REPUBLIC OF YEMEN

MINISTRY OF OIL AND MINERAL

PETROLEUM EXPLORATION AND PRODUCTION AUTHORITY

 

 

 

 

 

 

 

 

A STUDY ON THE RESERVOIR ROCKS OF QISHN FORMATION (Masila Block 14)

 

 

 

 

 

 

 

 

 

By: Dr. Eng. Mohammed Darsi Abdulrahman Nedham

Doctor of Science (Geologist), PEPA ’s Office (Aden)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Aden (June 2oo3)

 

 

 

WHAT MASILA BLOCK AND QISHN FORMATION MEANS FOR CANADIAN NEXEN INC.?

 

First of all, and before I am going to write any word as an introduction to my study on the reservoir rocks of Qishn Formation in Masila Block (14). I would like to draw the attention of all people, who work as decision makers in the Ministry of Oil and Minerals (MOM) and the Petroleum Exploration and Production Authority (PEPA) on the great importance of answering the above-mentioned question.

 

We must know, that Masila Block (See, Fig. (1)) has a great meaning for Nexen Company, because of the following reasons:

1.                  Approximately 44% of Nexen's overall production comes from the Masila Block (Yemen), which representing just over one third of the company's cash flow.

2.                  Nexen has a 52% working interest in and operate the Masila Project, which is the largest single source of oil production in Yemen and has grown steadily since discovery in 1990.

3.                  To date, the 15 fields that comprise the Project have produced over 665 million gross barrels of oil from total gross recoverable reserves of just over one billion barrels.

4.                  Nexen has the right to produce oil from the Masila fields until 2011 and the right to negotiate a five-year extension.

5.                  During 2002, $402 million ($209 million net) was invested to drill and equip 74 new development wells and expand existing infrastructure. Gross production was maintained throughout the year at approximately 226,900 barrels per day.

6.                  The economics of Masila production are attractive. Historic finding and development costs are approximately US $2 per barrel and operating costs have averaged US $1 per barrel, resulting in excellent returns for shareholders!

 

All the above mentioned reasons makes Nexen not just take care of Masila Block and Qishn Formation, (I mean the Qishn clastic member, which is the main producing reservoir in this area and the main subject of this study), but also to work actively on exploring outside the Masila Block. In my opinion, the strategic point of view and the excellent steps taken by the heads of Nexen Inc. led to the following main result and present fact:

 

(Nexen, NOW, hold interests in seven exploration licenses (Block 50 Block 51 Northern Blocks 11, 12, 36, 54 and 59) comprising over 20 million acres of undeveloped land, the majority of which are located in northeastern Yemen close to the Saudi Arabian border. (See Fig. (2))

 

Due to what mentioned above I am sure that we in Yemen are highly in need for building not just the high qualified Yemeni oil team but also for building the first National Oil Exploration Company. Am I right? Now, it is the suitable time for Yemeni specialists, who found a great chance to work with those kind of high-qualified and experienced foreign specialists, to learn from the newest in their field of specialization. Our scientific cooperation and friendship must continue with all and forever. If we really want to see the whole plains clearly, we must climb the highest mountain.                                                

 

i

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Fig. (1) Masila Location (Nexen Inc., Data)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Fig. (2) Nexen Blocks in Yemen (Nexen Inc., Data)

 

 

 

ii

 

 

 

 

 

INTRODUCTION

 

 

Masila Block 14 is operated by Canadian Occidental Petroleum Yemen on behalf of its partners Occidental Peninsula, Inc. and Consolidated Contractors International, Ltd., (CANADIAN NEXEN PETROLEUM YEMEN as known now), and is located in the Hadhramaut region, in east-central Republic of Yemen. Oil was first discovered on the Block in late 1990 with Commerciality declared in late 1991. Oil production at Masila began in July 1993.

 

There are now 15 oil fields known in Masila, Block 14: (See, Fig. (3)) 1. Camaal (C), 2. North Camaal (NC), 3. Sunah (S), 4. Northeast Sunah (NES), 5. Heijah (HJ), 6. Hemiar (HR), 7. South Hemiar (S.HR), 8. West Hemiar (W.HR), 9. Tawila (T), 10. Haru (HU), 11. Nazeia (NZ), 12. Dahban (D), 13. Bainoon (ND), 14. Qataban (QAT), and 15. Gabal-Isbeel, containing 56 pools within the Masila Block. Total proven ultimate recoverable oil reserves are approaching 900 million STB. Proven, probable and possible reserve estimates are in excess of one billion barrels of recoverable oil.

 

The Masila fields are in the Jurassic- to Lower Cretaceous-aged, Saar Graben. Almost 90% of the Masila reserves are reservoired in the Qishn Formation of the Lower Cretaceous Upper Qishn Clastics Member. Oil is also found in at least seven other reservoirs consisting of Lower Cretaceous and Middle to Upper Jurassic age clastics and carbonates as well as fractured granitic basement.

 

In this study I used real subsurface data related to 93 wells, penetrated the productive and non-productive fields of the studied area. All above-mentioned wells penetrated Qishn formation the main subject of this study, where I made geostatistical calculations and analysis, to explain the process of sedimentation mathematically for Qishn formation generally and its subdivision in detail. Showing the maximum, minimum and the average of Qishn formation thickness, its members, sub members, units and sub units in detail for every well, for every productive field and for Masila Block as a whole.

 

The most important thing I have done during my study to the pervious and the present data, informations and published materials on the reservoir rocks of Qishn Formation is that I focused on the main producing horizon (the Upper Qishn Clastics Member). The Upper Qishn represents an upward transgressive sequence from braided river deposits into tidally influenced shorelines, overlain by subtidal and shelf deposits.

 

Important Notices:

1.                  Yemeni reserves of raw oil were estimated to be about 4 billion barrels, of which 1380 million barrels are found in Marib, 1580 billion barrels in Masila, 250 million barrels in Shabwah, and 750 million barrels in Gannah.

2.                  Arab investment in Yemen heading toward $1 billion Yemen, Economics, 9/23/1997

 

 

 

iii

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Fig. (3) Masila Block Oil Fields (Nexen Inc., Data)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Iv

 

 

 

 

MAIN TOPICS OF THIS STUDY

 

 

The main topics of this study on the reservoir rocks of Qishn Formation (Masila Block 14) are the following:

 

1.                                          To show the great importance of Masila (Block 14) and the reservoir rocks of Qishn Formation for Nexen Inc.

 

2.                                          To give a brief on the whole pervious activities done on studying the Geological Research History Work of the eastern part of the Republic of Yemen (the study area and the adjacent areas).

 

3.                                          To follow Qishn formation location on the whole surface, to study it in the sub surface of the studied area and to highlight the upper Qishn clastics rocks stratigraphy.

 

4.                                          To study the Qishn Formation in Masila Block 14 as whole and in detail, its subdivision, ages, sequence stratigraphy, general lithology, lithology, its drilling parameters averages, mud parameters, its Paleogeography, and its sedimentation thicknesses in the study area by making 20 tables on Qishn formations and it sub sequences.

 

5.                                          To explain the petroleum system of Qishn Formation, its source rocks, maturation, migration, reservoir rocks, traps and seals.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

v

 

 

 

NATURE OF THIS STUDY

 

Prompted largely by this interest, my research study plan on studying the reservoir rock of Qishn Formation was concentrated on its achievement on the following important point:

 

1.                  Study and examination of all primary information connected with the subject from various sources.

2.                  Sorting of this information in accordance with its importance.

1.                  Making number of tables and maps.

2.                  Checking of all data and making necessary tests on them.

3.                  Follow-up of the historical development of the reservoir rocks of Qishn Formation through the making of varying geostatistical and mathematical calculation for the interested section of Qishn formation and its subdivision from its bottom till the surface.

