Saudi Aramco - Operational Geology Manual

I N D E X _______________________________________________________________

Section S u b j e c t Page _______________________________________________________________

Intorduction 4 I Geological Overview 7

1. Hofuf, Dam, and Hadrukh Formations 7 2. Dammam Formation 10 3. Rus Formation 12 4. Umm Er Radhuma Formation 12 5. Aruma Formation 13 6. Wasia Formation 14 7. Shu’aiba Formation 16 8. Biyadh Formation 16 9. Buwaib Formation 17 10. Mid-Thamama Formation 17 11. Yamama Formation 17 12. Sulaiy Formation 17 13. Hith Formation 18 14. Arab Formation 18 15. Jubaila Formation 18 16. Hanifa Formation 20 17. Tuwaiq Mountain Formation 21 18. Dhruma Formation 23 19. Marrat Formation 24 20. Minjur Formation 25 21. Jilh Formation 25 22. Sudair Formation 26 23. Khuff Formation 27 24. Unayzah Formation 27 25. Berwath Formation 31 26. Jubah Formation 32 27. Jauf Formation 32 28. Tawil Formation 34 29. Qalibah Formation 35 30. Sarah Formation 36 31. Zarqa Formation 37 32. Qasim Formation 38 33. Saq Formation 38 34. Burj Formation 42 35. Siq Formation 42 36. Basement 42

II Casing Points 45

1. Rus Formation Casing Point (30” Casing) 45 2. Aruma Formation Casing Point (24” Casing) 51 3. Ahmadi Member Casing Point (24” CSG) 56 4. Biyadh Formation Casing Point (18 5/8” CSG) 63 5. Mid-Thamama Casing Point (18 5/8” CSG) 67 6. Hith Casing Point (18 5/8” CSG, 13 3/8” CSG) 71 7. Arab-D Casing Point (18 5/8” CSG, 13 3/8” CSG) 75 8. Jilh Formation Casing Point (18 5/8” CSG) 82 9. Khuff Formation Casing Point 87

III Wellsite Core Handling 96

1. Introduction 96 2. Conventional-Core Handling Procedures 97 3. Preserved-Core Handling Procedures 102 4. Exploration wells’ Core Handling Procedures 103 5. Safety Precautions 104

IV Drilling Mud Effects on Cuttings Examinations 112

1. Drilling Mud additives 112

2. Natural Fluorescence: UV- Light 115

V General Wellsite Requirements 117

4

INTRODUCTION

The main objective of this manual is to provide a quick reference of wellsite field related

geological issues to new geologist and trainees. It is also intended to share the knowledge

and experiences that are common to Wellsite Geology with other disciplines in Area

Exploration, Reservoir Characterizations, Reservoir Engineering and Drilling.

The manual provides an overview of the stratigraphy of the Arabian Peninsula while

focusing on the most common lithological description on formation and potential

reservoir cuttings within Saudi Aramco’s operating areas. At the same time, it relates

trends in the rate of penetration (ROP) to picking of formation tops. This data is essential

to reduce probable hole problems and to ensure safe picking of casing points. The manual

also provides an overview of pitfalls of cuttings description and hydrocarbon

fluorescence evaluation while dealing with different types of drilling mud. The manual

also covers and provides detail instructions on wellsite core handling procedures while

alerting new geologists to a number of important safety issues.

SECTION I

GEOLOGICAL OVERVIEW

SECTION I: Geological Overview

7

SECTION I: GEOLOGICAL OVERVIEW:

TERTIARY

Miocene and Pliocene

1. Hofuf, Dam, and Hadrukh: These formations are usually exposed at the surface or start below the weathered

surface. It can only be found in some localized areas in the eastern region of Saudi

Arabia. It contains layers of limestone, chart, marl, sandstone, and shale beds.

Refer to (Figures 1.1, 1.2, 1.3 and 1.4) for a more detailed lithology, facies, and

fossils descriptions. Note: fossils are extremely difficult to see in the cuttings

samples.

The quality of cutting samples from these formations is usually poor. Very few

strip logs show the lithology description of this section. Furthermore, loss of

circulation is possible in this section.

Rate of penetration (ROP) has a random nature and differs from one place to

another.

Figure 1.1: Hofuf formation type section (Source: Powers et al. Geology of the Arab. Pen.)


8

Figure 1.2: Dam Formation type section (Source: Powers et al. Geology of the Arab. Pen.)

Figure 1.3: Hadrukh Formation type section (Source: Powers et al. Geology of the Arab. Pen.)


9

Figure 1.4: Hofuf, Dam, Hadrukh, Dammam, and Rus Formation type log in Al Hassa area

(Source: BRGM, 1977. Al-Hassa Development Project: ground water resources study and

management program.)


10

Eocene

2. Dammam Formation:

Dammam formation consists of five members: (top to bottom)

1. Alat 2. Khobar 3. Alveolina 4. Saila 5. Midra

Loss of circulation is possible and, therefore, the lithology descriptions are found in

few strip logs (Figures 1.4, and 1.5).

Alat Limestone:

Alat member is composed of two main sections:

1. Light colored chalky, dolomitic limestone and porous limestone.

2. Dolomitic fine-grained orange marl.

The pre-Neogene unconformity is picked on the appearance of the non-sandy

limestone.

Khobar Member:

It is composed of light brown, partially recrystallized, tight, nummulitic limestone

at the top, followed by a yellowish-brown, soft, marly limestone. At the bottom of

the Khobar member is another tight limestone and marl layer. Loss of circulation is

possible in soft limestone layer.

Alveolina Member:

This member is composed of Light-tan, partially recrystallized limestone. The

Alveolina member also contains gray and blue-gray, pyretic, shale.

Saila Shale Member:

Saila is a dark-brownish-yellow, subfissile clay-shale, underlain by gray limestone.

Saila contains also gray and blue marl.

Midra:

The top of Midra is picked by the appearance of the yellow-brown earthy clay

shale below the limestone of the Saila member.


11

Midra gives the drilling fluid a sudden distinctive brown color after the blue clay of

the overlaying Alveolina zone.

Figure 1.5: Type log from type localities and subsurface (Source: BRGM, 1977. Al-Hassa

Development Project: ground water resources study and management program.)


12

3. Rus formation:

Rus formation is a regular casing point. For picking the Rus formation, refer to the

casing-points section in this manual, (SECTION-II).

Lower Eocene-Late Paleocene

4. Umm Er Radhuma (UER) Formation:

The UER is a major aquifer in Saudi Arabia. It is mainly consists of limestone

and/or dolomite. Thin beds of shale and marl are present, especially toward the

lower part of the formation.

Loss of circulation is highly possible in the UER because of the soft nature of its

carbonates.

ROP tends to be relatively fast in the UER. ROP makes it easier to distinguish the

top of UER from the RUS limestone, in the Ghawar area.


13

CRETACEOUS

Upper Cretaceous

5. Aruma Formation:

Aruma is composed of a thin layer of shale at the top, followed by a thick section

of limestone and/ or dolomite that is interbedded with shale and marl layers. The

shale may contain lignite or pyrite. (Figure 1.6)

ROP in the Aruma limestone is relatively slower than that in the UER. Loss of

circulation may occur in the upper part of the Aruma formation.

Aruma contains an oil bearing reservoir. It has produced oil from the Lawah field

and other fields, especially off-shore wells (Marjan carbonate Reservoir)

Lower Aruma shale:

Within the Aruma formation is the Lower Aruma shale (LAS). It is usually green,

gray, fissile, partially calcareous shale and varying to marl and argillaceous

limestone.

ROP slows down relative to the upper limestone section.

LAS is a common casing point. Refer to the casing points section in this manual for

more details on picking the LAS top.


14

Figure 1.6: Aruma Formation type section. (Source: Powers et al. Geology of the Arab. Pen.)

6. Wasia Formation:

Wasia formation consists of seven members: (top to bottom)

1. Mishrif 2. Rumaila 3. Ahmadi 4. Wara 5. Mauddud

6. Safaniya 7. Khafji

Wasia includes several loss of circulation zones.


15

Wasia-Aruma Unconformity: this unconformity can be identified by shale and

ironstone appearance. It is also easier to identify when Wasia starts with the sand

sections of Wara or Safania member, which exhibit fast ROP.

