Characteristics and Mechanism of Source Rock Development Controlled by Sedimentary Microfacies in River-delta System: Case Study of Coal-measure Source Rock in Enping Formation in Pearl River Estuary Basin

doi:10.19657/j.geoscience.1000-8527.2020.106

Abstract

Abstract:

Coal-measure source rocks are important sources of oil and gas. Conventional research of source rocks mainly focuses on single-well analysis, which depends heavily on the degree of exploration and available data. It lags behind exploration, and is thus difficult to predict favorable hydrocarbon-generating sags. The coal-measure source rocks of the Enping Formation in the Pearl River Estuary basin are systematically studied here, in combination with sedimentology and geochemistry. The favorable geological conditions, characteristics, and favorable facies for these coal-measure source rocks are revealed, and the sedimentary model of coal-measure source rock in river-delta system is established. Based on the analysis of sedimentary facies and geochemical indicators (organic matter abundance, hydrocarbon generation potential, hydrogen index), the characteristics and mechanism of source rock controlled by sedimentary microfacies are revealed. There are several favorable geological conditions for the development of coal-measure source rock in river-delta system of the Enping Formation: (1) steady tectonic subsidence, and largely balanced sedimentation and subsidence rates; (2) warm humid climate with flourishing vegetation; (3) widely distributed river and delta. The coal seam has thin single layer, multiple vertical layers, and poor horizontal continuity. Coal-measure source rocks in fluvial and deltaic environment are both rich in organic matter, which may have derived mainly from terrestrial higher plants. The hydrocarbon generation potential and hydrogen index of these coal-measure source rocks are similar in fluvial and deltaic environment. The coal-measure source rocks of river-delta system are highly heterogeneous, and are controlled by sedimentary facies. From channels and distributary channels to fluvial swamps and deltaic plain swamps distal from rivers and distributary channels, the organic matter abundance increases and the organic matter types improves. The fluvial swamp and deltaic plain swamp microfacies are the most favorable sedimentary facies for the formation of coal-measure source rocks in river-delta systems. Paleogeographical conditions such as paleotopography, hydrodynamic and redox conditions are important factors that formed difference source rocks in different microfacies. The sedimentary model of coal-measure source rock formation in different microfacies and the distribution characteristics of coal seams in river-delta systems is newly established.

Key words: river-delta system, coal-measure source rock, coal seam, sedimentary model, Pearl River Estuary basin

CLC Number:

TE122.1

LI Yan, DENG Yunhua, LI Youchuan. Characteristics and Mechanism of Source Rock Development Controlled by Sedimentary Microfacies in River-delta System: Case Study of Coal-measure Source Rock in Enping Formation in Pearl River Estuary Basin[J]. Geoscience, 2021, 35(04): 1065-1077.

Figures/Tables 15

Fig.1 Map showing the tectonic units (a) and integrated stratigraphic histogram (b) of Pearl River Estuary basin [40]

Fig.2 Burial and sedimentary characteristics of Pearl River Estuary basin

Fig.3 Sporopollen composition of the Pearl River Estuary basin (well LHAA)

Fig.4 Deltaic distribution of Enping Formation in the Baiyun-Liwan depression [44]

Table 1 Statistics of coal seams in well PYBB

煤层号	顶深 /m	底深 /m	厚度 /m	煤层号	顶深 /m	底深 /m	厚度 /m
1	4 196.20	4 197.20	1.0	11	4 409.00	4 410.40	1.4
2	4 231.80	4 232.60	0.8	12	4 463.14	4 463.84	0.7
3	4 237.00	4 239.10	2.1	13	4 466.30	4 467.20	0.9
4	4 244.66	4 246.06	1.4	14	4 468.00	4 468.80	0.8
5	4 249.70	4 250.70	1.0	15	4 483.00	4 483.90	0.9
6	4 281.50	4 282.80	1.3	16	4 511.90	4 512.80	0.9
7	4 293.40	4 294.80	1.4	17	4 631.10	4 632.30	1.2
8	4 296.50	4 297.20	0.7	18	4 657.40	4 658.60	1.2
9	4 301.50	4 302.70	1.2	19	4 680.20	4 682.40	2.2
10	4 312.40	4 313.50	1.1	20	4 790.30	4 791.10	0.8

Fig.5 Sedimentary sequence of coal seams in the Pearl River Estuary basin (well PYAA)

Fig.6 Single layer thickness of Enping Formation coal seams in fluvial and deltaic environment of the Pearl River Estuary basin

Fig.7 Characteristics of coal seams in Enping Formation in the Pearl River Estuary basin

Fig.8 TOC (a) and S1+S2 (b) histograms for the Enping Formation coal-measure source rocks in fluvial and deltaic environment of the Pearl River Estuary basin

Fig.9 HI vs. Tmax plot for the Enping Formation coal-measure source rocks in fluvial and deltaic environment of the Pearl River Estuary basin

Fig.10 Sporopollen composition of the Pearl River Estuary basin (well HZAA)

Fig.11 (S1+S2) vs. TOC plot for the Enping Formation source rocks in different fluvial microfacies in the Pearl River Estuary basin

Fig.12 (S1+S2) vs. TOC plot for the Enping Formation source rocks in different deltaic microfacies in the Pearl River Estuary basin

Fig.13 Core sketches and core photos (well PYBB)

Fig.14 Sedimentary model of coal-measure source rock development in a river-delta system

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