Secondary migration of hydrocarbons in the Zhujiang Formation in the Huixi half-graben, Pearl River Mouth Basin, South China Sea

Abstract

The process and mechanisms of secondary hydrocarbon migration in the Huixi half-graben, Pearl River Mouth Basin, were investigated on the basis of geological analysis of the strata and study of the porosity and permeability of the reservoir rocks, fluid potential, oil properties, and geochemistry of oil-source correlation. The results suggest that the hydrocarbons of the Zhujiang Formation in the Huixi half-graben were derived from source rocks of the Eocene Wenchang Formation and the Eocene-Oligocene Enping Formation in the Huizhou Sag. The hydrocarbons migrated laterally from northeast to southwest. The sandstone in the upper member of the Zhujiang Formation exhibited superior physical properties (porosity and permeability) and connectivity than the lower member. Thin sandstone beds with good physical properties and stable distribution in the upper member of the Zhujiang Formation were the main carrier beds for lateral hydrocarbon migration. Résumé :Les processus et les mécanismes de migration secondaire des hydrocarbures dans le demi-graben d'Huixi, dans l'embouchure du bassin de la rivière Pearl, ont été étudiés en se basant sur l'analyse géologique des strates et la détermination de la porosité et de la perméabilité des roches réservoir, le potentiel de fluides, les propriétés du pétrole et la géochimie de la corrélation pétrole-source. Selon les résultats, les hydrocarbures de la Formation de Zhujiang dans le demi-graben d'Huixi proviendraient des roches-mères de la Formation de Wenchang (Éocène) et de la Formation d'Enping (Éocène-Oligocène) dans l'affaissement d'Huizhou. Les hydrocarbures ont migré latéralement du nord-est au sud-ouest. Le grès dans le membre supérieur de la Formation de Zhujiang présentait de meilleures propriétés physiques (porosité et perméabilité) et une meilleure conductivité que le membre inférieur. De minces lits de grès avec de bonnes propriétés physiques et une distribution stable dans le membre supérieur de la Formation de Zhujiang constituaient les principaux lits réservoirs pour la migration latérale des hydrocarbures. [Traduit par la Rédaction]

Characterizations and accumulation of lacustrine source rocks in the Zhu I Depression, Pearl River Mouth Basin, China

“…Recently, the Pearl River Mouth Basin, located at the northern continental margin of the South China Sea, has become one of the most important offshore hydrocarbon exploration frontiers in Southeastern Asia (Figure 1a; Jiang, Zhu, Deng, & Hou, 2012;Zhu, Zhang, Zhong, & Liu, 2010). Previous hydrocarbon exploration activities have shown that there are four hydrocarbon-rich sags in the Zhu I Depression of the Pearl River Mouth Basin, including the Lufeng, Huizhou, Xijiang, and Enping sags; they also confirmed that source rocks are the key factor controlling the distribution of hydrocarbon plays in the Pearl River Mouth Basin (Gan et al, 2009;Guo, Xie, & Xiang, 2000;Gong, Wang, Zhu, Li, & Xu, 2013;Hou & Zhang, 2008;Lu, Wang, Zhang, Zhang, & Sun, 2011;Liao, Lin, Liu, Oung, & Wang, 2016;Peng et al, 2016;Ru & Pigott, 1986;Wu, Zhu, Shao, & Xu, 2016;Wu, 1984;Zhong, 1994;Xia & Wu, 1996;Zhu et al, 1997;Zhu et al, 2010). The current water depths in the Zhu I Depression are less than 500 m (Figure 1b) (Guo et al, 2000;Jiang et al, 2012;Li et al, 2013;Zhu, Zhang, & Gao, 2008).…”

“…The source rocks in the Pearl River Mouth Basin mainly developed in shoreline to shallow and moderate to deep lacustrine environments, swamp and fluvial transitional environments, and littoral delta marine environments (Figure ; Peng et al, ; Zhu et al, ). All sags, except for the Hanjiang Sag, contain shore–shallow and middle–deep lacustrine facies (Li, Xie, et al, ; Peng et al, ; Zhu et al, ; Zhu et al, ). There are three source rock intervals in the Zhu I Depression (Guo et al, ; Li, Tao, Sun, He, & He, ; Zhu et al, ), including the lacustrine source rocks of the Wenchang Formation, the transitional source rocks of the Enping Formation, and the marine source rocks of the Zhuhai Formation.…”

“…Therefore, the Zhu I Depression is an ideal natural laboratory for exploring source rock deposition models controlled by multiple factors. Recently, this has received more and more attention because of its huge exploration potential (Li, Xie, Huang, Hui, & Lin, ; Jiang et al, ; Peng et al, ; Quan et al, ; Wu et al, ; Xie et al, ). Since the 1980s, a series of oil fields have been discovered with a few gas fields.…”

Reconstruction of the Cenozoic History of Hydrocarbon Fluids from Rifting Stage to Passive Continental Margin Stage in the Huizhou Sag, the Pearl River Mouth Basin

“…The modeling results indicate that hydrocarbon generation potential of the Wenchang Fm in the Huixi half-graben is much higher than that in the Huibei halfgraben, with oil generation potential of 70 mg/g⋅TOC and gas generation potential of around 150 mg/g⋅TOC. Hydrocarbon expulsion of the Wenchang Fm began at 33.9 Ma and was Wenchang dark mudstone and shoreline-shallow lacustrine Enping dark mudstone and accumulated via lateral migration from the deeply buried source rocks in the HZS [2,3,43,44,47]. The modeling results indicate that oil expulsion in the HZS is mainly from the Eocene Wenchang source rocks and occurred during postrift stage.…”

“…The sandstones of the Zhujiang Fm show considerable variation in porosity and permeability, with the measured porosities ranging from 5% to over 30% (Figure 11(b)) and the measured permeabilities ranging from 0.1 to over 1000 mD ( Figure 11(c)). The average porosity and permeability of the upper Zhujiang Fm are 17.6% and 750 mD, respectively, and the average porosity and permeability of the lower Zhujiang Fm are 18.7% and 587 mD, respectively [47]. Overall, the Wenchang and Zhujiang Fm are strongly heterogeneous.…”