 

 

 

AIM OF THIS STUDY

 

 

The study was aimed at the problems outlined in the previous two sections. This study is the first investigation work-study, done by me on the reservoir rocks of Qishn formation of Masila Block 14, which aims to:

 

1.                  Help understanding of the great importance of the studied area.

2.                  Help understanding of the pervious and present geological activities in the area.

3.                  Help understanding of the reservoir rocks of Qishn formation, surface, sub surface geology and the upper Qishn stratigraphy.

4.                  Help understanding of Qishn formation sequence stratigraphy.

5.                  Help understanding of Qishn formation (Masila, Block 14) petroleum system.

6.                  Give new discussions points, recommendations and conclusions.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Vi

 

 

 

 

CONTENTS

 

WHAT MASILA BLOCK AND QISHN FORMATION MEANS FOR CANADIAN NEXEN INC.?   ----------------------------------i

INTRODUCTION   ----------------------------------------------------------------------------------------------------------------------------iii

MAIN TOPICS OF THIS STUDY   ----------------------------------------------------------------------------------------------------------------------v

NATURE OF THE PROBLEM   -------------------------------------------------------------------------------------------------------------------------vi

AIM OF THIS STUDY   ------------------------------------------------------------------------------------------------------------------------------------vi

CONTENTS   -----------------------------------------------------------------------------------------------------------------vii

LIST OF FIGURES   --------------------------------------------------------------------------------------------------------ix

LIST OF TABLES   ----------------------------------------------------------------------------------------------------------x

 

CHAPTER 1: THE EASTERN PART OF THE REPUBLIC OF YEMEN GEOLOGICAL RESEARCH HISTORY WORK  

1.1 PERVIOUS ACTIVITIES IN MASILA BLOCK AND ITS ADJACENT AREAS   -----------------------------------------------1

1.1.1                                                                                INRODUCTION

1.1.2                                                                                PERVIOUS WORKS BASED ON MY CLASIFICATION AND DIVISION

 

CHAPTER 2: THE RESERVOIR ROCKS OF QISHN FORMATION (MASILA, BLOCK 14) – GEOLOGY  

2.1 INTRODUCTION   --------------------------------------------------------------3

2.2 QISHN FORMATION RESERVOIR GEOLOGY

2.3 UPPER QISHN CLASTICS – STRATIGRAPHY   -------------------------9

 

CHAPTER 3: QISHN FORMATION AND ITS SUBDIVISION (IN DETALS)

3.1 INTRODUCTION   -------------------------------------------------------------10

3.2 QISHN FORMATION IN THE OUTCROP

3.3 QISHN FORMATION IN THE SUBSURFACE (IN DETAILS)

3.3.1 Qishn Carbonate Member   ------------------------------------------21

3.3.1.1 Qishn Carbonate Member - Age

3.3.1.2 Qishn Carbonate Member - Lithology in General

3.3.1.3 Qishn Carbonate Member - Lithological Description

3.3.1.4 Rate of Penetrations for Qishn Carbonate Member

3.3.1.5 Gases in Qishn Carbonate Member

3.3.1.6 Drilling Parameters for Qishn Carbonate Member

3.3.1.7 Qishn Carbonate Member – Subdivision   ------------24

                                    3.3.1.7. 1 C1

3.3.1.7.2 C2

3.3.1.7.3 RS (Red Shale)

3.3.1.7.4 C3   

3.3.2 Qishn Clastic Member   ----------------------------------------------26

3.3.2.1 Qishn Clastic Member - Age

3.3.2.2 Qishn Clastic Member - Lithology in General

3.3.2.3 Qishn Clastic Member - Lithological Description

 

 

vii

 

 

 

3.3.2.4 Rate of Penetrations for Qishn Clastic Member  

3.3.2.5 Gases in Qishn Clastic Member

3.3.2.6 Oil Shows in Qishn Clastic Member

3.3.2.7 Drilling Parameters for Qishn Clastic Member

3.3.2.8 Qishn Clastic Member – Subdivision   ----------------29

                                    3.3.2.8.1 Upper Qishn Clastic Sub Member   ----------30

                                    3.3.2.8.1.1 S1   ------------------------------------31

3.3.2.8.1.1.1 S1A

3.3.2.8.1.1.2 S1B

3.3.2.8.1.1.3 S1C

3.3.2.8.1.2 S2    ------------------------------------33

                        3.3.2.8.1.2.1 S2A

            3.3.2.8.1.2.2 S2B

                        3.3.2.8.1.2.3 S2C

            3.3.2.8.1.2.4 S2D

3.3.2.8.1.3 S3   ------------------------------------35

3.3.2.8.2 Lower Qishn Clastic Sub Member   --------  -36

                                                3.3.2.8.2.1 LQ1

3.3.2.8.2.2 LQ2

3.3.2.8.2.3 LQ3

3.3.2.8.2.4 LQ4

 

CHAPTER 4: QISHN FORMATION PETROLEUM SYSTEM   -----------------40

4.1 INTRODUCTION

4.2 SOURCE ROCKS

4.3 MATURATION

4.4 MIGRATION             

4.5 RESERVOIR ROCKS     

4.6 TRAPS AND SEALS       

 

CHAPTER 5: DISSCUSION POINTS, RECOMMENDATIONS AND CONCLUSION  

5.1 DISSCUSION POINTS   --------------------------------------------------------41

5.2 RECOMMENDATIONS   ------------------------------------------------------42

5.3 CONCLUSIONS   ----------------------------------------------------------------43

 

ACKNOWLEDGEMENTS   -----------------------------------------------------------------44

REFERENCES   -------------------------------------------------------------------------------45

ABOUT THE AUTHOR   --------------------------------------------------------------------46

 

 

 

 

 

 

 

 

 

Viii

 

 

 

LIST OF FIGURES

 

 

Fig. (1) Masila Location   ---------------------------------------------------------------------ii

Fig. (2) Nexen Blocks in Yemen   -----------------------------------------------------------ii

Fig. (3) Masila Block Oil Fields   ------------------------------------------------------------iv

Fig. (4) Regional Stratigraphy (showing our study area)   --------------------------------4

Fig. (5) Regional Frame Work (showing Masila Block Location due to Say’un al- Masila Basin   -----------------------------------------------------------------------------------5

Fig. (6) Regional Setting (showing Masila Block Location, due to Masila High)   ---6

Fig. (7) Stratigraphy of Masila (showing Qishn Clastics Member and its related subdivision)   -----------------------------------------------------------------------------------7

Fig. (8) Regional cross section between Tawila-1, Tawila-17, Heijah-2, Camaal-3

and Sunah-3 wells   -----------------------------------------------------------------------------8

Fig. (9) Qishn Carbonate Member, Thickness Map   -------------------------------------22

Fig. (10) Qishn Carbonate Member, Three Dimension Model   -------------------------23

Fig. (11) Qishn Clastics Member, Thickness Map   ---------------------------------------27

Fig. (12) Qishn Clastics Member, Three Dimension Model   ----------------------------28

Fig. (13) Qishn Formation, Thickness Map   -----------------------------------------------38

Fig. (14) Qishn Formation, Three Dimension Model   -----------------------------------39

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Ix

 

 

 

 

LIST OF TABLES

 

Table (1): Qishn Formation of Masila Block, its Subdivision Tops and Thicknesses   -----------------------------------------------------------------------------------11

Table (2) Qishn Carbonate of Masila, Block 14 Thicknesses   ----------------------21

Table (3) Qishn Carbonate (C1) of Masila, Block 14 Thicknesses   --------------------24

