Article pubs.acs.org/EF
Characteristics and Hydrocarbon Generation of the Marine Source Rock of the Upper Oligocene Zhuhai Formation in the Baiyun Sag, Pearl River Mouth Basin, South China Sea Zhenglong Jiang* School of Marine Sciences, China University of Geosciences, Beijing 100083, People’s Republic of China ABSTRACT: The Baiyun Sag, located in the northern South China Sea, is rich in oil and gas. The marine mudstone in the Upper Oligocene Zhuhai Formation of the Upper Oligocene has not previously been considered as the main source rock and was thus selected for a thermocompression simulation experiment to verify its hydrocarbon generation potential. The experimental results were used to calculate the hydrocarbon generation kinetic parameters, and the hydrocarbon generation process of the marine mudstone was simulated. The mudstones of the Upper Oligocene Zhuhai Formation in the deepwater area of the Baiyun Sag are effective source rocks. The dark shallow marine mudstones of the Upper Oligocene Zhuhai Formation from well C generate hydrocarbons at a rate of 179.79 kg/ton of total organic carbon. As a set of active source rocks, the Upper Oligocene Zhuhai Formation has reached the low mature to mature stage and mainly generates oil in the marginal areas of the Baiyun Sag, whereas they have reached a highly overmature stage and generate both oil and gas in the central areas.
1. INTRODUCTION The Baiyun Sag is the largest sag of the Zhu II Depression in the Pearl River Mouth Basin, with an area of approximately 15 000 km2. Its water depth ranges from 200 to 2800 m (Figure 1).1−4 Successful exploration resulted in the discovery of the LW3-1, LH34-2, LH29-1, and LH16-2 gas/oil and gas fields in the deepwater area of the Baiyun Sag (LH is the abbreviation of LiuHua, and LW is the abbreviation of LiWan), and part of the oil was proven to originate in the Upper Oligocene Zhuhai Formation source rock.5−9 According to the results of the analysis of its organic matter abundance, the mudstone in the Upper Oligocene Zhuhai Formation is rich in organic matter, has good hydrocarbon generation potential, and is another set of effective source rock aside from the Eocene Wenchang and Eping Formations.10 The distribution of Zhuhai Formation is wider than Wenchang and Enping Formations and is being more and more important to the deepwater exploration in the northern South Chin Sea. To obtain a comprehensive understanding of the oil and gas generation of the Zhuhai source rock and lay the foundation for an further analysis of the rules governing hydrocarbon accumulation and preservation, it is very important to analyze its thermal evolution and hydrocarbon generation. This study focused on the characteristics and simulated hydrocarbon generation of the Zhuhai source rock in Baiyun Sag. On the basis of a thermocompression simulation experiment, the kinetic equation for hydrocarbon generation11 was established and the relevant processes were analyzed.
and Dongsha events in the northern margin of the South China Sea) (Figure 2).14−16 2.1. Stratigraphy. The strata of the Baiyun Sag are chronologically composed of the Paleocene to Eocene Shenhu, Eocene Wenchang, the late Eocene to Lower Oligocene Enping, Upper Oligocene Zhuhai, Lower Miocene Zhujiang, Middle Miocene Hanjing, Upper Miocene Yuehai, and Pliocene Wanshan Formations and the Quaternary stratum.17 The Shenhu and Wenchang Formations represent the deposition of the rift stage; the Enping Formation represents the deposition of the rift depression stage; the Zhuhai Formation represents the deposition of the transition stage; and the Zhujiang, Hanjiang, Yuehai, and Wanshan Formations, along with the Quaternary stratum, represent the deposition of the depression stage18 (Figure 2). According to Liu et al.13 and He18, the Upper Oligocene Zhuhai Formation is composed of littoralneritic sandstone and mudstone deposits. The Upper Oligocene Zhuhai Formation develops multiple sets of delta foreset deposit cycles with sand−shale interbeds. During the middle stage of the Upper Oligocene Zhuhai Formation deposition, the study area experienced a large-scale marine transgression and deposited a widely distributed layer of mudstone. 2.2. Depositional Environment of the Upper Oligocene Zhuhai Formation. During the Upper Oligocene Zhuhai Formation deposition, the paleogeomorphology was described as follows: the Baiyun Sag was a shallow-water shelf; the Panyu Lower Massif showed a wide and gentle landform with early form of palaeohigh in the northeast and northwest; and the shelf break developed near the southern uplifted zone in the south. The paleo-Pearl River system, which developed during the late Oligocene, contributed a large amount of lithic
2. GEOLOGICAL SETTING The study area lies in the Pearl River Mouth Basin and adjacent oceanic basin, located in the mid-northern margin of the South China Sea (Figure 1). The South China Sea region has experienced multiple tectonic events since the Cretaceous (named the Shenhu, Zhuqiong I, Zhuqiong II, Nanhai, Baiyun, © 2017 American Chemical Society
Received: November 11, 2016 Revised: January 7, 2017 Published: January 9, 2017 1450
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Figure 1. Location of the study area and tectonostratigraphic cross section (aa′) (modified with permission from refs 12 and 13). Wells A, B, and C are shown. E2wc, Eocene Wenchang Formation; E3ep, Lower Oligocene Enping Formation; E3zh, Upper Oligocene Zhuhai Formation; N1zj, Lower Miocene Zhujiang Formation; N1hj, Middle Miocene Hanjiang Formation; and Sea + Q + N2ws + N1yh, seawater + Quaternary, Upper Pliocene Wanshan Formation, and Upper Miocene Yuehai Formation.
