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Week 3- notes
Reservoir Rock & Source Rock Types: Classification,
Properties & Symbols
Reservoir rock : A permeable subsurface rock that contains petroleum. Must be both porous and permeable.
Source rock : A sedimentary rock in which petroleum forms.
- Reservoir rocks are dominantly sedimentary (sandstones and carbonates); however, highly fractured igneous and metamorphic rocks have been known to produce hydrocarbons, albeit on a much smaller scale
- Source rocks are widely agreed to be sedimentary
- The three sedimentary rock types most frequently encountered in oil fields are shales, sandstones, and carbonates
- Each of these rock types has a characteristic composition and texture that is a direct result of depositional environment and post-depositional (diagenetic) processes (i.e., cementation, etc.)
- Understanding reservoir rock properties and their associated characteristics is crucial in developing a prospect
Week 3- notes
Different Forms of Sedimentary Rock:
- Sandstones
- Conglomerates
- Halite (rock salt)
- Gypsum
- Anydrite
- Limestone
- Chalk
- Coquina
- Coal
Week 3- no
D
Pr
H
O
otes
Schem and gra
Description:
roperties:
- Compo
- Clay pa contrib
- Behave
- Widely organic
- A weak
History:
Occurrence:
atic illustrating adations of eac
ctively dark-bro with smooth lat el to deposition
osed of clay an
articles are pla butes to shale’s
e as excellent s
y regarded to b cs
k rock highly s
ited on river flo
ost abundant se
g the three dist ch.
Shales -- So
own to black in teral surfaces (n nal direction)
d silt-sized par
ty and orient th s characteristic
seals
e the main sou
susceptible to w
oodplains, deep
edimentary roc
inctive sedime
urce Rocks an
n color (occasi normal to depo
rticles (q.v., we
hemselves norm c permeability
urce of hydroca
weathering and
p oceans, lakes
ck (about 42%)
entary rocks, sa
d Seals:
ionally a deep d ositional direct
eek 2 notes)
mal to induced
arbons due to o
d erosion
s, or lagoons
andstone, shale
dark green), oc tion) and irregu
d stress (overbu
original compo
e, and limeston
ccasionally dar ular vertical sur
urden); this
sition being ric
ne,
rk rfaces
ch in
Week 3- notes
Geologic Symbol:
- Horizontal, evenly-spaced dashed lines
Standard basic geologic symbol for shale. May be modified to illustrate further detail.
*For a complete version of the Standard Geologic Map Symbolization refer to URL: http://ngmdb.usgs.gov/fgdc_gds/geolsymstd/download.php
Sandstones and Sandstone Reservoirs:
Description:
- Composed of sand-sized particles (q.v., week 2 notes)
- Recall that sandstones may contain textural features indicative of the environment in which they were deposited: ripple marks (alluvial/fluvial), cross-bedding (alluvial/fluvial or eolian), graded- bedding (turbidity current)
- Typically light beige to tan in color; can also be dark brown to rusty red
Classification:
- Sandstones can be further classified according to the abundance of grains of a particular chemical composition (i.e., common source rock); for example, an arkosic sanstone (usually abbreviated: ark. s.s.) is a sandstone largely composed of feldspar (feldspathic) grains….Can you recall which continental rock contains feldspar as one of its mineral constituents???
- Sandstones composed of nearly all quartz grains are labeled quartz sandstones (usually abbreviated: qtz. s.s.)
Properties:
- Sandstone porosity is on the range of 10-30%
- Intergranular porosity is largely determined by sorting (primary porosity)
- Poorly indurated sandstones are referred to as fissile (easily disaggregated when scratched), whereas highly indurated sandstones can be very resistant to weathering and erosion
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Bartlesville SShoestring San nds: Cross-secttion and Regioonal Map
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D
C
D
otes
Description:
- Grains varying column
- Many o be used for mar
- Dolom
- Usually
Classification:
- Divide carbon
- Limest Bounds
Dunham classifi
(clasts) are lar g in size and sh n (neritic)
of these clasts d for correlativ rker beds used
mites are a produ
y light or dark
d into limeston ate – CaMg(CO
tones can be di stones accordin
ication scheme
Carbonates an
rgely the skelet hape, that eithe
can be identifi ve purposes or a d in regional str
uct of solution
gray, abundan
nes (calcium ca O 3 ) 2 )
vided further i ng to the limes
e of limestones
nd Carbonate R
tal or shell rem er lived on the o
ed by skilled p age range datin ratigraphic cor
recrystallizatio
nt fossil molds a
arbonate -- CaC
nto Mudstones stones depositio
s based on depo
Reservoirs:
mains of shallow ocean bottom (
paleontologists ng; also benefi rrelations
on of limeston
and casts, vugg
CO 3 ) and dolo
s, Wackestones onal texture; se
ositional textur
w marine dwel (benthic) or flo
and micropale ficial in establis
nes
gy (vugular) po
omites (calcium
s, Packstones, ee Dunham cla
res.
