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NIGERIAN NATIONAL PETROLEUM
CORPORATION
FOUNDATION SKILLS TRAINING
PROGRAM
GEOSCIENCE PRACTICAL REPORT
CLASS D
SEPTEMBER 2012
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EXECUTIVE SUMMARY
In order to obtain a basic idea of rocks and geology, a visit to the lab was
organized by the Nexus training team. During this visit, rock samples were
examined and thin sections of some of these rocks were observed under
the microscope; cores obtained from sandstone reservoirs were also
examined.
This report is divided into three parts titled ROCK, CORES and THIN
SECTIONS respectively. The ROCKS part covers twenty-one (21) rocks with
each rock described by the name, the type, the texture as well as other
physical properties of the rock. Visual Images of each rock is also displayed
as well as information its hydrocarbon implication.
The CORES part covers the description of the cores that were displayed and
the answers to the questions that were asked in the practical manuscript;
the importance of cores to the petroleum industry was also discussed
briefly.
The THIN SECTIONS part contains information on the thin sections of rock
that was viewed under the microscope. The hydrocarbon implications of
these rocks were also discussed.
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TABLE OF CONTENTS
TITLE PAGE 1
EXECUTIVE SUMMARY 2
TABLE OF CONTENTS
3
PART 1 – ROCKS 4
PART 2 – CORES 15
PART 3 – THIN SECTIONS
17
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PART 1 – ROCKS
SPECIMEN NO: 1
Hydrocarbon Implication: This rock cannot be a source rock or reservoir rock for
petroleum deposits because it is poorly sorted and has very low porosity.
SPECIMEN NO: 2
Rock Type: Metamorphic
Rock Name: Granite Gneiss
Colour: Grey and Pink alternations
Texture: Coarsely granular (gneissose
texture)
Structure: foliated and banded
Grain Size: medium - coarse
Sorting: poor
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Hydrocarbon Implication: K-Feldspar is of no importance in the HydrocarbonExtraction Industry because it has a very low porosity.
SPECIMEN NO 3:
Hydrocarbon Implication: This mineral rock has tightly interlocked grains with
very low porosity and therefore cannot be a reservoir or source rock for crude oil.
SPECIMEN NO 4:
Mineral Type: Feldspar
Mineral Name: k-Feldspar
Colour: Salmon Pink
Texture: Perthitic
Structure: Crossed twinning and fractured
Grain Size: Fine-grained
Sorting: very good
Mineral Type: Quartz
Mineral Name: Milky Quartz
Colour: brownish milk
Texture: fibrous
Structure: massive with interlocked grains
Grain Size: fine
Sorting: good
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Hydrocarbon Implication: This rock is important in the Oil and Gas Industry
because a lot of oil has been found in the carbonate reservoirs of the Middle East.
SPECIMEN NO: 5
Hydrocarbon Implication: This mineral cannot serve as a source or reservoir
rock. It is poorly sorted with low porosity. However, it is a very important weighting
material in drilling fluids.
SPECIMEN NO: 6
Mineral Type: Carbonate
Rock Name: Calcite
Colour: milky with brown impurities
Texture: granular
Structure: Cleavage with conchoidal
fractures
Grain Size: coarse
Sorting: good
Mineral Type: Barite
Mineral Name: Barite
Colour: Pinkish White
Texture: aphanitic
Structure: perfect cleavage with irregular
fractures
Grain Size: fine – medium grained
Sorting: poor
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Hydrocarbon Implication: Kaolin has a low shrink-swell capacity and its grainsare tightly packed therefore it can act as a cap rock in the petroleum system.
SPECIMEN NO: 7
Hydrocarbon Implication: Sorting is poor and porosity is low, this implies that
this rock is not a good candidate for storing crude oil.
SPECIMEN NO: 8
Mineral Type: Clay
Mineral Name: Kaolin
Colour: chalky white with grey impurities
Texture: aphanitic
Structure: massive with cleavage
Grain Size: fine
Sorting: fair
Rock Type: Metamorphic
Rock Name: Marble
Colour: cloudy white
Texture: phaneritic
Structure: mineral cleavages with joints
Grain Size: medium – coarse grained
Sorting: poor
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Hydrocarbon Implication: This rock cannot be a hydrocarbon reservoir.
