Hydrocarbon Accumulation Characteristics and Prospectivity Prediction on Medium-Shallow Sequences in Rift Basins: Case Study on the 2nd Member of Shahejie Formation in Bonan Sag

doi:10.19657/j.geoscience.1000-8527.2020.04.20

Abstract

Abstract:

The medium-shallow traps of rift basin often covered source rocks, and the reservoir has the characteristics of multi-sourced hydrocarbons. To deepen the understanding of hydrocarbon accumulation characteristics and delineate favorable exploration targets on medium-shallow sequences in rift basins, we took the 2^nd member of the Shahejie Formation in the Bonan sag as an example. Based on data of drilling, logging, seismic and other analyses, we demonstrate that three source rock suites (Es₄^s, Es₃, Es₁) in the Bonan sag may have provided the oil and gas for hydrocarbon accumulation in Es₂, during the deposition of Upper Guantao Formation and Upper Minghuazhen Formation. Fault system is likely a key condition for hydrocarbon accumulation, which connects oil sources and provides a vertical channel for oil and gas migration. Physical properties of the reservoir determines the oil-bearing properties, which in turn determines the degree of oil endowment. Oil and gas migration and accumulation regularity of “two-stage reservoir-forming and multi-sourced hydrocarbon” exists in the 2^nd member of Shahejie Formation, and the single-sourced oil and mixed-source oil reservoirs were formed in different types of traps with the different hydrocarbon migration and accumulation regularities. The model of “multi-sourced hydrocarbon” and its major controlling factors indicate the favorable exploration direction of Es₂ in Bonan sag, The favorable exploration direction is likely the central beach-bar sandstone, the southern fan delta-front edge and the southwestern multi-type reservoir development zone. The focus of oil and gas exploration in each area is likely different, and so is the risk of exploration.

Key words: medium-shallow sequence in rift basin, hydrocarbon accumulation feature, multi-sourced hydrocarbon, prospectivity analysis, Bonan sag, Shahejie Formation (2^nd member)

CLC Number:

TE122

LIU Peng, DU Pengwei. Hydrocarbon Accumulation Characteristics and Prospectivity Prediction on Medium-Shallow Sequences in Rift Basins: Case Study on the 2^nd Member of Shahejie Formation in Bonan Sag[J]. Geoscience, 2020, 34(04): 849-857.

Figures/Tables 9

Fig.1 Regional location and hydrocarbon accumulation elements profile of Es2 in Bonan sag

Fig.2 Integrated Paleogene stratigraphic column of Bonan sag

Fig.3 N-S-directed profile of transport framework in Bonan sag

Fig.4 Uniform temperature histogram of Es2 in Bonan sag

Fig.5 Depositional and burial history of Y284 in Bonan sag

Fig.6 Multi-sourced reservoir-forming model of Es2 in Bonan sag

Fig.7 Oil-bearing histogram of sandbodies (different thickness) of Es2 in Bonan sag

Table 1 Physical interval statistics of reservoirs(different thickness) of Es2 in Bonan sag

<2 m储层						2~6 m储层
孔隙度			渗透率			孔隙度			渗透率
区间/%	所占比例/%		区间/10^-3 μm²	所占比例/%	区间/%	所占比例/%			区间/10^-3 μm²	所占比例/%
<5	39.1	<1		49.5	<5		6.3	<1		10.3
5~10	30.2	1~10		33.0	5~10		12.7	1~10		24.8
10~15	20	10~30		13.2	10~15		27.4	10~30		20.1
15~20	7.6	30~50		1.1	15~20		38.0	30~50		22.0
20~30	3.1	50~100		1.6	20~30		13.5	50~100		13.1
>30	0	>100		1.6	>30		2.1	>100		9.8

Fig.8 Comprehensive evaluation map of the favorable oil and gas exploration areas of Es2 in Bonan sag

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