material from the northwest and provided the sediment for the Upper Oligocene Zhuhai Formation in the Baiyun Sag.13 Prodelta facies developed in the southeast of the Baiyun Sag (Figure 1). Thick mudstone of the Upper Oligocene Zhuhai Formation was discovered during the drilling process within well C in the south of the Baiyun Sag (Figure 1), and the mudstone is composed of marine delta front and prodelta facies sediments.10 A substantial amount of marls was discovered at the top of the Upper Oligocene Zhuhai Formation in the LW4 well.10 The lithology of the Upper Oligocene Zhuhai Formation in the Baiyun Sag consists of sand and mudstone interbeds as well as limestones, whereas the Upper Oligocene Zhuhai Formation is primarily composed of delta and littoralneritic facies sediments (Figure 3). In terms of seismic reflection, in general, the Upper Oligocene Zhuhai Formation is characterized by a typical oblique delta with a S-shaped progradational configuration, indicating that the Upper Oligocene Zhuhai Formation is composed of a set of fastgrowing, thick sand and mud alternating neritic shelf−delta sediments with a massive distribution area and expanded from
the Baiyun Sag to Zhu I depression with rising sea levels (Figures 3 and 4). In addition, the delta of the Upper Oligocene Zhuhai Formation experienced coastal progradation with rapid tectonic subsidence, followed by an intense marine regression action, which occurred during the late period of Zhuhai deposition, and the delta extended to the Baiyun Sag with a large foreset deposit on the seismic map.13 From the bottom to the top, the Upper Oligocene Zhuhai Formation can be divided into six third-order sequences: sequence 1 (SQ1)− sequence 6 (SQ6) (Figures 3 and 4).
3. MATERIAL AND METHODS 3.1. Source Rock of the Upper Oligocene Zhuhai Formation and Sample. 3.1.1. Source Rock of the Upper Oligocene Zhuhai Formation. The organic matter abundance of all six sequences of the Upper Oligocene Zhuhai Formation was determined on the basis of the analysis of the mudstone cutting and core samples of the Upper Oligocene Zhuhai Formation from wells, such as well C (Figures 3 and 5 and Table 1). The total organic carbon (TOC) content of sequence SQ1 ranges from 1.04 to 1.46%, with a mean TOC content of 1.25%. The TOC content of sequence SQ2 ranges from 0.99 to 1.29%, with a 1451
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Figure 2. Stratigraphic column with formation, main seismic reflectors, tectonic events, and unconformities of the Baiyun Sag (modified with permission from refs 4, 17, and 19). mean of 1.12%. The TOC content of sequence SQ3 ranges from 1.06 to 1.32%, with a mean of 1.25%. The TOC content of sequence SQ4 ranges from 0.9 to 1.22%, with a mean of 1.03%. The TOC content of SQ5 ranges from 0.97 to 1.47%, with a mean of 1.2%. The TOC content of SQ6 is 1.1% (only one sample). The drilling and seismic data demonstrate that the Upper Oligocene Zhuhai Formation consists of a set of neritic shelf and delta sediments. The source rocks of the Upper Oligocene Zhuhai Formation are mainly black in color and form layers, with mean TOC contents ranging from 1.1 to 1.25% and S1 + S2 values mainly ranging from 2 to 4 mg/g.8 Organic matter type: The marine source rock of Upper Oligocene Zhuhai Formation came from the terrestrial higher plant with the organic matter types of II2 and III.5−8 The hydrogen index (HI) and the maximum peak temperature of pyrolysis (Tmax) can be used to characterize the organic matter type of a source rock.20 The mudstones of the Upper Oligocene Zhuhai Formation have relatively high values of HI and Tmax that are, mainly, indicative of type II2 organic matter; thus, the mudstones of the Upper Oligocene Zhuhai Formation mainly contain type II2 organic matter (Figure 6). Organic matter maturity: The whole-rock vitrinite reflectance (Ro) results for well C of the Upper Oligocene Zhuhai Formation range from 0.43 to 0.57%; thus, the Upper Oligocene Zhuhai Formation is at the low mature stage (Figure 5). 3.1.2. Samples of Zhuhai Source Rock. The sample was selected from the core of well C at a depth of 3780.75 m, and it has been divided into six parts for the thermocompression simulation experiment. It is the source rock of the Upper Oligocene Zhuhai
