Characteristics of depositional environments of middle Miocen of Thien Ung – Mang Cau structure of Nam Con Son basin (LV tốt nghiệp)

characteristics of depositional environments of middle Miocen of Thien Ung – Mang Cau structure of Nam Con Son basin (LV tốt nghiệp)characteristics of depositional environments of middle Miocen of Thien Ung – Mang Cau structure of Nam Con Son basin (LV tốt nghiệp)characteristics of depositional environments of middle Miocen of Thien Ung – Mang Cau structure of Nam Con Son basin (LV tốt nghiệp)characteristics of depositional environments of middle Miocen of Thien Ung – Mang Cau structure of Nam Con Son basin (LV tốt nghiệp)characteristics of depositional environments of middle Miocen of Thien Ung – Mang Cau structure of Nam Con Son basin (LV tốt nghiệp)characteristics of depositional environments of middle Miocen of Thien Ung – Mang Cau structure of Nam Con Son basin (LV tốt nghiệp)characteristics of depositional environments of middle Miocen of Thien Ung – Mang Cau structure of Nam Con Son basin (LV tốt nghiệp)characteristics of depositional environments of middle Miocen of Thien Ung – Mang Cau structure of Nam Con Son basin (LV tốt nghiệp)characteristics of depositional environments of middle Miocen of Thien Ung – Mang Cau structure of Nam Con Son basin (LV tốt nghiệp)characteristics of depositional environments of middle Miocen of Thien Ung – Mang Cau structure of Nam Con Son basin (LV tốt nghiệp)characteristics of depositional environments of middle Miocen of Thien Ung – Mang Cau structure of Nam Con Son basin (LV tốt nghiệp)

VIETNAM NATIONAL UNIVERSITY, HANOI VNU UNIVERSITY OF SCIENCE FACULTY OF GEOLOGY Nguyen Thuy Linh CHARACTERISTICS OF LITHOFACIES – PALEOGEOGRAPHY AND SEQUENCE STRATIGRAPHY OF MIDDLE MIOCENE FORMATION IN THIEN UNG-MANG CAU STRUCTURE OF NAM CON SON BASIN Submitted in partial fulfillment of the requirements for the degree of Bachelor of Science in Geology (International Standard Program) Hanoi - 2017 VIETNAM NATIONAL UNIVERSITY, HANOI VNU UNIVERSITY OF SCIENCE FACULTY OF GEOLOGY Nguyen Thuy Linh CHARACTERISTICS OF LITHOFACIES – PALEOGEOGRAPHY AND SEQUENCE STRATIGRAPHY OF MIDDLE MIOCENE FORMATION IN THIEN UNG-MANG CAU STRUCTURE OF NAM CON SON BASIN Submitted in partial fulfillment of the requirements for the degree of Bachelor of Science in Geology (International Standard Program) Supervisor(s): Prof.Dr Tran Nghi Hanoi - 2017 Acknowledgment Thesis of bachelor is one of the most valuable experiences in student’s life I would not be able to finish my thesis of bachelor without the support of Vietnam University of Science – Viet Nam National University and specially my supervisor, Prf Tran Nghi Firstly, I would like to say thank you to Prof Tran Nghi for his supervision He always gave me the best advice and enthusiastic guidance Without his valuable support This project cannot have been possible Secondly, I would like to thank the VNU University of Science for letting me fulfill my studying process here I am excessively grateful for all teachers in the Faculty of Geology who have taught me knowledge and experience about geology for completing my thesis Despite of the best efforts, there would be remaining of mistakes and omission in the thesis I hope to receive comments in order to have better one Finally, I am so thankful for all again Student Nguyen Thuy Linh Content Nguyen Thuy Linh Nguyen Thuy Linh CHARACTERISTICS OF LITHOFACIES – PALEOGEOGRAPHY AND SEQUENCE STRATIGRAPHY OF MIDDLE MIOCENE FORMATION IN THIEN UNG-MANG CAU STRUCTURE OF NAM CON SON BASIN List of abbreviation Co Fm I Li Md Me Q Ro So Sk TST HST LST TƯ - MC Compaction coefficient Formation Secondary variation coefficient Cement Medium grain size Effective porosity Quartz Rounded coefficient Sorted coefficient Symmetry coefficient Trasgressive system tract Highstand system tract Lowstand system tract Thiên Ưng – Mãng Cầu List of figure List Table Table.1.1: Classification diagram of sandstone according to F.J Pettijohn (1973) Error: Reference source not found Table 1.2: Classification and nomenclature of arkose