Middle East Technical University

Department of Geological Engineering

5640300

Summer Practice I

Turkish Petroleum Corporation

(Trkiye Petrolleri Anonim Ortakl)

Exploration Department

(Arama Daire Bakanl)

Name: Selen Caner

ID: 1624311

5th Semester, 3rd Year

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TABLE OF CONTENTS TABLE OF CONTENTS..2 LIST OF FIGURES..4 1. INTRODUCTION ............................................................................................................................... 5

1.1. Description of the Company ......................................................................................................... 5

1.1.1. Company Name ..................................................................................................................... 5

1.1.2. Company Location ................................................................................................................. 5

1.1.3. Organizational Structure of the Company............................................................................. 5

1.1.4. Number and Duties of Engineers Employed ......................................................................... 5

1.1.5. Main Area of Business ........................................................................................................... 5

1.1.6. A Brief History of the Company ............................................................................................. 5

2. THE PETROLEUM ............................................................................................................................. 6

2.1. Properties of Petroleum ............................................................................................................... 6

2.1.1. Density ................................................................................................................................... 6

2.1.2. Volume .................................................................................................................................. 6

2.1.3. Viscosity ................................................................................................................................. 6

2.1.4. Fluorescence .......................................................................................................................... 7

2.1.5. Colour and Smell ................................................................................................................... 7

2.1.6. Calorific Value ........................................................................................................................ 7

2.2. Forming Petroleum ....................................................................................................................... 7

2.3. Rocks and Environment ................................................................................................................ 8

2.3.1. Presence Conditions .............................................................................................................. 9

2.3.2. Traps .................................................................................................................................... 10

3. EXPLORATION ............................................................................................................................... 12

3.1. Field Work .................................................................................................................................. 12

3.2. Potential Oil Bearing Rocks ........................................................................................................ 17

3.2.1. TOC Analysis ........................................................................................................................ 18

3.2.2. Pyrolysis Analysis ................................................................................................................. 18

3.2.3. Vitrinite Reflectance Analysis .............................................................................................. 18

3.2.4. SCI (Spor Colour Index) Analysis .......................................................................................... 18

3.3. Geophysics .................................................................................................................................. 18

3.3.1. Gravity Method ................................................................................................................... 18

3.3.2. Magnetic Method ................................................................................................................ 19

3.3.3. Seismic Method ................................................................................................................... 19

3.3.4. Seismic Stratigraphy ............................................................................................................ 19

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3.4. Geodesy and Maps ..................................................................................................................... 19

4. DRILLING ....................................................................................................................................... 21

4.1. Drilling Mud ................................................................................................................................ 21

4.2. Sampling ..................................................................................................................................... 22

4.3. DST (Drill Stem Test) ................................................................................................................... 23

4.3.1. DST Tools ............................................................................................................................. 24

4.3.2. The Test ............................................................................................................................... 24

4.3.3. DST Chart ............................................................................................................................. 24

4.4. Casing and Cementing ................................................................................................................ 25

4.5. Perforation ................................................................................................................................. 26

4.6. Swabbing .................................................................................................................................... 26

4.7. Log .............................................................................................................................................. 26

4.8. Check Shot ............................................................................................................................. 28

4.9. Well Classification ................................................................................................................. 28

4.10. Recording the Well Data ................................................................................................... 28

5. CONCLUSION ................................................................................................................................. 29

REFERENCES .........................................................................................................................................30 APPENDICES .........................................................................................................................................31

APPENDIX A: Organizational Structure of TPAO ...........................................................31

APPENDIX B: South Eastern Anatolia and the Autochthonous Lithostratigraphic Units

of Southeast Turkey .......................................................................................32

APPENDIX C: Seismic Stratigraphic Section...................................................................33

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LIST OF FIGURES

1- Rock samples show colours under UV light if carrying hydrocarbons..7 2- Oils characteristic movement....8 3- Migration of oil...9 4- Basalt with cracks can act as reserves..10 5- Anticline trap10 6- Fault trap...11 7- Unconformity trap.11 8- Section example 1 Adyaman. ..12 9- Section example 2 Adyaman.13 10- Finding strike.14 11- A Nerinea, left, and fossils found at the field work, right.14 12- Graptolites..15 13- Topographic cross-section Adyaman.15 14- Topographic cross-section at Village...16 15- Cendere Flower Structure from Karaku...16 16- Oil seepage.17 17- Crystallized oil...17 18- Meridian slices where Turkey is located....20 19- Minute sizes of sheets....21 20- On land and at the sea these rigs are used for drilling...21 21- Samples are put in Petri dishes with water.23 22- Basic DST format24 23- DST Chart...25 24- An oil bubble getting out of the perforation crack.26 25- A log sample...27 26- Check shot..28

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1. INTRODUCTION

The purpose of my summer practice was to experience the work environment and collecting

information about, at least one, geology related business. In the end, that one geology related

area turned out to be oil exploration. For starters I was pretty sure that I do not want to do

anything about oil and gas. Actually I applied to MTA at first, however their approval papers

was not going to make it to the schools deadline, thus I did not want to risk it and applied to TPAO. Fortunately, that was the correct move which even changed my opinion about this

particular field. During these six weeks, we had seminars about different topics related to

petroleum, searching techniques and how to acquire it. For other times, we were hosted by

engineers working with various departments, so we observed and also attended to fieldwork at

one point.

1.1. Description of the Company

1.1.1. Company Name Turkish Petroleum Corporation (Trkiye Petrolleri Anonim Ortakl TPAO) is the company where I had my summer practice.

