河套盆地临河坳陷中-新生代烃源岩分布地震预测

河套盆地临河坳陷作为低勘探程度区,明确生烃灶分布是盆地油气勘探的关键任务。而该盆地钻井稀少,缺乏采样分析资料,严重制约着烃源岩早期预测。因此利用有机地球化学、地震沉积学和地球物理技术,综合预测了主力烃源灶的分布。研究表明,白垩系固二段及渐新统临二段发育低频-强振幅相和弱振幅-空白相两类偏泥地震相,低频-强振幅相发育范围广泛,对应有机质丰度较高的暗色泥岩,而弱振幅-空白相发育较广泛,对应有机质丰度较小的灰黑色、灰色泥岩;固二段最有利的半深湖相烃源岩呈“多湖”分布特征,而临二段半深湖相烃源岩集中分布于北东部;两套烃源岩厚度具有北厚南薄的特征,临二段烃源岩最厚可达700 m;综合评价分析认为固二段发育两个生烃灶,其中西南部的生烃灶面积大、有机质丰度高、厚度较大,是最有利的生烃灶;临二段在北东部发育一个生烃灶,面积大、有机质丰度较高、厚度大,可作为最有利的生烃灶。实践表明,该方法在稀井、少井条件下能有效预测主力生烃灶分布,对油气成藏认识提供重要参考,同时为低勘探领域烃源岩分布早期预测及评价提供了新思路和方法体系。

Seismic Prediction for Mesozoic-Cenozoic Source Rock Distribution in the Linhe Depression,Hetao Basin

Degree of exploration in the Linhe Depression (Hetao Basin) is low, thus it is crucial to determine the source rock distribution for oil and gas exploration. However, due to the scarcity of drilling and sample analysis, early prediction of the source rock distribution is seriously limited. Therefore, distributions of main source kitchens are predicted with various organic geochemical, seismic sedimentological, and geophysical techniques. The results show two types of seismic facies, i.e. low-frequency and strong-amplitude facies, and weak-amplitude and blank facies in the Guyang Formation (2nd member) and Linhe Formation (2nd member). Low-frequency and strong-amplitude facies is widespread, corresponding to dark organic-rich mudstone.Blank facies is also widely developed, corresponding to gray-black/gray organic-poor mudstone. The most favorable semi-deep lacustrine source rocks in the Guyang Formation (2nd member) are characterized by being “multi-lacustrine”, while the semi-deep lacustrine source rock in the Linhe Formation (2nd member) is mainly distributed in the northeast. In general, the source rocks thicken toward the north, reaching 700 m thick for the Linhe Formation (2nd member). Comprehensive evaluation and analysis show that two source kitchens were developed in the Guyang Formation (2nd member), and the southwestern source kitchen is the most favorable because of their large area and thickness, and high organic matter abundance. Only one source kitchen was found in the Linhe Formation (2nd member), which is large and thick in the northeast, and has high organic matter abundance, making it the most favorable. Previous work indicated that this method can effectively predict the source kitchen distributions under few/sparse-well conditions, and provided important reference for the local hydrocarbon accumulation. The work offers a novel way for early source-rock distribution prediction in districts with low degree of exploration.