sandstones Error: Reference source not found Table 1.3 Classification and nomenclature of graywake sandstones Error: Reference source not found Table 1.4: The correct equation % grain size into the real grain size .Error: Reference source not found (only clastic grains) Error: Reference source not found Table 1.5: The correct equation % grain size into the entire rocks Error: Reference source not found Table 1.6: Classification of sorted grades Error: Reference source not found Table 1.7 : Classification of secondary variation degree Error: Reference source not found Table 3.1: Evaluation ability of reservoir rock [13] Error: Reference source not found Nguyen Thuy Linh Bachelor Thesis INTRODUCTION The exploration has carried out more than a half of the century Viet Nam has identified eight petroleum sedimentary basins of Cenozoic age on the continental shelf and marine zones of Viet Nam There are basins, it includes: Red River sedimentary Basin, Hoang Sa sedimentary Basin, Phu Khanh sedimentary Basin, Nam Con Son sedimentary Basin, Cuu Long sedimentary Basin, Tu Chinh – Vung May sedimentary Basin and Malay – Tho Chu sedimentary Basin in order from North to South The Petroleum Industry contributes about one-third to the national budget every year Nam Con Son basin in general and Central regions in particular Nam Con Son basin is an important object of oil and gas search in Vietnam oil basin system and it has been invested in research since the 70s of the 20th century because historical circumstances as well as the complex of the geological characteristics of the basin so the work of study to assess the characteristics of lithology and depositional environments are not realized in a uniform This is an important prerequisite to assess oil and gas potential in the area, so I have chosen thematic titled “characteristics of depositional environments of middle Miocen of Thien Ung – Mang Cau structure of Nam Con Son basin.” Thesis focus on researching the environmental characteristics of the Middle Miocene sediments and range research focuses on Thien Ung - Mang Cau structure, the central area Nam Con Son basin The purpose of topic: The topic purposed we know the lithological composition, the environmental characteristics, sedimentary rock, lithofacies, and sedimentary systems in the middle Miocene period Since, it contribute for search and exploration oil and gas on the basis of constitution and development of source rock, reservoir rock and seal rock and evaluation of petroleum potential Term of thesis includes: Chapter 1: Overview Chapter 2: Sequences stratigraphy and relationship with lithofacies – paleogeography Chapter 3: Evaluation of petroleum potential Nguyen Thuy Linh Bachelor Thesis CHARACTERISTICS OF LITHOFACIES – PALEOGEOGRAPHY AND SEQUENCE STRATIGRAPHY OF MIDDLE MIOCENE THIEN UNG-MANG CAU STRUCTURE OF NAM CON SON BASIN Abstract: The paper introduces sequence stratigraphy and lithofacies paleogeography of middle Miocene of the Thien Ung – Mang Cau structure in the center area of Nam Con Son basin based on the analysing results of lithologic thin section and structural characteristics of core samples Basin of middle Miocene has systems tracts: (1) Lowstand systems tracts (LST); (2) Transgressive systems tracts (TST); (3) Highstand systems tracts (HST) Each systems has feature of lithofacies and representative paragenetic sequence It is conformed absolute and relative sea level Lowstand systems tracts included main paragenetic sequences: (1) Alluvial sand, silt LST facies (ar); (2) Delta silt, sand, clay LST facies (amr); and (3) Shallow marine clay, silt, sand LST facies(mt/amr) Transgressive systems tracts included main paragenetic sequences: (1) Coral reef (TST) facies (mt Co); (2) Lagoon, bay limes, clay (TST) facies (mt); (3) Shallow marine sand, silt, clay consist limes (TST) facies (amr/amt); (4) Alluvial sand, silt (TST) facies (at) and (5) Limes-dolomite (TST) facies Highstand systems tracts concluded main facies: (1) Coral reef (HST) facies; (2) Shallow marine sand, silt, clay (HST) facies (amt/amr); (3) Lagoon, bay limes (HST) facies (mr) Keywords: Lithofacies – paleogeography, sedimentary systems tracts, sequences stratigraphy, paragenetic sequence, lowstand systems tracts, highstand systems tracts Nguyen Thuy Linh Bachelor Thesis CHAPTER 1: OVERVIEW GEOGRAPHYCAL LOCATION Nam Con Son occupies about 100.000km kilometers and located from 6o 00' to 90 45' north latitude and 1060 00' east longitude The northern boundary of the basin is the Con Son zone of uplift, in the west and the south it is KHorat - Natuna zone of uplift, while the east is the Tu Chinh - Vung May basin and the Phu Khanh basin in the east.