Upload
raymond-joseferd
View
243
Download
2
Embed Size (px)
Citation preview
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 1/106
Reservoir Geoscience
PCB2013
Fundamentals of Reservoir Geology
Assoc. Prof. Swapan Kumar Bhattacharya
Petroleum Geoscience Depratment
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 2/106
Course outline(Reservoir Geoscience)
Dr. Swapan Kumar Bhattacharya (Course coordinator).
Coursework: (50%)
Test-1 (20%)
Quizz (10%)
Test/Lab. ( 5%) Exercises (5%)
Assignments (10%)----------------------------------------Final Examination: (50%)
REFERENCES:Stratigraphic reservoir characterization for petroleum geologists,geophysicists and engineers – Roger M. Slatt.
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 3/106
Learning Outcomes
Students should be able to :
• Interpret the Depositional Environment of
sedimentary rocks
• Analyse petrophysical properties and
subsurface facies from log and seismic
• Interpret Reservoir Distribution and Geometry
• Describe Hydrocarbon Distribution in a reservoir through
geophysical and geochemical studies
3
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 4/106
Learning Outcome-1
1. Interpret the Depositional Environment of
sedimentary rocks
Fundamentals Transport & Deposition Geological Control
(1) Classification (1) Physical Processes (1) Control of
(2) Texture (2) Bedforms & Sed. Str. environment on
(3) Structure (3) Py. & Sec. Structures reservoir limits
and reservoir
properties
4
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 5/106
Learning Outcome-2
Analyse petrophysical properties and subsurface facies from log and seismic
Poro- perm Clastic facies Carb. facies
5
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 6/106
Learning Outcome-3 &4
Interpret Reservoir Distribution and Geometry
&
Describe Hydrocarbon Distribution in a Reservoir
Reservoir Continuity Reservoir Continuity
(1) Geological Time (1) Basin Architecture
(2) Steno’s Principles (2) Sequence boundary
(3) Lithostratigraphy (3) Diagenesis related to
(4) Geological Events Unconformities(4) Slope & Basin floor fans
• Describe Hydrocarbon Distribution in a reservoir through
geophysical and geochemical studies: Res. Size, Shape &
modeling, Res. Geophysics.
6
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 7/106
A stratum (plural: strata ) is a layer of sedimentary rockwith internally consistent characteristics that distinguish it
from other layers. The "stratum" is the fundamental unit ina stratigraphic column and forms the basis of the study of
stratigraphy.
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 8/106
Sedimentary structures
Sedimentary structures are particularly important in the
interpretation of earth history. These rocks form at the
earth’s surface and as layer upon layer of sediment
accumulates, each records the nature of the environment atthe time the sediment was deposited (bed geometry).
Sedimentary structures are large-scale features of
sedimentary rocks such as parallel bedding, cross bedding,
ripples, and mudcracks that are best studied in the field.
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 9/106
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 10/106
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 11/106
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 12/106
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 13/106
Detrital/Clastic sedimentary rocks can be classified by grain size
differences (size & shape)
PAB 1023 Petroleum Geoscience 13
Conglomerate
Breccia
Sandstone
Shale
All these rocks have clastic textures – the rocks are composed ofparticles (fragments) that are cemented together
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 14/106
Chemical and biochemical sedimentary rocks
PAB 1023 Petroleum Geoscience 14
Limestones – composed of calcite
Travertine Coquina
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 15/106
Chemical sedimentary rocks
PAB 1023 Petroleum Geoscience 15
Evaporites
Gypsum
Rock salt
Chert (silica)
Flint
Agate
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 16/106
PAB 1023 Petroleum Geoscience 16
Coal forms from plantmaterial in continentalsediments
On the continental
shelves, the organic remains of marine plants and animals are buried in
sediment, and become oil and gas
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 17/106
PAB 1023 Petroleum Geoscience 17
1. Original Horizontality- all sedimentary rocks are
originally deposited horizontally. Sedimentary rocks
that are no longer horizontal have been tilted from their
original position."Strata either perpendicular to the horizon orinclined to the horizon were at one time parallel tothe horizon." Steno, 1669
Principles of Stratigraphy
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 18/106
Principles of Stratigraphy
PAB 1023 Petroleum Geoscience 18
2. Lateral Continuity- sedimentary rocks arelaterally continuous over large areas."Material forming any stratum were continuousover the surface of the Earth unless some other
solid bodies stood in the way." Steno, 1669
3. Superposition"...at the time when any given stratum was beingformed, all the matter resting upon it was fluid,and, therefore, at the time when the lower stratumwas being formed, none of the upper strataexisted." Steno, 1669.