6.1. Mishrif Member:

Mishrif member composed mainly of soft limestone that is interbedded by thin

shale stringers. Mishrif is a gas-oil reservoir in some of the off-shore wells.

6.2. Rumila Member:

Generally, the Rumila member is composed mainly of multi-colored shale.

However, Rumila includes a limestone gas-reservoir in some of the off-shore wells.

Praealveolina member: is composed mainly of limestone and/or dolomite. It is

interbedded by shale sections which, in turn, cause the E-shaped ROP curve, as

mentioned in the casing point section- Ahmadi casing point. Also, Praealveolina is

a probable loss of circulation zone.

This section is not a member in the published stratigraphic column used currently

in wellsite. However, Praealveolina member top has been frequently picked by

wellsite geologists as a separate formation, as can be seen from older strip logs.

6.3. Ahmadi Member:

Refer to the casing points section in this manual for Ahmadi Identification.

6.4. Wara Member:

Wara is generally consists of layers of siltstone or shale and sandstone. It is

considered to be a loss of circulation zone in many areas. Wara is an oil reservoir in

some of the off-shore wells.

6.5. Mauddud Member:

Mauddud is a highly possible loss of circulation zone with fast ROP. It consists of

different kinds of carbonates depending on the location of the well.


16

6.6. Safania Member:

Safania is mainly composed of clean sandstone and layers of shale or siltstone. In

some of the off-shore wells, Safania is a major reservoir. Safania is another loss of

circulation zone in Wasia.

6.7. Khafji Member:

Khafji is also composed of sandstone and siltstone. It is also a reservoir in the off-

shore fields.

Lower Cretaceous

7. Shu'aiba Formation:

Shu’aiba mainly consists of different types of carbonates depending on the well

location. The vast extent of Shu’aiba is porous with fast ROP. Shu’aiba is an oil

and gas reservoir in some of the off-shore wells.

In many areas Shu’aiba is a loss of circulation zone.

Shu’aiba is an oil bearing reservoir in Shybah and many off-shore fields.

8. Biyadh Formation:

Biyadh is a casing point in some wells, as described in the casing point’s section

(SECTION II).

Biyadh consists of quartz sandstone interbedded by shale and thin beds of

ironstone. In the Jubair field, Biyadh is a sandstone reservoir.

Biyadh exhibits a relatively faster ROP compared to the boundary formations. A

thin section of carbonate exists, also, in Biyadh. However, this thin section of

carbonates dominates the formation toward the off-shore fields.

The Zubair oil reservoir found in the northern fields and off-shore wells exists in

the Biyadh formation.


17

9. Buwaib Formation:

Generally, Buwaib is composed of three distinct layers: (top-bottom)

1. Argillaceous Limestone Section: multi-colored, and exhibit different levels

of dolomatization depending on the location of the well.

2. Sandstone section: exhibits poorly sorted quartz sandstone and interbedded

by siltstone in some wells. This sandstone section is an oil reservoir in some

of the northern and off-shore fields such as Rimthan field.

3. Sandy Limestone: multi-colored limestone, dolomitized in part.

10. Mid-Thamama:

Mid-Thamama is composed of hard carbonates (limestone) which exhibit a slow

ROP. Mid-Thamama does not appear on the latest stratigraphic column. However,

it is sill used frequently in the current wells’ geological programs.

11. Yamama Formation:

Yamama is mainly composed of soft carbonates (calcarnitic limestone). This

section is the Upper Ratawi reservoir which has produced oil in many fields such

as Marjan, Sharar, and Khurasania fields. At the bottom of Yamama is another

section of limestone.

12. Sulaiy Formation (lower Ratawi Reservoir):

Like Yamama, Sulaiy is mainly composed of carbonates (limestone). Dolomite is

also present with different level of dolomitization from one area to another.

Sulaiy exhibits a faster ROP due to the abundance of the soft calcarnite. In fact, the

top of Sulaiy has a distinctive drilling break that can be used as a marker when

doing well correlations.

The Lower Ratawi reservoir exists at the top part of Sulaiy. Water flow may occur

in the Sulaiy formation.


18

JURASSIC

13. Hith Formation:

Hith is predominantly composed of a thick layer of anhydrite interbedded

occasionally by thin carbonate beds (dolomite, limestone, dolomitic limestone,

calcareous dolomite). (Figure 1.10)

Manifa carbonate-reservoir, if present, exists at the top part of Hith. It has produced

oil in Abu-Hadria and Manifa fields among others.

Thin layers of salt (halite) exist in Hith anhydrite. It is difficult to find halite in the

cutting samples. However, it could easily be identified by the distinctive fast

drilling breaks. Also, the level of chloride increases significantly in the drilling

mud.

Hith is a casing point as described in the casing points section.

14. Arab Formation:

Arab formation consists of 4 members, Arab-A, B, C, D. It consists of porous

layers of soft carbonates separated by anhydrite. The porous layers contain the

Arab reservoirs and the anhydrite units seal these reservoirs. (Figures 1.7, and 1.10)

ROP slows down in the anhydrite units and speeds up in the soft carbonates.

Salt stringers occur in the Arab formation. Salt can be identified by distinctive fast

ROP breaks and an increase of chloride in the drilling mud.

15. Jubaila Formation

Jubaila is generally made of well-indurated argillaceous limestone. ROP is

distinctively slower than the overlaying Arab formation and the underling Hanifa

formation. (Figure 1.8) shows a more detailed lithology description from the

outcrop. In some areas Jubaila contains a thin oil reservoir. (Figure 1.10) shows

Jubaila Formation from a well in the Qatif area.


19

Figure 1.7: Arab Formation type section and reference section (Abqaiq-71) (Source: Powers et al.

Geology of the Arab. Pen.)


20

Figure 1.8: Jubaila Limestone reference section. (Source: Powers et al. Geology of the Arab. Pen.)

16. Hanifa Formation:

Hanifa is another carbonate formation. The top is marked by a thick bed of oolite-

pellet calcarenite. The formation is made of alternating aphanitic and calcarenitic

limestone, much of it oolitic. Argillaceous limestone units and thin beds of shale

are also present. Dolomatization has occurred in some parts of Hanifa. (Figure 1.9)

Hanifa is an oil reservoir in many areas. ROP is relatively faster than the boundary

formations.


21

Figure 1.9: Hanifa Formation reference section. (Source: Powers et al. Geology of the Arab. Pen.)

17. Tuwaiq Mountain Formation:

Generally, the Tuwaiq Mountain formation is a massive, compacted, limestone

section (mainly aphanitic limestone and calcaranitic limestone). Porous units of

limestone occur at the upper part of the formation, forming the Hadria reservoir

which has produced oil in the Fadhili, Ramlah, and Qatif fields. Also, the Upper

Fadhili oil reservoir is present at the lower part of the formation. Thin beds of shale

and marl are occasionally present in the formation. (Figure 1.10)

ROP is generally slow except in the reservoir zone.


22

Figure 1.10: Sequence stratigraphy of the Middle to Late Jurassic of the Qatif field. (Source: Plate

Sequence Stratigraphy, GeoArabia, Special Publication 2, Bahrain.)


23

18. Dhruma Formation:

Dhruma consists of: (top to bottom)

1. Upper Dhruma, which is subdivided into the Hisyan and Atash members

2. Middle Dhruma

3. Lower Dhruma which contains the Dhibi unit

18.1. Upper Dhruma: (top to bottom)

18.1-A: Hisyan member: Usually, it starts with a bed of shale, but not in all areas.

Below, beds of carbonates (limestone and/or argillaceous limestone) and shale are

alternating.

The majority of Hisyan drills relatively slower than the lower part of Tuwaiq

Mountain formation (Upper Fadhili Reservoir), above, and Atash (Lower Fadhili

Reservoir).

18.1-B: Atash member: the top is also marked by shale. Below, a thicker bed of

limestone that is interbedded by shale units. Atash limestone exhibits reservoir

quality units, such as in the Lower Fadhili Reservoir.

18.2. Middle Dhruma:

Middle Dhruma is composed mainly of limestone, containing beds of clean

calcarnite at different levels with good porosity. Sharar Reservoir and Faridah are

examples of these porous layers.