1.1.2. Company Location TPAO headquarters is located in Ankara; however the company has district managements at

Adyaman, Batman and Trakya.

1.1.3. Organizational Structure of the Company According to the 2009 Annual Report, organizational structure of TPAO is shown in the

Appendix A.

1.1.4. Number and Duties of Engineers Employed According to the Annual Report TPAO has published at 2009, the total number of their

employees is 4.498, and 1679 of them are working at Batman District Management, 453 of

them are at Trakya District Management, and 849 of them are at Adyaman District Management.

1.1.5. Main Area of Business This corporation is working on oil and gas exploration industry, including drilling,

production, refinery and marketing.

1.1.6. A Brief History of the Company TPAO was established in 1954 as the national hydrocarbon exploring company, and since

then they are working on various fields to be able to provide Turkeys one of the basic needs. Once working on every aspect from exploration to marketing, TPAO carried on by mainly

exploration, drilling and production after 1983.

2004 was the start of important improvements in their work fields. Natural gas was discovered

in the Western Black Sea region and they also started working on new basins, including

offshore ones.

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Always having international contacts and partners, TPAO enlarged its work internationally by

taking shares of different projects carried out in Azerbaijan. It is also known that, Libya has

an important place among their other exploration fields. They still have active

communications with Turkmenistan, Syria, Iraq, Egypt, Russia, Georgia and Brazil.

Lastly, TPAO is part of the Baku-Tbilisi-Ceyhan Crude Oil Pipeline and South Caucasus

Natural Gas Pipeline projects.

2. THE PETROLEUM

The word petroleum comes from the two Latin words Petro and Oleum, meaning Stone and Oil respectively. It mainly includes hydrogen and carbon, however can also contain nitrogen, oxygen and sulphur. It can exist in all three states; gas, liquid and solid. To be able

to distinguish from the refined oil, the basic liquid state is called Crude Oil. Also the name

Natural Gas was given to distinguish it from the produced gas. In the solid state, oil includes

heavy hydrocarbons and goudron.

The main compounds, hydrogen and carbon, are the reason the crude oil and the natural gas

are also named hydrocarbons. Crude oil is the liquid hydrocarbon, formed by the transformed organic material which has

been stored inside porous rocks. The name indicates that it is not yet processed.

Natural gas is a mixture of light hydrocarbons such as methane, ethane, butane, and propane.

It can be found underground alone or alongside petroleum.

2.1. Properties of Petroleum

2.1.1. Density The density of oil is indicated according to the values under 60F (15.5C) temperature and

1atm pressure. It changes with the chemical content of the crude oil, such as the percentage of

the heavy and light hydrocarbon amount, gases, sulphides or temperature.

Density is expressed as API or Baume. TPAO prefers API. 0.6-1.00 gr/cm3 and 27

0-35

0 API

are the average values of density for the oil around the world.

The density has a great effect on the oil prices, for these properties affect the processing. Less

density means higher prices.

2.1.2. Volume The volume of oil is measured under the same conditions with its density, under 60F (15.5C)

temperature and 1atm pressure, and it is expressed by 1 Barrel, which is 159 litres. The

volume of Natural Gas is expressed bu ft3 or m

3 under the same conditions. Again the decisive

factors are temperature, pressure and the substances dissolved in the oil.

2.1.3. Viscosity Viscosity is a fluids resistance to flow; it changes according to oils composition. It increases with the increasing density and amount of heavy compounds; decreases with the increasing

temperature and amount of gases.

Viscosity unit is Poiz. To have the value of 1Poiz, a liquid must move 1cm inside a 1cm2

(cross-section area) tubes under 1dyn pressure in 1 seconds.

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2.1.4. Fluorescence With this property trace amounts of oil can be detected in rocks, for the petroleum shows

different colours like yellow, green and blue under UV light. (Fig 1).

Figure 1: Rock samples show colours under UV light if carrying trace hydrocarbons.

However, minerals and mud can also show fluorescence, thus theirs should not be mixed up

with the target oil bearing samples. Another point to be mentioned is that if the fluorescence is

decreasing among the viewed samples from the vicinity, it may indicate an oil-water contact.

In addition to all these it is known that according to the API gravity oil changes colour under

the UV light:

2o 10o : Colourless Dull Brown 10o 18o : Yellow Brown - Golden 18o 45o : Golden Dull Yellow 45o and above : Bluish White Blue To see these colours clearly, samples should not be waited for vithout their volatiles it is hard

to spot the fluorescence.

2.1.5. Colour and Smell Petroleum looks green with a reflective light and yellow, red, or black with a refractive light.

The colour gets darker with the increasing density.

The oil can paint the rocks. According to the stain it leaves it is possible to determine the gravity of the oil. High gravity gives a slightly light colour and low gravity gives a dark

colour. Black, asphalt-like remnants imply that the oil has lost its volatiles.

Unsaturated hydrocarbons give a classic odour, however, the ones with sulphur and nitrogen

smells bad. The smell can be strong, intermediate or weak; however it is so distinctive that it

is possible to understand whether the oil is light or heavy.

2.1.6. Calorific Value It has an inverse proportion to the density of oil.

2.2. Forming Petroleum There are two theories on how the oil forms; inorganic and organic theory. Inorganic theory

states that oil forms with reduction of the carbon under high temperatures, while the organic

theory states that it forms when the chemical structure of the organic matter is changed.

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All animals and plants are deposited at the bottom of seas, lakes, rivers or streams with the

transported material such as sand, clay and minerals when they cease to live. This

precipitation and sedimentation goes for millions of years and the materials accumulate more

and more. This causes a pressure to the bottom, and accordingly the material is compressed.