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 19/106
Principles of Stratigraphy
PAB 1023 Petroleum Geoscience 19
4. Cross-Cutting Relations
"If a body or discontinuity cuts across a stratum,it must have formed after that stratum.“
5. Law of Inclusions- this law states that rockfragments (in another rock) must be older thanthe rock containing the fragments.
6.Law of Faunal Succession- This law wasdeveloped by William Smith who recognized thatfossil groups were succeeded by other fossilgroups through time.
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 20/106
PAB 1023 Petroleum Geoscience 20
There are three
Types of rocks
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 21/106
The Earth’s crust consists of three kinds of rocks:
• Igneous rocks solidify from magma (or molten rock)
• Sedimentary rocks form from materials that are eroded fromother rocks
• Metamorphic rocks are rocks that have changed due to being
heated and/or compressed.
PAB 1023 Petroleum Geoscience 21
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 22/106
Formation of Sedimentary Rocks(Processes)
Deposition - occurs
when geologic agentcan no longer transportmaterial
PAB 1023 Petroleum Geoscience 22
• The basic processes involved in the formation of a clastic (granular)
sedimentary rocks are: weathering (erosion), transportation, deposition,
compaction (lithification) and diagenesis.
Weathering -mechanical or chemical break downof rock
Transportation -
movement of sedimentby gravity, wind, water (geologic/geomorphicagents)
Compaction (lithification) - pressureof overlying sediments packs grains andsqueezes connate water from pores
Cementation - pore spaces fill with abinding agent, typically - calcite, quartz, ironoxide, precipitated from circulating water.
Crystallization ordiagenesis - new mineralsgrow, or existing crystalsgrow larger as time passes -helps hold rock together.
Sedimentary rocks
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 23/106
Weathering
PAB 1023 Petroleum Geoscience 23
• Mechanical or physicalweathering is the breakdown of
rock into particles without
producing changes in the
chemical composition of the
minerals in the rock.
• Ice is the most important agent of mechanical weathering.
• Water percolates into cracks and
fissures within the rock, freezes,
and expands. The force exerted
by the expansion is sufficient to
widen cracks and break off pieces of rock.
Inside Lower Antelope Canyon, looking out with the sky near the top of the frame. Characteristic layering in the sandstone is visible.
• Heating and cooling of the rock, and the resulting expansion and contraction, also
aids the process.
• Mechanical weathering contributes further to the breakdown of rock by increasing
the surface area exposed to chemical agents.
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 24/106
PAB 1023 Petroleum Geoscience 24
Products of weathering
Primary Residual Dissolved
Minerals Minerals Ions
Feldspar Clay minerals K+, Ca+2, Na+
Aluminum hydroxide
Fe-Mg minerals Hematite & Mg+2
Limonite
Quartz Quartz Silica
Primary Solids that Ions that are carriedMinerals remain in soil away in water
----------Detrital/Clastic sediments------ Chemical & biochemicalsediments
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 25/106
Introduction
PAB 1023 Petroleum Geoscience 25
• Sedimentary rock is one of
the three main rock groups
(along with igneous and
metamorphic rocks)
• It is formed in three main
ways:
• by the deposition of theweathered remains of
other rocks (known as
'clastic' sedimentary
rocks);
• by the deposition of the
results of biogenic activity;
and
• by precipitation from
solution.
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 26/106
PAB 1023 Petroleum Geoscience 26
Sediments - loose debris that has not been lithified
• Sedimentary rocks include common types such as conglomerate,
sandstone, siltstone, shale, chalk, limestone, coal and etc.
• Sedimentary rocks cover 75% of the Earth's surface. The sedimentary
rock cover of the continents of the Earth's crust is extensive, but the total contribution of sedimentary rocks is estimated to be only 5% of the total. As such, the sedimentary sequences we see represent only a thin layer over a crust consisting mainly of igneous and metamorphic rocks.
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 27/106
PAB 1023 Petroleum Geoscience 27
Classification ofSedimentary Rocks
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 28/106
PAB 1023 Petroleum Geoscience 28
Detrital/Clastic sediments & rocks are classified by grain size
The grain size indicates the energy of the transporting agent.Turbulent water carries large particles, wind carries fine dust
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 29/106
29
Sedimentology
Fd is the frictional force acting on the
interface between the fluid and the particle
R is the radius of the spherical object
v is the particle's velocity
η is the fluid's viscosity
V s is the settling velocity
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 30/106
PAB 1023 Petroleum Geoscience 30
DistanceProvenance
P o t e n t i a l Grain size distribution
Sedimentology
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 31/106
Formation
PAB 1023 Petroleum Geoscience 31
• Sedimentary rocks are formed from overburden
pressure (burial) as particles of sediment are
deposited out of air, ice, or water flows carrying the
particles in suspension.