SPECIMEN NO: 9
Hydrocarbon Implication: Coal is relevant in the Oil and Gas industry. Apart
from being a source of energy itself it is also a reservoir for the famous Coal bed
Methane (CBM).
Rock Type: Igneous
Rock Name: Potassium Syenite
Colour: dark grey with black spots
Texture: perthitic
Structure: massive
Grain Size: coarse- grained
Sorting: poor
Rock Type: Sedimentary
Rock Name: Coal
Colour: black
Texture: soothy
Structure: mineral cleavages and layering
Grain Size: fine
Sorting: good
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SPECIMEN NO 10:
Hydrocarbon Implication: This igneous rock is of no relevance to petroleum
formation or accumulation. Deposits of weathered materials of granite will be
coarse-grained but poorly sorted and matrix supported, therefore cannot be a
reservoir rock.
SPECIMEN NO: 11
Hydrocarbon Implication: This mineral is poorly sorted and cannot be a
reservoir rock.
Rock Type: Igneous rock
Rock Name: Granite intruded by Dolerite
Dyke
Colour: dark grey with pinkish spots
Texture: phaneritic
Structure: massive with closely packed
grains.
Grain Size: coarse
Sorting: poor
MineralType: Augen
Mineral Name: Augen-Gneiss
Colour: pink with black bands
Texture: porphyroblastic
Structure: large lenticular eye-shaped
grains
Grain Size: medium - coarse
Sorting: poor
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SPECIMEN NO 12:
Hydrocarbon Implication: This rock cannot be a hydrocarbon reservoir.
SPECIMEN NO: 13
Hydrocarbon Implication: Sorting is poor and porosity is low, this implies that
this rock is not a good candidate for storing crude oil.
Rock Type: Igneous
Rock Name: Biotite Granite
Colour: Pink with dark spots
Texture: phaneritic
Structure: massive
Grain Size: coarse grained
Grain Shape: angular to subangular
Rock Type: Metamorphic
Rock Name: Banded Biotite Gneiss
Colour: Pink with black bands
Texture: Phaneritic
Structure: Massive
Grain Size: medium grained
Grain Shape: angular to subangular
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SPECIMEN NO: 14
Hydrocarbon Implication: Sorting is poor and porosity is low, this implies that
this rock is not a good candidate for storing crude oil.
SPECIMEN NO: 15
Hydrocarbon Implications: This rock cannot be a hydrocarbon reservoir.
SPECIMEN NO: 16
Rock Type: metamorphic
Rock Name: Pegmatite
Colour: brown with pinkish coloration and
dark spots
Texture: phaneritic
Structure: joints and cracks
Grain Size: very coarse grained
Grain Shape:
Rock Type: Igneous
Rock Name: Syenite
Colour: dark grey
Texture: Phaneritic
Structure: massive
Grain Size: coarse grained
Grain Shape: Angular
Rock Type: Sedimentary
Rock Name: Ferroginised Sandstone
Colour: Reddish Brown
Texture: medium to fine grained
Structure: burrows
Grain Size: medium – coarse grained
Grain Shape: rounded
Sorting: moderately sorted
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Hydrocarbon Implication: This is a good reservoir rock as it is well rounded and
moderately sorted. Sand stone reservoirs are predominant in the Niger Delta.
SPECIMEN NO: 17
Hydrocarbon Implication: This cannot be a good reservoir as it has very low
porosity, however it can serve as a cap rock for a petroleum reservoirs
SPECIMEN NO 18:
Rock Type: Sedimentary
Rock Name: Claystone
Colour: Grey
Texture: Fine
Structure: Fissile planes
Grain Size: Fine grained
Grain Shape: Not visible
Sorting: moderately sortedRock Type: Sedimentary rock
Rock Name: Black Shale
Colour: Grayish Black
Texture: Fissile
Structure: Slaty Cleavages
Grain Size: Fine grained
Grain Shape: Invisible
Sorting: well sorted
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Hydrocarbon Implication: Black shale can serve as a cap rock for petroleumreservoirs.
