class d geoscience report

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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

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



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



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



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 Name: Marble

Colour: cloudy white

Texture: phaneritic

Structure: mineral cleavages with joints

Grain Size: medium – coarse grained

Sorting: poor



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



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



SPECIMEN NO 12:

Hydrocarbon Implication: This rock cannot be a hydrocarbon reservoir.

SPECIMEN NO: 13



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 Name: Banded Biotite Gneiss

Colour: Pink with black bands

Texture: Phaneritic

Structure: Massive

Grain Size: medium grained

Grain Shape: angular to subangular



SPECIMEN NO: 14



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 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

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 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



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 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: 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 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 Name: Phylitic Schist

Colour: Grey

Texture: Phaneritic

Structure: Cleavage, not well defined,

flaky plates

Grain Size: Medium to fine grained

Grain Shape: angular



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


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.



5. AMPHIBOLITE

Type of rock: Metamorphic


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.

class d geoscience report

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