• As sediment deposition builds up, the overburden (or
'lithostatic') pressure squeezes the sediment intolayered solids in a process known as l ithification ('rock formation') and the original connate (water)
fluids are expelled.
• (The term diagenesis is used to describe all the chemical, physical, and biological changes, including cementation , undergone by a sediment after its initial deposition and during and after its lithification,exclusive of surface weathering.)
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 32/106
PAB 1023 Petroleum Geoscience 32
A sedimentary rock comprises of (1) grains (2)
cement & matrix and (3) voids
Lithification and diagenesis (as they proceeds)both reduces porosity and permeability and thus
degrades the reservoir quality. Lithification reducesporosity by compaction only whereas, diagenesisreduces porosity by compaction, cementation,dissolution and deposition of new minerals.
GrainMatrix/Cement Pore
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 33/106
PAB 1023 Petroleum Geoscience 33
Change of
porosity
with depth
Sedimentary Processes
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 34/106
PAB 1023 Petroleum Geoscience 34
Sedimentary Processes
1
•Detrital/Clastic sediments arefragments of primary orresidual minerals.
•Chemical and biochemical
sediments are precipitatedfrom water.
4
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 35/106
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 36/106
Coarsely Crystalline
• Precipitated from water orrecrystallized from finematerial:
– Carbonates
• Limestone (calcite)CaCO3
• Dolomite, CaMg(CO3)2
– Evaporites
• Gypsum, CaSO4*2H20
(cement, wallboard)• Anhydrite, CaSO4
• Salt, NaCl, KCl
PAB 1023 Petroleum Geoscience 36
Fine-Grained
(Cryptocrystalline)
Some limestones
Chert - quartz-rich
Flint – fine quartz
Chalcedony – banded quartz
Whole Fossil Rocks
Formed from calcite fossils
or material with high organiccontent such as coal
Fossiliferous limestone -fossils sand-size or coarser
Coal (peat, lignite)
Oil shale
Fish fossil
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 37/106
PAB 1023 Petroleum Geoscience 37
Fish fossil
AmmonitesCoral fragments
Marine life
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 38/106
Lithification – change from
sediment to sedimentary
rock
Processes are:
compaction, cementation,
recrystallization
PAB 1023 Petroleum Geoscience 38
Typicalcements arecalcite, silica
andhematite/iron
oxides
Diagenesis
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 39/106
Textures & Structures
• Texture is the size, shape and arrangement
(packing & fabric) of the component elements
of a sedimentary rock.
• Structures deal with larger features of the rock
such as bedding, tracks, trails etc.
PAB 1023 Petroleum Geoscience 39
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 40/106
Size Classification
• > 256mm: Boulder• 256mm – 64mm: Cobble
• 64mm – 4mm: Pebble
• 4mm – 2mm: Granule
• 2mm – 1/16mm: Sand
• 1/16mm – 1/256mm: Silt
• < 1/256mm: Clay
PAB 1023 Petroleum Geoscience 40
Wentworth Scale
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 41/106
Shape Classification
Class 1. b/a >2/3 c/a<2/3 Oblate
Class 2 b/a >2/3 c/a>2/3 Equiaxial
Class 3 b/a <2/3 c/a<2/3 Triaxial
Class 4 b/a <2/3 c/a>2/3 Prolate
PAB 1023 Petroleum Geoscience 41
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 42/106
Shape Classification
PAB 1023 Petroleum Geoscience 42
b/a
0
2/3
1
c/a 2/3 1
Tabularor
Oblate
Triaxial/Bladed
Equiaxial
Prolate
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 43/106
Various textural properties of clastic sediments and sedimentary rocks
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 44/106
Shape Classification
PAB 1023 Petroleum Geoscience 44
Roundness: Sharpness of edges and corners.
It is defined as the average radius of curvatureof the corners of the grain image divided by the
radius of the maximum inscribed circle.
