Tài liệu Characterization of the cenozoic petroleum system in the northeastern offshore song hong basin

MINISTRY OF EDUCATION AND TRAINING HA NOI UNIVERSITY OF MINING AND GEOLOGY ____________________ TRAN CHAU GIANG CHARACTERIZATION OF THE CENOZOIC PETROLEUM SYSTEM IN THE NORTHEASTERN OFFSHORE SONG HONG BASIN Subject area: Engineering geology Code: 62.52.05.01 SUMMARY OF DOCTORAL THESIS WORK HANOI -2014 The thesis work has been completed at: Ha Noi University of Mining and Geology Principal Advisors: 1) Professor, Doctor of Science. Mai Thanh Tan 2) Dr. Le Tuan Viet Judge 1: Associate Professor, Doctor. Pham Huy Tien Judge 2: Dr. Nguyen Huy Quy Judge 3: Dr. Cu Minh Hoang The doctoral thesis work will be defend at the University Council of Scoring Thesis Meeting at the Hanoi University of Mining and Geology at …….hour, day ……., month……year …….. You can find out the thesis in the libraries: National Library, Hanoi or Library of Ha noi University of Mining and Geology 1 INTRODUCTION The necessity Song Hong Basin is complex sedimentary basin, including several tectonic elements with different oil and gas potential. The VPIIDENMITSU (2005-2007) project has confirmed non-marine dual petroleum system (lacustrine and fluvio-deltaic) in the Song Hong basin by advanced geochemical analysis. Due to no oil – source rock correlation, the characterization of petroleum system in the Northeastern offshore Song Hong basin has yet to be confirmed. In 2008, the oil discovery by 106-HR-1X has proven the hydrocarbon potential of the Pre- Cenozoic carbonate basement Play. Next well 106-HR-2X was drilled through the oil reservoir bearing in the Pre – Cenozoic carbonate basement and penetrated a thick shale. It is a questionable that this Pre- Cenozoic shale is a new source rock. Well 107-PL-1X drilled in 2013 in the rich organic source area, and has the same structural trend as 106-HR prospects. However the well was dry. Other latest exploration wells have discovered gas condensate with heavy H2S and CO2 polluted in the reservoir fluid. These facts show many issues have to resolved such as the quality and distribution of source rocks, or which risk factor of geological parameters in the petroleum system have affected the results of exploration in the area of Northeastern (NE) offshore Song Hong basin. Therefore, the topic "Characterization of the Cenozoic petroleum system in the Northeastern offshore Song Hong Basin" was chosen with the objectives and research tasks are as follows: Objectives: 2 - To get better understand about the characterization and area distribution of petroleum source rocks of Cenozoic sediments in the NE offshore Song Hong Basin. - Contribute to improve the methodology for petroleum systems evaluation and risk analysis in exploration. Tasks: - Integrate geological data and geophysical data to clarify the regional geological setting. - Research to clarify the characterization and level of maturity and timing of HC generation and migration, identify the origin oil generated source rock in the NE offshore Song Hong Basin. - Determine the area distribution of source rocks and HC potential areas. Object and scope of the study: The scope of the study include the block 106 area, Northwestern of block 102 and North part of block 107 offshore Song Hong basin that separated to others area by Song Lo fault. The objective to study is Cenozoic petroleum system. Thesis protection: Thesis 1. Study results of the geochemical characterization identified a lacustrine petroleum system related to the Oligocene source rock exist in the NE offshore Song Hong Basin. The source rock contains moderate to good organic richness, kerogen type II and mixed type II/ III, locates in the grabens and half grabens within the study area. Based on all available geochemical data of the Miocene shale and Pre- Cenozoic shale that identifies these shales are not qualified to be a source rock. 3 Thesis 2. Based on the study of factors impact on risk of the petroleum system such the origin, maturity, the Oligocene sediment thickness and the distribution of potential prospects, restore the geological development through the ages that are enable to identify the Thuy Nguyen graben has lowest exploration risk. Next is the Kien An graben. The South Bach Long Vi Island area and NW edge of block 102 are the areas of high exploration risk. New findings of the thesis work: - Based on latest exploration data, results of thesis work has contributed accurately geochemical characteistics of the NE offshore Song Hong basin. The Pre- Cenozoic shale below the carbonate layer bearing