STATUS OF THESIS ASSESSMENT OF A SYNRIFT PLAY IN SOUTH DENT GRABEN (OFFSHORE EAST SABAH) I, HARMINZAR BINTI MANSOR hereby allow my thesis to be placed at the Information Resource Center (IRC) of Universiti Teknologi Petronas (UTP) with the following conditions: I. The thesis becomes the property of UTP 2. The IRC ofUTP may make copies of the thesis for academic purposes only 3. The thesis is classified as CJ Confidential 0 Non confidential Reason: As instructed by Petroleum Management Unit (PMU), Petronas. Endorsed by PRAM,PMU PRAM,PMU Level 22, Tower 2, Level 22, Tower 2, Petronas Twin Towers, Petronas Twin Towers, KLCC KLCC Date: 22/1/08 11 UNIVERSITI TEKNOLOGI PETRONAS Approval by Supervisor The undersigned certify that they have read, and recommend to The Postgraduate Studies Programme for acceptance, a thesis entitled "Assessment of a synrift play in South Dent Graben (offshore East Sabah)" submitted by Harminzar Mansor for the fulfillment of the requirements for the degree of Master of Science in Petroleum Geoscience. Signature: Main supervisor: Dr Arthur Van Vliet Date: zz/•jo~ Ill UNIVERSITI TEKNOLOGI PETRONAS ASSESSMENT OF A SYNRIFT PLAY IN SOUTH DENT GRABEN (OFFSHORE EASTSABAH) By HARMINZAR MANSOR A THESIS SUBMITTED TO THE POSTGRADUATE STUDIES PROGRAMME AS A REQUIREMENT FOR THE DEGREE OF MASTER OF SCIENCE IN PETROLEUM GEOSCIENCE BANDAR SERI ISKANDAR, PERAK JANUARY, 2008 IV DECLARATION I hereby declare that the thesis is based on my original work except for quotations and citations which have been duly acknowledged. I also declare that it has not been previously or concurrently submitted for any other degree at UTP or other institutions. Signature :~ Name : Harrninzar Mansor Date v ASSESSMENT OF A SYNRIFT PLAY IN SOUTH DENT GRABEN (OFFSHORE EASTSABAH) ABSTRACT South Dent Graben is located offshore of East Sa bah at the south part of the Sandakan Sub basin. This basin is a very lightly explored area. There is only one exploration well drilled here. The stratigraphy of this basin mainly divided into two parts: synrift sediments and post rift sediments. They are separated by the breakup unconformity that represents the Middle Miocene Unconformity (MMU). Post rift sediment consists of the Sebahat Formation, the Ganduman Formation and the Togopi Formation. The interpretations and petroleum play analysis of the post rift sediments have been done in 2005. Basically this project is a continuation from the 2005 project but focused more on the synrift sediments. Synrift sediments are represented by Segama Group (Libung and Tungku Formation), deposited during Early- Middle Miocene. Five horizons have been interpreted: Top Basement, Base Purple, Base Brown, Base Green and Middle Miocene Unconformity. From the seismic interpretation and mapping that has been done, no economic size structural trap or stratigraphic play appears in the synrift sediments. Synrift sediments only present in a small part of the basin and later overlain by extensive postrift sediments through out the whole basin. Even though the north part of the basin has hydrocarbon occurrences in the synrift sediments (Tanjong Formation/Segama Group), the reservoir appears more equivalent to the Tanjong Formation. High proportion of volcaniclastic sediments and conglomerates is the reason that the Segama Group is not a good reservoir. Besides that, a calculation from the Vrms also shows very high interval 1 1 velocity ranging from 3000ms' to more than 4000ms' , suggesting that the sediment is compacted, has a low porosity and may not be a good reservoir. VI TABLE OF CONTENTS STATUS OF THESIS II APPROVAL PAGE Ill TITLE PAGE IV DECLARATION v ABSTRACT VI TABLE OF CONTENTS VII LIST OF TABLE IX LIST OF FIGURES X CHAPTER ONE: INTRODUCTION I. I OBJECTIVE 1.2 LOCATION AREA 1.3 PROJECT DATABASE 2 l.3.I SEISMIC 2 1.3.2 WELL 3 I.4 PROBLEMS ENCOUNTERED 4 CHAPTER TWO: LITERATURE REVIEW 2.I TECTONIC EVOLUTION OF SABAH 5 2.2 STRATIGRAPHY OF SABAH 9 2.3 VOLCANIC ACTIVITY IN SABAH IO 2.4 SANDAKAN SUB BASIN IO 2.4.I DENT PENINSULA STRATIGRAPHY (ONSHORE) I2 2.4.2 STRATIGRAPHY I3 2.4.3 SOURCE ROCK POTENTIAL I4 2.4.4 RESERVOIR I5 2.4.5 MATURITY I5 CHAPTER THREE: METHODOLOGY 3.I DATA COLLECTING I6 3.2 SEISMIC INTERPRETATION I6 3.3 MAPPING 22 VII 3.4 VELOCITY CALCULATION 22 CHAPTER FOUR: RESULT 4.1 SEISMIC INTERPRETATION 25 4.2 MAPPING 42 4.3 VELOCITY CALCULATION 48 CHAPTER FIVE: CONCLUSION AND RECOMMENDATION 51 REFERENCES APPENDIX A: Velocity calculation results VIII LIST OF TABLE Table 4.1 Color code that have been used to interpret horizon in this project 25 IX LIST OF FIGURES Figure 1.1 Location