Table (4) Qishn Carbonate (C2) of Masila, Block 14 Thicknesses   --------------------25

Table (5) Qishn Carbonate (RS) of Masila, Block 14 Thicknesses   --------------------25

Table (6) Qishn Carbonate (C3) of Masila Block 14, Thiknesses   ---------------------26

Table (7) Qishn Clastics of Masila, Block 14 Thicknesses   --------------------------29

Table (8) Upper Qishn Clastics of Masila, Block 14 Thicknesses   -----------------30

Table (9) Upper Qishn Clastics (S1A) of Masila, Block 14 Thicknesses   -------------31

Table (10) Upper Qishn Clastics (S1B) of Masila, Block 14 Thicknesses   -----------32

Table (11) Upper Qishn Clastics (S1C) of Masila, Block 14 Thicknesses   -----------32

Table (12) Upper Qishn Clastics (S2A) of Masila, Block 14 Thicknesses   -----------33

Table (13) Upper Qishn Clastics (S2B) of Masila, Block 14 Thicknesses   -----------34

Table (14) Upper Qishn Clastics (S2C) of Masila, Block 14 Thicknesses   -----------34

Table (15) Upper Qishn Clastics (S2D) of Masila, Block 14 Thicknesses   -----------35

Table (16) Upper Qishn Clastics (S3) of Masila, Block 14 Thicknesses   -------------35

Table (17) Lower Qishn Clastics of Masila, Block 14 Thicknesses   ---------------36

Table (18) Lower Qishn Clastics (LQ1) of Masila, Block 14 Thicknesses   ----------36

Table (19) Lower Qishn Clastics (LQ2) of Masila, Block 14 Thicknesses   ----------37

Table (20) Qishn Formation of Masila, Block 14 Thicknesses   ---------------------37

 

 

Important Notice:

All above-mentioned tables done by me based on my study to:

1.                  The Masila Block Field Development Location Map in General.

2.                  Sunah, Heijah, Camaal, Hemiar, … ,Haru and Naziah Fields

3.                  The Geological Summary of the Masila Block

4.                  The Masila Block Stratigraphic Column

5.                  The Geological Sections done by me for Sunah-1, Naar-1, Maljan-1, Ressib-1, Deelun-1 Wells.

6.                   Masila Block Formation Tops and Thicknesses (The table done in 1993, 1997 and updated in 2002, by Nexen Inc.)

7.                  An old table done by me as a part of my study to Masila Block in the past. The main aim of the above mentioned table is to give interested persons in Masila Block general informations (such as: Block Area, Productive and non-productive fields, No. of wells in every Productive and non-productive fields and the Sedimentary Cover) and also geological informations (such as: the stratigraphical sections, thicknesses, lithology, source rocks characteristics and reservoir rocks characteristics)

 

 

 

 

 

 

X

 

 

 

CHAPTER 1

 

THE EASTERN PART OF THE REPUBLIC OF YEMEN GEOLOGICAL RESEARCH

HISTORY WORK

 

 

1.1 PERVIOUS ACTIVITIES IN MASILA BLOCK AND ITS ADJACENT AREAS

 

1.1.1                                INRODUCTION

The Republic of Yemen is beside the richest hydrocarbon province in the world. Oil only discovered in the early 1980’s in the offshore (Sharmah Well). It is known, that Nexen Inc. (formerly known as Can Oxy Company) discovered oil in Masila Block in 1990 in the Qishn Clastics Member of Qishn Formation.

 

 

The Masila Block has 1250 km² in size. The Estimated Reserves is 1.1 billion barrels recoverable and the Cumulative Production is 600,000,000 barrels (Due to March 2002 wells production reports), where the daily production was 230,000 b/d.

 

1.2 PERVIOUS WORKS BASED ON MY CLASIFICATION AND DIVISION

 

According to my new classification and first division to the whole geological research history work in the Republic of Yemen to four stages (See Yemen Times Newspaper. Issue 2-January 10th through January 16 2000, Vol. IX Culture Page, Issue 10 - March 6 through March 12 2000, Vol. X, Culture Page and Issue 15 - April 10 through April 16 2000, Vol. X, Culture Page). It is so clear now, that:

 

1. On the First Stage (The First Systematic Geological Observation Stage or Carter’s Stage), 1852-1901:

 

No kind of geological studies had been detected in the Masila area.

 

2. On the Second Stage or the Hinterland Studies Stage, (1902-1946) and the Third Stage (The First Systematic more detailed Stratigraphic and Geological Studies Stage or Beydoun, Z.R.'s Stage, (1947-1967):

 

The Petroleum Concessions Ltd, one of the Iraq Petroleum Company and associated companies (IPC and Associated companies) had carried out little exploration work in the area between 1937 and 1960. During that time they made geological field mapping, investigation, supplemented by aerophoto studies, photogeologic and mapping covering the entire territory were carried out.

 

 

 

1

3. On The Third Stage (The First Systematic more detailed Stratigraphic and Geological Studies Stage or Beydoun, Z.R.'s Stage), 1947-1967:

 

During this stage the adjacent areas started to be studied by scientist and oil companies. Bunker, D.G. wrote about the southwest Borderlands of Rub al Khali, in 1953. From 1961 to early 1967, Pan American International Oil Company through a subsidiary, Pan American Hadhramawt Oil Company (PAHOC) drilled four wells (Hoowarin, Tarfayt and Core Hole 88 reached Precambrian basement and the forth was abandoned in the Cretaceous sediments).

 

4. The Forth Stage or The Yemeni Geologists Stage (1968 – until Today):

 

During this stage many important scientific works happened in Yemen, which at the end led to the creation of the concision map of Yemen, the birth of Masila Block and its oil discoveries.

 

It is known that, the Petroleum and Minerals Board (the PMB) was established, in 1970 in former South Yemen. During the period from 1970 to 1973, the joint of former South Yemen-Algerian Petroleum Company (SYAPCO) drilled Taur-1 in 1974 and Taur-2 was commenced. In 1974, a group of experts from Cuba assumed the drilling operation from SYAPCO and with former PMB completed Taur-2, Taur-3 and drilled Thamud-1 and Hathout-1. In September 1976, the functions of the PMB were broadened and the Petroleum Exploration Board (the PED) was created (The Petroleum Exploration and Production Board, Aden Branch – As known now), was led different activities on studding the geology of this area. As a result of their work on the Yemeni sector of Rub al Khali basin, wells as Taur-2, Taur-3 and Hathout-1 was drilled. A group of the P.E.D.’s Engineers, Technician and workers, work hard on this area, their work is highly appreciated.

 

Between 1975 and 1979, as a part of its assistance program, TechnoExport, the former Soviet Technical Assistance Organization, had recorded aeromagnetic surveys covering most of former South Yemen and also a gravity survey had been conducted over specific areas of interest.

 

On Mar. 27 1979, B. Kuzin and Mohammed Ba’abad made a Stratigraphic Correlation, for wells drilled in that area correlative with wells located in the adjacent area at that's time.

 

The field investigation had been augmented from time to time by Czechoslovakian and German technical personnel.

 

Agip SpA (from 1978 to 1980): conducted landsite airphoto interpretation and a field mapping project along the coastal outcrop belt as part of its offshore exploration effort in the Sayhut Block. On 1981 Agip recorded 110 km of seismic on the coastal plain east of Mukalla.

 

Petroleo Brasileiro SA (Petrobras): shot a regional seismic program and drilled three unsuccessful test wells in the area to the north of the Masila Block in Jeza syncline and relinquished the area in 1987.               