Angular 0 to 0.15Sub-angular 0.15 to 0.30Subrounded 0.30 to 0.50Rounded 0.50 to 0.70Well Rounded 0.70 to 1.00
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 45/106
Sedimentary Structures
Inorganic Organic
PAB 1023 Petroleum Geoscience 45
Mechanical / Primary Chemical / Secondary
A:Planar Bedding Structures
1.Laminations
2. Cross Bedding
3. Graded Bedding
B. Linear Bedding Structures
1. Striations
2. Sand Lineations3. Spatulate Casts
4. Ripple Marks
C. Bedding Plane Irregularities
A. Solution Structures
1. Stylolites
2. Corrosion Zones
3. Vugs
B. Accretionary Structures
1. Nodules
2. Concretions3. Crystal aggregates
4. Veinlets
5. Color Banding
A: Petrifactions
B: Miscellaneous
1. Boring
2. Tracks & Trails
3. Casts & Mould
4. Faecal Pellets
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 46/106
Sedimentary Structures
Inorganic Organic
PAB 1023 Petroleum Geoscience 46
Mechanical / Primary Chemical / Secondary
C. Bedding Plane Irregularities
1.Wave & swash Marks
2. Pits & Prints (rain)
3. Cut-outs, Scoops
D. Deformed & Distorted
Bedding.
A. Solution Structures
1. Stylolites
2. Corrosion Zones
3. Vugs
B. Accretionary Structures
1. Nodules
2. Concretions3. Crystal aggregates
4. Veinlets
5. Color Banding
A: Petrifactions
B: Miscellaneous
1. Boring
2. Tracks & Trails
3. Casts & Mould
4. Faecal Pellets
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 47/106
CONCLUSION
• Layering and bedding are the main basic principle toidentify sedimentary rocks by naked eyes.
• Sedimentary rocks divided into two main categories,i.e. clastic (detrital) or non-clastic (chemical).
• The sedimentary structures appear indicating theirdepositional environment.
• The importance of sedimentary rocks in O & G
Industry.
PAB 1023 Petroleum Geoscience 47
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 48/106
Formation
PAB 1023 Petroleum Geoscience 48
• Sedimentary rocks contain important
information about the history of the Earth.• They contain fossils (the preserved
remains of ancient plants and animals ).• Sedimentary rocks can contain fossils
because they form at temperatures &
pressures that don't destroy fossilremnants, unlike igneous & metamorphic
rocks,.
• The composition of sediments provides
us with clues as to the original rock.
• Differences between successive layers
indicate changes to the environment
which have occurred over time or
Paleogeography.• Uniformitarianism - The present is the key to
the past – the most important concept.
Large scale features of sedimentary rocks
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 49/106
PAB 1023 Petroleum Geoscience 49
Large-scale features of sedimentary rocks 1) Stratification or bedding – each layer (stratum or bed) of
sediment indicates the kind of environment in which the
sediment was deposited
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 50/106
Types of Sediment
PAB 1023 Petroleum Geoscience 50
Detrital / Clastic – mineral & rockfragments
Chemical – halite (NaCl) crystalsthat precipitate from water
Biochemical – shells made ofcalcite (CaCO3) by organismsthat extract the ions from water
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 51/106
Weathering
PAB 1023 Petroleum Geoscience 51
• Chemical weathering is the breakdown
of rock by chemical reaction. In this
process the minerals within the rock arechanged into particles that can be easily
carried away.
• Air and water are both involved in many
complex chemical reactions.
• The minerals in igneous rocks may be
unstable under normal atmosphericconditions, those formed at higher
temperatures being more readily
attacked than those which formed at
lower temperatures.
• Igneous rocks are commonly attacked by
water, particularly acid or alkaline
solutions, and all of the common igneous
rock forming minerals (with the exception
of quartz which is very resistant) are
changed in this way into clay minerals
and chemicals in solution.
Igneous rocks weathered into sandy –clayey soils and gravels, which are the main source of modern sediments
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 52/106
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 53/106
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 54/106
Factors which influence clastic depositional systems.
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 55/106
Classification of heterogeneities in reservoirsaccording to scale. From the smallest to thelargest:
Microscopic.
Mesoscopic.
Macroscopic.
Megascopic.
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 56/106
Microscopic or pore/grain-scale heterogeneities are related to pores andarrangement of grains, including pore volume (porosity), pore sizes and
shapes, grain-to-grain contacts that control permeability, and grain types.
Mesoscopic or well-scale heterogeneities can be recognized in thevertical dimension, such as in cores or well logs. Such heterogeneitiesinclude bedding and lithologic types, stratification styles, and the natureof bedding contacts.
Macroscopic or interwell scale heterogeneities occur at the scale of wellspacing. Such heterogeneities include lateral bed continuity ordiscontinuity as a result of stratigraphic pinchout, erosional cutout, orfaulting.
Megascopic or field wide heterogeneities, such as overall geometry andlarge-scale reservoir architecture (related to structure and/ordepositional environment), normally can be delineated by 2D or 3Dseismic, well tests, production information, and field-wide well logcorrelation.