All those organic substances become trapped along with water inside. In time with the effect

of heat coming from beneath, radioactivity and the pressure these substances undergoes

chemical and molecular changes. At the end of all these changes gases, liquids and solids

form. With further changes the liquid ones are named crude oil and the gases are named

Natural Gas.

Organic material coming from the sea forms oil, while the continental organic material

usually forms gas.

When viewed, the history of the world shows all the possible movements for the oil

formation. According to all the plate movements, it is easy to detect the places of deposition

and also of the oil must be present.

2.3. Rocks and Environment

Sedimentary rocks are one of the key elements of this process. As the sediments accumulate

at different environments, they entrap organic substances, alive or dead. The biological

conditions should be proper, like having enough hydrocarbons, as much as the rate of

sedimentation. As known clearly, sediments have different grain sizes thus they form rocks

with varying porosities. To get use of the oil, the rock hosting it must be both porous and

permeable, so that it can also move.

There is a problem here. In the course of diagenesis, clays and cement can disable porosity

and permeability. They could be filling or paving the grains, pores and cracks. Kaolinites,

Illites, Chlorites and Smectites play the main roles, causing swelling and microporosity, by

reducing permeability, porosity.

As the oil forms it is transferred to other rocks by pressure closing the pores between the

grains. By its nature, oil moves upwards. (Fig 2). The movement can also go on at the rock it

has been collected as a result of the density differences, for water can be present there.

Figure 2: Oils characteristic movement.

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These two basic movement episodes are named Primary Migration and Secondary Migration respectively. (Fig 3).

Figure 3: Migration of oil.

The oil is migrating; however these places where it started off and where it is collected are

very crucial.

2.3.1. Presence Conditions One of the most important information that has been given is the fact that petroleum is only

possible with these;

1- Source Rock

2- Reservoir

3- Trap (Cap Rock).

Source rock is the main character, where the oil forms from the organic material, and has the

appropriate conditions such as porosity and permeability. They are usually shale and

limestones. The formation of the oil and gas inside the source rock is a function of time,

accordingly, to determine the places where the hydrocarbons are deriving, and when, the

Geothermal History should be known, giving the temperature changes in the history.

Then when the time comes, with the primary migration, oil travels to the Reservoir Rock. It is

collected here and it is usually the final place where the oil can be extracted. They are usually

limestones, dolomites or sandstones, but the rocks having enough fractures can also act as

reservoirs. (Fig 4). However, to keep it there safe and sound, there should be a Trap. This is

for both keeping the oil inside the reservoir rock and the other material out. Thus these can be

shales, marls or limestones with clay. There are many geological structures where a trap can

happen, these include mainly anticlines, folds, faults.

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Figure 4: Basalt with large cracks can act as reservoir.

2.3.2. Traps As described above, trap is the last place where the oil travels and settles. (Fig 5-6-7).

We have been told that by its nature, on an inclined surface, oil moves upward while the water

flows down. According to this statement the movement of oil inside the traps are recognized

and predicted.

Anticlines are generally the best traps around the world. Although faults are act as traps this

does not mean that all faults are traps. They need to have the proper conditions to do that,

such as being inside sands and shales and structure wise there are a several cases for a true

trap formed by faults.

Figure 5: Anticline trap.

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Figure 6: Fault Trap

Figure 7: Unconformity Trap

Reservoir Geology is an additional department working on the reservoirs. They determine the

reservoir conditions and its motion. Such conditions are the pressure and temperature. For the

remaining information, amount of water and oil, conditions enabling the traps and migration,

and properties the fluids inside reservoir are considered.

Reservoir Rocks are classified into three groups which are Clastic Rocks, Carbonate Rocks

and the others. Clastic ones are mainly sandstones, conglomerates, siltstones and shales with

fissures. Carbonate ones are limestone and dolomites and they are the main reservoir rocks

around the world. The others group includes the metamorphic and igneous rocks having fractures so that they can carry such fluids.

Reservoirs are studied because it is needed to foresee the performance of the reserve.

Reservoir Simulation is a technique that enables this application. A model is formed for a

reservoir and further studies are applied onto it. It is based on differential equations, and they

work with the limits of the basin itself. When this is applied as computer based, the reservoir

is split into certain areas and the equations are solved for each part one by one. Having steady

boundaries, some reservoirs dynamics can be calculated even without the help of a computer. But however the solution is applied needed conditions for a reservoir simulation does not

change: Boundaries, Starting Conditions and Equations.

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3. EXPLORATION

This section will be explaining the ways of searching the oil.

It is clear that oil needs to be taken out, but first engineers need to find the exact places. To be

able to do this, places having the proper sedimentary basins, their rock types, formation

origins, ages and structures should be determined at first. Of course they are making guesses

based on some information collected by different ways. The two important ones are field

work and geophysics. With the help of them together, it becomes really easy to detect the

sources, reservoirs, caps and eventually the oil.

3.1. Field Work For the field work, the history and a map of the area is necessary. At TPAO, these information

are present, however, on our week of field work, one of the missions was to renew the

geological maps. To be able to see the recent changes on the area, many parts of the land is

checked again, and the new information is added.

As a part of the Summer Practice, TPAO sent interns to their District Managements for the

field work. Therefore I have been to Adyaman District Management.

As we discover the different formations and their relations with each other (Fig 8-9), all the

information that has been given the day before we go, which was a summary of the

stratigrapghy of South Eastern Anatolia and the Autochthonous Lithostratigraphic Units of

Southeast Turkey (See Appendix B) diagram, have started to settle down.