2

 

 

 

CHAPTER 2

 

THE RESERVOIR ROCKS OF QISHN FORMATION (MASILA, BLOCK 14) – GEOLOGY

 

 

2.1 ITRODUCTION

It is known, that oil trapped in sands of the Qishn Formation, the main subject of this study, in the following structures: Camaal, North, Sunah, North East Sunah, Heijah, Hemiar, South Hemiar, West Hemiar, Tawila, Haru, Nazeia, Dahban, North Dahban, Qataban, and Gabal-Isbeel.

Note 3: Oil has also been discovered in the Kohlan Formation (at Sunah; for example), in addition there have been significant oil shows from fractured basement (at Sunah; for example) and the Saar Formation (at Camaal; for example). In my opinion ongoing exploratory drilling is expected to inhance present discoveries and to find oil in additional horizons and traps.

Subsidence in the Masila area began with a marine transgression in Upper Jurassic time over the Pre Cambrian basement peneplain. The Kohlan Formation sands were deposited as a transgressive lag that passes gradationally upwards into the shallow marine carbonates of Shuqra Formation. A period of rifting in the late Jurassic led to restricted conditions and deposition of the Madbi shales, the oil source rocks for the discoveries. The Madbi shales are overlain by the deep-water limestones of the Naifa Formation of uppermost Jurassic to lowermost Cretaceous age. Lower Cretaceous shales and carbonates of the Saar Formation and the clastics and carbonates of the Qishn Formation, the main subject of this study, were deposited. The Upper Cretaceous and the Lower Tertiary sediments are predominantly clastic with interbedded carbonates becoming more carbonate rich into the Tertiary.

The Masila area has undergone several periods of rifting, resulting in a complexly faulted basement structure. Uppers Jurassic rift basins are bounded by the basement high blocks over which the Jurassic has been eroded and is either thin or absent. Subsequent periods of rifting led to reactivation of the basement faults and normal faulting through the Cretaceous (the Lower Cretaceous age of Qishn Formation) and the Tertiary section over the basement highs.

 

 

2.2 QISHN FORMATION RESERVOIR GEOLOGY

The Qishn reservoir sandstones have both high porosity (18-21%), and high permeability (<10 Darcies). They are relatively homogenous and continuous in the lower section and are more heterogeneous in the middle-upper section. The uppermost marine sandstones are mature and very homogeneous. The major field accumulations are tilted, normal, fault block structures located over basement paleohighs, and are dependent upon juxtaposition against overlying Qishn carbonates. The carbonate-dominated pre-Qishn section, including the source rock, is not present on the paleo-highs, and is thickest in the basement lows.

 

 

 

3

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Fig. (4) Regional Stratigraphy, showing our study area

(Beydoun et al., 1998)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

4

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Fig. (5) Regional Frame Work, showing Masila Block Location due to Say’un al-Masila Basin (Nexen Inc., Data)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

5

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Fig. (6) Regional Setting, showing Masila Block Location due to

Masila High (Nexen Inc., Data)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

6

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Fig. (7) Stratigraphy of Masila, showing Qishn Clastics Member and its related subdivision (Nexen Inc., Data)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

7

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Fig. (8) Regional cross section between Tawila-1, Tawila-17, Heijah-2, Camaal-3 and Sunah-3 Wells (Nexen Inc., Data)

 

 

 

 

 

 

 

 

 

 

8

 

1. The Upper Qishn Clastics of Cretaceous age are the primary producing reservoirs in the Masila Block Development area.

 

2. Cretaceous Qishn Clastics Member, Yemen, was deposited in a rift basin connected to the Paleo-Indian Ocean - an ideal set-up for tidal amplification and domination. Recoverable hydrocarbon reserves are 1.1 bbl. Facies associations are consistent with an estuarine system – sand shoals, tidally influenced point bars, mud flats, etc.

Lower Qishn onlap resulted in deposition of tidal estuarine to bay-facies. A sequence boundary truncates the Lower Qishn at the base of the S3, a low-accommodation braidplain deposited close to the shoreline. A flooding surface at the top of the S3 heralds S2 progradational, tide-dominated deltaic deposits. Delta progradation culminated in clastic dolomitic deposits on the coastal plain. With subsequent transgression, S1C deposits show rising water table and a nonmarine flooding surface, overlain by tidal-flat/inlet deposits. Ongoing transgression resulted in wave-ravinement overlain by shallow shelf clastics and deeper shelf carbonates of the S1B. The overlying S1A comprises bioturbated, clastic shelf deposits related to a drop in sea level. Accommodation was relatively high, except for low accommodation associated with regional sheet sandstone of the S3. Qishn Clastic sediments meet the criteria of a macrotidal, tide-dominated estuary, yet a more appropriate analog is the Tigress-Euphrates River and delta flowing into the Arabian Gulf. Is the latter a tidally influenced delta flowing into a gulf - or a large bayhead delta? Application of existing terminologies - estuaries, syn-rift clastics, deltaic, strait, Gulf, bay - is confusing to the practicing explorationist, particularly when attempting to convey a mental image of the environmental setting of the reservoir.

 

 

2.3 UPPER QISHN CLASTICS – STRATIGRAPHY

The Upper Qishn Clastics have been proven productive over the Sunah, Heijah, Camaal and other productive structures. The interval is defined as the predominantly sandstone section abruptly overlying the shalier Lower Qishn Clastics and underlying the sealing Qishn Carbonates. It ranges in thickness from 61 meter in Heijah-1 to 76 m in Sunah-1.

 

Important Notice: We are highly in need to make a restudy on all Upper Qishn Clastics samples cored in productive structures. Through standard core analysis and special core analysis and petrographic analysis, we can give a full more detailed restudy on the Upper Qishn Clastics reservoir geology and petrophysics.

 

The Upper Qishn Clastics is subdivided into three lithostratigraphic units, which in descending order are SI, S2 and S3. Each sequence contains reservoir quality sands and in my opinion it must be correlated not just in specific structures, but amongst all above mentioned Upper Qishn Clastics productive structures.

 

 

 

 

 

 

9

 

 

 

CHAPTER 3

 

QISHN FORMATION AND ITS SUBDIVISION

(IN DETALS)

 

3.1: INTRODUCTION

It is known that Qishn Formation (Lower Cretaceous Age) is synonym to Lower Cretaceous part of Little, 1925. It is equivalent to Shuaiba Formation (Present in the Kingdom of Saudi Arabia and the United Arab Emirates). In this study I used 93 wells penetrated Qishn Formation in different productive and non-productive fields of Masila Block, where I concentrated my study on the reservoir rocks of Qishn formation. (See, Table (1))

 

 

3.2 QISHN FORMATION IN THE OUTCROP

· In Mahra Province at Ras Sharwayn near Qishn town as the name implies. Thickness 411 m, from base upwards mainly limestone and marl.

· Near Al-Mukalla at Jabal ar Rays. Thickness 32 m, from base upwards mainly sandstone, marls and limestone.

· In Wadi Masila near Qalana (Thickness 628 m, for the first section 338 m and for the second section 290 m), from base upwards mainly sandstones, dolomites and lime-mustone for the first section mainly marls and marly limestone.

· In Masila – Thickness 498 m. Mainly limestone, with several sandstone, marl and shale zones in the lower part.

· Jabal Ghuba (near Brum) – Thickness 63 m. mainly of sandstones and gypsiferous marls and siltstone and some conglomeratic layers, is capped by the fossiliferous limestone carrying orbitolinas.

· Jabal Billum – the Jurassic Qishn contact is marked by sandy dolomitic limestone.

· Al-Mintaq – The base is marked by a thick conglomerate or sandstone with some pebbles generally locally derived from the under lying Jurassic or basement, this marks the advent of the Cretaceous Sea.

