NIGERIAN NATIONAL PETROLEUM CORPORATION
FOUNDATION SKILLS TRAINING PROGRAM
GEOSCIENCE PRACTICAL REPORT
CLASS D
SEPTEMBER 2012
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.
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
PART 1 – ROCKS
SPECIMEN NO: 1
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
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
Mineral Type: Feldspar
Mineral Name: k-Feldspar
Colour: Salmon Pink
Texture: Perthitic
Structure: Crossed twinning and fractured
Grain Size: Fine-grained
Sorting: very good
Hydrocarbon Implication: K-Feldspar is of no importance in the Hydrocarbon Extraction Industry
because it has a very low porosity.
SPECIMEN NO 3:
Mineral Type: Quartz
Mineral Name: Milky Quartz
Colour: brownish milk
Texture: fibrous
Structure: massive with interlocked grains
Grain Size: fine
Sorting: good
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: Carbonate
Rock Name: Calcite
Colour: milky with brown impurities
Texture: granular
Structure: Cleavage with conchoidal fractures
Grain Size: coarse
Sorting: good
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
Mineral Type: Barite
Mineral Name: Barite
Colour: Pinkish White
Texture: aphanitic
Structure: perfect cleavage with irregular fractures
Grain Size: fine – medium grained
Sorting: poor
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: Clay
Mineral Name: Kaolin
Colour: chalky white with grey impurities
Texture: aphanitic
Structure: massive with cleavage
Grain Size: fine
Sorting: fair
Hydrocarbon Implication: Kaolin has a low shrink-swell capacity and its grains are tightly packed
therefore it can act as a cap rock in the petroleum system.
SPECIMEN NO: 7
Rock Type: Metamorphic
Rock Name: Marble
Colour: cloudy white
Texture: phaneritic
Structure: mineral cleavages with joints
Grain Size: medium – coarse grained
Sorting: poor
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
Rock Type: Igneous
Rock Name: Potassium Syenite
Colour: dark grey with black spots
Texture: perthitic
Structure: massive
Grain Size: coarse- grained
Sorting: poor
Hydrocarbon Implication: This rock cannot be a hydrocarbon reservoir.
SPECIMEN NO: 9
Rock Type: Sedimentary
Rock Name: Coal
Colour: black
Texture: soothy
Structure: mineral cleavages and layering
Grain Size: fine
Sorting: good
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).
SPECIMEN NO 10:
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
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
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
Hydrocarbon Implication: This mineral is poorly sorted and cannot be a reservoir rock.
SPECIMEN NO 12:
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
Hydrocarbon Implication: This rock cannot be a hydrocarbon reservoir.
SPECIMEN NO: 13
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
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: 14
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:
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
Rock Type: Igneous
Rock Name: Syenite
Colour: dark grey
Texture: Phaneritic
Structure: massive
Grain Size: coarse grained
Grain Shape: Angular
Hydrocarbon Implications: This rock cannot be a hydrocarbon reservoir.
SPECIMEN NO: 16
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
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
Rock Type: Sedimentary
Rock Name: Claystone
Colour: Grey
Texture: Fine
Structure: Fissile planes
Grain Size: Fine grained
Grain Shape: Not visible
Sorting: moderately sorted
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
Rock Name: Black Shale
Colour: Grayish Black
Texture: Fissile
Structure: Slaty Cleavages
Grain Size: Fine grained
Grain Shape: Invisible
Sorting: well sorted
Hydrocarbon Implication: Black shale can serve as a cap rock for petroleum reservoirs.
SPECIMEN NO: 19
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
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: 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
Hydrocarbon Implication: Conglomerates are not good reservoirs as their sorting is poor
SPECIMEN NO: 21
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
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.
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).
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. 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:
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
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 boldcoloured 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, cemented together by
calcium carbonate.
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.