Genetic pattern of belt-wide petroliferous phenomenon in the eastern Pearl River Mouth Basin and its practical application

Abstract

The Pearl River Mouth Basin (PRMB) covers an area of approximately 20×10 4 km 2. However, oil-gas fields detected in this area thus far are highly concentrated and controlled predominantly by second-order structural belts, the seven largest of which aggregate proved oil reserves of 7.7×10 8 m 3 , accounting for 86% of the total discovered reserve in the basin. These second-order structures have one common phenomenon: oil is contained in all traps present in them. In other words, they are all belt-wide petroliferous reservoirs. Research has identified eight types of second-order structural belts under two categories in the eastern PRMB. Their petroliferous properties are subject to three typical constraints: petroliferous properties of subsags hosting these structural belts, locations of these belts in the petroleum system, and availability of traps prior to the hydrocarbon expulsion and migration. The formation and distribution of oil reservoirs in these belts are characterized by subsag-belt integration and "three-in-one". The former indicates that sags and the second-order structural belts within the supply range of the sags constitute the basic units of hydrocarbon accumulations and are therefore inseparable. The latter indicates that a belt-wide petroliferous second-order structural belt always contains three important elements: hydrocarbon richness, effective pathway and pre-existing traps.

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

“…For the two main source rocks (Wenchang Formation and Enping Formation), the generation and migration period started in 16-10 Ma and the subsequent peak expulsion period was reached gradually (at 10-5 Ma). The structure of the study area tended to be stable after the Dongsha movement (about 10 Ma), which was favorable for petroleum accumulation and preservation (Shi et al 2014). Therefore, the oil distribution pattern should not be affected by biodegradation or later tectonic movement.…”

“…Recent exploration has indicated that the geological reserves of hydrocarbons in the Huixi half-graben amount to 22.09 × 10 8 t, accounting for 34.3% of the Pearl River Mouth Basin reserves. More than 50% of the Huixi reserves are in the Zhujiang Formation (Shi 2013;Shi et al 2014). This finding further supports the Huixi half-graben being a major hydrocarbon-rich area in the Pearl River Mouth Basin.…”

“…Previous petroleum exploration has shown that there are two main source rocks in the Zhu I Depression: the Eocene Wenchang Formation and the Eocene-Oligocene Enping Formation (Shi 2013;Shi et al 2014). These two source rocks and their geochemical characteristics are described in the following subsections.…”