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 57/106
Figure: Classification of heterogeneities in reservoirs according to scale.From the smallest to the largest, these are microscopic, mesoscopic,macroscopic, and megascopic heterogeneities
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 58/106
Level 4: architectural elements of specific reservoir typescomprising a continental (Level 1), fluvial (Level 2),meandering river deposit (Level 3) composed of floodplain,point bar, cut bank, mud plug, fining-upward, and cross-
bedded elements (Level 4).
For fluvial systems (as an example), these subdivisions, orlevels, are:
Level 1: regional environments of deposition (i.e.,continental, mixed or marine);
Level 2: major type of deposit (continental: fluvial, eolian,lacustrine or alluvial deposit);
Level 3: more specific types of deposit (continental, fluvial:meandering river, braided river, or incised valley fill);
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 59/106
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 60/106
The above discussion refers only to stratigraphic and
sedimentologic features of reservoirs and not to tectonic orstructural features.
Tectonic features include folds, faults, fractures, diapirs
(salt and shale), microfractures, and stylolites (chemicalcompaction)
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 61/106
Figure: Tectonic features at both seismic and subseismic scales, including faults, folds,diapirs and fractures. These features, both large and small, can influence reservoirperformance.
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 62/106
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 63/106
PAB 1023 Petroleum Geoscience 63
Reservoir Characterization
“The principal goal of reservoir characterization
is to outsmart nature to obtain higherrecoveries with fewer wells in better
positions at minimum cost throughoptimization”.
Halderson and Damsleth (1993)
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 64/106
PAB 1023 Petroleum Geoscience 64
Reservoir Characterization
(Reprinted with permission of Institut Francais du Petrole.)
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 65/106
PAB 1023 Petroleum Geoscience 65
Reservoir Characterization
If a proper reservoir characterization is conducted for a field and it leads
to an incremental improvement in production beyond what was
anticipated, then there is economic value to the characterization. For
example, if the characterization of a field that was originally estimated to
contain 100 MMBO recoverable improves that field‟s recovery by anadditional 5%, an extra 5 MMBO is produced.
Production improvements can come about through a better
understanding of the geologic complexities of the field which may result
either from sound geologic evaluation and/or new technologies applied
to the field from improved reservoir characterization.
Recovery in many mature fields has improved by using 3D seismic
to image fine-scale stratigraphic and structural
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 66/106
PAB 1023 Petroleum Geoscience 66
Reservoir Characterization
(A) Simplistic perception of a continuous reservoir sandstoneundergoing waterflood.(B) Stratigraphic and structural complexities between wells thatcan affect the waterflood.
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 67/106
PAB 1023 Petroleum Geoscience 67
Reservoir Characterization
This field was to be subjected to an expensive tertiary recovery project andthe positions, orientations and number of faults were quite important.
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 68/106
68
Reservoir Characterization
Schematic illustration of multilateral horizontal wells drilling into sandstones(yellow/white), exhibiting stratigraphic pinchout, offset stacking andcompartmentalization by shales, and good lateral and vertical continuity andconnectivity. Horizontal drilling is ideally suited for stratigraphically andstructurally complex reservoirs.
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 69/106
69
Reservoir Characterization
(A) Net pay thickness determined from well control only and (B) from3D seismic and well control The 3D seismic clearly shows the highdegree of compartmentalization of the reservoir sandstone. Note thatsome sandstone thicks have not been penetrated by wells (black dots),so represent untapped parts of the total reservoir.
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 70/106
PAB 1023 Petroleum Geoscience 70
Reservoir CharacterizationStatic reservoir properties are those rock and fluid properties that normally
do not change during the life of a field. They are the result of primary
depositional processes coupled with postdepositional burial, diagenesis,
and tectonics
Static properties include:
• stratigraphy
• geometry
• size
• lithologies
• structure
• initial porosity and permeability
• temperature.
Reservoir Characterization
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 71/106
Reservoir CharacterizationDynamic properties are those that do change significantly during the life of
a field. For example, fluid saturations, compositions, and contacts, as well as
reservoir pressure, change as the field is produced. Porosity and permeabilitycan change as the reservoir pressure changes over time or as injected fluids
react with formation minerals (either to precipitate new minerals that fill pore
spaces or to dissolve minerals and thereby provide new pore spaces).
Dynamic properties include:
• fluid saturations
• fluid contacts• production and fluid-flow rates
• pressure
• fluid compositions, including gas-to-oil ratio (GOR) and water-to-oil ratio
(WOR)
• acoustic (seismic) properties.