Formation. Its lithology is black mudstone; the TOC content is 1.0%; and the type of the organic matter is type II2. 3.2. Thermocompression Simulation Experiment. The simulation experiments were performed by individual heating of the original samples (Zhuhai source rock) at separate temperature levels in a closed system.17 The experimental apparatus was a GCF-0.25L model (Liaoning, China).17,18,20−24 According to our test conditions, the heating time can be set to 24, 48, or 72 h when the simulation temperatures are less than or equal to 300 °C. When the simulation temperatures are equal or greater than 325 °C,25−27 the heating time is usually set no more than 24 h because the kerogen cracking reactions are accelerating and the vitrinite reflectance value shows a positive correlation with time and temperature. The Ro values of source rock remanent after each thermocompression simulation experiment at a fixed temperature are measured, and the relation between the hydrocarbon generation and the thermal evolution (Ro) is established. The simulated experimental conditions were set as follows: (1) simulation temperatures of 250, 300, 350, 400, 450, and 500 °C, (2) sample particle size of 5−10 mm at 50−70 g for each experiment, and (3) water addition of approximately 10−20 wt % of the sample. The products were collected for further analysis in each experiment, such as the contents of oil and gas, the composition of oil and gas, and the residue. 3.3. Technology for Calibrating the Chemical Kinetic Parameters. 3.3.1. Chemical Kinetic Parameters. It is supposed that the hydrocarbon-forming process is composed of a series of parallel first-order reactions with its activation energy, frequency factor, and original hydrocarbon generation potential of kerogen.17,28−36 The 1452
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Figure 3. Sequence division and comparison of the Upper Oligocene Zhuhai Formation in the line from wells A−C (see Figure 1 for the well locations).
Figure 4. Seismic reflection characteristics of the Upper Oligocene Zhuhai Formation (see Figure 1 for the location of line bb′). calculation can be achieved by two-dimensional basin modeling software (Basin Mod 2D).17 3.3.2. Basin Mod 2D. One of the main differences between Basin Mod 2D and one-dimensional (1D) is that hydrocarbon migration is considered in the Basin Mod 2D and can be calculated and plotted. Thus, the hydrocarbon generation and oil cracking under open, semiopen, semi-closed, or closed conditions can be modeled by Basin Mod 2D. However, the semi-open or semi-closed condition is difficult to achieve under the experimental conditions. The cracking proportion of the oil in source rock is different under each of these experimental
conditions. In this manner, the chemical kinetic parameters and oil cracking kinetic parameters, with the appropriate limit of the simulation experiment results of the Upper Oligocene Zhuhai Formation source rock, can be calculated by Basin Mod 2D.
4. RESULTS 4.1. Experimental Results. A thermocompression simulation experiment was conducted on a black mudstone sample of the Upper Oligocene Zhuhai Formation from well C (a total 1453
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Figure 5. Geochemical profiles of the Upper Oligocene Zhuhai Formation of well C (see Figure 1 for the well location).
Table 1. Source Rock Percentage and Organic Matter Abundance of the Upper Oligocene Zhuhai Formation of Well C third-order sequence
depth (m)
thickness (m)
percentage content of source rock (%)
color
SQ6 SQ5 SQ4 SQ3 SQ2 SQ1
3130−3182 3182−3347 3347−3503 3503−3627 3627−3742 3742−3849
39 130 131 108 93 89
75.00 78.79 83.97 87.10 80.87 83.18
light gray black light gray light gray black black
TOC (%) (min−max/average) (samples) 1.10 0.97−1.47/1.20 0.90−1.22/1.03 1.08−1.32/1.25 0.99−1.29/1.12 1.04−1.46/1.25
(1) (9) (14) (5) (3) (4)
Figure 6. Relationship between Tmax and HI of the Upper Oligocene Zhuhai Formation source rock in well C (modified with permission from refs 5 and 8).