Figure 8: Section example 1- Adyaman.

As told, the main formations that are usually seen around Adyaman, from youngest to oldest, were elmo, Midyat Group, Germav, Besni, Terbzek, Kastel, Sayndere, Karaboaz, Karababa, Derdere, Sabunsuyu, and Areban. In the area; Karaboaz and Karababa-A are source rocks; Karababa-C and Derdere are reservoirs; Kastel and Sayndere are cap rocks. elmo is a Miocene aged mixed layer, containing pebbles, sands, marls, silts and carbonate rocks, and it is from a continental environment. Midyat group includes mainly the Eocene

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aged Hoya formation, which is a limestone and dolomite layer, including fossils, accordingly

from a carbonate platform environment. Germav, marls, silts and sands, Besni, fosilliferous

limestone, Terbzek, conglomerates, and Kastel, sands, silts and marls, are included in the rnak Group aged mostly Maastrichtian and Paleocene.

Figure 9: Section example 2 Adyaman.

These four are oceanic deposits. Sayndere is a Campanian aged silty limestone, and from the same group Karaboaz is also a limestone with fossils. Karababa, separated as A, B, C itself, Derdere, Sabunsuyu and Areban are from the Mardin group, aged early Cretaceous in general,

are limestones with changing fossil ingredients and dolomites.

As these also indicates, Adyaman is a unique place having had various environments in its history, such as deep ocean, continental rise and shelf, shore, and terrestrial.

Before start searching for a place to find oil, it was crucial to know these. From that point we

started examining them with the engineers working there. The controller at the camp was

Remzi Aksu. Alper Durukan, Frat Sren and Ali lmez were the other geology and geophysics engineers who were accompanying us. While our stay, they were working on

several different jobs. One was to show geophysicists a couple of places for further

information, of which we also took advantage, for they told some geological details one by

one with diagrams. Another was to renew old sheets, and for that we spent time travelling and

finding outcrops to note on the maps. On the way, we were told about the strike, dip, and dip

directions of the beds and how to draw cross-sections by just viewing them as we go. We

learned how to measure strike, dip, and dip directions with a compass. (Fig 10). We used

Brunton Compass for the process.

For taking different measurements with the compass we used almost each side of the device.

For measuring strike we made sure that one of the bottom edges of the device is on the

bedding plane as we try to fix it to the horizontal, then noted the value it points. For

measuring dip and dip direction; western side of the compass is justified vertically and

perpendicular to the strike. Then we turn the device until the swing in the compass reaches a

balance. The dip is read from the indicator showing 60-0-60.

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Figure 10: Finding strike.

And another job was to fix a mistake, done before when the former maps were being

prepared. Basically, it is newly discovered that, where the limestone bed Hoya is indicated on

the sheets, there should be another similar limestone bed, which is Frat. Our work was to find the places where Hoya and Frat outcrops and to distinguish them by using the fossils they contain.

Along these objectives, I and my intern friends also tried to name rocks and minerals around,

and to find the correct environments. With the help of the engineers working with us, we also

collected some fossils. (Fig 11-12). We have been informed about their names and the ages.

These include Loftusia, Rudists, Graptolites, Nummulites, Echinid, Nerinea, and Orbitolides.

Figure 11: A Nerinea, on the left, and fossils found at the field work, on the right.

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Figure 12: Graptolites.

The importance of the V rule was continuously emphasized. Also including the special

circumstances, point of the V shape of the structure shows the upper formations. To

understand it clearly we have been shown some live examples on the topography.

Figure 13: Topographic cross-section Adyaman.

One of the places we had to apply to the map was an ancient turbidity site. Conglomerates

with transitive sandstones and sands were examined. (Fig 13).These beds were tracked for

some time to check the continuity, and small scale faults were discovered as we go.

On the way to at Village, 1589m, ophiolites and many other outcrops (Fig 14), indicating the ancient oceanic crust, were examined. Changing of the rock types as we change elevation

was observed. Serizitization, chloritization and serpentinization, with talk formation, were

observed on them.

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Figure 14: Topographic cross-section at Village

At one stop a mica schist outcrop was examined. Through the top, shale outcrops were found.

The flaky form of them was indicating that they were in the first stages of metamorphism.

This could also be meaning that they had lost their petrol.

On the way back, when another road was used, they stopped at the North of Karaku to show us a clear anticline, which was a part of the Cendere Flower Structure (Fig 15). We learned

that a flower structure forms by the forces applied on the beds as a result of faults,

consequently appearing like a flower.

Figure 15: Cendere Flower Structure from Karaku.

The camp leaders found out that there has been a seepage spotted at the outbacks of Besni,

thus one day was spent trying to find the area, and to examine the rocks that have been

causing the seepage. (Fig 16).

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Figure 16: Oil seepage.

Having found the seepage after climbing up and down for some time, we discovered that the

formations there, the ones that should be acting as reservoirs, does not contain enough pores,

so the oil is not kept but thrown out of the system, and when losing its volatile substances

they look like black crystals on the rocks. (Fig 17)

Figure 17: Crystallized oil.

We saw one oil well ambayat-1, however it is forbidden to give information about it. The important thing here was the fact that, thanks to the Bozova Fault, lifting Sayndere and Karaboaz formations up, companies are now able to gather oil from these layers.

3.2. Potential Oil Bearing Rocks At the end of a field work, with the collected samples, rocks potentials to become source rocks can be deciphered by some tests.