Acoustic properties, which are measured and documented as seismic attributes, are dependent
upon porosity, fluid type and content, and the nature of the reservoir rock. Seismic attributes are
dynamic, because fluid type and content change during oil and gas production. By comparing
seismic attributes at different times in the life of a field, it is possible to indirectly measure fluid
movement in the reservoir.
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 72/106
PAB 1023 Petroleum Geoscience 72
Reservoir CharacterizationThe three main stages of field development are
exploration (through to discovery),appraisal, and
production.
In exploration, one starts with a conceptual geologic model, which may be
based on geologic knowledge of the area, including basin evolution,
structure, and stratigraphy.
Conventional 2D or 3D seismic-reflection analysis normally is thenext phase of exploration, because subsurface seismic profiles and 3D
volumes can provide a regional-scale image of the area being explored If
the seismic data reveal potential drill sites, and a well is drilled, the well is
logged with conventional logging tools to determine rock and fluid properties
in the wellbore.
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 73/106
Fig. 2.2. Diagram showing some of the different data types used in the
study of reservoirs. Clockwise from upper left are conventional welllogs, a conceptual geologic model, 2D and 3D seismic reflection data(shallow and deep), outcrops, cores and borehole image logs, andgeologic reservoir models. Not shown are geochemical andbiostratigraphic data, which also are important in reservoir
characterization.
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 74/106
Fig. 2.3. Exploration, discovery, development, and
production stages in the evolution of a reservoir overtime (steps 1 –9). Geophysics, geology, and petroleumengineering all play dominant roles at different times inthe life of a field.
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 75/106
Computers and the computing environment (see pages
35-37)
Computers are essential tools for reservoir characterization. Most
organizations provide adequate computing environments for their
staff, from secretaries to geoscientists and engineers.
Some individuals and very small companies still prefer to hang
cross sections on walls with a piece of string as a datum, or tointerpret paper copies of seismic lines and well logs.
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 76/106
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 77/106
A - Seismic-reflection and subsurface imaging
1- Two-dimensional (2D) seismic
2- Three-dimensional (3D) seismic
3- Four-dimensional (4D) seismic
4 - Cross-well seismic investigation
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 78/106
1- Two-dimensional (2D) seismic (see pages 38 – 39)
Seismic-reflection acquisition, or “shooting”, provides an image
of the subsurface that is not as detailed as the true geology, but
that is adequate for imaging large- to medium-scale geologic
structures and stratigraphy. Seismic-reflection analysis has
become the dominant tool used in hydrocarbon exploration, and
with some resolution limitations, it is becoming widely used for
characterizing reservoirs.
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 79/106
2- Three-dimensional (3D) seismic (see pages 42 – 44)
In the early 1980s, the technology for acquiring and processing
seismic data had improved enough that the costs were reduced and
it became practical and economic to shoot 3D, rather than 2D
seismic surveys.
The advantage of a 3D survey is obvious – a three-dimensional
image of the subsurface is much more useful for exploration and
field development than is one or more 2D vertical images. Three-
dimensional seismic is designed to image a large area of thesubsurface, including up to and beyond the size of a reservoir, both
areally (horizontally) and stratigraphically (vertically) (Fig. 2.13).
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 80/106
Fig. 2.13. Graph showing the vertical resolution of a reservoir on the horizontal axis andthe horizontal coverage of the reservoir on the vertical axis. Cores can exhibit
sedimentary features down to the scale of a millimeter or less, but the areal coverage is
very small (15 cm, or 6 in, diameter). At the other extreme, 3D surface seismic covers a
large area of a reservoir, but the features must be on the order of tens of meters to be fully
resolved and imaged. Various other tools measure properties between these two end
members.
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 81/106
3- Four-dimensional (4D) seismic (see page 44)
4D seismic measures dynamic reservoir properties. The underlying
principle of 4D seismic is that acoustic properties of reservoir
strata will change as a function of change in fluid content and type
within the rock’s pore spaces.
4 - Cross-well seismic investigation (see pages 51 – 53)
Cross-well seismic is one of the only methods that canimage subseismic-scale lateral and vertical attributes at
interwell spacings. The method involves placing a seismicsource string down one well and a set of geophonereceivers down another well, and then shooting theseismic to obtain images between the wells (Fig. 2.26).
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 82/106
Fig. 2.26. Cross-well seismic provides an energy source that
generates sound waves within a borehole. Receivers arranged in a
series are placed down another well to detect the sound waves.Behavior of the waves from source to receiver can be related back
to rock and fluid properties, such as lateral and vertical
variations in porosity, at much higher resolutions than can be
acquired from conventional surface seismic reflection.
