PETROLEUM GEOLOGY AND EXPLORATION POTENTIAL OF SOUTH LOKICHAR BASIN IN EAST AFRICAN RIFT SYSTEM
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摘要:
东非裂谷系是新生代陆内裂谷盆地群，分为西支和东支，以往被认为勘探风险较大。东支的South Lokichar盆地自2012年以来不断获得油气发现，促使学者对以往结论进行反思。通过对盆地的地震、钻井等地质资料综合研究，分析了其石油地质特征及成藏规律，并预测了盆地的勘探潜力与有利勘探方向。South Lokichar盆地作为小型断陷湖盆，具有西断东超的结构，自渐新世以来充填了河流—(扇)三角洲—湖泊沉积体系。钻井及露头资料揭示：盆地的下中新统Lokhone组和渐新统Loperot组烃源岩品质好，处于成熟—高成熟阶段；中新统的下Auwerwer段扇三角洲砂体储集物性较好，与上覆区域性泥岩盖层形成良好的储盖组合。盆地西部陡坡带主要发育构造圈闭，已发现的油田规模较大，储量占全盆地的99%；东部缓坡带保存条件较差，油气发现少。South Lokichar盆地西北部断块圈闭较发育，钻井证实具备与西部陡坡带相似的成藏条件，是有利的勘探区带。
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关键词:
- 东非裂谷 /
- 东支 /
- South Lokichar盆地 /
- 石油地质特征 /
- 勘探潜力
Abstract:The East African Rift System (EARS) is a Cenozoic intercontinental rift basin group consisting of two main rifts: the Western Branch and Eastern Branch. Exploration risk in EARS was considerable high in the past decades. However, since 2012, several oil discoveries have been found in South Lokichar Basin in the Eastern Branch. Scholars began to rethink the previous conclusions. Through integrated studies of seismic, well and other geological data from the South Lokichar Basin, its petroleum geological features and reservoir-forming mechanisms revealed, exploration potential evaluated and prospecting direction predicted. The Basin has a small-scale, mono-faulted structural characteristics, faulting in the west and overlapping in the east, and has been filled with a fluvial-(fan) delta-lacustrine depositional system since Oligocene. Based on the analysis of samples of wells and outcrops, it was determined that both the Miocene Lokhone shale and the Oligocene Loperot shale are high quality source rocks with mid-high maturity, the Miocene Lower Auwerwer fan delta sand is a good reservoir, and it forms a good combination with the overlying regional mudstone. In the western steep slope zone of the basin, structural traps were developed and large-scale oil fields formed with the reserve accounting for 99% of the whole basin. In the eastern gentle slope of the basin, however, poor containment condition led to only small-scale oil discoveries. In the northeastern area of the basin, fault-block traps are developed, which makes it a favorable exploration zone. Recent data from wells has confirmed that this area has similar petroleum accumulation conditions with the western steep slope zone.
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