oil has terrestrial lithoface, deposites under oxidizing condition environment, with poor organic contain that is not qualified to be a source rock. - The new structural maps were built have contribution to get better understand of Late Oligocene inversion event affect oil and gas potential of the area of Northeatern Offshore Song Hong basin. The scientific and practical contributions: * Scientific contribution: The results of research allowed identify the characterizations and the distribution of source rock to get better understand of petroleum system in NE of Song Hong basin, offshore Vietnam. * Practical contribution: Contribute to improve the effectiveness of HC potential assessment for the NE of Song Hong basin, and to serve the Oil companies in the exploration and exploitation activities. The layout of the thesis: The thesis consists of 04 chapters excluding the introduction and conclusions, recommendations, papers publication and reference 4 lists. The entire content of the thesis is presented in 135 pages, 24 tables and 89 figures. Chapter 1 SUMMARY GEOLOGICAL STRUCTURE IN THE NORTHEAST AREA OFFSHORE SONG HONG BASIN 1.1. Overview the geology of study area 1.1.1. Location Study location is part of Northeast Song Lo fault offshore Song Hong basin. Water depth from 30-40m. (fig.1.1) 1.1.2. Exploration history Fisrt exploration work began in 1978. In 1988, first PSC was signed for block 106, and a part of block 102, 103 and 107 between PVN and TOTAL. In 1992, IDEMITSU – PVN signed a PSC for block 102/91. Next the blocks 102 – 106 with total area of 10700 between km2 PVN was and signed ATI Petroleum Inc in 2000. Recently, this PSC has relinquished area and maintained in area of 225 Fig. 1.1: Structural map of Top basement Song Hong basin and study area location (N.T.Dau. et al, 2012) km2. The remaining area now is block 102/10 and block 106/10 with PVEP operator. From 1990 to present, in the study area were acquired more than 15,000 km of 2D, 5 and over 3000 km2 of 3D seismic, more than 10 exploration wells. Several studies are available as Geochemical model of Song Hong Basin (N.T Dau, L.V Hien, 1997), Outcroup study in Bach Long Vi island, Do Son, Kien An, Elephant Mountain, and Cat Ba Island (P.Q Trung, 1998), Investigate the amount of HC generated and migrated from source rock to trap in the Song Hong basin by SIGMA 2D and BSS softwares (N.T.B Ha, 2010), Final Report on the analysis and modeling Song Hong Basin (VPI - GEUS, 2001), Report on Characterization of petroleum systems in the Song Hong Basin by State of the art Geochemical Technology (VPI-IDENMITSU, 2007). 1.2. Regional setting 1.2.1 Lithostratigraphy Song Hong Basin stratigraphic units consist of: (i) Pre-Cenozoic basement; (ii) Phu Tien Formation (E2pt); (iii) Dinh Cao Formation (E2đc); (iv) 1 Phong Chau Formation (N1 pc); (v) Phu Cu Formation (N12pc); (vi)Tien 3 (N1 th); Hung (vii) Formation Vinh Bao Formation; (viii) Formation of Hai Duong - Kien Xuong (N2-Q) (Figure 1.2). 1.2.2 Tectono-structure There exist in the study area Fig.1. 2: Stratigraphic column of 02 fault systems. The NW-SE the offshore Northeast and NE-SW fault systems. S.Hong basin (After N.T.Dau et.al, 2012) 6 These fault systems created structural type of dipping down to the basin center and formed a series of grabens alternate half grabens. The identified structural zonnation (Figure 1.3): Hai Phong Shelf: The shelf located in the northeastern part of the study area, covers a large area of the block 106 and block 101. Thanh Nghe undifferentiated Fig.1. 3: Fault systems and structural zonnation monocline: It is located to the West of the Song Chay fault. Central trough: can be subdivided as a) Miocene Inversion Zone b) Dong Quan trough North-East differentiated monocline: mades up of grabens, half grabens, horsts, and basement uplifts. Detaily consists of: a) Kien An Graben b) Tien Lang - Chí Linh horst c) Thuy Nguyen half graben d) Trang Kenh Nose e) Western Bach Long Vi trough f) Yen Tu Horst g) Southern Bach Long Vi trough Tectonic evolution was constructed based on restoration cross sections. The study results show the similarities and differences over the period of development of the region on the two banks of Song Lo 7 Fault. In Paleocene-Eocene to the Early Oligocene and Pliocene – Quaternary period are similar but different in period from late Oligocene to late Miocene. 