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 83/106
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 84/106
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 85/106
Classification of sandstones on the basis of their mineral composition
Geological Controls on Reservoir Quality
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 86/106
PAB 1023 Petroleum Geoscience 86
Geological Controls on Reservoir Quality
Porosity:
Permeability:
Capillarity:
Tortuosity:
Direct Measurement of porosity:
Pore spaces can be examined directly in sedimentary rocks,
either in a hand sample or by cutting a “thin section” (0.030
mm thick) of the rock. To prepare a thin section, a small slab
of rock is cut from the larger sample and is placed in
a chamber containing colored epoxy (normally, either blue or
red). Then, either pressure or a vacuum is applied to thesealed chamber until the epoxy fills the pores and pore
throats. This procedure is done at elevated temperature to
lower the viscosity of the epoxy. The rock is allowed to cool,
and the thin section is cut. Figure 5.1 shows a thin section of
a sandstone with pale gray-pink quartz grains.
Geological Controls on Reservoir Quality
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 87/106
PAB 1023 Petroleum Geoscience 87
Geological Controls on Reservoir Quality
Thin-section photomicrograph of a quartz-rich sandstone. Quartzsand grains are pale colored and the blue /dark-gray is dyed epoxyin pore space. Brown/black material is fine cement crystals andclay minerals that partially fill pore spaces and pore throats(narrow spaces between grains). Some of the quartz grains exhibitquartz cement rims. Sand grains are about 0.150 mm in diameter.
Using a thin section, it is possible
to estimate the area of pore
space relative to the area of rockby “point counting” pore spaces
using a polarizing microscope. In
practice, 200 or 300 equally
spaced points on a thin section
are counted as “grain”, “cement”,
or “pore”, and the arealpercentage of pore space is
calculated.
Geological Controls on Reservoir Quality
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 88/106
PAB 1023 Petroleum Geoscience 88
Geological Controls on Reservoir Quality
Pores and pore throats, as well as grain boundaries, also can be observed with
a scanning electron microscope. is a high-magnification, 3D scanning
electron photomicrograph of quartz grains comprising a sandstone. Clay mineral
crystals have accumulated in the pore throats of the sandstone and on the
faces of the quartz grains.
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 89/106
PAB 1023 Petroleum Geoscience 89
Scanning electron photomicrograph of clay mineral particles lininga pore throat between two sand grains and bridging the grains.Such bridging reduces permeability and porosity of sandstones.White scale bar is 10 microns in length.
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 90/106
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 91/106
PAB 1023 Petroleum Geoscience 91
Cartoon illustrating 3.75 cm (1.5 in) long, horizontal core plugs extractedfrom a full-diameter core for routine core analysis. The photograph of threepieces of core show where core plugs were extracted. The plug from coreA is representative of the entire piece of homogeneous sandstone. The
plug from core B is representative only of the thin sandstone from which itwas extracted. The plug from core C crosscuts different sandstone(light-colored) and shale (dark-colored) laminae, so it is representative onlyof the average reservoir quality of the combined laminae.
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 92/106
PAB 1023 Petroleum Geoscience 92
In recent years, a rapid, reliable method has been developed to measure
permeability over a very small sample of rock using a laboratory
minipermeameter. This instrument measures the rate of flow of air from asmall-diameter tube (approximately 1-mm aperture) into and through the rock.
This air-flow rate can then be related to rock permeability through calibration.
A core-plug permeability value has been obtained on the slab of finely
laminated sandstone; a single core-plug permeability is 19 md(millidarcys). However, the core plug was cut through several laminae, so
the value is not really representative of the heterogeneous permeability
resulting from this fine-scale lamination. Individual spot values of
permeability shown on the diagram were taken with a minipermeameter.
There are at least two orders of magnitude of variation in permeability
within the laminae (from <0.5 to 38.5 md). The spot measurements provide a more accurate representation of the vertical permeability‟s
heterogeneity than does the single core-plug measurement.
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 93/106
PAB 1023 Petroleum Geoscience 93
Diagram of a slab of corethrough which a core plug
permeability value of 19 mdhas been obtained. Individualspot values of permeabilityshown on the diagram weretaken with aminipermeameter. There are
at least two orders ofmagnitude of variationin permeability within thelaminae (from <0.5 to 38.5 md). Diagram is after Weber (1987).(Reprinted with permission ofthe Society of SedimentaryGeology (SEPM).)
