东尼日尔盆地Termit坳陷油气富集规律及Dibeilla-1井发现的意义

Petroleum Migration and Accumulation in Termit Depression of East Niger Basin and Implications for Discovery of Well Dibeilla

东尼日尔盆地属于西非裂谷系,是发育于前寒武系—侏罗系基底之上的中、新生代裂谷盆地。该盆地构造演化表现为晚白垩世大规模海侵、早白垩世和古近纪两期裂谷叠置。后期古近纪叠置裂谷发育于广泛分布的晚白垩世海相烃源岩之上,形成主要的成藏组合。国外石油公司自1970年开始对该盆地进行大规模的油气勘探,近40年间,在Termit坳陷西部Dinga断阶带的古近系组合中发现商业油气,其他区域甩开勘探未获突破。中石油于2008年6月获得Termit坳陷的勘探许可,面临着如何在短期内快速评价油气潜力、扩大勘探成果并发现新的含油气区带的难题。对Termit坳陷油气运移和富集规律研究表明,除了西部的Dinga断阶带之外,东部Araga斜坡带也是有利的油气富集区带。以此为指导在Araga斜坡带Dibeilla构造优选部署了Dibeilla-1井,获得重大发现,随后周边滚动探井Dibeilla N-1和Admer-1井也获得商业发现,3口井估算地质储量约0.9×108t。Dibeilla-1井的发现使得Araga斜坡带成为继Dinga断阶带之后的另一个油气富集带,证实了Araga斜坡带的勘探潜力,同时提升了相邻Bilma区块的勘探价值。

The East Niger Basin, which belongs to western section of Central Western Africa Rift System (WCARS), is a Mesozoic-Cenozoic rift basin developed on the Precambrian-Jurassic crystallized basement. It is characterized by a great transgression in the Late Cretaceous, and the superimposition of the Early Cretaceous and Paleogene rifting. The Paleogene assemblage is the main play that developed on the widely distributed marine source rocks of Late Cretaceous. Several foreign oil companies have made extensive exploration in the East Niger Basin since 1970, and commercial oil was encountered in the Dinga faulted terrace. CNPC started hydrocarbon exploration in the Termit Depression in June 2008. In order to discover more additional oil reserves within a short time span, how to evaluate and to map out quickly the potential petroleum fairways was the main challenge for Chinese explorationists. The Araga slope, standing opposite to the Dinga faulted terrace, was eventually considered as one of the most potential exploration trends based on a fully petroleum migration and accumulation study. Consequently, the Well Dibeilla-1 was proposed and optimized to test the Dibeilla prospect, which came out as a great discovery. Taking into account for the subsequent drilling of the Well Dibeilla N-1 and Well Admer-1, approximately 90 million tons of OOIP were estimated under Dibeilla structural zone. The success of the Well Dibeilla-1 brought about the naissance of a new petroleum accumulation zone after the Dinga faulted terrace in the Termit Depression. Moreover, it showed a bright future of the exploration in the adjacent Block Bilma.