南海南部北康盆地生物礁的类型及油气勘探前景

The style and hydrocarbon prospects of reefs in the Beikang Basin, southern South China Sea

南海南部北康盆地发育大量的生物礁,蕴藏丰富的油气资源。文章基于北康盆地高精度地震数据及钻井数据的研究表明,北康盆地的生物礁成像较好、类型齐全,有点礁、台地边缘礁、块状礁、层状礁、塔礁、环礁共6类型。其发育演化可以分为4个阶段,分别为早中新世的初始发育阶段、中中新世早期的繁盛阶段、中中新世晚期的衰退阶段和晚中新世的淹没阶段。古近纪及早中新世的断裂活动产生了大量的构造高点,为生物礁的初始发育创造了条件,而中中新世以来基底快速沉降导致的相对海平面的快速上升决定了生物礁主要发育于中中新世时期,而晚中新世以来相对海平面持续上升,致使生物礁退积到隆起顶部,从而进入淹没阶段。北康盆地的生物礁数量多、规模大,而且很少受后期成岩作用的二次改造,具备优质储层形成的前提。同时,区域烃源岩、疏导体系、盖层及生物礁的分布等油气地质条件,决定了中部隆起西部和东部隆起东部是北康盆地今后生物礁油气勘探的重点区域。

During the Miocene,there were a number of reefs developed in the Beikang Basin,which constitute potential forhydrocarbon exploration.The high-resolution seismic data and numerous well drilling data have provided an opportunity tounderstand the evolution of reefs in the study area.Six types of reefs were identified,i.e.,point reef,platform-edge reef,block reef,bedded reef,pinnacle reef,and atoll reef,and their development could be divided into four stages.In early Miocene,a few point reefs small in size initiated in this basin and they flourished in the early middle Miocene and mainly developed around the CentralUplift and Eastern Uplift.However,the reefs began to wither in the late middle Miocene in response to a rapid relative sea level risewhich was caused by the loading subsidence.Since late Miocene,with the continuous rising of the relative sea level,many reefsformerly developed around the Central Uplift and Eastern Uplift have been submerged and only some atoll reefs have survivedaround the islands on the Eastern Uplift.Additionally,the numerous reefs which are little influenced by later diagenesis arefavorable reservoirs for hydrocarbon exploration.The match relation of regional hydrocarbon rock,dredged system and thedistribution of reefs indicates that the west of Central Uplift and the east of Eastern Uplift seem to be the favorable exploration zonesfor the hydrocarbon exploration of reefs in the Beikang Basin.