150.5 kg/ton of TOC. The Ro values range from 0.64 to 1.27% during the main hydrocarbon generation period (Table 2). 4.2. Kinetic Equations of the Hydrocarbon Generation. Wells A, B, and C (located in Figure 1) were taken as the simulation examples. The hydrocarbon generation kinetic parameters of kerogen in the Upper Oligocene Zhuhai Formation source rocks were adjusted using the Basin Mod 1D and 2D, and then, they were used for the hydrocarbon generation simulation.17 According to the experiments and simulation results, the Zhuhai source rock is in the main hydrocarbon generation stage (Table 2 and Figure 7), the activation energy values range from 46 to 63 kcal/mol (Table 3 and Figure 8), the frequency factor is 1.91 × 1013 s−1, and the original hydrocarbon generation potential values range from 4 to 12%. The hydrocarbon generation potential values generally exhibit a normal distribution, with high levels of 7−12% corresponding to activation energy values of 50−60 kcal/mol.
of six points from 250 to 500 °C) to obtain parameters such as the hydrocarbon generation rate, oil generation rate, and gas generation rate. The maximum hydrocarbon generation rate is 179.79 kg/ton of TOC, and the maximum gas generation rate is
5. DISCUSSION 5.1. Effective Source Rocks in Zhuhai Formation. Mud thickness of the Upper Oligocene Zhuhai Formation source rock: On the basis of the statistics of drilling wells, the Upper Oligocene Zhuhai Formation on the Panyu Lower Massif
Table 2. Thermal Simulation Experimental Data of the Dark Mudstone from the Upper Oligocene Zhuhai Formation in Well C simulation temperature (°C)
sample load (g)
TOC (%)
gas generation (kg/ton of TOC)
oil generation (kg/ton of TOC)
hydrocarbon generation (kg/ton of TOC)
Ro (%)
250 300 350 400 450 500
100 100 90 90 80 70
1 1 1 1 1 1
4.96 25.26 45.20 102.94 167.40 150.50
65.60 104.80 116.44 57.53 18.33 29.29
70.56 130.06 161.64 160.47 185.73 179.79
0.64 0.94 1.27 1.92 2.06 3.13
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Figure 7. Comparison between the numerical simulation results of the hydrocarbon generation using basin modeling and the thermocompression simulation data for the black mudstone from well C (see Figure 1 for the well location).
Table 3. List of the Chemical Kinetic Parameters for the Dark Mudstone in the Upper Oligocene Zhuhai Formation from Well C hydrocarbon generation of kerogen XiH (0−1) 0.04 0.05 0.06 0.07 0.08 0.11 0.12 0.1 0.09 0.08 0.07 0.05 0.04 0.04
crude oil cracking
Ei (kcal/mol)
Ai (s−1)
46 48 49 50 51 53 55 57 58 59 60 61 62 63
× × × × × × × × × × × × × ×
1.91 1.91 1.91 1.91 1.91 1.91 1.91 1.91 1.91 1.91 1.91 1.91 1.91 1.91
13
10 1013 1013 1013 1013 1013 1013 1013 1013 1013 1013 1013 1013 1013
XiH (0−1)
Ei (kcal/mol)
0.05 0.1 0.25 0.3 0.2 0.1
53 55 58 60 62 63
Ai (s−1) 1.91 1.91 1.91 1.91 1.91 1.91
× × × × × ×
1013 1013 1013 1013 1013 1013
composed of a large set of mudstones with thin sand layers (Figure 4). The TOC content and S1 + S2 values of this set of mudstones increase with depth (Figure 5). According to the evaluation standards for the classification of organic matter abundance of Chinese source rocks,21 all of the geochemical data show that the Upper Oligocene Zhuhai Formation is a set of lower medium abundance source rocks. For instance, the TOC contents of the mudstones of the Upper Oligocene Zhuhai Formation from well C range from 1.0 to 1.5%; the S1 + S2 values range from 2 to 4 mg/g (Figure 5); and the maximum hydrocarbon generation rate is 179.79 kg/ton of TOC. The source rock has a higher organic matter content in the prodelta (more than 1.0%) than that in the delta front (less than 1.0%) (Figure 3). 5.1.2. Petroleum Geochemical Characteristics of the Upper Oligocene Zhuhai Formation Source Rock. The oleanane content in the Zhuhai Formation is higher than those in the Upper Oligocene Zhujiang, the Late Eocene to Lower Oligocene Enping, and Eocene Wenchang Formations, but the Enping Formation has a higher bicadinane content, which can be recognized as the markers of terrigenous higher plants.8 In well C, the extraction from the sandstone in the Upper Oligocene Zhuhai Formation has more oleanane, less bicadinane, and more pentacyclic triterpenoids than sterane compounds and a low content of 4-methyl sterane series and the extracted hydrocarbon from the sandstone in the Upper
Figure 8. Distribution of the activation energy and hydrocarbon generation potential for the black mudstone of the Upper Oligocene Zhuhai Formation in well C (see Figure 1 for the well location).