area of this project 2 1.2 Basemap of the seismic lines in the SB306 block 3 1.3 Summary of Sebahat-1 well 4 2.1 NW -SE cross section across Sa bah during Cretaceous-Eocene 6 2.2 NW-SE cross section across Sabah during Oligocene-Early Miocene 7 2.3 NW -SE cross section across Sa bah during Early Miocene­ Middle Miocene 8 2.4 NW -SE cross section across Sa bah during Late Miocene-Pliocene 9 2.5 The structural elements in Sandakan Sub Basin II 2.6 Lithostratigraphy map of South Dent 12 2.7 Lithostratigraphy ofSandakan Sub Basin 14 3.1 SB30604-04 seismic line show the erosional truncation as the indicator to Base Green 18 3.2 Other erosional truncation as indicators of Base Green 19 3.3 Onlap end to basement 20 3.4 On lap seismic reflections as indicator of Base Purple 21 3.5 Graph of relative error versus interval thickness in ms (using the Dix formula) 23 4.1 Interpreted SB30604-04 seismic line 26 4.2 Interpreted SB30604-06 seismic line 27 4.3 Interpreted SB30604-08 seismic line 28 4.4 Interpreted SB30604-1 0 seismic line 29 4.5 Interpreted SB30604-12 seismic line 30 4.6 Interpreted SB30604-14 seismic line 31 4.7 Interpreted SB30604-05 seismic line 32 4.8 Interpreted SB30604- I I seismic line 33 4.9 Interpreted SB30604-19 seismic line 34 4.10 Interpreted SB30604-23 seismic line 35 4.11 Interpreted SB30604-27 seismic line 36 4.12 Interpreted SB30604-31 seismic line 37 4.13 Interpreted SB30604-39 seismic line 38 X 4.14 Interpreted SB30604-43 seismic line 39 4.15 Interpreted SB30604-45 seismic line 40 4.16 Interpreted SB30604-53 seismic line 41 4.17 Middle Miocene Unconformity (MMU) time structure map 43 4.18 Base Green time structure map 44 4.19 Base Brown time structure map 45 4.20 Base Purple time structure map 46 4.21 Basement time structure map 47 4.22 Summary of the velocity results on SB30604-04 49 4.23 Summary of the velocity results on SB30604-06 50 XI CHAPTER I INTRODUCTION 1.1 OBJECTIVE The main objective of this project is to assess synrift sediments and prospectivity in the South Dent Graben, Sabah, Malaysia. 1.2 LOCATION AREA The south Dent Graben is located offshore of the East part of Sabah. It is under SB306 acreage. This area is virtually unexplored. Total area of this block is 8184km2 The block is currently open block area. The basin in this area is known as Sandakan Sub Basin. This project only focuses on the south part of the Sandakan Sub Basin. 2 Sulu Se. S' OO' 58332 Figure 1.1 Location area of this project 1.3 PROJECT DATABASE 1.3.1 SEISMIC Two seismic surveys have been done in SB306: 1. ESB99 Series - This survey has been shot by Petronas in 1999. It comprises 1500 line km 2. SB30604 Series- Shot by Petronas in 2004 and comprises 1471 line km. For this project only SB30604 have been used in the interpretation to avoid misties between the two vintages. 3 Figure 1.2 Basemap of the seismic lines in the SB306 block 1.3.2 WELL There is only one exploration well in the SB306 acreage which is Sebahat-1. The well was drilled in 1973 by Sabah Teiseki Oil. Total depth of this well is 3700m TVDSS. Sebahat-1 is a dry well and only has minor gas shows from the cuttings. 4 Fo rm ~tlon lithology Foss il Shows Seismic Ties predoo'nlrl!y sen:tstooe no tom no sl1cHv Togopl SB8.6Ma rMrlf ITIUd!tone wth calareous ,....,., Gandurnan no shaN seemsOIII{Tde S811.6Ma meil'tf M$1one, coral frll9flCR$ go$ $hoi¥ -ones end some (tronspaled?) Sebahat lmeUones TO 3700m I Adapted from PETRONAS (2006) I Figure 1.3 Summary of Sebahat-1 well 1.4 PROBLEMS ENCOUNTERED There are some problems encountered during this project like: 1. Lack of data such as check shot or VSP data. The only information is velocity data from the seismic (stacking velocities). 2. The interpretation doesn't have calibration from the Sebahat-1 well. This because the well has been drilled to 3700m and only penetrated the post rift sediments. 5 CHAPTER II LITERATURE REVIEW 2.1 TECTONIC EVOLUTION OF SABAH There are several stages of tectonic evolution of Sabah based on Tongkul, 1991 a and PETRONAS, 1999: I. Pre Cretaceous This refers to Sabah Crystalline Basement as 'older metamorphosed oceamc basement with rare acid intrusive rocks'. 2. Early Cretaceous- Early Eocene There were several unstable deep troughs in a block faulted domain that emerged from the older basement in Early Cretaceous time. Shallow marine limestones were deposited on the highs and the oceanic basins were filled with ophiolite complexes and covered with pelagic sediment. The ophiolite complex is known as 'new oceanic basement' and forms the basement to the thick sedimentary systems of Sabah (Hutchinson, 1989).