Middle Dhruma can be identified by the strong-negative drilling break after the fast

drilling in the Lower Fadhili Reservoir, if present.

18.3. Lower Dhruma:

The majority of the Lower Dhruma consists of shale, except for the Dhibi

limestone member at the upper part. Thin beds of Gypsum are present.


24

19. Marrat Formation:

The majority of Marrat is made of limestone. Anhydrite is found in various wells at

the top of Marrat. A distinctive brick red pyretic shale layer is present within the

formation. This shale section could be identified by a negative drilling break.

(Figure 1.11) shows more details of lithology.

Marrat reservoir exists in the calcaranitic limestone section at the upper part of the

formation.

Figure 1.11: Marrat Formation reference section (Source: Powers et al. Geology of the Arab. Pen.)


25

TRIASSIC

20. Minjur Formation:

Upper Minjur:

The top of Minjur is marked by the appearance of multi-colored loose sandstone

and shale. It is interbedded by layers of siltstones, claystone, and shale. Thin

ironstone stringers are found, also, within the formation.

Minjur exhibits good reservoir quality, but it is wet. However, oil has been

produced from the Minjur formation in the Jauf field.

Lower Minjur:

Sandstones are interbedded by siltstones and shale. Drilling is alternately fast (in

the sandstone) and slow (in the siltstone).

21. Jilh Formation:

The Jilh top is marked by the appearance of anhydrite and/or carbonates

(commonly oolitic limestone) after the Minjur sandstone and/or shale.

Jilh formation is divided into:

1. Upper Jilh

2. Lower Jilh

21.1. Upper Jilh Formation:

Upper Jilh can be divided into the following rock units:

• Interbedded light gray, off-white dolomite, dolomitic limestone. Shale is

abundant in this unit, which contributes to the ROP slowing down.

Anhydrite is present as well as salt stringer. These salt stringers, if present,

can be traced by the distinctive fast drilling breaks.

• Jilh Dolomite: The Jilh Dolomite rock unit is marked by the appearance of

the sucrosic (clean) dolomite or dolomitic limestone. This section has more

porosity than the overlain section. Also, shale percentage


26

decreases/disappears at the Jilh dolomite. This porous section contains the

Jilh Reservoir.

ROP increases relative to the upper section.

21.2. Lower Jilh:

Below the Jilh Dolomite is a rock unit that is marked by the increased appearance

of shale again after the Jilh Dolomite. ROP is relatively slower in this section

relative to the Jilh Dolomite. (Base Jilh Dolomite)

Base Jilh Dolomite is a common casing point, as mentioned in the casing point

section in this manual.

Like the upper Jilh, the lower Jilh is composed mainly of carbonates (dolomite,

dolomatic limestone, and limestone), anhydrite, and shale. However, the Lower Jilh

is known to be a high pressure zone. Therefore, casing is set in the Base Jilh

Dolomite to increase the mud weight to compensate for the high-pressure zone.

22. Sudair Formation:

The upper Sudair is predominantly composed of shale (mostly brick-red shale).

However, the upper Sudair exhibits reservoir quality stringers (dolomite) outside of

Saudi Arabia (Kuwait).

The lower Sudair contains layers of carbonates and anhydrite as well as shale and

siltstone. ROP is relatively slow.


27

PERMIAN

23. Khuff Formation:

Khuff is a massive interbedded limestone, dolomite, and dolomitic limestone

formation with occasional anhydrite. Shale is present especially toward the lower

part. The formation is divided into three members, Khuff-A, B, C, D anhydrite, and

Khuff-E. (Figure1.12) shows more detailed lithological description of the section.

The formation has two common casing points, as described in the casing points

section.

The Khuff formation contains three gas reservoirs (Khuff A, B, and C).

The rate of penetration varies between the reservoir zones and the less porous

sections.

PERMIAN/CARBONIFEROUS

24. Unayzah Formation:

Unayzah formation is a major clastic formation in the stratigraphic column. It has

been previously divided into three members Unayzah-A, B, C. Lately, a new

subdivision of the formation has been adopted in SAUDI ARAMCO (Figure 1.13).

However, the old classification of the formation is still widely used.

Generally, Unayzah consists of sandstone sections interbedded by siltstone and/or

shale layers. Unayzah-A is the most porous section of all Unayzah units. (Figure

1.14) shows a detailed description of the Unayzah formation from Hawtah-6.

The sandstone-siltstone special distribution has a random nature within the

formation. Therefore, the wellsite geologist should not totally rely on correlations

with the offset wells.

Unayzah contains four reservoirs Unayzah-A, A2, B, and C. They mainly produce

gas. Unayzah A, and B has produced oil in central Arabia only.


28

ROP drills relatively fast in the porous sandstone units and slows down in the

siltstone.

Figure 1.12: Khuff Formation reference section Source: Powers et al. Geology of the Arab. Pen.)


29

Figure 1.13: Unayzah new stratigraphic classification (Saudi Aramco)


30

Figure 1.14: The Unayzah Formation and “basal Khuff clastics” sequence in HWTH-6 (Source:

Plate Sequence Stratigraphy, GeoArabia, Special Publication 2, Bahrain.)


31

CARBONIFEROUS

25. Berwath Formation:

Berwath is composed mainly of shale interbedded by thin layers of dolomite. A

thin layer of sandstone is present toward the lower boundary with Jubah. (Figure

1.15)

Figure 1.15: Berwath and Jubah Formations in Abu-Safah-29 (Source: Plate Sequence

Stratigraphy, GeoArabia, Special Publication 2, Bahrain.)


32

DEVONIAN

26. Jubah Formation:

Jubah is a sandstone formation interbedded by siltstone and/or silty-shale

(Figures1.15, 1.16). The sand in Jubah sandstone is mostly medium and coarse

grained sandstone that contains subrounded and rounded quartz grains. In the lower

part, sandstone beds are light gray and contain light and dark minerals that give it a

“salt and pepper” appearance. Ferruginous and manganiferous cement and grain

coatings are common. Mica occurs, also.

27. Jauf Formation:

The Jauf formation is subdivided into 5 members:

1. Murayr (Fiyadh) 2. Hammamiyat 3. Subbat: contains Jauf Reservoir

4. Qasr 5. Sha’iba

(Figure 1.16) shows a generalized description of the formation.

Figure 1.16: Jubah, Jauf, Tawil, and Qalibah Formations corss-section(Source: Plate Sequence

Stratigraphy, GeoArabia, Special Publication 2, Bahrain.)


33

Figure 1.17: Generalised stratigraphic column of the Jauf Formation of nowthwest Arabia (Source:

Plate Sequence Stratigraphy, GeoArabia, Special Publication 2, Bahrain.)


34

28. Tawil Formation:

Tawil is another clastics formation. It contains mainly sandstone and siltstone.

(Figure 1.18) shows lithology description from the outcrop.

Figure 1.18: Tawil Formation Reference section (Source: Explanat-

ory notes to the geologic map of the Al Qalibah Quadrangle,

sheet 28C, Saudi Arabia)


35

SILURIAN

29. Qalibah Formation:

Qalibah is subdivided into 2 members:

1. Sharawra: sandstone interbedded by shale and siltstone

2. Qasaiba: mostly shale and siltstone with a layer of sandstone that contains

the Mid-Qasaiba gas reservoir.

(Figure 1.19) shows a more detailed lithology description of this formation from

Udaynan-1. (Figure 1.20) shows an outcrop description of the formation.

Figure 1.19: Subsurface composite reference section of Qalibah Formation in central Arabia

(Source: Plate Sequence Stratigraphy, GeoArabia, Special Publication 2, Bahrain.)


36

Figure 1.20: Surface reference section of the Qalibah Formation at Al Qalibah (Source: Plate

Sequence Stratigraphy, GeoArabia, Special Publication 2, Bahrain.)

30. Sarah Formation:

To understand the Sarah formation, it is important to understand its depositional

origin. Sarah sandstone is originally deposited by giant glacial channels. Therefore,

the sandstone of Sarah is poorly sorted. Also, the thickness of the Sarah formation

varies significantly within a small area.

