Petroleum Origins and Accumulation Patterns in the Weixinan Sag in the Beibu Gulf Basin, Using Subsag B as an Example

This paper investigates the origin and migration characteristics of petroleum in the northeastern part of the Baiyun Depression, Pearl River Mouth Basin (PRMB). The discovered petroleum in the study area is mainly located in the Lower Zhujiang Member (N 1 z 2) and mainly originated from the Enping Formation source rocks in the eastern sag. Active faults (vertical migration) and N 1 z 2 sandstones (lateral migration) acted as the petroleum migration systems. The fault activities in the Dongsha event controlled the episodic petroleum migration. Fractures in the fault zones provided effective conduits, and overpressure was the driving force. The vertical migration could not cross the fault zones laterally. The petroleum injection areas in the carrier beds were the contact zones of petroleum-migration faults and carrier beds. The lateral migration was steady-state migration, and buoyancy was the driving force. The migration pathways in the carrier beds were controlled by the structural morphology. Secondary petroleum migration in the study area could be divided into two parts: vertical migration along the fractures in the fault zones and lateral migration through preferential petroleum migration pathways (PPMPs) in the carrier beds. The petroleum migration behaviors, including migrating direction, driving force, and migration pattern, in the faults and sandstone carrier beds were quite different. This study provides a typical example for comprehending secondary migration processes and has great importance for determining future exploration targets in the deep-water area of the PRMB.

Section: Origin Of the Petroleummentioning

confidence: 99%

Petroleum Migration Characteristics in the Northeastern Part of the Baiyun Depression, Pearl River Mouth Basin, South China Sea

Zeng

Wang

Guo³

et al. 2021

“…Commonly, fault activities are favorable for the development of lacustrine system in rift phases. High quality lacustrine source rocks are preferentially developed in rifted lacustrine basin (He et al, 2019;Gao et al, 2020;Cheng et al, 2020). Therefore, As a consequence, there is a great hydrocarbon potential in deep-water regions of the northern South China Sea (Zhu et al, 2009).…”

mentioning

confidence: 99%

Distribution Prediction of Middle‐deep Lacustrine Source Rocks in Eocene Wenchang Formation in the Kaiping Sag, Pearl Mouth Basin

Xiong¹,

Xie²,

Zhao³

et al. 2021

Oil and gas shows are rich in drilling wells in Kaiping sag, however, large oilfield was still not found in this area. For a long time, it is thought that source rocks were developed in the middle-deep lacustrine facies in the Eocene Wenchang Formation, while there is no source rocks that in middle-deep lacustrine facies have been found in well. Thickness of Wenchang Formation is big and reservoirs with good properties could be found in this formation. Distribution and scale of source rock are significant for further direction of petroleum exploration. Distribution characterization of middle-deep lacustrine facies is the base for source rock research. Based on the sedimentary background, fault activity rate, seismic response features, and seismic attributes were analyzed. No limited classification method and multi-attributes neural network deep learning method were used for predicting of source rock distribution in Wenchang Formation. It is found that during the deposition of lower Wenchang Formation, activity rate of main fault controlling the subsag sedimentation was bigger than 100 m/Ma, which formed development background for middle-deep lacustrine facies. Compared with the seismic response of middle-deep lacustrine source rocks developed in Zhu I depression, those in Kaiping sag are characterized in low frequency and good continuity. Through RGB frequency decomposition, areas with low frequency are main distribution parts for middle-deep lacustrine facies. Dominant frequency, instantaneous frequency, and coherency attributes of seismic could be used in no limited classification method for further identification of middle-deep lacustrine facies. Based on the limitation of geology knowledge, multi-attributes of seismic were analyzed through neural network deep learning method. Distribution of middle-deep lacustrine facies in the fourth member of Wenchang Formation is oriented from west to east and is the largest. Square of the middle-deep lacustrine facies in that member is 154 km 2 and the volume is 50 km 3. Achievements could be bases for hydrocarbon accumulation study and for exploration target optimization in Kaiping sag.

“…Therefore, it's an ideal place for analyzing the relationship between the structure and oil distribution. A lot of researches have been done in the Beibuwan Baisn (He et al, 1993;Zhu et al, 1998;Ding et al, 2003;Bao et al, 2006;Lu et al, 2007;Luo et al, 2008;Sun W et al, 2008;Sun J F et al, 2008;Liu et al, 2009;Yang et al, 2009;Yang et al, 2011;Wang et al, 2011;Xu et al, 2013;Zhao et al, 2013;Hu et al, 2014;Yang, 2016;Fu et al, 2019;Gao et al, 2020). Based on the analysis of the mechanism of fault-controlled reservoir, Luo and Pang (2008) pointed out that the deep antithetic fault system is the main controlling factor for the formation and distribution of the reservoir in the Fushan Sag.…”

mentioning

confidence: 99%

Hydrocarbon Enrichment and Main Controlling Factors in Offshore Rift Basins of China: A Case Study in the Beibuwan Basin

Zhang

Wu²,

Li³

et al. 2021

Beibuwan Basin is an important offshore oil and gas bearing basin of China. However, the distribution of oil and gas in different sags is uneven, and the rule of hydrocarbon accumulation and main controlling factors have not been clearly understood in this basin. Based on abundant seismic, well and analytical data, the differences and main controlling of tectonic evolution, sedimentary filling and source rock quality in sags are analyzed, and combined with the study of geothermal filed, the main controlling factors of differential hydrocarbon generation in sags of the Beibuwan Basin are clarified. On the basis of the research above, the hydrocarbon enrichment of the basin is clarified through the systematic analysis of reservoir-caprock assemblage and accumulation characteristics of different structural units. The results show that there are four NE-trending sag zones in the basin, and under the influence of fault activity, the scale of sags is regularly distributed. The scale of rifts in different sag zones decreases gradually from northwest to southeast and the scale of rifts in the middle of a single sag zone is normally larger than that at two ends. Under the control of the sag-controlling faults activity, paleoproductivity and organic matter preservation conditions, the quality of source rocks in sags of the Beibuwan Basin decreases from northwest to southeast. The hydrocarbon-rich sags in the Beibuwan Basin were formed under the control of source rocks and geothermal field, and the distribution of large-medium scale fields is controlled by the favorable structural traps in the rift strata of inner gentle slope zone. The understanding of the hydrocarbon enrichment and main controlling factors in the Beibuwan Basin also provides a significant guidance for the oil and gas exploration in other rift basins.