SPECIMEN NO: 19
Hydrocarbon Implication: Limestone is a good petroleum reservoir as its grains
are well sorted and it has sufficient porosity to store hydrocarbons.
SPECIMEN NO: 20
Rock Type: Sedimentary
Rock Name: Limestone
Colour: Light brown
Texture: Crystalline to fine grained, chalky
Structure: Crystalline
Grain Size: Medium grained - fossiliferous
Grain Shape: Angular to subangular
Sorting: Moderately sorted
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Hydrocarbon Implication: Conglomerates are not good reservoirs as their sorting ispoor
SPECIMEN NO: 21
Hydrocarbon Implication: This rock cannot be a source rock or reservoir rock for
petroleum deposits because it is poorly sorted and has very low porosity.
Rock Type: Sedimentary
Rock Name: Conglomerate
Colour: Reddish Brown
Texture: Rounded pebble to cobble sized
grained in a finer grained matrix
Structure: No visible structure
Grain Size: Coarse grained
Grain Shape: angular to sub-angular
Sorting: poorly sorted
Rock Type: Metamorphic
Rock Name: Phylitic Schist
Colour: Grey
Texture: Phaneritic
Structure: Cleavage, not well defined,
flaky plates
Grain Size: Medium to fine grained
Grain Shape: angular
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PART 2 – CORES
Cores are sections of representative formation taken from the reservoir; they are
obtained by using special drill bits but side wall cores can also be obtained from
the side of the formation. Figure 1 shows a core with the holes showing plugs
taken for routine and special core analysis (SCAL).
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Figure 1: Core Section
OBSERVATIONS
REASONS FOR OUTSIDE COATING
1. To preserve the fluid inside the core sample so that the sample remains
representative of formation conditions.
2. To ensure that the unconsolidated core are kept intact to maintain the
integrity of the core.
SMALL HOLES IN THE CORES
1. The holes in the core samples indicate the areas where 1” or 1.5” plugs (see
Figure 2) have been taken from the cores for routine or special core analysis
(SCAL). These plugs could be horizontal or vertical depending on the
bedding plane direction along which they were taken.
FORMATION OF THE ROCKS
The cores were obtained from sandstone formation which is a sedimentary rock.
Sedimentary rocks are formed by deposition of sediments from weathered rocks.
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This deposition occurred in a geologic time sequence, hence the sequential
bedding planes visibly seen on the cores.
Figure 2: Core Plugs.
PART 3 – THIN SECTIONS
The thin sections that were observed under the microscope are as follows:
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1. DOLERITE
Type of rock: Igneous
Hydrocarbon Implication: None
Dolerite is the name given to basic igneous rocks found in small intrusions
that are intermediate in grain size between basalt and gabbro. Small
intrusions (dykes and sills) cool more quickly than large intrusions, but more
slowly than lavas erupted at the surface.
2. OOLITHIC LIMESTONE
Type of rock: Sedimentary
Hydrocarbon Implication: Good reservoir
Oolitic limestone is made up largely of sand-sized, rounded pellets of
calcium carbonate, which are formed in warm shallow water where
carbonate sediment is moved about by currents. It is well developed having
both concentric and radial structure. There is an early cement of fine
radiating, ferroan calcite fringes. the main inter granular cement is ferroan
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3. MARBLE
Type of rock: Metamorphic
Hydrocarbon Implication: None
Metamorphosed limestone is called marble. The calcium carbonate re-forms
itself into larger, interlocking crystals of calcite (e.g. the pearly-coloured
crystals in the centre). The impurities are converted into new metamorphic
minerals. In this case, the larger bold-coloured crystals are forsterite
(magnesium silicate, a variety of olivine)
4. SANDSTONE
Type of rock: Sedimentary
Hydrocarbon Implication: High quality reservoir
This sandstone is made of quite well rounded grains of quartz, cementedtogether by calcium carbonate.
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5. AMPHIBOLITE
Type of rock: Metamorphic
Hydrocarbon Implication: None
This rock was originally a basic igneous rock (basalt or dolerite). When
metamorphosed, the heating and compression changed the original
minerals to hornblende (green) and feldspar (colourless), and gave the rock
a banding of minerals.