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3.2.1. TOC Analysis The amount of organic substances inside the sedimentary rocks is expressed by the Total

Organic Carbon. In case of having low values from this analysis, tests would no longer carry

out. To be a potential source, there are certain TOC values for different kinds of rocks, e.g. %

0.5 for shales, %3 for limestones. In case of having the adequate values, other tests are

applied.

3.2.2. Pyrolysis Analysis This test is applied by heating the samples, for some certain results; S1, S2 and Tmax. S1

shows the loose hydrocarbons inside the rock, S2 shows the hydrocarbons ejected with the

decaying kerogens. Tmax is the temperature value taken from the S2 measurement.

According to the results, zones labelled mature are not used, for it means that the hydrocarbons are gone.

3.2.3. Vitrinite Reflectance Analysis Vitrinites come from the plants, and by using their shiny appearances this test is applied.

Their reflecting properties change as the rocks depth changes. For carbonate rocks mostly include animal remnants, they do not bear vitrinites, thus this analysis is not usually applied

on them.

3.2.4. SCI (Spor Colour Index) Analysis The idea is that spores and pollens have change in their colours under different temperatures.

Accordingly, while their colour is normally yellowish, they become orange, red, brown or

black with increasing temperatures.

But, of course to make a balanced deduction all these test have to be considered together.

As I have observed on these fieldworks, any detail is important; however, what can be seen on

the surface is limited. This is where the geophysics comes to help.

For a detailed work of underground structures, geophysics provides a good help.

3.3. Geophysics When all the information taken from the field work and the seismic maps are combined,

geological engineers decide on where to give a spot for drilling.

Now that the oil has been spotted, it is time to take it out.

Without the geophysics help it cannot be counted as everything is known about the area merely with field work.

There are mainly three methods that are really helpful: Gravity, Magnetic and Seismic.

3.3.1. Gravity Method It depends on the law of gravitation and its purpose is to determine the distribution of the

masses underground and the anomalies which they may cause on the gravitational field of the

Earth. Because of the structural shape differences at various parts of the world the

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acceleration values are also differ. These changes, which can be caused by the rotation of the

Earth, latitude, height, topography or geological properties, can be spotted by the gravity

method. Especially with this method, it is highly possible to detect the salt domes, having low

densities, and reefs, having higher densities, compared to their domains.

3.3.2. Magnetic Method It aims to differentiate the rocks according to their magnetic properties. This method can be

applied from land, sea or air. At the oil researches the magnetic field of a specific field is

measured. The changes that may be encountered are generally the resulting effects of two

things: changes in the magnetic field of the earth and the rocks volume and the magnetic sensibilities. At the oil researches, magnetic or metamorphic rocks, rich in terms of

ferromagnesian minerals, are the main sources of the anomalies reached by the magnetic

method, for the sedimentary rocks magnetic susceptibilities are low, thus they do not show any obvious anomalies on the maps.

3.3.3. Seismic Method It is the most helpful but the most expensive one among all three. This method helps to create

a map of the older formations with collecting the reflected waves from the formation contacts.

The waves are created by a hit to the ground or by explosions. Geophones are the devices

collecting the waves from the ground level, and they transfer them as electrical impulses. The

important thing recorded here is the time covering the round trip of a wave.

Before completing graphs all the outside noises are cleaned.

The differences of the round trip times are caused by density, porosity and saturation of the

rocks, and they vary in all rocks. However, ice and salt structures can sometimes show same

velocities with volcanic rocks, thus their graphs can be similar and easily be mistaken with

each other. In such cases the engineers interpreting them should be careful.

Continuous lines on the seismic sections mean bedding structures. If they are not clearly seen

those areas can be interpreted as igneous or metamorphic rocks, turbidites and salts. (See

Appendix C for the section).

3.3.4. Seismic Stratigraphy Interpreting the seismic stratigraphic sections is based on the examination of the combination

of the reflections and their relations with each other. Reflections are the black and white

stripes and shapes showing the underground formation structures. They are formed by the

bedding planes where the velocities and density contrasts are measured. Interpreting includes

facies analyses. The attenuation of the reflections is especially examined to find their causes.

It is also important to state the conditions of the reflections, such as parallel or complex.

The basic laws of the stratigraphy are used in the interpretation, this way it is easier to

determine the environmental conditions and the sediments at those sites.

A warning should be given about the scales of these sections. As all other maps and cross-

sections they are also scaled and this is very important to keep this in mind when interpreting,

for only two reflection lines can correspond to 60m.

All these work is done properly, however there is a huge element that cannot be hold

separately from any of it, Maps.

3.4. Geodesy and Maps That is how we find our way around, thus one of the basic equipment of a geologist. Everyone

must have seen or used a map in their lifetime; however we need more than an acquaintance.

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Thus we have been told about the Geodesy, which is the science of describing the earth, and it

works with some basic assumptions.

The shape of the earth is accepted as geoidal. It should be though as the sea surface continuing all around the world, leaving continents above.

Datum is an important system for this science. It is again a baseline, used for describing any

point on the earth with horizontal and vertical coordinates. It again characterizes the shape

and the size of the earth, but is different from the geoidal shape of the earth.

There are several of them used by various continents, such as WGS Datum, the one Turkey

uses (WGS-84), European Datum International, North American Datum Clarke 1866, etc. To

avoid coordinate deviations same datum should be used for different mapping procedures.

Geographic Coordinate System (GCS) is what have been used to define a coordinate system

to the earth. According to this, earth has 180 latitudes and 360 longitudes, the prime parallel

line is equator and the prime meridian is the one that passes Greenwich, London.