The Sarah Reservoir has produced oil from several wells in central Arabia. (Figure

1.21) shows core descriptions of the formation.


37

ORDVICIAN

31. Zarqa Formation:

Similar to Sarah, Zarqa sand was deposited during glacial advance. Therefore, the

sand is distinctively poorly sorted, yielding a low porosity sandstone section.

Figure 1.21: Sarah and Zarqa Formation from the reference section at Jaz az Zarqa, central Arabia

(Source: Plate Sequence Stratigraphy, GeoArabia, Special Publication 2, Bahrain.)


38

32. Qasim Formation:

Qasim formation is subdivided into 4 members: (top to bottom)

1. Quwarah: contains Quwarah gas Reservoir 2. Ra’an 3. Kahfah:

contains Kahfah gas Reservoir 4. Hanadir

1. Quwarah Member: Sandstone beds occur in Quwarah. The sandstone is

bounded by siltstone layers. The sand stone contains the Quwarah gas

Reservoir.

2. Ra’an Member: Ra’an is predominately composed of clay. (Figure 1.22)

3. Kahfah member: Kahfah is composed mainly of sandstone which contains

Kahfah gas Reservoir. Silty claystone occurs toward the upper part of the

Kahfah. (Figures 1.22, 1.23)

4. Hanadir Member: Hanider is mainly composed of claystone interbedded

by siltstone. Sandstone occurs toward the lower part of Hanadir

ORDOVICIAN/CAMBRIAN

33. Saq Formation:

Saq is predominantly composed of multi-colored, poorly to well-sorted quartz

sandstone. Thin layers of siltstone are present. (Figure 1.24) shows a generalized

stratigraphic section of the Saq.

Saq is subdivided into: (top-bottom)

1. Sajir member

2. Risha


39

Figure 1.22: Sedimentological log of the At-Tirq 2 measured section; upper part of the Hanadir

Member and the Kahfah Member (Source: Qasim Formation: Ordovician Strom- and Tide-

Dominated Shallow-Marine Siliciclastic Sequences, Central Saudi Arabia. GeoArabia v. 6, no.2,

p.233-268.)


40

Figure 1.23: Sedimentological log of the At-Tiraq 1 measured section; Upper part of the Hanadir

Member and Kahfah Member ( Source: Qasim Formation: Ordovician Strom- and Tide- Dominated

Shallow-Marine Siliciclastic Sequences, Central Saudi Arabia. GeoArabia v. 6, no.2, p.233-268.)


41

Figure 1.24: Generalized Stratigraphic section of the Saq Sandstone (Source: Geologic map of the

Buraydah quadrangle, sheet 26G, Kingdom of Saudi Arabia, Saudi Arabian Deputy Ministry of

Mineral Resources Geosciences Map Series GM-114)


42

CAMBRIAN

34. Burj Formation:

Burj is mainly composed of shale and carbonates.

35. Siq Formation:

Siq is composed mainly of sandstone.

PRECAMBRIAN

36. Basement:

It is time to seriously consider pulling out of hole (POOH).


43

REFERENCES

Powers, R. A., L. F. Ramierez, C. D. Redmond, and E. L. Elberg, 1966. Geology of

the Arabian Peninsula: Sedimentary Geology of Saudi Arabia, U.S. Geological

Survey,

Sharland, P.R., R. Archer, D.M. Casey, R.B. Davies, S.H. Hall, A.P. Heward, A.D.

Horbury and M.D. Simmons 2001. Arabian Plate Sequence Stratigraphy,

GeoArabia, Special Publication 2, Bahrain.

Manivit, J., D. Waslet, A. Berthiaux, P. Le Strat, and J. Fourniguet, 1986. Geologic

map of the Buraydah quadrangle, sheet 26G, Kingdom of Saudi Arabia, Saudi

Arabian Deputy Ministry of Mineral Resources Geosciences Map Series GM-114,

scale 1:250, 000, with text 32 p.

Bureau de Recherches Geologiques et Minieres (BRGM), 1977. Al-Hassa

Development Project: ground water resources study and management

program. Ministry of Agric. Water, Riyadh

Dominique Janjou, Mohammed A. Halawani, Mohammed S. Al-Muallem,

Christian Robeline, Jean-Michel Brosse, SerCourbouleix, Jacques Dagain, Antonin

Genna, Philippe Razin, M. John Roobol, Hassan Shorbaji, Robert Wyns, 1996,

Explanatory Notes to the Geologic Map of the Al Qalibah Quadrangle, Sheet

28C, Saudi Arabia

Senalp, M., A.A. Al-Duaiji, 2001. Qasim Formation: Ordovician Strom- and

Tide- Dominated Shallow-Marine Siliciclastic Sequences, Central Saudi Arabia.

GeoArabia v. 6, no.2, p.233-268.

SECTION II

CASING POINTS

Reviewed by: Rifat HajiSmail, WSGU Geologist

Manahi Al-Otiebi, WSGU Geologist

SECTION II: Casing Points

45

1. Rus Formation Casing Point: (30” Casing) Introduction: Rus casing is intended to prevent shallower formations collapsing (Hofuf, Dam, Hadrukh, and Dammam). These shallow formations are mainly loose with loss of circulation zones, such as the Khobar Member. Therefore, such a large sized hole collapsing is highly possible. A secondary objective of the Rus casing is to protect the Umm Er Radhuma aquifer below Rus. There are two different geological casing-settings for the Rus Formation.

A. Rus Collapse (Ghawar Area): In the Ghawar area (Ain Dar, Uthmaniyah, Hawyah, Haradh, and areas toward the southern part of Abqaiq), the Rus anhydrite disappears from the section and the Rus top starts with carbonates. Unlike the rest of Ghawar fields, the majority of Shadugum exhibits anhydrite at the top of the Rus. B. Rus Anhydrite: Outside of the Ghawar area such as Tinat, Waqar, Midrekah, Northern fields, off shore wells, and Shadgum from Ghawar area, the Rus top is associated with the anhydrite appearance.

Casing Point Identification:

1. Geology (Cutting Samples): The last sections of Dammam Formation (Saila, and Midra members), which are above Rus, are mainly composed of shale, red clay, and marl. However, sand could possibly show up in the samples due to the caving in from the sand zones in the upper sections. Limestone, also, exists in the Dammam Formation. To pick the top of Rus, there are two different scenarios: A. Rus Collapse (Ghawar Area): In the Ghawar area the Rus is identified by the first appearance of carbonates (limestone) after drilling through 30 to 40 ft of Midra and Saila shale and marl. In the Ghawar area anhydrite disappears totally from the Rus Formation and will not be seen in samples. A few traces of gypsum can be seen in some places and should not be confused for anhydrite. (Figure 2.1.1: HRDH-56) (Figure 2.1.2: Ain Dar-270).


46

B. Rus Anhydrite: Outsides of the Ghawar area the top of Rus is picked with the first appearance of anhydrite in the samples. The limestone that exists in the Ghawar area is rarely seen. (Figure 2.1.3: FZRN-12) (Figure 2.1.4: SHDGM-223) 2. Rate of Penetration (ROP):

A. Ghawar Area: The softer carbonates of Rus exhibit a relatively faster ROP compared to the Dammam Formation. (Figure 2.1.1: HRDH-56) B. Rus Anhydrite: On the other hand, when Rus starts with Anhydrite ROP slows down relative to the overlaying section. (Figure 2.1.3: FZRN-12)

Figure 2.1.1: HRDH-56

Figure 2.1.2: Ain Dar-27

Figure 2.1.3: FZRN-12

Figure 2.1.4: SHDGUM-223


51

2. Aruma Formation Casing Point: (24” CSG) Introduction Aruma casing is placed in the Lower Aruma Shale. Usually, a loss of circulation occurs in Umm Er Radhuma above Aruma, and therefore, picking Lower Aruma Shale (L.A.S) depends mostly on the ROP correlations and could, also, be estimated by the isopach from the nearest wells. Casing Point Identification: 1. Geology (Cutting Samples): The majority of Aruma formation consists of carbonates (limestone, and dolomite). A few stringers of shale are present. However, the Lower Aruma Shale is the thickest shale section, and it is the most noticeable shale section for its thickness. Up to 100% shale is observed in the samples and will be in more than one sample. (Figure 2.2.1: TINT-2) (Figure 2.2.2: MAGHRIB-2) 2. Rate of Penetration (ROP): Normally, the dominant carbonate sections of Aruma drill relatively fast. When getting into the L.A.S, drilling will start to slow down. (Figure 2.2.3: SHDGM-230) 3. Isopach Estimation In many other cases, the characteristic of sudden decrease of ROP when getting into L.A.S is not always evident. (Figure 2.2.4: FZRN-13) and (Figure 2.2.2: MAGHRIB-2) show that a number of the Aruma carbonates sections slow down drilling prior to drilling through L.A.S. For cases like FZRN-13, where there is a loss of circulation and an unclear ROP trend, the isopach (thickness) of Aruma from the adjacent wells provides a reasonable estimation of where to expect L.A.S. Consulting the reservoir geologist is recommended, in cases like FZRN-13, to acquire a further insight into how the Aruma Formation behaves between the offset wells and your well.