developed a delta plain facies representing 40% of the total source rock thickness; for instance, the thickness of 193 m accounted for 38.45% of the entire formation in well A. However, the facies of the delta front and prodelta developed in the Upper Oligocene Zhuhai Formation represented 80% of the total source rock thickness (Figure 3); for instance, the thickness of 590 m accounted for 82.06% of the entire formation in well C. The source rock of the Upper Oligocene Zhuhai Formation is typically more than 100 m in the drilled wells of the Baiyun Sag. 5.1.1. Organic Matter Abundance of the Zhuhai Source Rock. The Upper Oligocene Zhuhai Formation of well C is 1455
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Figure 9. Simulated diagram of the thermal evolution in wells A, B, and C (maturity data of well B from ref 17). Zh is the Oligocene Zhuhai Formation; Zj-1 and Zj-2 are the members of the Miocene Zhuhai Formation; Hj (Hj-1 + Hj-2) is the member of the Miocene Hanjiang Formation; Yh is the member of the Miocene Yuehai Formation; Ws is the member of the Pliocene Wanshan Formation; Q is Quaternary; and Yh-Q is the member of the Miocene Yuehai to Quaternary (see Figure 1 for the well locations).
Oligocene Enping and Upper Oligocene Zhuhai Formations. From the oleanane content, half of the crude oil was generated by the Zhuhai marine source rock.5 5.1.3. Source Rock Thermal Evolution. The mudstones of the Upper Oligocene Zhuhai Formation from well C contain type II2 kerogen, with Ro values ranging from 0.43 to 0.57%,
Oligocene Zhuhai Formation originated mainly from the Zhuhai source rock.8,37 In addition, the Zhuhai source rock contributed partially to the gas condensate and crude oil in the LH29-1 and LH16-2 structural reservoirs.9 The crude oil has high oleanane and bicadinane contents in the Baiyun Sag, demonstrating that it is generated by the Late Eocene to Lower 1456
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highly mature to overmature stage with both oil and gas generation (Figures 9B, 10, and 11B), the simulated Ro values of the bottom of the Upper Oligocene Zhuhai Formation are more than 1.25% (Figures 9B and 10), and the Ro values are from 0.96 to 1.2% in the top−medium section of the Upper Oligocene Zhuhai Formation from well B (Figures 9B and 10). 5.2. Hydrocarbon Generation. Wells A, B, and C were used as examples to analyze the thermal evolution and hydrocarbon generation of the Zhuhai source rock in the Baiyun Sag. 5.2.1. Thermal History of the Upper Oligocene Zhuhai Formation. The Baiyun Sag experienced three evolutionary stages: the rift stage (Paleocene to Early Oligocene), the transition stage (the Late Oligocene), and the depression stage (Early Miocene to the present).4,17,38,39 The corresponding heat flow evolved from the rifting heat flow model to the passive continental margin basement heat flow model, and the thermal history of the Baiyun Sag can be simulated on the basis of its burial history and the measured Ro values of wells A and C (Figure 9).17,40−48 The thermal evolution simulation results for well A indicate that the Upper Oligocene Zhuhai Formation has a relatively
Figure 10. Isogram of simulated Ro of the bottom of the Upper Oligocene Zhuhai Formation in the Baiyun Sag (see Figure 1 for the well locations).