1.3. Data base The documents use in thesis work are more than 15000 km 2D seismic, gravity maps of the Bac Bo Gulf, Vietnam geological maps, well logs and obtained rock samples were analyzed for the Petrography, Geochemistry, and Biostratigraphy studies. Especially with 500 m of core samples from Enreca – 3 well in Bach Long Vi island to study sedimentary, litho-facies, and geochemistry of Oligocene sediment. Chapter 2 RESEARCH METHODS 2.1. Petroleum system and its role in oil and gas exploration Petroleum system concept appears too many different definitions. The term “system” includes source rock and reservoir rock, oil source correlation are considered a key factor in determining system (Dow W.G, 1972). Synthesis of the concept put forward by many authors, petroleum system is understood as a natural system where exist generated petroleum source rocks with all the geological elements and geological processes related to the ability to accumulate oil and gas may occur. In 1988, L.B Magoon had established a system classification, which distinguishes the petroleum systems to sedimentary basins, Plays and Prospects. Depend on the level of research, petroleum system is evaluated as an overview to detail as scale of a country, sedimentary basin, a play and to each independent prospect. The basic methods of assessment can be summarized as follows: 8 + Analysis petroleum system was evaluated on the basis of the total volume of HC generated/rock volume by Exxon. + Analysis petroleum system was evaluated on the prediction of petroleum geology characteristic (Delphi method), mainly based on the experience of experts. + Analysis petroleum system was evaluated on Geochemical material balance based on the calculation of the amount of oil and gas generated from source rock, as well as oil and gas were migrated and can accumulate in the trap. + Analysis petroleum system was evaluated on extrapolation of production history. + Analysis petroleum system by Play fairway analysis (based on geological model and statistical data) allows determine the change of the geological factors related to the oil and gas accumulation in an Figure 2.1: Play concept considered region. [CCOP, 2000] In the thesis work, Play assessment is applied to solve remaining problems in petroleum system in the study area. 2.2. The geochemical methodology Complex sets of geochemical index in evaluating the capacity of HC generation of sediments used in the thesis are: + Combust a crushed sample of rock at 600ºC + Pyrolysis method Rock-Eval standards (RE) + Bitumen extraction method + Chromatography (GC) + Mass spectrometry analysis (GC-MS) 9 + The vitrinite reflectance (Ro,%) 2.3. Geochemical modeling Geochemical modeling can reproduce the processes relating to petroleum system in computer from past to present time, which enables to assess the timing and location of generation, migration and accumulation of Oil and Gas. The soft ware used is SIGMA-2D. Principles for SIGMA model is explained detail as figure 2.2. 2.4. Petroleum system analysis According to Magoon and Dow (1994) to study a petroleum system have to analyze four basic elements includeing: source rock, Fig 2.2: SIGMA 2D outline reservoir, seal and the overlying rock layer with the combination of three processes are: the formation of oil and gas traps, the oil and gas generation, migration and conservation of oil and gas after trapped. 2.5. Geological risk assessment The purpose of risk assessment in petroleum system analysis is to estimate the probability of discovery prior to drill of a prospect/play. The probability of discovery is defined as the product of the following major probability factors, each of which must be evaluated with respect to presence and effectiveness. According to CCOP risk assessment guideline, the 04 factors are: Reservoir (P1), Trap (P2), Petroleum charge system (P3), and retention after accumulation (P4). 10 The probabilities of these factors are estimated with respect to the presence and effectiveness of the geological process associated with them. The probability of discovery is calculated using the formula: P = P1*P2*P3*P4 (2.1) Where P: Probability of discovery oil and gas (or probability of simultaneous occurrence of the events associated with each independent) P1: The probability of the presence of reservoir rock includes: i) P1a: Probability of existence of reservoir facies; ii) P1b: Probability of effectiveness of the reservoir P2: The probability of the presence of a trap includes: i) P2a the probability of presence of the mapped structure and ii) P2b the probability of effective seal mechanism for the mapped structure P3: The probability factor for the petroleum charge system includes: i) P3a the probability of effective source rock and ii) P3b the probability of effective migration P4: Probability