Figure 2.2.1: TINT-2

Figure 2.2.2: MAGHRIB-2


Figure 2.2.4: FZRN-13


56

3. Ahmadi Member Casing Point: (24” CSG) Introduction: When Ahmadi casing is planned, it is intended to seal all the highly-possible loss of circulation zones above Ahmadi (Umm Er Radhuma, Lawhah, Rumaila, and Mishref). Ahmadi’s shale provides a firm casing shoe, unlike Wara loose sand below Ahmadi. Therefore, casing is set in Ahmadi to avoid further losses of circulation. Casing Point Identification: 1. Geology (Cutting Samples) Ahmadi formation is mainly composed of a thin carbonates section at the top and a dominant shale section below. It has been a customary practice, in wellsite, that the casing point of Ahmadi is calculated 30’ to 50’ below the top of the shale section. (Figure 2.3.1: UTMN-600) In offshore fields, the geology of Ahmadi is different. It consists mainly of carbonates. However, Ahmadi is not a casing point in these fields. (Figure 2.3.2: MRJN-29) 2. Rate of Penetration (ROP) When drilling into Ahmadi a loss of circulation is common due to the many losses of circulation zones above Ahmadi. Therefore, the Ahmadi casing point is usually picked by observing the ROP. Ahmadi casing is commonly characterized by the E-shaped ROP curve, in which 3 separate stringers of slow drilling are observed, due to carbonates stringers of Praealveolina. After encountering the E-shaped ROP, a relatively faster ROP is detected due to the shale of Ahmadi. (Figure 2.3.3: SHDGUM-230) (Figure 2.3.4: AIN DAR-277) In many situations the E-shaped ROP is not observed. Instead 2, 4 or 5 stringers of slow drilling are detected by the ROP, (Figures 2.3.5-6). This is mainly due to the different drilling parameters adopted in different drilling rigs and, also, due to variations of lithology of the upper part of Ahmadi and the Praealveolina limestone from one area to another. To ensure that you have drilled through the carbonates of Praealveolina and Ahmadi, and reached the shale, it is recommended to drill up to 25 ft below the third stringer of slow ROP. If the ROP continues to be fast after the 25 ft, then you are assured that the shale section has certainly been reached. If drilling slows down, significantly, before drilling through the 25 ft, it indicates a high probability of another carbonates stringer. It is also recommended to drill this section with a constant weight on the bit, if possible, to ensure that ROP trends are due to the formation, and not the drilling parameters.

Figure 2.3.1: UTMN-600

The E-shaped ROP curve

Figure 2.3.2: MRJN-29



Figure 2.3.4: AIN DAR-277





63

4. Biyadh Formation Casing Point: (18 5/8” CSG) Introduction: Biyadh casing is intended to seal off the loss circulation zone of Shu’aiba and, also, the swelling shale of upper Biyadh. Therefore, it is placed +/- 300 feet into Biyadh. Casing Point Identification: 1. Geology (Cutting Samples) The top of Biyadh is characterized by quartz sandstone and shale underlay Shu’aiba carbonates section. This dramatic change of lithology clearly indicates the Biyadh top. (Figure 2.4.1: SHDGUM-239), (Figure 2.4.2: HRDH-52) A loss of circulation is probable and cutting samples might not be available. 2. Rate of Penetration (ROP) Biyadh ROP is considerably faster than the overlaying Shu’aiba carbonates section, (Figure 2.4.2: HRDH-52). The ROP break is less dramatic in many other situations. (Figure 2.4.3: HRDH-56).





67

5. Mid-Thamama Formation Casing Point: (18 5/8” CSG) Introduction: Mid-Thamama casing is not a regular casing point. It is planned when Biyadh casing is skipped. Mid-thamama casing serves the same purposes that the Biyadh casing serves, i.e. to seal off Shu’aiba loss zone and the swelling of Biyadh shale. Casing Point Identification: 1. Geology (Cutting Samples) Mid-Thamama top is easier to pick when cuttings are available. The last section of Buwaib Formation, that overlays Mid-Thamama, consists of siltstone and shale. The top of Mid-Thamama is marked by the appearance of limestone (hard limestone) in the cuttings. (Figure 2.5.1: HRDH-52) (Figure 2.5.2: SHDGUM-239) (Figure 2.5.3: TINT-2) 2. Rate of Penetration (ROP) Top of Mid-Thamama limestone is hard and, hence, slows down drilling relative to the overlaying section. (Figure 2.5.1: HRDH-52).



Figure 2.5.3: TINT-2


71

6. Hith Formation Casing Point: (18 5/8” Casing, 13 3/8” Casing) Introduction: Hith is, also, not a regular casing point. It is planned when Biyadh and Mid-Thamama casings are skipped. It meets the same objectives served by Biyadh and Mid-Thamama casings. This casing point is placed +/- 100 feet into Hith. Casing Point Identification: 1. Geology (Cutting Samples) Hith is picked when anhydrite starts to appear in the cutting samples, after Sulaiy carbonates. (Figure 2.6.1: HRDH-60) (Figure 2.6.2: HRDH-56) (Figure 2.6.3: ST-39) 2. Rate of Penetration (ROP) Ideally, Hith’s anhydrite slows down drilling after Sulaiy carbonates, (Figures 2.6.2-3). However, this trend is not always clear especially when using a PDC bit. 3. Isopach Picking Hith is an easy task when cuttings are available. However, if a loss of circulation is present, then a good estimation is achieved by reviewing the nearest wells’ isopach for Sulaiy to estimate the top of Hith.



Figure 2.6.3: ST-39


75

7. Arab-D Member Casing Point (18 5/8” CSG, 13 3/8” CSG) Introduction: This casing is set in the Arab-D Member (5 -10 feet above the top of Arab-D Reservoir) to seal off all the high pressure water flow zones above Arab-D Reservoir. The sections overlaying Arab-D Reservoir require drilling with a high mud weight. Therefore, it is necessary to set the casing above Arab-D Reservoir to maintain a lower mud weight to drill the soft Arab-D Reservoir. Extra precautions are necessary when picking this casing point to avoid penetration into the highly porous Arab-D Reservoir which results in a severe loss of circulation, (Figure 2.7.1: SHDGUM), and drilling hazards. Casing Point Identification: 1. Geology (Cutting Samples) The key for picking the Arab-D casing point is to pay attention to the Post Arab-D Stringer which is present in the lower part of Arab-D Member. This carbonate stringer is usually 5- 10 feet above the Arab-D reservoir and therefore provides a good indication that you are getting extremely close to the casing point. (Figure 2.7.2: HWYH-200), (Figure 2.7.3: NYYM-2) However, do not wait to see the stringer in the cutting samples. It will be too late when you get the carbonates of this stringer in the samples because of the fast drilling and long lag time. Instead, detect the stringer using the ROP method. 2. Rate of Penetration (ROP) The anhydrite in Arab-D Member slows down the ROP. Post Arab-D Stinger, on the other hand, will significantly speed up the ROP. The stringer is only 2-8 feet in thickness; therefore, it is highly recommended that the well-site geologist observes the ROP from the geolograph at the rig floor to closely detect the increase of ROP in Post Arab-D stringer. (Figure 2.7.4: DARB-1), (Figure 2.7.5: HRDH-56), In the Qatif area as well as in some parts of Ghawar, such as Uthmaniyah, and south western Haradh, there are usually two separate stringers above the Arab-D reservoir (Figure 2.7.6: QTIF). It is recommended to discuss the geology, ROP and gas indications with the reservoir geologist. 3. Isopach It is suggested that the wellsite geologist keep a record of the thicknesses of Arab members from the nearby wells. It usually provides a good estimate of where to pick the tops. However, you should not totally rely only on this piece of information.