[5] Sedimentary parameters analysed from the lithologic thin section of about middle Miocene age of drilling wells T-1, T-2, T-3 and T-6 (Fig 1.1) Fig 1.1: Geography location of TƯ - MC in Nam Con Son Basin [5] STUDIED HISTORY REVIEW Oil and gas exploration activities in Nam Con Son Basin began in the 1970s of the last century There were 26 foreign contractors surveyed nearly 60,000km 2D seismograph and 5,400km2 3D seismographs, drilled 78 wells, quality test and exploration wells, determined mines and 17 oil discovery Now, foreign contractors are active Research on the geological and hydrocarbon resources of Nam Con Son basin has many study project, Nguyen Thuy Linh Bachelor Thesis especially the topics of state have contributed and effectively in the exploration and mining However, Nam Con Son basin has complex geology conditions, it is necessary to continue researching with new methods and technologies to establish the scientific basis for planning the exploration and exploitation in this sedimentary basin Based on the characteristics and results of each period, the history of studies on the Nam Con Son Basin can be divided into periods: Before 1975, 1976 – 1980, 1981 – 1989 and 1990present [5] 2.1 Before 1975 USA and British company such as Mandrell, Mobil Kaiyo, Pectin, Esso, Union Texas, Sun Marathon and Sunning Dale surveyed region and explored oil in Nam Con Son basin very early 1975 On the basis of the research results obtained at the end of 1974 and in early 1975, Pecten and Mobil drilled five wells in different parcel and structures (Mía - 1X, DH - 1X, Hồng - 1X , Dừa - 1X, and Dừa - 2X), in which Dừa - 1X wells have detected oil At the end of this period, there were reports It presented about evaluating research results for the parcel, and which the most important and remarkable was the Mandrell Report Inside, this paper presents two maps, anomaly magnetic maps and gravity maps of / 500,000 for the whole continental shelf of Vietnam However, at this stage, it had not yet a general report about the structural characteristics and geological development history of the whole region and each other plots 2.2 1976 – 1980 The AGIP and BOW VALLEY companies surveyed (14,859 km 2D seismic networks up to 2x2 km) and drilled wells (04A -1X, 04B - 1X, 12A - 1X, 12B - 1X, 12C - 1X, 28A - 1X, 29A - 1X) Based on the geological, geophysical and drilling surveys, the above companies have established isochronous diagrams according to the reflecting layers at different ratios and have summarized reports “Seismic demonstrated and evaluated of petroleum potential of Vietnam continental shelf" by Daniel S and Netleton AGIP has Nguyen Thuy Linh Bachelor Thesis The sediment accumulation area are the most largest than other period TƯ MC structure are flooded In TST, seismic section of TƯ - MC is mood and not contineous so it is shallow marine, lagoon with strong flow (Fig 2.5, 2.2) There are facies: 1) coral reef facies; 2) shallow marine sandstone, siltstone, claystone contain limestone facies (TST); 3) limestone – dolomite facies (HST) (Fig 2.10) T4 B B ’ Fig 2.10: Geologycal section show the sediment facies in TST of TƯ MC structure in Nam Con Son Basin Coral reef facies (mtCo): Middle Miocene, topography differentiation process was very strong, it created many uplift and down throw block They are distributed in the eastern part of the TƯ-MC structure [12] These uplift are underground island and make chance development of coral reef in Middle