东沙隆起珠江组生物礁类型及勘探方向

Types of organic reef and exploration direction in Zhujiang Formation of Dongsha uplift

珠江组生物礁是东沙隆起重要的油气勘探领域,勘探潜力巨大,目前已发现了多个油气田与含油气构造。综合古地理位置与形态,将珠江组生物礁划分为台缘礁、台内点礁、环礁、块礁及陆棚塔礁5种类型,不同类型生物礁的外部形态与内部充填不同。平面上,台缘礁呈串珠状分布于隆起中南部台缘带,点礁、环礁、块礁呈不规则星点状分布于台地内部。古地貌背景决定了生物礁类型,台缘礁发育于早期地貌坡折上,位于油气从凹陷向隆起运移的必经之路,成藏条件最好,邻近惠州凹陷及白云凹陷的礁体是下一步勘探的突破方向。点礁、塔礁的发育受控于早期断洼的翘倾作用,规模较小,早期断洼的供烃能力尚不明确,靠近北部凹陷带的礁体是勘探的优先选择。块礁、环礁围绕台内局部隆起分布,已发现的块礁油气田位于隆起中南部的油气运移主路径上,远离该区的礁体缺乏油气来源,勘探风险较大。

The organic reef in Zhujiang Formation of Dongsha uplift is an important area with great potential for oil and gas exploration, where several oil ＆ gas fields and hydrocarbon bearing structures have been discovered. Based on a comprehensive consideration of the palaeogeographic location and landform, the organic reef can be classified into five types, including platform margin reef, intraplatformal point reef, atoll, massive reef and tower reef in shelf zone. Each type of reef has various external form and internal fillings. In a planar view, the platform margin reef in string-of-beads pattern is distributed in platform margin of the central and southern uplift; the rest in an irregular star-like pattern are distributed in the interior of the platform. The types of reefs are determined by palaeogeomorphic environment. Platform margin reef is developed in the early slope break zone, which is a necessary path- way for hydrocarbon migration from sag to uplift, and thus has the best reservoir-forming conditions. The reefs adjacent to Huizhou sag and Baiyun sag are expected to be the next exploration breakthrough. As influenced by the tilted fault blocks during the early rifting stage, the patch and tower reefs are developed in a small scale. Due to uncertain hydrocarbon supplying ability of the early fault depression, the reefs nearby northern sags are given the first priority for exploration. Atoll and massive reef are mainly distributed a- round regional uplifts in the platform. However, the oil ≥ gas fields discovered in massive reef are located at the major hydrocarbon migration pathway of mid-southern uplift, far from which the reefs are lack of hydrocarbon sources and have a high exploration risk.