Figure 2.7.1: SHDGUM

Figure 2.7.2: HWYH-200

Figure 2.7.3: NYYM-2

Figure 2.7.4: DARB-1


Figure 2.7.6: QTIF

2 Post Arab-D St


82

8. Jilh Formation Casing Point: (18 5/8” Casing) Introduction: Jilh casing is designed to case off the Jurassic section prior to drilling into the Lower Jilh. The Lower Jilh section is generally a high pressure zone and, therefore, requires a much higher drilling-mud weight. This casing point is critical and demands special attention not to drill more than 30 ft to 40 ft below Base Jilh Dolomite to avoid encountering the high pressure zone prior to setting the casing. Casing Point Identification: 1. Geology (Cutting Samples) Minjur Formation, which overlays Jilh Formation, is a clastic section. The top of Jilh Formation is picked by the appearance of carbonates in the samples. The samples will also contain shale accompanied with sand and traces of anhydrite in some areas. Then, Jilh Dolomite section is picked by the appearance of the distinctive, clean, light colored, sucrosic dolomite or dolomitic limestone. It is highly probable to see shale also in the samples due to shale caving down into the hole from the upper section. However, the percentage of caving shale decreases in the Jilh Dolomite section and the sucrosic Dolomitic limestone percentage increases. Then, Base Jilh Dolomite is picked when the shale percentage increases again in the samples and the sucrosic dolomite decreases or disappears. Anhydrite is also found in the B.J.D. (Figure 2.8.1: HWYH-200), (Figure 2.8.2: SHDGUM-238) 2. Rate of Penetrations (ROP) Usually, ROP increases in the Jilh Dolomite and then slows down at the upper part of Base Jilh Dolomite. (Figure 2.8.3: HRDH-60), (Figure 2.8.4: HRDH-52) 3. Isopach It is suggested to review the thickness of Jilh Dolomite from the nearest wells to estimate the top and the Base of Jilh Dolomite. If the offset wells are close enough, it could provide a close estimation.

Figure 2.8.1: HWYH-200





87

9. Khuff Formation Casing Sets: (9 5/8” Casing, 7” liner) Introduction: In Khuff Formation, there are two points where casing is set:

A. Top of Khuff Formation (10’ to 15’ below the top): This casing is set when the Lower Jilh has a high pressure zone that requires a high mud weight. So, the casing is set at the top of the Khuff Formation, prior to drilling into the porous Khuff-A Reservoir, to prevent the heavy-drilling mud from breaking into the formation causing a loss of circulation and drilling hazards.

B. Below Khuff-D Anhydrite: If no high pressure zone is encountered in Jilh, then

this casing is set 400-550’ below the top of Khuff-D Anhydrite. Casing Point Identification 1. Geology (Cutting Samples):

A. Khuff formation: Top of the Khuff Formation is easily identified by the appearance of clean carbonates (chalky limestone) in the samples after Sudair. (Figure 2.9.1: SHDGUM-223), (Figure 2.9.2: NYYM-2)

B. Khuff-D Anhydrite: is picked by the appearance of Anhydrite in the samples

below the base of Khuff-C Reservoir. Khuff-D Anhydrite exists in two separate stringers. These two stringers are separated by a 20 ft to 30 ft of carbonates section. The top of Khuff-D Anhydrite is picked at the first appearance of the first Anhydrite stringer. (Figure 2.9.3: AIN DAR-277), (Figure 2.9.4: DARB-1), (Figure 2.9.5: NYYM-2)

2. Rate of Penetrations (ROP): A. Khuff Formation: Picking the top of Khuff by ROP characteristics is not very credible, because it does not have a distinctive characteristic (increase or decrease) relative to the overlaying Sudair section. It usually, but not commonly, drills faster than Sudair shale, (Figure 2.9.6: AIN DAR-277). However, this is not a very distinctive feature to completely rely on. It depends on the drilling parameters (bit type, weight on bit…etc). It is, also, highly possible that ROP decreases as drilling gets into Khuff.

B. Khuff-D Anhydrite: Anhydrite usually drills slower than the overlaying Dolomite section. The opposite could be true, especially with diamond bits. (Figures 2.9.3-5)


88

3. Circulating bottoms up: Circulating bottoms up and examining the samples allow the geologists to safely pick the Khuff top. Since the ROP is not reliable in the case of picking the top of “Khuff Formation”, and the casing point is only 10 ft below the top of Khuff Formation. Also, because of the longer lag time to get samples, it is suggested that the wellsite geologist stops drilling and circulate bottoms up from the expected Khuff Formation.




Figure 2.9.4: DARB-1



SECTION III

WELLSITE CORE HANDLING

Reviewed By AbdulHafiz Masri, Core Coordinator

SECTION III: Wellsite Core Handling

96

SECTION III: Wellsite Core Handling: 1. Introduction:

Coring is an expensive operation and, more importantly, provides valuable geological

information to the Exploration Organization. Every part of the core is indispensable and

should not be taken for granted. Only proper core handling by the wellsite geologist can

ensure attaining the desired benefits and objectives of the core.

Core handling includes:

• Measuring the recovered core.

• Assigning the proper depths to the core tubes after it has been cut.

• Assigning the proper orientation to the core tubes (top-bottom).

• Describing the core on location, if needed (lithology, and hydrocarbon shows).

• Ensuring that the core tubes are properly stored and put into core boxes to be sent

to the core-lab store in Dhahran, unless otherwise instructed.

• Filling out the core data sheet.

• Writing clearly and properly assigning core tags for each core tube.

Planning ahead, even before going to the rig location, ensures a successful core handling.

Planning ahead requires acquiring general information regarding the core. Such

information, and more, can be obtained by reading the core-meeting minute and meeting

the core proponent for further inquiries. Planning ahead will save you the troubles of

going to the rig unprepared and lacking tools and information.


97

2. Conventional-Core Handling Procedures:

A. plan ahead:

A-1. Read the core meeting minute before leaving for the rig or meet the core

proponent to find out about the following:

• Length of the core

• Formation compatibility. Fractures and faults that could possibly cause

core jamming and you should be aware of possible jamming zones.

• Significant change of rock hardness in the interval being cored. Change of

hardness of core from hard to soft could, sometimes, cause jamming if not

carefully dealt with by the coring service company. Therefore, notifying

the core hand of the zones of significant hardness change could help

maintain better coring parameters.

• Best offset wells for correlations. Preferably an offset well that has a

coring job done on the same section.

A-2. The following are tools needed to accomplish the job efficiently:

• Core tags and plastic straps that are provided by the Wellsite Geology

Unit.

• A Hammer and a small chisel to take samples from the core.

• Two screw drivers, to screw the caps clamps, to avoid wasting time

searching for them in the rig.

• A calculator will come in handy to calculate core tubes depths and other

calculations.

• Two measuring tapes.


98

B. When you get to the rig location, meet with the coring personnel and rig foreman

to make sure they are aware of the core requirements.

Also, as soon as you get to the rig location, make sure that the core shipping-

boxes are available.

C. Pulling out of hole for possible jamming is definitely not your decision. However,

when cutting a core, Rate of Penetration (ROP) might significantly slow down.

This could indicate a possible core jam that requires pulling out of hole. The core

hand will definitely come to ask you if you think the slow down is due to a

change of the formation hardness. Answer him in the light of your meeting with

the core proponent. Also, review the offset wells for any significant slow down.

Sometimes, offset wells’ trends are not accurate enough and do not apply to your

well, especially when coring in Unayzah, which is one of the highly cored

sections, because of its random sandstone-siltstone spatial distribution (facies

change).

ROP slow down is only one indication of jamming. The core hand has other

indications of jamming such as change of pressure and torque. He is the expert in

the coring operation. You just provide him with the geological consultations that

might help him make better decisions.