 

 

3.3 QISHN FORMATION IN THE SUBSURFACE (IN DETAILS)

 It is known, that Qishn formation in Yemen is subdivided into three members:

 

1. Qishn Carbonate Member

2. Qishn Clastic Member

3. Sa’af Member

 

Due to my study to the above mentioned area I gave more attention to the following subdivision of Qishn Formation:

 

3.3.1 Qishn Carbonate Member

3.3.2 Qishn Clastic Member

 

 

 

10

 

 

3.3.1 Qishn Carbonate Member: (See, Table (2), Figs. (9) and (10))

 

3.3.1.1 Qishn Carbonate Member - Age: (Barremian to Aptian but in the extreme east may go down to Late Hauterivian and up to ?Early Albian Age)

 

3.3.1.2 Qishn Carbonate Member - Lithology in General: Principally carbonates as the name implies but includes subordinate shales and occasional sands and generally reflect a nertic environment.

 

3.3.1.3 Qishn Carbonate Member - Lithological Description: In my study area, Qishn Carbonate Member ’s lithology is mainly of Lime-Mudstone to Lime-Wackstone with thin streaks of Shale.

 

Limestone: Mudstone to Wackstone, occasionally Packstone, white to grayish white, pale yellow brown, cryptocrystalline to occasionally microcrystalline, moderately hard to hard, chalky, argillaceous grading to marly Limestone, with pyrite crystals.

 

Shale: Dark bluish grey, olive grey, reddish brown, firm, fissile, calcareous in places, with abundant pyrite.

 

Table (2) Qishn Carbonate of Masila, Block 14 Thicknesses

(Done by: Dr. Mohammed Darsi)

 

 

 

 

 

 

 

 

 

 

21

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Fig. (9) Qishn Carbonate Member, Thickness Map

(Taking in account the whole eastern part of the Republic of Yemen, the western part of Sultanate of Oman border and the Kingdom of Saudi Arabia border with the Yemeni sector of Rub al-Khali Basin; Done by: Dr. Mohammed Darsi)

 

 

 

 

 

 

 

22

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Fig. (10) Qishn Carbonate Member, Three Dimension Model

(Taking in account the whole eastern part of the Republic of Yemen, the western part of Sultanate of Oman border and the Kingdom of Saudi Arabia border with the Yemeni sector of Rub al-Khali Basin; Done by: Dr. Mohammed Darsi)

 

 

 

 

 

 

 

 

 

 

 

 

 

23

 

3.3.1.4 Rate of Penetrations for Qishn Carbonate Member:

Average ROP in Limestone 28 Min/M.

Average ROP in Shale 22 Min/M.

 

3.3.1.5 Gases in Qishn Carbonate Member:

Background gas levels averaged 0.1 units.

 

3.3.1.6 Drilling Parameters for Qishn Carbonate Member:

WOB 20-25 klbs

RPM 90-100

SPM 540 gpm

SPP 1500 psi

 

MW 9.4 PPG

FW  42-43

 

3.3.1.7 Qishn Carbonate Member - Subdivision: In Masila Block, Qishn Carbonate Member subdivided into the following units:

 

3.3.1.7. 1 C1 (See, Table (3))

3.3.1.7.2 C2 (See, Table (4))

3.3.1.7.3 RS (Red Shale) (See, Table (5))

3.3.1.7.4 C3 (See, Table (6))

 

 

 

Table (3): Qishn Carbonate (C1) of Masila, Block 14 Thicknesses

(Done by: Dr. Mohammed Darsi)

 

 

 

 

 

24

 

Table (4): Qishn Carbonate (C2) of Masila, Block 14 Thicknesses

(Done by: Dr. Mohammed Darsi)

 

 

 

 

Table (5) Qishn Carbonate (RS) of Masila, Block 14 Thicknesses

(Done by: Dr. Mohammed Darsi)

 

 

 

 

 

 

 

 

 

 

25

 

 

Table (6) Qishn Carbonate (C3) of Masila, Block 14 Thicknesses

(Done by: Dr. Mohammed Darsi)

 

 

 

3.3.2 Qishn Clastic Member: (See, Figs. (11), (12) and Table (7))

 

3.3.2.1 Qishn Clastic Member – Age: (Generally Hauterivian – Early Barremian, especially in the eastern province, to Barremian - Early Aptian in the west (?))

 

3.3.2.2 Qishn Clastic Member - Lithology in General: Principally clastics as the name implies, includes coarse clastics in some sections as well as fine sands, silts and mudstones, shales, as well as marls.

 

3.3.2.3 Qishn Clastic Member - Lithological Description: In my study area, Qishn Clastic Member is mainly of Sandstone with Claystone streaks and traces of Anhydrite. A trace of Coal was logged also.

 

Sandstone: Quartz, colourless, grayish white, brownish grey, medium grained, moderately sorted to well sorted in places, subrounded to subangular, poor to moderate intergranular porosity, with calcareous cement.

           

Claystone: Light grayish green, reddish brown, soft to firm, blocky, slightly silty, subfissile in places graded to Shale. Towards the base Claystone was replaced by Clay, which was highly washable.

           

Traces Anhydrite: Off white to white, colourless, amorphous, occasionally crystalline, soft, locally hard, calcareous in places.

           

Coal: Black, firm to moderately hard, laminated, vitreous luster, earthy and pyretic.

 

 

26

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Fig. (11) Qishn Clastics Member, Thickness Map

(Taking in account the whole eastern part of the Republic of Yemen, the western part of Sultanate of Oman border and the Kingdom of Saudi Arabia border with the Yemeni sector of Rub al-Khali Basin; Done by: Dr. Mohammed Darsi)

 

 

 

 

 

 

 

 

27

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Fig. (12) Qishn Clastics Member, Three Dimension Model

(Taking in account the whole eastern part of the Republic of Yemen, the western part of Sultanate of Oman border and the Kingdom of Saudi Arabia border with the Yemeni sector of Rub al-Khali Basin; Done by: Dr. Mohammed Darsi)

 

 

 

 

 

 

 

 

 

 

 

28

 

 

Table (7) Qishn Clastics of Masila, Block 14 Thicknesses

(Done by: Dr. Mohammed Darsi)

 

 

 

3.3.2.4 Rate of Penetrations for Qishn Clastic Member:

Average ROP in Sandstone 15 Min/M, with maximum of 7 Min/M.

Average ROP in Claystone 20 Min/M.

Average ROP in Anhydrite 25 Min/M.

 

3.3.2.5 Gases in Qishn Clastic Member:

Background gas levels slightly increased through some sections ranging from 0.5 to 1.0 API units. A gas peak was recorded at some wells with a maximum of 14.1 unit. The chromatographic analysis of which broke down in some wells as follows:

C1= 0.77U; C2= 0.11U; C3= 0.98U; C4= 0.2 U     

 

3.3.2.6 Oil Shows in Qishn Clastic Member:

A good oil shows was observed through the sandstones of the Qishn Clastics Member of the Qishn Formation. Light brown oil stain, bluish white and bright fluorescence, and straw yellow chloroethane cut of dull to bright intensity.

 

3.3.2.7 Drilling Parameters for Qishn Clastic Member:

WOB 23 klbs; RPM 93; SPM 698 gpm; SPP 2350 psi

 

MW  9.3-9,4 PPG; FW  43-48

 

3.3.2.8 Qishn Clastic Member – Subdivision:

The Qishn Clastic Member is subdivided into two sub members:

 

3.3.2.8.1 Upper Qishn Clastic Sub Member

3.3.2.8.2 Lower Qishn Clastic Sub Member

 

29

 

3.3.2.8.1 Upper Qishn Clastic Sub Member: (See, Table (8))

Production is mainly from the Lower Cretaceous of the Upper Qishn Clastic Sub Member, a sandstone-dominated sequence that reflects deposition during an overall transgression.