There are four meridians on which Turkey is located. 27o- 33

o 39o 45o. (Fig18).

Figure 18: Meridian slices where Turkey is located.

Because the measurement is based on degrees, minutes and seconds, they are also shown like

that on the sheets. Black and white continuous stripes on the sides of the sheets indicate

minutes. They have certain lengths according to the sheet, and each indicates 1minute. By

measuring their lengths it is easy to figure out the half minutes.

Scaling is another important information about maps, however for we know many things

about scaling now I just wanted to give a drawing (Fig 19) showing the relativity of the

minute system.

Figure 19: Minute sizes of sheets.

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4. DRILLING At this point, after all the work has been done to find an exact place for a well, the physical

work begins.

Drilling is done for the production, although it can be used for searching purposes only.

According to the given place for a well, continental or oceanic, there are certain similar ways

to extract the oil successfully. There are both onshore and offshore rigs. They do not have big

differences in the sense of equipment.

Onshore rigs differ for their capacity to reach different depths, and respectively they would

have proper heights. However, the offshore ones have varying designs according to the depth

they are working. There are five main offshore rig types; Barge, Jack-Up, Fixed Platform,

Semi-Submersible and Drill Ship. (Fig 20).

Figure 20: On land and at sea these rig are used for drilling.

Barge is used in stagnant waters like marshes and lakes. Jack-Ups are used at depths up to

150m. Fixed platforms are used at depths up to 305m. Semi-Submersible rigs can be used at

depths between 150-600m, and lastly from 600m Drill Ships fit for the job.

Wellsite Geologists are the main people working at these places and they are responsible for

basically everything going on at the rig. They track the changes inside the well and

hydrocarbon evidences, they control the mud data, the providing of borehole samples and

their tests and reports.

4.1. Drilling Mud Before talking about anything else, Drilling Mud should be introduced. This was one of the

first things we have been told at the introduction of the Exploration Department.

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The drilling mud, prepared from bentonite, is used during drilling, circulating inside the well.

It is very useful in various ways. With the pressure it provides to the wall of the well prevents

the corruption, removes all the excavations, prevents overheating and protects drill pipes.

The mud has a certain recipe, and by checking its normal values, changes in the system or any

problem can be detected.

The most important duty of the mud is to balance the pressure of formations. In some cases

its hydrostatic pressure can be greater or less than the formation pressure, and this can cause

inward or outward flows. Results that may occur under these circumstances will be described

below.

One of the important actions is the fact that, with its nonstop movement, mud lifts all the

drilled goods upwards. The collected samples are saved according to their properties and

formation data as Mud Logging.

Of course everything does not work in order all the time. If the controls are not done properly,

some problems may occur. Engineers and mud logger are always on the job, checking the

material coming from the well by the drilling mud. There are some situations that can mean

important things to these people about the drilling process.

-During the drilling gases or liquids can slip into the mud, if there is a difference of

hydrostatic pressure between the mud and the drilled formations gas/liquid amount. For the normal mixture of the mud is known, the amount of added gas can be easily calculated. And

for the liquids, the solution is more or less the same. Of course under these conditions, mud

undergoes some physical and chemical changes, and needs to be renewed.

-On the other hand, it is also possible to lose some of the mud into the cracks on the

formations, such as faults or may be some porous formations. These leakages happen because

of the hydrostatic pressure differences. Such cracks could be containing water, thus their

hydrostatic pressures are less than that of the wells. Thus, until the pressures are balanced,

mud goes into those cracks. By adding extra mud into the system, this problem can be

checked, however to avoid the extraordinary situations, this problems should be diagnosed as

early as possible. Having lost any amount of mud into the formations, these leakages are

always costly for the companies.

They cause a waste of time, mud and the geological data, as it may be carrying many

informative samples to the griddles.

The velocity of the mud moving inside the well is important, for it moves the samples up.

Therefore mud must be moving fast, and pumps are used to provide this. They supply high

pressure with pistons and keep the mud cycle working.

4.2. Sampling Samples are collected along the drilling process. For their densities are larger than that of

drilling mud, with effect of gravity, they move slower than the mud, mostly at the bottom.

The engineer should make observations considering this, for it means they are not showing

the formations the drill is cutting at the moment, they must be from a couple of meters above.

Some part of the collected samples is archived, another part is kept until the end of the drilling

process and another part is taken away for laboratory examination. This part is very important

in cases of entering the reservoir and passing the formation contacts. Washed and put in a

Petri dish with some water (Fig 21), to prevent reflections, the sample is analysed according

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to its, lithology, colour, hardness, porosity, minerals, fossils, grain size, cement and

hydrocarbons.

Figure 21: Samples are put in a Petri dish with water.

There is always the possibility of not being able to see the hydrocarbons on a fresh sample. In

this case the samples are treated with CCl4, sometimes after being crashed, and viewed by

flourbox. Borehole samples are an important part of the drilling. They are taken out as whole cylinders.

The process is used for more detailed information about the stratigraphy and the

hydrocarbons; and because the samples are larger, to work on the necessary data of porosity,

permeability, saturation, fossil content, and chemicals gets easier.

According to the types of the wells, searching, retaining, or production, samples are collected

at different levels. It is usually every 2m at searching and retaining wells and 10m (2m around

the target formation) at production wells.