D. When the core barrels come out to the surface, make sure you know the order of

the inner core barrels: the number of inner tubes in each run depends on the

planned length of core cut. Usually, each coring run will include two inner core

barrels. In that case it is easy to distinguish the top core barrel from the bottom

barrel, because the bottom core barrel will have the shoe attached to it (Figure

3.1). When there are three core barrels, you should pay attention to distinguish

between the second and third core barrels. To distinguish between the second and

third core barrels be on the rig floor when the core barrels are being brought out to


99

the surface. The first core barrel to come out of the hole is the very top inner

barrel. The second barrel is the middle barrel. And, of course, the last barrel to

come out is the very bottom barrel.

E. Write down your notes and measurements clearly on a piece of paper while

working on the cat walk, so you can use it later to fill out the “Core Data Sheet”.

DO NOT count on your memory to fill out the core data.

F. Only when all core barrels are being laid down on the cat walk, can you start

making your measurements and markings.

G. First measure the length of missing core from the top side of the core by inserting

the measuring tape inside the top core barrel. Also measure the missing core from

the shoe. Subtracting the total missing length from the total length of the core

assembly (core barrels, shoe, and bearing joints between core barrels) gives you

the recovered core length. See (Diagram 3.1), to identify the different parts of the

inner core barrels.

H. Before starting to make markings on the core tubes, it is recommended that you

clean the mud off the core barrels using water and cloths. Cleaning the core

barrels will make it easier to write on the core barrels and will ensure that your

writings do not come off later.

I. Now, the core barrels are ready to be marked. Give yourself all the time you need

for marking and numbering the core tubes. Do not rush.

• Marking: make a mark every 3 feet on the core barrels. These marks indicate

where the core barrels are cut to make the 3 feet core tubes. The core in the

shoe stays in a separate core tube (~ 1.5’). So, start making the 3 feet marks

from the end of the shoe to the end of the first core barrel. Then the core in the

bearing joint between barrels, if present, stays also in a separate core tube (~ 1


100

foot). Next, continue making the 3 feet marks on the second barrel to the end

of core barrels. If the end of the top core barrel is empty, then, use this extra

amount of core barrel to make 2 core tubes. One for the core in the shoe and

the other for the core in the bearing. (Diagram 3.2)

• Numbering: start numbering the core tubes with the shoe being core tube #1

and increase numbers going upward. (Diagram 3.2).

• Orientation: indicate by writing on the core tubes at the bottom end and top

end. In one core tube, the bottom end is the end that is closer to the bottom of

the hole, or closer the shoe (Diagram 3.2). Also, draw the black and red stripes

to indicate the bottom from top, as shown in (Diagram 3.3).

J. Now the core barrels are ready to be cut into 3 feet long tubes by the core saw.

Conventional core tubes are suppose to be cut in an angle with water. It does not

matter if you start cutting from top to bottom or vise versa as long you have made

the right marking, numbering, and orientation on the core barrels.

K. When cutting the core tubes, pieces of the core might fall out. Place back these

fallen core pieces in the right orientation.

L. Vibrations of the core saw eject loose core parts outside the core barrel. Therefore,

cap the open ends to prevent losing pieces of the core.

M. Before capping the bottom end, take a sample for examination. The samples

description goes to the strip log. Each sample is used to describe the top 3 feet.

N. Now that the core barrels are cut into 3 feet tubes, make sure each tube is capped

from both ends and secured by the metal clamps around the plastic caps. Place a

plastic strap at the bottom end to be used later for hanging the core tags (Figure

3.2).


101

O. Now, you should be ready to fill out the core data sheet, and make the core tags.

Also, this is a good time to add the lengths of all the core tubes to calculate the

length of the recovered core. Compare the result with your initial calculation from

step G.

P. Place the core tags on the proper tubes. Also, write the core number and well

name on every tube (Figure 3.3, and 3.4). Core number indicates the core run

number. If there were 2 core runs in Arab-D formation, for example, then the first

core number in Unayzah, for example, will be core number 3.

Q. Make a final check up on your work and, then, place the core tubes inside the

designated core boxes in the order of their numbers. Then, ensure that the box’

covers are properly attached. Use duck tape or straps to close the covers, if

necessary.

R. Make sure that all received foam beds are placed back inside the core shipment

boxes, if not used.

S. Make sure that the rig foreman places an order to transport all the core boxes to

the core store in Dhahran (DPC-155, BLDG-3170) as soon as the coring job is

done. Core boxes are supposed to be transported on a truck separately, and not

with other rig materials, to avoid any damage to the cores.


102

3. Preserved-Core Handling Procedures:

Conventional core handling procedures apply for preserved cores, provided that you

strictly meet the following requirements:

• Do not use water to cut the core tubes. Instead cut dry.

• Do not use the steel clamps to seal the plastic caps. Instead use the silver duck

tape. Also, use the silver duck tape to attach the core tags. (Figure 3.5)

• Place the tubes in the ProtecCore and seal it immediately. Make sure that the

ProtecCore is not damaged.

• Then, wrap the tube with bubble-wrap at least twice to protect the ProtecCore

from being damaged during handling and transportation. Also, it is necessary to

ensure that the tube ends are covered with bubble-wrap. (Figure 3.6)

• Write on the bubble-wrap the well number, core number, and tube number. Also,

label the top and bottom for orientation.

• Core boxes should be transported immediately to the Saudi Aramco core store,

unless directed to a different location.


103

4. Exploration Wells’ Core Handling Procedures:

Conventional core handling procedures apply for exploration wells’ cores. However,

cores that are cut in exploration wells require a complete description of the core on

location.

Therefore;

• The cores are taken out of the core tubes and placed in the 3 feet core trays to be

examined on location.

• The red and black stripes are labeled on the core directly.

• All information and labels (well number, core number, and tray number) are placed

on the bottom side of the core trays. (Diagram 3.4)

• After examination a wooden cover is used to seal the core trays and then strapped to

secure the core inside the core tray.

• NOTE: foam beds are not sent with the core boxes to exploration wells, because they

are not used with the core trays.


104

5. Safety Precautions:

1. Wear your safety gear at all time, including ear plugs.

2. Make sure that everyone who works with you on the cat walk understands the

nature of has role. Stop at any time you feel someone is confused and might cause

an accident, especially if it is his first time working on the cat-walk and cutting

core barrels.

3. Do not start marking the core tubes until all core tubes are laid down. Keep the

worst in mind, i.e. the cables carrying the core tubes from the rig floor to the cat

walk might snap in the air and crash down. Keep an eye also on the crane and its

operator when moving the core cradle around the cat walk. Better yet, stay at the

far end of the cat walk until all core barrels are laid down.

4. Be aware of scattering pieces of rock when you take samples by a hammer. It

could cause serious damage if they hit your face or the person holding core tubes.

Make sure that the person’s face holding the tube is not at the same level with the

core tube end where you take a sample and that he is looking the other direction.

This is a time where everyone around should be wearing their safety goggles.

5. Also, be aware of fine pieces of aluminum that could fly behind and in front of

the core saw when core barrels are being cut.

6. Be gentle when you lift core tubes from the ground, to avoid back injuries.

7. Be extra cautious if you are operating at the end of a crew shift. People tend to be

fatigued and slow in reaction.


105

Figure 1: The shoe: it prevents the core from slipping out of the core barrel.

Figure 2: the plastic straps are placed under the metal clamps on the bottom end


106

Figure 3: write the well name, core number, and tube number clearly.

Figure 4: The Necessary labels (well name, core number, tube number, and top-bottom)

on one side and the red and black stripes on the other side


107

Figure 5: Preserved core, sliver duck tape is used to seal caps and attach core tags (photo

is a courtesy of AbdulHafiz Masri, Cores Coordinator)

Figure 6: Persevered core wrapped inside bubble-wrap (Photo Courtesy of AbdulHafiz

Masri)

TOP TINT-1, core#1, Tube#2 Bottom


108

2.23

TO

P SU

B

2.24

CO

RE

BA

RR

EL

26.0

0 1.