 

Table (8) Upper Qishn Clastics of Masila, Block 14 Thicknesses

(Done by: Dr. Mohammed Darsi)

 

 

 

Upper Qishn Clastic Sub Member subdivided into three units:

 

3.3.2.8.1.1 S1

3.3.2.8.1 .2 S2

3.3.2.8.1.3 S3

 

 

3.3.2.8.1.1 S1

Important Notice: The base of S1, which it is the top of S2 is marked by the correlative lowest bed of S1 sequence, a thin basal conglomeratic, muddy, calcareous sandstones, with abundant shale clasts and shells.

 

 

3.3.2.8.1 .2 S2

Important Notice: The base of S2 is marked by the correlative shales of S2-D, which directly overly the thick sand S3.

 

 

3.3.2.8.1.3 S3

 Important Notice: S3 abruptly overlies the Lower Qishn Clastics section of shales and sands.

 

 

30

 

3.3.2.8.1.1 S1

The S1 sequence is composed of upper porous quartzose sand and lower, tight, muddy, calcareous sand. The upper quartzose sand marks the top of the Upper Qishn Clastics and its oil-bearing sand, which ranges in pay thickness from 2.8 m in Camaal-2 to 9.1 m in Sunah-2. The S1 sequence is widespread and thicking of the S1 sand occurs off the crest of the structures. (My pervious studies to Camaal fields prove this fact)

 

The S1 sand is a fine to medium grained, moderately to well sorted and poorly cemented quartzose sand interbedded with thin calcite cemented sands. The Mineralog shows 10% of clay potassium feldspar. Based on the presence of low angle planner cross-bedding with rippled tops, shell lags at the base of cross-bedded units and glauconite company researchers suggest deposition in a shallow marine environment.

 

S1 is subdivided into three sub-units:

 

3.3.2.8.1.1.1 S1A: (See, Table (9))

It is marine sandstone, forms at the top of this regional open marine shale, and is characterized by an overall coarsening-upward sequence. The top of the S1A is marked by another thin,regional, open marine shale.

 

 

Table (9) Upper Qishn Clastics (S1A) of Masila Fields Thiknesses

(Done by: Dr. Mohammed Darsi)

 

 

 

3.3.2.8.1.1.2 S1B: (See, Table (10))

It is marine sandstone. The top of the S1B is marked by a regional, open-marine -shale.

 

 

31

 

 

Table (10) Upper Qishn Clastics (S1B) of Masila, Block 14 Thicknesses

(Done by: Dr. Mohammed Darsi)

 

 

 

Important Notice: The proximal clastic-dominated followed by carbonate-dominated (coquinas) shelf deposits of the S1B and finally subtidal sandstone bars of the S1A are produced as a result of continued transgression.

 

 

3.3.2.8.1.1.3 S1C: (See, Table (11))

It is deposit of tidal flats; tidal channels and fine-grained bay fill deposits.

 

 

Table (11) Upper Qishn Clastics (S1C) of Masila, Block 14 Thicknesses

(Done by: Dr. Mohammed Darsi)

 

32

 

Important Notice: The two sub-units, the tidal S1C and the marine S1B, overlie the S2 sub-unit.

 

 

3.3.2.8.1.2 S2:

S2 is a thick muddy paleosols unit that can form a vertical flow barrier, which is interpreted to be a non-marine expression of a relative rise of sea level. It is a fluvial to marginal marine, characterized by tidally influenced channels and tidal deposits. The S2 is normally about 25 m thick, and arranged in an overall fining upward sequence.

 

The S2 sequence of interbedded sands and shales is further subdivided into for sequences, which in descending order are S2A, S2B, S2C and S2D. Each sub-sequence contains reservoir quality sands over different parts of the study area. In contrast to S1, the S2 reservoir sands show less continuity, and S2A and S2B show the lowest continuity.

 

Lithofacies in S2 include tidal channel reservoir sandstones, crevasse splay reservoir sandstones and tidal flat non-reservoirs of interbedded silty mudstones and muddy sandstones.

 

 

S2 is subdivided into four sub units:

 

3.3.2.8.1.2.1 S2A: (See, Table (12))

 

 

 

Table (12) Upper Qishn Clastics (S2A) of Masila, Block 14 Thicknesses

(Done by: Dr. Mohammed Darsi)

 

 

 

33

 

3.3.2.8.1.2.2 S2B: (See, Table (13))

 

 

 

Table (13) Upper Qishn Clastics (S2B) of Masila, Block 14 Thicknesses

(Done by: Dr. Mohammed Darsi)

 

 

 

3.3.2.8.1.2.3 S2C: (See, Table (14))

 

 

 

Table (14) Upper Qishn Clastics (S2C) of Masila, Block 14 Thicknesses

(Done by: Dr. Mohammed Darsi)

 

 

 

34

3.3.2.8.1.2.4 S2D: (See, Table (15))

 

 

Table (15) Upper Qishn Clastics (S2D) of Masila, Block 14 Thicknesses

(Done by: Dr. Mohammed Darsi)

 

 

 

3.3.2.8.1.3 S3: (See, Table (16))

 

The S3 sequence is massive sand section about 15 m thick, marking the base of the Upper Qishn Clastics section. Lithofacies in S3 are the same as S2, except that the meandering tidal channel facies is dominant. The sand grains are subrounded, weakly to moderately consolidated with minor calcareous and silica cement. The Mineralog shows about 10% clay content and less than 5% potassium-feldspare. Clays are primarily illite/smecitite with lesser kaolinite.

 

Table (16) Upper Qishn Clastics (S3) of Masila, Block 14 Thicknesses

(Done by: Dr. Mohammed Darsi)

 

35

 

3.3.2.8.2 Lower Qishn Clastic Sub Member: (See, Table (17))

The Lower Qishn Clastics are the shales and sands found between the Upper Qishn Clastics and the Saar Formation. The sands are tidal channel in origin and have limited areal extent. The sands are fine to medium grained and quartzose.

 

Table (17) Lower Qishn Clastics of Masila, Block 14 Thicknesses

(Done by: Dr. Mohammed Darsi)

 

 

Lower Qishn Clastic Sub Member is subdivided into four units:

 

3.3.2.8.2.1 LQ1: (See, Table (18))

 

Table (18) Lower Qishn Clastics (LQ1) of Masila, Block 14 Thicknesses

(Done by: Dr. Mohammed Darsi)

 

 

 

36

3.3.2.8.2.2 LQ2: (See, Table (19))

Table (19) Lower Qishn Clastics (LQ2) of Masila, Block 14 Thicknesses

(Done by: Dr. Mohammed Darsi)

 

 

3.3.2.8.2.3 LQ3

3.3.2.8.2.4 LQ4

Important Notice:

It must be known that above mentioned fields majorities occupy separate normal fault-bounded structures, aligned along a NE-SW oriented structural high trend (called the Masila High). These faults were formed by late stage reactivation of faults initially created during Late Jurassic to Early Cretaceous active rifting. On the highs a relatively thin veneer of Lower Cretaceous sandstones and carbonates rest unconformably upon granitic or metamorphic basement. In the adjacent paleo-lows, a significantly thicker stratigraphic section exists in which carbonates predominate.

(See, Table (20), Figs. (13) and (14)) as a conclusions.