4.3. DST (Drill Stem Test) (Fig 22)

Being an important stage of drilling, DST is applied in an open well to see what fills the

formations which show indications of hydrocarbons. The basic system on this test is to

eliminate the extra pressures and to make the rock simply cast its content with its own

pressure. At this test it is also possible to learn the reservoir pressure and its limits, if taken

any oil, its API and viscosity,

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Figure 22: Basic DST format.

4.3.1. DST Tools Drill stem test is made with its own tools. Packer is the swelling plastic which isolates the

aimed formation from the top and the bottom. Valve controls the flowing, when opened it lets

the content of the formation flow into the tool kit by another piece, hollow rod, which filters

the substance.

4.3.2. The Test For clear results, the well must be in a good state. Corruptions on the wall or the places where

the well becomes narrow or broad can cause problems. Because of these reasons, the well is

cleaned in a way by Short-Trip and circulation before the test.

Short-Trip is moving of the drilling tool kit out and in again for one time. It is used to see if

the well is clean; and circulation is again to clean the well, but at this part the set is not moved

instead, mud is pumped and let circulate for some time. This helps to collect the remaining

dirt and take it out of the well.

DSTs generally have two periods, each including one flow and one shut.

As tools are lowered into the well, Recorder books the hydrostatic pressure changes. When

the tools reach the bottom with an additional weight the packers are set. In a several minutes

the content of the formation starts flowing into the hollow rod. This is the first flow. This is

the part when usually the flowing substance is actually the mud and other fluids that entered

into the formation during drilling. As the material goes into the tools it squeezes the air inside,

consequently the air goes upward. This is recorded at the surface, when the air comes out

blowing, as the pace of the flow. According to this pace the engineer decides on the flow

time, usually 10-15 minutes, and then the first shutting starts. This is the part when the tool

series are kept spinning for some time for making the system retain its normal pressures.

After this, the second period starts with the second flow. This time the original content flows

in and after a certain amount of time the second shutting is starts. At the end packers quit the

set position and the tools are detached.

4.3.3. DST Chart (Fig 23). Along this process a chart is prepared with respect to the pressure values.

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Figure 23: DST Chart.

IHMP: Initial Hydrostatic Mud Pressure

IFP: Initial Flow Pressure

FFP: Final Flow Pressure

ISIP: Initial Shut-In Pressure

FSIP: Final Shut-In Pressure

FHMP: Final Hydrostatic Mud Pressure

This chart shows the pressure change through time of two periods. The line between A and B

is the effect of the mud pressure on the lowered DST tools. Point B is where the IHMP is

measured, indicating the mud pressure of the target depth. Point C shows the pressure value of

the mud when it got squeezed by the setting packer. At D, first flow starts, thus the value

gives IFP. Between D and E, first flow is seen as the fluids come out of the formation to the

set. Point E shows the FFP of the first flow, then the first shut-in starts. Through the point F,

system tries to get back to a static pressure, then at that point the first shut-in ends and ISIP is

taken. Second period is the same. Between F and G it is the second flow and at G, IFP2 is

taken. G to H is where the flow happens and at H we take FFP2. The packers are unset after

the H-I shut-in and reading FSIP. Point J is where the FHMP is recorded. The line between J

and K is exactly the opposite of A-B where the tools are being lifted up.

4.4. Casing and Cementing During the drilling process, some metal pipes, called casing, are placed into the well and

cemented. This way the walls cannot collapse, formations are not affected by the drilling mud,

the water cannot flow into the well from other formations, the pressure stays balanced and the

drilling tools are easily put in.

Originally they are divided into 3 types: Surface Casing, Intermediate Casing and Production

casing. Engineers at TPAO regard only the outer diameters of casing pipes. As the drilling

continues the diameter decreases. Generally, according to the depth, 3 different casing pipes

are used in the wells around Adyaman, 13-3/8 to 7 or at deep wells to 5. After getting placed into the well the pipes are cemented to the walls of the well, therefore

filled with cement completely or up to some certain level.

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4.5. Perforation Perforation is basically the work of creating holes on the pipes that have been cemented. This

is done to create ways for the content of a formation to flow. (Fig 24). The common way to do

it is to place bullets at the site of a targeted formation, and fire them from the surface.

Figure 24: An oil bubble getting out of the perforation crack.

Sometimes, acid is injected into the formations to clear the pores and to increase the

production.

4.6. Swabbing This is usually the last work can be done on a well getting prepared to start production. It aims

to reduce the hydrostatic pressure of the fluid inside well and cause a fresh flow into the well

from the formation. This would continue until a convenient flow rate is reached or the well is

dried. For the first case the production starts and for the latter the well is either left or

perforation is applied again.

4.7. Log Logging includes the recording of the physical data of the cut formations at the well site. It

can be applied during the drilling or when the drilling of the well section is completed.

Log is used to get many information; to determine the lithology, porosity, permeability and

hydrocarbon potential of the formations; wells diameter; thickness, depth, dip, velocity and temperature of the formations and correlate them; and pressures. It is usually done before the

casing process, by lowering the necessary devices to the target depths.

After getting the log results the responsible engineer checks the formation contacts. (Fig).This

was the application we also did at TPAO by using Gamma Ray and Sonic Logs together. (Fig

25). From the changes in the lines movement it is easy to detect the changes, and then a certain depth is given according to the numbers on the log that shows the change. Another

important data is the porosity, oil-water contact, and its saturation and to get them SP-GR,

Sonic and Resistivity Logs are used.

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Figure 25: A Log sample.

Here are explanations for some of the log types.

SP measures the conductivity of the water inside the formation. Results look as a straight line

where the shales are and that is called shale baseline. GR (Gamma Ray Log) measures the radioactivity of the formation. For the radioactive

elements are usually concentrated inside shales and clays, the amount of shale and clay inside

a formation is what GR Log implies.