12

CO

RE

H

EA

D

STA

BIL

IZE

R

4.00

2.23

STA

BIL

IZE

R

4.00

STA

BIL

IZE

R

4.00

2.23

CO

RE

BA

RR

EL

26.0

0

LD

A

DJU

STIN

G

SYT

EM

O

. TU

BE

3.74

Stan

dard

Pi

lot

Shoe

A

ssem

bly

1.38

30

.00

30.0

0 1.

00

1.00

Inne

r T

ube

Inne

r T

ube

Inne

r T

ube

Stab

.

Inne

r T

ube

Ext

. L

.D. A

djus

ting

Syst

em Diagram 3.1: Inner

tube (right), and Outer tube parts


109

Inner tube Stabilizer –“Bearing”

(1 ft)

B

#12

T

2

B

T

B

T

T

T

T

T

T

T

T

T T

T

T

T

T

T

T

T

T

T

B

B

B

B

B

B

B

B

B

B

B

B

B

B

B

B

B

B

4

5

6

7

8

9

10

11

13

14

15

16

17

18

19

20

21

22

#1

T

B

The Shoe Tube (1.38 ft)

Core Barrel #1 (30 ft) Core Barrel #2

(30 ft)

Diagram 3.2: Marking and numbering of the cores; the core in the shoe stays in a separate tube as well as the core in the bearing. The core barrels are divided into 3 feet core tubes. There are two standard lengths of core barrels, 30 ft and 20 ft. This diagram is showing a 30 ft long barrel. Inner tube stabilizer does not usually come with the 20 feet core barrels. Numbering starts from the shoe and increasing going upward. Red and black stripes go onto the other side of core barrels to indicate orientation of the core. B stands for Bottom. T stands for Top.

3


110

Diagram 3.3: The black and red stripes are marked on the inner core barrel that if you are facing the inner core barrel, with it standing up or coming out of the hole, the red stripe will be to your right, and the black stripe will be to your left. In the case of exploration wells, the stripes are marked directly on the core itself.

Diagram 3.4: Exploration wells’ core handling. After the core tubes are cut, the core is placed inside the core trays, to be examined. Labels and tags are marked and placed on the bottom side of the trays.

SECTION IV

DRILLING MUD EFFECTS ON CUTTINGS SAMPLES

EXAMINATIONS

SECTION IV: Drilling Mud Effects on Cuttings Examinations

112

SECTION IV: Drilling mud Effects on Cuttings Examinations The drilling mud is the medium in which cuttings are transported outside of the hole and

to the shale shaker.

There are two main types of Mud:

1. Water Based Mud: It is the most common mud type. Before examining cuttings,

the cuttings must be washed with running water while in the sieves.

2. Oil Based Mud: This kind of mud uses diesel instead of water as mud base. This

kind of mud makes it extremely difficult to examine the cuttings for hydrocarbon

shows. Cuttings should be washed with a detergent or diesel before examinations.

1. Drilling Mud Additives

Most of the drilling mud additives dissolve in water. As a result, it disappears when

washed with water in the geologist lab.

However, few of the mud additives do not dissolve in water and appear in the cutting

samples trays examined by the geologist. It is necessary that the wellsite geologist be

aware of such solids to ensure accurate descriptions of the cutting samples.

If the wellsite geologist is not fully aware of the mud additives, it creates confusion and

inaccurate descriptions of the cuttings samples.

The following are the most common mud non-dissolving additives:

1. SOLTEX:

Soltex is a petrochemical additive. It does not dissolve in water and appears with cutting

samples as black grains (Figure 4.1, 4.2). Soltex is used to prevent shale swelling and

caving. It is usually used in high pressure and temperature zones.

Soltex is usually used in formations where shale is abundant (e.g. Sudair, and Unayzah)


113

Soltex is a hydrocarbon based chemical. Therefore, it shows hydrocarbon fluorescence

under the UV light.

2. BENTONITE:

Bentonite is another petrochemical based additive. It is used to increase the mud capacity

of holding cuttings to prevent accumulations of cuttings at the hole bottom during

connections.

Since it is a hydrocarbon based additive, Bentonite will show hydrocarbon fluorescence

under the UV light.

3. MICA:

Mica is added to the mud in potential loss of circulation zones. It appears like glass chips

and resembles the mica found in clastic formations. It is difficult to distinguish between

the mica added to the mud and that coming from the formation. Therefore, communicate

with the mud engineer to find out if mica has been added to the mud.

4. NUT SHELLS:

Nut shells do not dissolves in water and could create confusion when it appears in the

cuttings samples. (Figure 4.3)

There are more mud additives that can show up in the cuttings samples. Therefore, it is

necessary to keep in touch with the mud engineer to be aware of the mud ingredients,

especially when noticing suspicious particles with the cuttings.


114

Figure 4.1: SOLTEX shows up with the cuttings as black grains

Figure 4.2: Soltex as it appears under the microscope


115

Figure 4.3: Nut shell as it appears in a white sandstone sample (under the microscope).

2. Natural Fluorescence: UV-Light

Oil Gravity Fluorescence Color

2° - 10° Non-fluorescent

10° - 18° Yellow to Gold

18° - 45° Gold to Pale Yellow

> 45° Blue White –White

Rock Minerals Fluorescence Color

Dolomite Yellow/ Brown

Limestone Brown

Chalk Purple

Shale Yellow/ Gray

Fossils Yellow-white/ Yellow Brown

Marl Yellow/ Gray

Anhydrite Gray/ Blue

Pyrite Yellow/ Brown/ Purple


116

2° - 10° Non-fluorescent

10° - 18° Yellow to Gold

18° - 45° Gold to Pale Yellow

> 45° Blue White –White

Rock Minerals Fluorescence Color

Dolomite Yellow/ Brown

Limestone Brown

Chalk Purple

Shale Yellow/ Gray

Fossils Yellow-white/ Yellow Brown

Marl Yellow/ Gray

Anhydrite Gray/ Blue

Pyrite Yellow/ Brown/ Purple

SECTION V

GENERAL WELLSITE REQUIREMENTS

SECTION V: General Wellsite Requirements

117

SECTION V: General Requirements:

1. Keep the strip log clean and organized. All information should be plotted with a

waterproof ink pin (Rapidograph), not pencil. On the other hand, formation tops

are marked with pencil.

2. Update the strip log on a daily basis. Plotting the strip log at the last minute

produces a messy outcome.

3. The strip log is a valuable record of the well, so record all necessary information,

including:

A. Mud data: it should be recorded every 1000 feet or whenever changed.

Also note the depths of any loss of circulation, if it occurs.

B. Bit record: including bit number, size, and type against the depth it was

changed

C. Problems of the hole and any significant events, if present. For example, if

the hole is tight, it will significantly create a false ROP reading. Therefore,

note such incidents on the strip logs so the ROP reading makes sense.

D. Write all information clearly so that it can be read easily by others.

E. Write your name with pencil at the top and bottom of the section you

worked on, so it is easy to refer back to you, if needed.

F. Casing depth and casing size should be marked with the casing symbol.

4. Plan ahead before going to the field, so you do not forget necessary equipments.

5. It is certainly better to leave early for the field rather than at the last minute, to

avoid stress and unsafe driving. Travel only during day time.

6. Take good care of your tools.

SECTION V: General Wellsite Requirements

118

7. Sample bags (washed and unwashed) should have the well name as well as the

depth marked clearly.

8. When writing the morning report, make sure that you divide the lithology groups

into sensible groups. For example, if the formation drilled has changed (e.g.

Sudair to Khuff), a new lithology group should be created for Khuff, since the

lithology has significantly changed.

9. Also, ROP intervals in the morning report should be broken down into logical

groups. For example, (5-80 min/5’) does not make sense, because it is a wide

range of ROPs.

10. Summarize the operations, instead of exactly copying the foreman’s report.

Include only events that matter for our unit. Engineering details are not necessary.

11. Calculate the lag time yourself, or at least check the calculations of whoever did it

12. Check, regularly, if the samples are collected properly for you and on time.

13. Before you leave the rig site, collect all the sample bags inside the designated

sacks. Do not over-load the sacks to the neck. Do not forget to label the sacks.

14. Also, make sure that the geologist room and lab are clean and ready to be used by

the next geologist.

Documents

Saudi Aramco - Operational Geology Manual