 

Table (20) Qishn Formation of Masila, Block 14 Thicknesses

(Done by: Dr. Mohammed Darsi)

 

37

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Fig. (13) Qishn Formation, Thickness Map

(Taking in account the whole eastern part of the Republic of Yemen, the western part of Sultanate of Oman border and the Kingdom of Saudi Arabia border with the Yemeni sector of Rub al-Khali Basin; Done by: Dr. Mohammed Darsi)

 

 

 

 

 

 

 

 

 

 

38

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Fig. (14) Qishn Formation, Three Dimension Model

(Taking in account the whole eastern part of the Republic of Yemen, the western part of Sultanate of Oman border and the Kingdom of Saudi Arabia border with the Yemeni sector of Rub al-Khali Basin; Done by: Dr. Mohammed Darsi)

 

 

 

 

 

 

 

 

39

 

 

 

CHAPTER 4

 

QISHN FORMATION PETROLEUM SYSTEM

 

4.1 INTRODUCTION

The petroleum system of the Masila Block (14) is related to an Upper Jurassic source rock sequence essentially deposited as deep marine deposits in a synrift setting (in some areas prerift sag). Qishn Clastic Member as a primary reservoir and the main subject of  our study  to the reservoir rocks of Qishn Formation, is a postrift reservoir. In detail, the petroleum system of our studied area is related to the presence of the following factors:

 

4.2 SOURCE ROCKS

The Upper Jurassic (Kimmeridgian) source rock of the Madbi Formation is organic-rich black shales deposited in the deeper portions of rifts in the Late Jurassic. Madbi Formation is the main potential source rocks for the reservoir rocks of Qishn Formation.

 

4.3 MATURATION

Source rocks began generating in the central rift basin in latest Cretaceous to

earliest Paleogene time and the process were largely completed by the end of Paleogene time. Degree of maturation: (Oil Window)   0.6. Type of kerogen: 1 and 2 type of organic mater types.

 

4.4 MIGRATION

In the Masila Basin, oil and gas migrated along faults to horst blocks. Numerous horst uplifts occur; however migration resulted in hydrocarbon accumulations, where sealed by Early Cretaceous carbonate (Qishn Carbonate Member). Heavy oil is known to occur marginal to the accumulation sites.

 

4.5 RESERVOIR ROCKS   

In the Masila Basin, the Early Cretaceous estuarine sandstones of the Qishn Formation (Berremian/Aptian), mainly the Upper and Lower Qishn Clastics Members are the primary reservoir. Porosity average: 18 % – 21 %. Permeability average: 140 – 2000 mD

 

4.6 TRAPS AND SEALS

The Qishn Carbonate Member (Aptian) provides the seal for the underlying Qishn Clastic Member in the Masila Basin.

 

 

 

 

 

 

 

 

40

 

 

CHAPTER 5

 

DISSCUSION POINTS, RECOMMENDATIONS AND CONCLUSIONS

 

5.1 DISSCUSION POINTS

1.                  Masila Block’s Fields are located within the Sirr-Sayun Rift Basin that formed during the Upper Jurassic when the Africa-Arabian Plate separated from the India-Madagascar Plate. The Sirr-Sayun Basin is a few hundred kilometres wide and several hundred kilometres long, and is oriented northwest southeast. The basin is bounded on the west by Jahi - Mukalla High, to the south by the South Hadramaut Arch, to the east by the Ras Fartak High and partially interrupted to the northwest by the Sayun High. The Masila Block is situated on an intragraben terrace, and is ideally located to access migrating hydrocarbons from mature deeper buried Jurassic Madbi source rocks.

 

2.                  I found that one of the most famous, more complex and interesting topic problems, which faces any researcher who would like to make any kind of academic works. Such as any kind of geological studies on Masila Block 14 reservoir rocks of Qishn formation or any other geological research studies on the whole area, is that:

a. We have a huge material in the Database Center of the Petroleum Exploration and Production Authority (P.E.P.A) and its offices around the country.

b. We till now don’t have any full-blooded Geo-Scientific Research Centers and the suitable laboratories, where we can make new restudies on all data and materials located now in our Databases Centers.

 

What we can do now? … In my opinion the first step we should take it, as a right step in the right direction, is that P.E.P.A. ’s Database Center must be open for all Yemeni nationality scientific researchers 24 hour per day. Because this step will encourage young Yemeni scientists and researchers to make a lot of studies used the above mentioned materials. I am sure, GOD and then History will keep the names of those Yemeni peoples, who work as decision-makers and give their time and life for their country and its young generation.

 

Important Notice:

I would like to drew the reader of this study attention on the following most important mater, that one of the most important problem which make it so difficult to write on the Yemeni Geology as a whole or partly is that the whole Yemen was divided to blocks. In my opinion dividing Yemen, as a whole to blocks is the real reason, which lead to the development of company-centered informal stratigraphic nomenclature schemes. Companies’ main principal objective was to facilitate operations within the individual company’s concession area rather than facilitating scientific research and any ultimate communication in journals. So to solve this question, we must scientifically divide just the sedimentary basins in Yemen to blocks in accordance to their categorisation. (No, for dividing Yemen as a whole to blocks. I said it in the past, say it now and will say it).

41

5.2 RECOMMENDATIONS

1. In the absence of the more detailed and accurate studies on the reservoir rocks of Qishn Formation, I suggest the following known steps as an emergency solution to our case of study:

a.                                           Modelling of the Qishn Formation as whole and specially the Qishn Clastic Member and its related subdivision in detail. This must included:

                                              ·          The gross thickness

                                              ·          Facies proportions and distribution (vertically and laterally)

                                              ·          Porosity modelling (vertically and laterally for each facies)

                                              ·          Permeability (vertically and laterally for each facies).

 

b. To model each of above-mentioned parameters, modelling steps must included the following:

                                              ·          Declustering the well data

                                              ·          Examine data and clean up if necessary

                                              ·          Identify and mathematically describe trends that exist

                                              ·          Remove trends from the data

                                              ·          Perform variogram analysis and determine variogram model

                                              ·          Simulate the parameter in 3-D space

                                              ·          Re-introduce the trends that were removed earlier

 

c. The geostatistical surfaces resieved as results of our pervious steps must be compared to maps generated by conventional geologic mapping methods in order to highlight the differences between the two techniques.

 

2. We are highly in need to make a restudy on all Upper Qishn Clastics samples cored in productive structures. Through standard core analysis and special core analysis and petrographic analysis, we can give a full more detailed restudy on the Upper Qishn Clastics reservoir geology and petrophysics.

 

3.  NOW, It is recommended that a very highly qualified team must lead local and regional studies on the Yemeni Sedimentary Basin by keeping contacts with all International Geoscientific Centers in and out side Yemen.

 

 

Important Notice:

We in the Republic of Yemen must give a high attention to the Environmental Geo-sciences. It is known that the global warming issue poses a number of potential challenges and opportunities for the oil industry. Ongoing negotiations are defining not only targets for greenhouse gas reduction but also mechanisms to enable countries and companies to respond. A broad range of options exists to reduce or sequester emissions. So it is recommended to discuss some of the important technical, economic, and political questions that surround the ultimate viability of this option.

 

 

 

 

42

 

 

 

5.3 CONCLUSIONS

1.                  One of the main conclusions of this study is that Qishn Formation as a whole and also its subdivision mostly thin to the south and to the east. This important conclusion, I received it as a result of my geostatistical and mathematical analysis study on every Qishn Formation ’s subdivision in detail.

 

2.                  As a result of this study, it is easy now to understand the great importance of studying:

a.       The Masila Block (14) as a part of Say’un Al-Masila basin.

b.      The pervious and present geological activities of the whole eastern part of the Republic of Yemen.

c.       The Qishn formation in the outcrop, the reservoir rocks of Qishn formation in the subsurface and the upper Qishn stratigraphy.

d.      The Qishn formation sequence stratigraphy.

e.       The Qishn formation (Masila, Block 14) petroleum system.

