petroleum reservoirs of the time on which erosion or non deposition
world occurred.
a. Shelfal/ Ramp Carbonates - the Types of Stratigraphy
largest and most prolific oilfields In 1. Chronostratigraphy – better described
the world as a product rather than a tool
- form the reservoir for more than -commonly derived from some
150 oil and gas fields and enhanced combination of seismic stratigraphy,
wby a dolomitization, mineral sequence stratigraphy and
leaching and fracturing biostratigraphy
b. Deep Water Carbonates – not so -uses a 2d chronostratigraphic chart
common 2. Biostratigraphy – old and well-
-oil fields can develop in carbonate established tool; mostly based on
turbidites and other resedimented observations made by geologists that
deposits the fossil assemblages in similar rocks of
c. Dolomite – reservoir occurs in most different ages are dissmilar.
continents and reservoirs range - it was recognized that in progressively
from precambrian through palezoic older rocks the suite of fossils contained
to mesozoic therein have fewer and fewer
- 80% in US are dolomite based similarities with extant species.
- associated with evaporitic rocks Problems: size, caving
d. Reef – holds 90% of the total oil in 3. Lithostratigraphy – oldest method
Western Canada Basin - relies on correlation of like lithologies,
- reef size is clearly important when rocks, which can be deposited in
considering the volume of different places at different times
reservoired petroleum - should only be applied with great care,
- have potential reserves at 28 only within a well defined
millions barrels biostratigraphic sequence
e. Karst – repressent of second major 4. Seismic Stratigraphy – based on
group of carbonate reservoirs not interpretation of seismic data.
linked to depositional environment. Two steps: a.) mapping the major
- product of mineral dissolution unconformity surfaces on the data, b.)
- features : caves, collapse breccias, description of interval between each
dissolutional enhanced joints and major unconformity (megasequence)
fractures and vugs -Megasequence – major tectonic units
- its porosity that is susceptible of in a basin fill
the rock to the penetration of the 5. Sequence stratigraphy – was developed
water from seismic stratigraphy
- does not guarantee a petroleum - explains in terms of relative sea-level-
reservoir, may not survive reburial, fluctuations and a combination of
infilling of karstified surface by eustatic sea level change and tectonic
muds may destroy potential. subsidence allows an understanding of
why they do.
- the basic unit of sequence stratigraphy
is of course the sequence – relatively
 conformable genetically related measure of migration of lithospheric
succession of strata bounded by plates across the Earth;s surface
unconformities or their correlative  Discontintinuities in the polar wander
conformities path in a srtatigraphic section may help
-parasequence – relatively to identify unconformities
conformable, genetically related
succession of beds or bed sets, bounded
by marine-flooding surfaces or their
correlative unconformities
-genetic sequences – maximum flooding
surfaces
- Type 1. A sequence when the sea level
falls sufficiently to expose the
shelf/slope break
-Lowstand systems tract (LST) –
sedimentation responds to the sea level
drop the slope fan and slope wedge
succeed the basin floor fan
-Transgressive Systems tract (TST) –
buries LST by gravity and formed during
rise of sea level
-Highstand Systems tract (HST) -
succeeds TST which builds over and
downlaps TST. Sediment pile aggrades
until accommodation space is
exhausted and progradation takes over.
When sea level falls, another sequence
is created
- Shelf Margin Systems Tract (SMST) –
coarse grade sedimentation which
occurs when sea level does not fall
below the shelf/slope break
- Type 2. Collectives of SMST,TST,HST.
Large sea level falls can shut down
carbonate factory. Exposure of shelf
promotes chemical weathering, karst
above water table and meteoric
diagenesis (cementation) below the
water table. Sea level fall may generate
sediment into the basin.
 Higher resolution than seismic
stratigraphy
6. Chemostratigraphy – relies on
producing correlatable chemical
fingerprints for two or more
stratigraphic section by analyzing a suite
of elements.
- best chemostratigraphic marker is
Iridium anomaly (peak) which is linked
to the impact of the comet with the
earth
-chemstratigraphy does not rely on a
single elemant
7. Magnetostratigraphy - relies on two
phenomena: a.) magnetic polarity of the
Earth’s field switches from normal to
reversed b.) “polar wander” which
measures the apparent movement of
the poles across the Earth’s surface
through time which is really the