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 94/106
PAB 1023 Petroleum Geoscience 94
Unconsolidated sands in cores present a special problem, because insertion
of the plugging tool into the sands will destroy the in situ arrangement and
packing of the grains and thus the porosity and permeability. An example of
plugs taken from unconsolidated cores is shown in Fig. 5.8. The extent to
which the original reservoir-quality values are modified by the plugging
process is not known, but undoubtedly this modification is quite variable and
not systematic.
A similar problem is encountered when one is attempting to obtain reservoir
quality measurements on sidewall cores. Forceful insertion of the plug into
the borehole wall can severely modify the in situ rock fabric. Any
measurements of porosity and permeability from sidewall cores should be
considered suspect.
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 95/106
PAB 1023 Petroleum Geoscience 95
Variations in porosity as a function of cubic and rhombohedral packingof sand grains. With cubic packing, each pore is outlined by four grain-to-grain contacts (in 2D view). In the tighter rhombohedral packing,each pore is defined by three grain-to-grain contacts, so within a givenarea (or volume, in 3D space), the porosity and permeability will bereduced. (Figure provided by T. Cross.)
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 96/106
PAB 1023 Petroleum Geoscience 96
Relatively coarser-grained sandstones exhibit higher permeabilities
than do relatively finer-grained sandstones, siltstones, and shales.More poorly-sorted sandstones exhibit lower permeability than do
better-sorted sandstones, because, in the former, small grains can
infiltrate into pore throats of adjacent grains.
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 97/106
PAB 1023 Petroleum Geoscience 97
A commonly observed
trend in sandstones is
the increase of
permeability with
increasing porosity
(Fig).
Such a porosityversus permeability
relation can usually
be related to grain
size and sorting (Figs.5.12 and 5.13).
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 98/106
PAB 1023 Petroleum Geoscience 98
Figure illustrating the
relationship of porosityand permeability for setsof sands and muds ofdiffering grain size. Aconstant sorting isassumed for individual
core plugs measured. Forany given grain size, thereis a clearly positivecorrelation betweenporosity and permeability.
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 99/106
PAB 1023 Petroleum Geoscience 99
Median grain size versuspermeability (log –log)crossplot for the samesamples shown in Fig. 5.13.Grain-size analysis wasconducted on the plugs
after the porosity andpermeability measurementshad been made. There is aclear trend of increasingpermeability with anincrease in grain size of the
plug sample.
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 100/106
PAB 1023 Petroleum Geoscience 100
Surface area of the sphere of the same volume as the fragment /
surface area of the object
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 101/106
PAB 1023 Petroleum Geoscience 101
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 102/106
102
• Neutron logs (NL or GRN) measure the
h d i t ti i
• A lower neutron log reading (fewerenergetic back scattered neutrons)
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 103/106
PAB 1023 Petroleum Geoscience 103
hydrogen ion concentration in a
formation.
– In clay-free formations where
porosity is filled with water orhydrocarbons the neutron log
measures liquid filled pores (the
only significant occurrence of
hydrogen).
– The neutron log measures energy
loss when neutrons emitted from
the tool collide with other
particles in the formation.
– The maximum energy loss during
a neutron collision occurs when
– A neutron collides with a particleof equal mass, that is a hydrogen
atom.
energetic back scattered neutrons)indicates abundant formationhydrogen.
– Clay rich formations containhydrogen in the crystalstructure ofthe clay mineralsand give anomalous values forliquid filled pore volume.
• Neutron log excursions (decreasingin value from right to left) indicate
higher proportions of hydrogen inthe Formation
– either increased liquid filledporosity or
– higher shale content.
• Neutron log excursions increasing
from left to right indicate
– less porosity and/or
– less shale
• Natural Gamma Ray (γ-ray) Logs
Decay of radioactive
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 104/106
104
– Decay of radioactive
elements produces high
energy gamma ray
emissions – Radioactive elements (K, U,
Th) are normally
concentrated in shaley rocks
while most sandstones are
very weakly radioactive. – Because radioactive
material is concentrated in
shale, shale has high gamma
ray log readings
– Clay-free sandstone andcarbonate rocks have low
gamma ray log readings
Reservoir Characterization
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 105/106
PAB 1023 Petroleum Geoscience 105
Reservoir Characterization
(Reprinted with permission of Institut Francais du Petrole.)
Reservoir Characterization
7/31/2019 Fundamentals of Reservoir Geoscience
http://slidepdf.com/reader/full/fundamentals-of-reservoir-geoscience 106/106
Reservoir Characterization
(Reprinted with permission of Institut Francais du Petrole.)