 

3.                  If we really want to be Excellent and long vision decision makers, we must identify the best mechanism or trend, that could be used to study the reservoir rocks of Qishn Formation and by the way to predict the better-developed methods.

 

4.                  In my opinion, the best mechanism or trend is that we must use the latest multi functional geological soft ware application which can gave the more accurate scientific solutions to our geological problems saving time and money.

 

5.                  We in the Petroleum Exploration and Production Authority, as a main part of the Ministry of Oil and Mineral Resources, must build a strong long vision strategy on studying the oil exploration and production future prospect. Because the first lesson I learned from this study, is that we must take in account our great Yemeni grandchildren interests, by making long-term studies on our sedimentary basins.

 

6.                  I believe in that Yemeni Geology, which took some care in the past and attracts many experts in the present time, is not going just to surprise all with its oil and gas discoveries, but also with its rich and useful data in the near future.

 

 

Important Notice:

Here, I would like to inform interested readers of this study, that I planned to continue this work by publishing a paper on my mathematical description to the reservoir rocks of Qishn Formations and its subdivision, based on its geostatistical data.

 

 

 

 

 

43

 

 

ACKNOWLEDGEMENTS

 

 

In this respect, I would like to extend my thanks to the Petroleum Exploration and Production Authority – (San’a), for their great trust on asking me to work on this study, especially Mr. Nabeel Al-Kaosi, Dr. Ahmed Ali Abdellah and Dr. Mohammed Ahmed Al-Zubairi (P.E.P.A – San’a). Mr. Abdullah Salem Ta’lab and Mr. Nagib Saeed Tabet (P.E.P.A – ADEN). Mr. Tawfik Ahmed Ismail and Mr. Mohammed Mahyoub (P.E.P.A ’s Office in CPF – Masila Block 14).

 

I would like to express my deep gratitude and sincere thanks to Mr. Victor W. Dudus (The Operation Geologist), Mr. L. A. Len Flexhaug (The Petrophysicist) and Al Jones (The Construction Superintendent) Canadian Nexen (CPF, Masila Block 14), for their help and support on fulfilling this study.

 

I have to thank Miss. Wafa and Miss. Fatimah Salem Khamis, for help and support.

 

Special thanks go to that kind of people, who work hard and in silence on building a bright future for our lovely Yemen, from both sides, the Yemeni Ministry of Oil & Mineral Resources (The Petroleum Exploration and Production Authority) side, the Nexen Inc. (Canadian Nexen Petroleum Yemen) side.

 

Someone said that "many people will walk in & out of your life, but only true friends will leave footprints in your heart." I'm so glad that all above mentioned people lift theirs in mine. Hope it is the right step in the right direction!

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

44

 

 

 

REFERENCES

 

 

1. Beydoun, Z.R., Bamahmoud, M.O., and Nani, A.S.O., 1993. The Qishn Formation, Yemen: lithofacies and hydrocarbon habitat. Marine and Petroleum Geology, 10 (4): 364-372.

 

2. Beydoun, Z.R., and others, 1998, International lexicon of stratigraphy, v. III, Republic of Yemen, (2^nd ed.): International Union of Geological Sciences and Ministry of Oil and Mineral Resources, Republic of Yemen Publication no. 34, 245 p.

 

3. Bosence, D.W.J., ed., 1997, Special issue on Mesozoic rift basins of Yemen: Marine and Petroleum Geology, v. 14, no. 6, p. 611-730.

 

4. Brannin, Joe, and others, 1999, Geological evolution of the central Marib-Shabwa basin, Yemen: GeoArabia, v. 4, no. 1, p. 9-34.

 

5. Nedham, M. Darsi, 2000. The Geological Research History Work in the Republic of Yemen during the period from 1852 until Today (Three papers). Yemen Times newspaper. Issue 2-January 10th through January 16 2000, Vol. IX, Culture Page, Issue 10 - March 6 through March 12 2000, Vol. X, Culture Page and Issue 15 - April 10 through April 16 2000, Vol. X, Culture Page.

 

6. Productivity Prediction from Well Logs in Variable Grain Size Reservoirs Cretaceous Qishn Formation, Republic of Yemen, Michael L. Cheng and Marco A. Leal: Canadian Petroleum Ltd., Calgary, Canada David McNaughton: Mincom Inc., Houston, Texas U.S.A.

 

7. Putnam, P.E., 1997, Upper Qishn (Lower Cretaceous) reservoirs at Masila, Yemen, CSPG-SEPM Joint Convention Core Conference, J. Wood and B. Martindale (compilers), p. 429-448.

 

8. Putnam, P.E., Kendall, G.A., and Winter, D. A. 1997, Estuarine deposits of the upper Qishn Formation (Lower Cretaceous) in the Masila region of Yemen, American Association of Petroleum Geologists Bulletin, v.81, p. 1306-1329.

 

9. The Masila Fields, Republic of Yemen, W.A. King¹, B.R. Mills¹, Scott Gardiner², and A.A. Abdellah³. (1) Nexen Inc. (Formerly Canadian Occidental Petroleum Ltd.), Calgary, AB T2P 3Z1, Canada, (2) Nexen Inc. (formerly Canadian Occidental Petroleum Ltd.), 1801 - 635 8th Avenue S.W, Calgary, AB T2P 3Z1, Canada, (3) Petroleum Exploration and Production Authority (PEPA), Yemen Ministry of Oil and Mineral Resources (MOMR), Yemen

 

10. Tide-Dominated Sedimentation in an Arid Rift Basin - Cretaceous Qishn Clastics, Masila Block, Republic of Yemen, Dale A Leckie and Tom Rumpel. Nexen Inc, Calgary, AB T2P 3P7, Canada, and phone: 403699-5902, [email protected]

 

11. Local, Regional, International and Global ’s World Web Site Internet Resources

 

45

 

 

ABOUT THE AUTHOR

 

 

* Dr. Eng. Mohammed Darsi Abdulrahman Nedham, born on November 17, 1963, Crater (Aden). 4 Languages (Arabic, English, Russian and Chinese with a basic course in German Languages). Petroleum Engineer, Geologist; Married have 3 sons. Education: Graduated from the Earth Science College of Jilin University as a Doctor of Science in Mineralogy, Petrology and Stratigraphy on May 29 2002 and also graduated from the Russian among People Friendship University in 1991 as a Petroleum Engineer, Geologist (M.S. degree) on June 29 1991. Appointments: Petroleum Exploration and Production Board, Aden Branch, Ministry of Oil and Mineral Resources; Petroleum Engineer; Senior Geologist; Representative; Coordinator. Publications: 10 scientific papers, 6 published in the Yemen Times Newspaper, 3 in China (2 in World Geology and 1 in the Journal of Geoscientific Research of Northeast Asia) and the last one in Russia. Two registered Patents. 18 Certificate from different institutes, centers, organizations and clubs. Membership: Fellow, Geological Association of Canada, a member of American Association of Petroleum Geologist and other memberships. Dr. Eng. Mohammed Darsi Abdulrahman Nedham began his professional career by working as petroleum engineer, geologist in the Petroleum Exploration and Production Board (Aden Branch). His scientific interest is concentrated on the Geological Research History Work, Earth science software application and basin-modeling problems. The most important thing, Dr. Darsi is ONE of the Who is Who in the 21^st Century for 2001 and 2002 (First and Second Publication), choosed by the International Geographical Centre, Cambridge, England.

 

Author ’s Picture

Dr. Eng. Mohammed Darsi Abdulrahman Nedham

 

 

 

 

 

46