Miocene Sea level change with short amplitude created coral rhythmic, original coral insert into crushed coral which is re-crystalization When sea level lower, waves are destroy and create coral shelf (Fig 2.11) 31 Nguyen Thuy Linh Bachelor Thesis Fig 2.11: Sandstone contain remain fossil, foraminifera on the bottom 2708,0 m in deep, GK T-1, XPL, x40, age N12 Limestone – dolomite facies (mt): It is distributed in the deepest terrain of the basin, pH greater than or equal 8.5 (Fig 2.12, 2.13, 2.14) Fig 2.12: Microgranular limestone contains organic matter has been bitumenation, 2644.2m in depth, Well T-1, XPL, x40, age N12 32 Fig 2.13: Core sample 2644,2-2645,0m in deep Nguyen Thuy Linh Bachelor Thesis Figure 2.14: Microcrystal dolomite-limestone containing organic matter with bitumenation; 2645.2m in depth; Well T-1,XPL, x40, age N12 Shallow marine sandstone, siltstone, claystone contain limestone facies (amr-amt): sediments mixed such as sand contain limestone, siltstone, claystone and sandstone contain limestone Sandstone, quartz – litic contain limestone and dolomite has medium sorted (So=2,0 - 2,5) and good rounded (Ro>0.6) (Fig 2.16) this is evidence of sedimentary environment [12] Quartz sand are good rounded, this is tidal environment with strong wave activities and limes and dolomite are shallow marine, lagoon environment This is result of sea level increased and strong activities of bottom flow This is confused and distributed sediment It created pinch-and-swell structure, flaser structure, lens structure and paraconglomerate in the direction of flow (Fig 2.15, 2.17) 33 Nguyen Thuy Linh Bachelor Thesis a) b) c) Fig 2.15: Core sample of drilling T2 a) 2752,10-2752,38 m; b) 2755,102755,25 m; c) 2760,3- 2760.5 m Fig 2.16: Lithic quartz siltstone, based cemnent, lagoon environment 2755,80 m in deep; GK T-2, age N12 Fig 2.17: Sandstone, siltstone with carbonat cenment poor sorted, medium rounded, 2703,6m in deep; GK T-1, XPL, age N12 34 Nguyen Thuy Linh Bachelor Thesis 2.2.3 Highstand system tract (HST) These facies were formed during the regression, from the highest the medium sea-level From the highest sea-level to the boundary between the erosional and depositional regions existed in the highstand phase The sediment accumulation area of HST is larger than LST but it is narrower than TST (Fig 2.5) The main material is terrigenous sediment that is transported by river so it has not contain carbonate To observe on the seismic sections, the seismic reflection terminations that represented for these lithofacies are downlap From the margin to the center of the basin, the facies differentiation is described as follows: firstly, less mineral, muddy sand tidal facies; and then, muddy clay shallow marine facies and calcareous mudstone bay facies Core sample has sandstone mixed with siltstone and claystone contain bitumen In this core sample, the sediment layers are parallel and cross bedding This is evidence for shallow marine with strong wave activities (Fig2.19) It has facies: 1)coral reef facies (mrCo); 2) shallow marine sandstone, siltstone, claystone facies (mt/amr) ; 3) lagoon claystone, limestone facies (mr) (Fig 2.18) T4 C C ’ Fig 2.18: Geologycal section show the sediment facies in HST of TƯ MC structure in Nam Con Son Basin 35 Nguyen Thuy Linh Bachelor Thesis Fig 2.19: Core sample Well T-1 2816.43-2816.63 m in depth Coral reef facies (mrCo): it is distributed around uplift and underground island In this period, enviromnet is not good for development of coral reef Coral reef has come between coral reef limestone orginal is block and crushed coral showed short amplitude of sea level change.