Resistivity Logs are also important to detect porosity in a formation. As the name indicates, it

measures the resistivity of the formations. Hydrocarbons do not conduct electricity, but water

does, and when it is salty it does even better. Because of these properties Resistivity Log

helps to differentiate water and oil zones.

BHC (Sonic) Log is based on the sound wave motion. Interval Transit Time, which is the time of a sound wave passing a certain length of formations, is dependent on the lithology and

porosity. And if the lithology is known, it is easy to find the porosity by using this method.

Density Log is also used for finding porosity. Compensated Density Log (CDL) measures the

electron density and Litho Density Log (LDL) measures the photo electricity of the

formations.

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4.8. Check Shot This application is done usually at the end of the drilling. Again it is used to measure the

seismic travel time and the P-wave velocity of the formations from the surface, but it is for the

well. Geophones are lowered into the well, according to the depth of the target formation. For

the system needs an energy source to create waves an airgun is used, and it is placed at the

surface inside a 4*4*4 pit. When the airgun is fired, it sends the waves and the geophones

record them from inside the well. (Fig 26).

The results obtained from this application can be used in different areas. Geophysicists

working at TPAO was correcting and re-forming their maps for certain formations by

comparing them to the seismic stratigraphy maps and log results, by using some computer

programs, which are also helpful to create the 3D maps of the area by using all these

information.

Figure 26: Check shot.

4.9. Well Classification A classification is made about the wells, according to what have been acquired from one.

The results can be oil, gas, oil or gas indication, water; however they might also become dry

or just left because of some technical reasons.

It is also known that there is a globally known classification of wells by American

Association of Petroleum Geologists and American Petroleum Institute. Accordingly they go

like this;

New Field Wildcat,

New Pool (Pay) Wildcat,

Deeper Pool (Pay) Test Well,

Shallower Pool (Pay) Test Well,

Outpost or Extension Test Well,

Development Well,

Service Well.

Lastly, if a well has the conditions >150C and >10.000psi it is classified as High Temperature High Pressure HPHT Well.

4.10. Recording the Well Data The engineers responsible for tracking the drilling process are supposed to add every new data

coming from the wells to a form. Such data can be drilling and borehole samples, test results,

contact points, well diameters, casing information, drilling mud observations, etc.

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The forms we filled usually had two parts. First one included the name and location of the

well, coordinates, starting and finishing dates, names of people working at the site, type of the

drilling machine and so on. But the second part included all the information from the well

about test results, samples, depth, contacts, diameters, casing and log.

All these information were coming from the drilling sites, as well as the laboratories working

on the samples.

Every morning, the engineers responsible for certain wells from three sites, collect the

necessary information from the common system where all these data are updated daily, and

meet to inform others, to decide whether they should carry on with the preceding steps or just

leave the well.

5. CONCLUSION As I mentioned at the introduction, I was not really into this area. However, spending two

weeks there was enough to see the benefits. I think I was a bit lucky to have been to the field

work, to the area that I actually be dealing with, Adyaman, on the first week, a huge motivational source it was, although I missed three days of lecture/seminars. I always thought

oil exploration as metal; pipes, rigs, pump. However this summer practice showed me that

there is also a field based part of it, and if you are lucky enough.

When we were back, already met the host engineers, I knew many things about the

formations, and the places they have been referring to. From that on it got easier. Observing

their work was most helpful to imagine yourself in those positions and also people working

around me, both at the field and at the head office, were very friendly. I have been introduced

to their friends from other departments. They talked to us about the realities of the work life,

and were always patient with our questions. When seminars ended, we already knew nearly

all the information, needed to understand what is going on around, so the last three weeks

were also exciting. In the mornings I studied with my engineer for the daily meeting, by

adding the updated information to the well files, and in the afternoons, although this was not

daily according to the well data in need, practiced log readings on the wells I know. By this I mean knowing their contact points, depths and others. We used daytime to revise, to clear

notebook information and to share knowledge. I must add that, the whole of this act was

really helpful about me learning the Turkish meanings of some geological words, although I

did not understand many things at the first week. Fortunately I had a friend with powerful

explanation ability and by the descriptions I had the chance to teach her the English names

while I am learning the Turkish ones. At the end I thought the only problem was my not

being able to identify fossils, for both at the field and behind the desk, it was necessary to

know at least a couple of them to find out more about the formations. However it cost me six

weeks of my vacation, it was a lovely experience in the end. But, I still do not want to be

working in this area if I will be sitting inside that tall building or near a tall rig.

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REFERENCES (n.d.). Retrieved from Trkiye Petrolleri A.O.:

http://www.tpao.gov.tr/v1.4/index.php?option=com_section&task=view&id=1

(2008). Retrieved from Trkiye Petrolleri A.O.: http://www.tpao.gov.tr/v1.4/condocs/tpao_yillikrapor09.pdf

Technical information and the figures, besides drawn ones and field photos, are summarised

from the presentations prepared by TPAO for the summer practice seminars which can be

confirmed by A. Cokun Namolu, mer Aksu, Sait Yksel, Taner Ta, Mertkan Aka, M. Akif Snnetiolu, and Blent Sadiolu.

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APPENDICES

APPENDIX A: Organizational Structure of TPAO

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APPENDIX B: South Eastern Anatolia and the Autochthonous Lithostratigraphic Units of

Southeast Turkey

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APPENDIX C: Seismic Stratigraphic Section.