of effective retention of HC in the prospect after accumulation. Tab.2.1: Probability of existence of reservoir facies Tab 2.2: Probability of effective reservoir with depth 11 In essence, the probability of discovered of an object is: P = P1a* P1b* P2a* P2b* P3a* P3b*P4 (2.2) Probability value of each parameter is defined rely on subjective knowledge, extrapolation from the analysis geological and statistical data. Following the guidance of CCOP, for example, the tables 2.1 and 2.2 describe the probabilities of P1a and P1b parameters. Chapter 3 CHARACTERIZATION OF SOURCE ROCK IN THE OFFSHORE NORTHEAST SONG HONG BASIN 3.1. Organic richness in source rock + Pre-Cenozoic sediments: very poor in organic matter and not be generated oil and gas. TOC values from 0.03 to 0.05% weight. Unmeasurable indicators S1, S2, PI, HI and Ro. + Eocene sediments: no wells confirm met Eocene. + Oligocene sediments: organic matter is moderate to good. 8/14 samples in 106-HR-1X well have TOC values> 1%. Samples on Bach Long Vi Island with TOC values from 1.5 to 6.59%, 10/100 samples have S1 value from 0.08 to 1.19 mg/g, and 99/100 samples with S2 > 10 mg/g, in average of 17 mg/g represented the organic contain from good to very good. + Lower Miocene sediments: all samples get very low value, so not analyisis. 3.2. Kerogen type + Oligocene sediments: Figures 3.1a and 3.1b (N.T.B.Ha, 2010) show the Oligocene (brown points) found in wells in block 107 and Chi Linh –Yen Tu host with HI values <300mgHC/gTOC for samples with low maturity distributed in kerogen type III. The sample has a higher maturity distributed in kerogen type II. Source 12 rock is able to generate mixture oil and gas and have reach maturity level. Figure 3.1a: Plot HI and Tmax by Figure 3.1b: Plot (S1 + S2 mg/g) the structural zonnation in the and TOC% by structural Song Hong Basin (NTB Ha, zonnation in Song Hong Basin 2010) (NTB Ha, 2010) Results of the well ENRECA 3 on Bach Long Vi Island show sample populations fall into the group of kerogen type II and I. Oligocene sediments have oil prone with capability from fair to good (Figure 3.2 a, b) . + Lower Miocene sediments: almost HI <200 mgHC/ gTOC, kerogen type III, expressed in gas prone. Four samples obtained at 106-YT-1X shown capable of oil generation. + Middle Miocene sediments: HI value changes from 50 to <300 mgHC/gTOC, kerogen type III, with gas prone. Samples at 106 YT1X with HI values up to 456-520 mg/g, kerogen type II/III with both oil and gas generation potential. The Mid. Miocene samples in 107PL-1X well are also have potential of both oil and gas generation. 13 Figure 3.2a: Plot HI and Tmax at Figure 3.2b: (S1+S2 mg/g) và well ENRECA 3 TOC % at well ENRECA 3 3.3. Depositional environement of organic matter The HI vs TOC diagram (Figure 3.3), results of gas chromatography (GC) (Figure 3.4) indicate depositional environment of organic matter of Oligocene source rocks in the study area is mainly lacustrine origin. Results of gas chromatography (GC) from Oligocene, Lower Miocene at 106-HR-1X, 106-HR-2X, 107-BAL-1X reflect the origin of organic matter was derived from high plants (Figure 3.5a, b).The Ts/Tm vs Oleanane/C30 Hopane diagram was used (Okui et al, 2007) to distinguish lacustrine petroleum system from fluvio-deltaic petroleum system. This plot indicates the oil from Ham Rong field is lacustrine origin. 3.4. Maturity of source rock + Oligocene sediments: Vitrinite index (Ro,%) from well Enreca -3 has value <0.4% and Tmax values from 410-440oC. Two shale samples in well 106-HR-2X (3209-3917m) with Tmax values measured 444-445oC are at oil window. Data reveal the Oligocene 14 sediments have varied thermal maturity level from low maturity to oil window. + All Lower and Middle Miocene samples from Ham Rong-Yen Tu and Pha Lai wells are immature. Figure 3.3: The diagram defines Oligocene depositional environment of organic matter in Song Hong Basin (points brown) (NTB Ha, 2010) Figure 3.4: The diagram defines depositional environment of organic matter by Pr / C17 and Phy / C18 in the study area (Ha, 2013) Figure 3.5a: The Figure 3.5b: Steranes C27- Oleanane/C30Hopane vs 28-29 triangle chart Ts/Tm diagram of study area 15 3.5. Oil to source rock correlation Oil sample from Ham Rong was analysed that shows normal crude oil and displays API gravity of 39,220API, moderate wax content (11,3%), moderate viscosity (4,058Cst) and moderately low pour point (270C). This oil is low sulphur content (0,062%Wt), low nickel and vanadium contents (Ni=1,70ppm, V=trace) suggesting characteristics of C class (After Barwise, A.J.C, 