[11] Shallow marine sandstone, siltstone, claystone facies (mt/amr) : The main material is terrigenous sediment that is transported by river in short amplitude of sea level change so it hasn’t carbonate (Fig 2.20, 2.21) Initially there was an accretionary wedge structure growth of the underground delta, after it transformed shallow marine environment with the bottom flow make sediment re-transported and re-distributed Fig 2.20 Coarse-grained grauwvack silstone, medium-well- rounded (Ro=0,6), medium sorting, based cemnet (matrix is more than chemical cement), 2757.1m in depth,Well T-2, XPL, x40, age N12 36 Nguyen Thuy Linh Bachelor Thesis Fig2.21: Coarse-grained grauwvack siltstone, poor sorted and poor rounded; 2757,1 m in the depth; XPL, Well T 2X Lagoon clay, lime facies (mr): it is far from shore, so sediment always deposited in the marine environment The facies is lagoon claystone, limestone facies and shallow marine sandstone, siltstone, claystone facies 37 Nguyen Thuy Linh Bachelor Thesis CHAPTER 3: EVALUATION OF PETROLEUM POTENTIAL BASED ON SEQUENCE STRATIGRAPHY AND LITHOFACIES PALEOGEOGRAPHY 3.1 SOURCE ROCK Source rock is rock has fine-grain size for example claystone, limesclaystone, limes –claystone contain organic matter There are main type of source rock which rock are able to generate oil, gas or coal there are several types of organic material found in rocks that will generate hydrocarrbons There are three general categories, one is algae, a second is marine planktonic organisms and bacteria and the third is terrestrial plants The organic rich rocks can form in deep water marine, swamps …but the most important that the environment have little oxygen and burial is very rapid because tectonic activities such as subsidence Then, sediments to continue to be deposited on top of the organic rich rocks With additional burial the temperature and pressure will rise in rock When temperature approximate 100 0C and pressure is 1000atm converts the organic matter into hydrocarbon Terrestrial plants are decomposed into peat, brown coal and gas (CH 4) and lower plant are decomposded into oil and companion gas (khí đồng hành) Diagenesis, petroleum and water are call fluid when bacterial effects can be quite effective in generating “biogenic” Catagenesis, corresponding to increasing burial depths, is a stage in which oil and light hydrocarrbon form (gas to condensates) and migrating oil and gas from source rock to trap [8] Petroleum potential of sedimentary rocks related with lithofacies and depositional environment which is distributed according to time and space of the system on the sequence Swamp clay facies (near the sea) and estuary is good condition for develop mangroves Thus, the sediment is deposited on top of the organic matter after long time to become coal seams and gas (CH 4) In TƯ - MC structure, this facies is smaller area than lagoon, bay clay facies Lagoon, bay clay facies contain organic matter (lower plant), they are very popular in this area [1] Both of two facies and sequence stratigraphy can divide source rock: 38 Nguyen Thuy Linh Bachelor Thesis - In lowstand systems tracts (LST), it is mainly generated oil Lagoon and bay is good condition for developing algae and bacterial and it formed claystone contain bitumen Content of bitumen is about 5-30% It is corresponding with quality of source rock from poor to well (Fig 3.1, 3.2) Fig 3.1: Bitumen containing claystone, orientated distribution, sericitization; 3033.8m in depth, Well T-2, XPL, x40, age N12 Fig 3.2 Fine- grained siltstone, medium sorting, organic materials bituminization that areorientated distribution, 2816.9m in depth, Well T-2, XPL, x40, age N12 Source rock have been able to generate gas has a small scale, it has lens shape and thin layer It is distributed around TƯ - MC uplift, swamp facies and mangroves It is small area so source rock has not potential generate petroleum 39 Nguyen Thuy Linh Bachelor Thesis 3.2 RESERVOIR ROCK Reservoir rock is a rock in which oil and gas accumulates Middle Miocene of TƯ - MC structure, lithofacies contain grauwack sandstone and arko sandstone with medium – well sorted and rounded, and it is formed in three systems tracts In lowstand systems tracts, river bed sand facies, channel river sand, river mouth sand dune sand facies, tidal flat facies is very popular In this facies, river mouth sand dune facies and tidal flat sand facies able to accumulate petroleum (Table 3.1) Place has strong wave activities, sand has good sorted and rounded (Ro>0.5; So