lling organisms oated in water
eontologists an shing index fos
orosity
m magnesium
Grainstones, an assification sch
s,
nd can ssils
nd heme
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Golden Lane OG Oil Field: Regio onal Map and SSequential Cross-sections
Week 3- no
Tr
R
otes
Transgression :
egression : Th
Transgress
The advancem
e Sea’s retreat
The transgre sequence of column)
Indicative of
Sands are de deep ocean b
This deposit and toward t
sions and Regre
ment of seas on
from the land.
ession/regressio sandstones, sh
f Coastal (trans
eposited near sh bottom
tional trend of the deep ocean
essions in the S
nto the land.
.
on cycle is pre hales, and limes
sitional)/ Marin
hore; muds alo
sediments grad n is called a fac
Sedimentary C
served in the ro stones (a patter
ne depositiona
ong continental
ding outward m cies change
Column
ock record by rn common in
l environment
l shelf; and ma
moving away fr
a repeating the stratigraph
arine organisms
rom the shoreli
hic
s on
ine
Week 3- nootes
Maarine Transgres ssion/Regression Sequence
Week 3- no
Case Exam
Glossary:
Anhydrite
Arenite : C
Argillaceo
Arkose : C deposition
Boundston deposition
Calcarenit calcareous
Calcareou
otes
mple:
e : An evaporat
Consolidated, c
ous : Shaly, or
Coarse-grained and limited gr
ne : Sedimenta : most algal ba
te : A clastic li sandstone.
us: Rock or oth
llowing figure as. Many like
te mineral of ca
clastic rock of
containing clay
, feldspathic, v rain transport.
ary carbonate ro ank and reef de
imestone comp
her material co
is a classic Ter it are observed
alcium sulfate.
sand sized part
yey constituen
variably sorted
ock the origina eposits.
prising over 50
ontaining up to
rtiary transgres d around the w
ticles: arkose,
nts.
sandstone con
al components
percent sand-s
50 percent cal
ssion/regressio orld.
sandstone, etc
ntaining angula
of which were
size calcium ca
lcium carbonat
on cycle on the
c.
ar grains, repres
e bound togethe
arbonate partic
te.
Gulf Coast
senting rapid
er in place duri
cles cemented a
ing
as a
Week 3- notes
Mud (sediment): A mixture of silt and /or clay particles and water. Diagenetically transformed into siltstone and/or shale.
Oolite : A sedimentary rock comprising concentrically precipitated calcium carbonate ooliths approximately one mm in diameter.
Oolitic limestone : A limestone, comprising calcareous ooliths, often having good reservoir potential.
Packstone : Granular carbonate rock, the grains of which occur in a self-supportine framework surrounded by some calcareous matrix.
Petroleum source rock : A sedimentary rock suitable for the generation of petroleum.
Quartz : Silicon dioxide.
Reef : A bank, ridge or mound constructed by calcareous animals and plants.
Reservoir rock : A permeable subsurface rock unit which contains petroleum.
Rock sequence : A progression of layered rocks often illustrative of specific stratigraphic characteristics.
Salt dome : A circular or elliptical, positive salt-cored structure which vertically penetrates or deforms the surrounding sediments.
Sandstone : A clastic sedimentary rock of sand-size particles.
Shale : A fine-grained, usually laminated, clastic rock of compacted clay or mud particles.
Silica : Silicon dioxide, quartz.
Siltstone : A rock made of silt.
Source rock : A sedimentary rock in which petroleum forms.
Turbidite : A turbidity current-deposited , graded clastic sequence.
Vug : A small void in a rock (typically carbonates) that is a result of the dissolution of fossil components or grains.
Wackestone: Mud-supported carbonate rock with more than 10% grains larger than 20 microns in diameter: calcarenite.