1984) derived from lacustrine source rocks. Results of gas chromatogram of the DST#1 oil from 106-HR-2X show the presence of saddle shape distribution decreases with increasing number of carbon atoms (Figure 3.6 and 3.7). Figure 3.6: C15+ saturates Figure 3.7: C15+ saturates chromatogram of oil and chromatogram of oil and extracts from 106-HR-1X extracts from 106-HR-2X Pristane/phytane ratio is 2,95 and 2,9 for 106-HR-1X ST4, and 106-HR-2X respectively. Consequently, these features are typical of organic matter derived from a terrestrially dominated source, deposited in submerged environment under reducing and weak oxidizing conditions. The GCMS analysis of saturate fraction of crude oil from Ham Rong field (Figs. 3.8a & 3.9a), the mass fragmentograms of m/z191 16 shows a wide Hopane distribution, gradually decreased with reducing number of carbon atoms, which are recognised as organic matter derived from a terrestrially dominated source, deposited in reducing environment condition. The presence of Oleanane is land plant indicators. Distribution of Tricyclic Terpanes sharply appearence from T2 to T8 suggested lacustrine algae have contributed in the parent material. (a) (a) (b) Figure 3.9 Gas (b) Figure 3.8: Gas chromatography- chromatography-Mass Mass Spectrometry (GCMS) of Spectrometry (GCMS) of saturates fraction of oil sample from saturates fraction of oil 106-HR-1X sample from 106-HR-2X The m/z 217 sterane distribution (Figures 3.8b and 3.9b) is characterised by C29 steranes are higher than those of C27 and C28. These features suggest the oil derived from terrestrial source. The 4Methyl C30-Sterane (peak 42) widely confirmed as the oil is derived mainly from lacustrine algal organic matter. 17 Oil – Source rock correlation defines the origin of oil generated from lacustrine algal organic matter that match with Oligocene source rocks in the study area. 3.6. H2S origin in crude oil Worldwide rift lakes in the Paleocene and Eocene have met in Spain, southern France, in Utah and Colorado (USA). They formed in surface of Carbon-Permian or Devon limestone. By this the carbonate material easily osmoses in the lake that created favorable condition for carbonate development of along the evaporation zone of lakes. The exploration wells in the study area have penetrated thin limestone in the Oligocene. Theoryly, the H2S and CO2 pollution in the oil reservoir in the Ham Rong fields were the product of thermal sulfate reduction process (of CaSO4) in carbonate rocks explained by Angler-Gofer Scheme formula: CaSO4 + CH4 = CaS + CO2 + 2H2O CaS + CO2 + H2O = CaCO3 + H2S (3.1) (3.2) Chapter 4 DISTRIBUTION OF SOURCE ROCK AND POTENTIAL ZONNATION IN THE OFFSHORE NORTHEART SONG HONG BASIN 4.1. Oligocene sediment distribution and evolution On the basis of seismic data and results of latest wells, Phd student have participated to re-interprete some seismic lines at VPI workstation. Results of biostratigraphic studies are used to identify and interprete the seismic reflection surface include: + Top Kainozoic basement + Top Lower intra- Oligocene (U500) 18 + Top of uncomformity is near top of Lower Oligocen (U400) + Top Oligocene (U300) + Top intra Middle Miocene (U220) + Top Upper Miocene (U100) Some of these seismic horizons just matched tie within a small area. Oligocene stratigraphic sequence in the center area of block 106 can divide into two parts separated by U400, which is relatively continuous. 107-TPA-1X supposedly was drilled to Eocene?/Oligocen (U500). Well ties to seismic data just observed in the small troughs in the NE Song Lo fault and the Southern part of Bach Long Vi Island. The structural maps of Top Basement, Top U400, Top U300 and the isopach map of Oligocen in scale 1/200.000 were built. The isopach maps of Lower Oligocene (U400-Bsmt) and Oligocene (U300-Bsmt) (Figures 4.1 and 4.2) represent the distribution area of Oligocene significant altenated in the offshore Northeast Song Hong basin. Figure 4.1 shows at the end of Early Oligocene time, 02 closed lakes systems trending NE-SW and NWSE were developed in the study area. The basement hosts within Ham Rong field area as boundary separate the lakes. In the Northern part of block 107, which is belong to South Bach Long Vi trough also has a deep lake. The lakes in Southeast edge of block 106 and North of block 107 tend to be open to the Southeast, while the closed lakes within the Northwest of blocks 102-106 and Northeast Yen Tu host remain stable development. Three (03) geological and physical seismic sections were selected cut through the main structural zonations in the study area to