characterization of the cenozoic petroleum system in the northeastern offshore song hong basin

HA NOI UNIVERSITY OF MINING AND GEOLOGY ____________________ TRAN CHAU GIANG CHARACTERIZATION OF THE CENOZOIC PETROLEUM SYSTEM IN THE NORTHEASTERN OFFSHORE SONG HONG BASIN Subject ar

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

INTRODUCTION

The necessity

Song Hong Basin is complex sedimentary basin, including several tectonic elements with different oil and gas potential The VPI-IDENMITSU (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:

- 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

- 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

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

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

a PSC for block 102/91 Next the

blocks 102 – 106 with total area

of 10700 km2 was signed

between PVN and ATI

Petroleum Inc in 2000 Recently,

this PSC has relinquished area

and maintained in area of 225

km2 The remaining area now is

Fig 1.1: Structural map of Top basement Song Hong basin and study area location (N.T.Dau et

al, 2012)

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,

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 (E 2 pt); (iii) Dinh

Cao Formation (E 2 đc); (iv)

Phong Chau Formation (N 1

th); (vii) 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

02 fault systems The NW-SE

and NE-SW fault systems

Fig.1 2: Stratigraphic column of the offshore Northeast S.Hong

basin (After N.T.Dau et.al, 2012)

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

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

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:

+ 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

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)

+ 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)

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

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

rock is able to generate mixture oil and gas and have reach maturity level

Figure 3.1a: Plot HI and Tmax by

the structural zonnation in the

Song Hong Basin (NTB Ha,

2010)

Figure 3.1b: Plot (S1 + S2 mg/g) and TOC% by structural zonnation in Song Hong Basin (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 1X 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 107-PL-1X well are also have potential of both oil and gas generation