and are at the low mature stage (Figures 5, 6 and 9C). The top−medium section of the Upper Oligocene Zhuhai Formation from well A is characterized by Ro values ranging from 0.5 to 0.7% and is also at the low−medium mature stage21 (Figure 9A). However, in the center of the Baiyun Sag, the source rock of the Upper Oligocene Zhuhai Formation is at the
Figure 11. Simulated diagrams of the hydrocarbon generation of the source rocks of the Upper Oligocene Zhuhai Formation in wells A, B, and C (see Figure 1 for the well locations). M, Miocene; P, Pliocene; and Q, Quaternary. 1457
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Energy & Fuels low degree of thermal evolution, with Ro values ranging from 0.64 to 0.78%, which is consistent with the test results (well A in Figure 9). The simulation results for the thermal evolution of well B suggest that the Upper Oligocene Zhuhai Formation has a relatively high degree of thermal evolution, with Ro values ranging from 0.96 to 1.92% (well B in Figure 9). The simulated thermal evolution of well C indicates that, at present, the Upper Oligocene Zhuhai Formation is characterized by a relatively low degree of thermal evolution, with Ro values ranging from 0.43 to 0.71% (well C in Figure 9), which is consistent with the test results. The simulated Ro values of the bottom section of the Upper Oligocene Zhuhai Formation reveal that the Upper Oligocene Zhuhai Formation is at the low mature to mature stage at the margin of the Baiyun Sag (range of Ro values of 0.5−1.0%) and at the highly mature to overmature stage in the center of the Baiyun Sag (range of the Ro values of 1.0−2.0%) (Figure 10). 5.2.2. Hydrocarbon Generation of the Upper Oligocene Zhuhai Formation Source Rock. When three wells were taken as examples, the hydrocarbon generation kinetic equations of the source rock in the Upper Oligocene Zhuhai Formation were established and used to simulate the oil and gas generation (Figure 11). The simulation results for the hydrocarbon generation of the source rocks from well A indicate that the dark mudstones of the bottom section of the Upper Oligocene Zhuhai Formation mainly generated oil and their main hydrocarbon generation stage started from 15.0 Ma to now (well A in Figure 11). The simulation results for the hydrocarbon generation of the source rocks from well B indicate that the dark mudstones of the Upper Oligocene Zhuhai Formation generated both oil and gas and that the dark mudstones of the Upper Oligocene Zhuhai Formation generated mainly oil from 16 to 7.0 Ma and generated mainly gas from 7.0 Ma to the present (well B in Figure 11). The simulation results for the hydrocarbon generation of the source rocks from well C indicate that the dark mudstones of the Upper Oligocene Zhuhai Formation generated mainly oil and the main hydrocarbon generation stage occurred from 13.0 to 4.0 Ma (well C in Figure 11).
Baiyun Sag, where the Upper Oligocene Zhuhai Formation developed prodelta facies, is a favorable area for hydrocarbon accumulation.
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Zhenglong Jiang: 0000-0002-2878-2994 Notes
The author declares no competing financial interest.
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ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (Grants 91328201 and 41030853) and the techniques of identifying hydrocarbon-rich depressions, predicting reservoirs and detecting hydrocarbons in the northern deepwater area of the South China Sea (2008ZX05025-03). The author thanks the reviewers and editors very much for their good and constructive comments and hard work.
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REFERENCES
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6. CONCLUSION In the present, the hydrocarbon generation kinetic parameters of the Upper Oligocene Zhuhai Formation source rock were established, the hydrocarbon generation was simulated in three wells, and following conclusions could be drawn: (1) The data of well C indicate that the prodelta source rock of the Upper Oligocene Zhuhai Formation located in the southeast deepwater area of the Baiyun Sag are characterized by thick source rock, relatively high organic matter abundance with mainly type II2 organic matter (the kerogen of type III is secondary), and a hydrocarbon generation rate of 179.79 kg/ton of TOC. Thus, it is a set of effective source rock. (2) On the basis of the thermal evolution simulation of the three wells, the Upper Oligocene Zhuhai Formation has reached the low mature to mature stage at the margin of the Baiyun Sag and the high to overmature stage in the center. (3) The main hydrocarbon generation stage of the source rock of the Upper Oligocene Zhuhai Formation occurred after the Zhujiang Formation deposition (after 16 Ma). The source rock of the Upper Oligocene Zhuhai Formation has mainly generated oil at the margin of the Baiyun Sag and has generated both oil and gas in the center. Thus, it is a set of active source rock. The southeast of the 1458
DOI: 10.1021/acs.energyfuels.6b02982 Energy Fuels 2017, 31, 1450−1459
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DOI: 10.1021/acs.energyfuels.6b02982 Energy Fuels 2017, 31, 1450−1459
