关键词: 裂谷盆地, Termit盆地, 盆地构造建模, 三维可视化

Abstract:
3D structural model building is a frontier technique in tectonic research with superior performance in practicability, accuracy and visualization. This technique is normally used for studying local structures, and its application in basinlevel model building has been challenging. Here, we applied 3D structural modeling to the complex structures of the Termit Basin, where two rifts were developed in the Early Cretaceous and Paleogene. Taking the basin (area 30000 km2) as a whole, we built a 3D structural model using 2D and 3D seismic data in addition to more than 100 sets of well logging data, and overcoming technical difficulties such as multifault system, structural complexity and large data volume. Layer and fault grading simulations, automatic fault rename and loop generation, and fault relationship definition, were successfully applied to the Termit Basin. Thus we have developed new tools for studying fine structures at the basin scale. We showed that structural sections in any directions or planes and any welltie sections in the entire basin can be extracted for model building; and 3D model of each zone or local structure can be built to make structural analysis more accurate. Our 3D geological structural model has been widely used in the Termit Basin exploration, in areas such as tectonic units division, explorationzone evaluation, target optimization and well location demonstration. The model showed that the overlapping sequences of the lower Cretaceous sag and upper Paleogene rift formed the big lower and small upper sag structures in the Termit Basin, respectively. It also showed that in the depression period of the Late Cretaceous, marine source rocks distributed widely; and later in the Paleogene, the superposed rifts formed above the marine source rocks, creating favorable loci for hydrocarbon to accumulate in the Paleogene. Based on the newly established basin structural model, the structural characteristics and hydrocarbon accumulation potential of each structural zone can be further defined. Specifically, the Fana low uplift, located between the Moul and Dinga Sags, has relatively well developed fractures for hydrocarbon migration and accumulation, making it the most favorable exploration zone in the Termit Basin. The Araga graben, where fractures were developed, presents good hydrocarbon accumulation conditions. In contrast, the Moul and Dinga Sags, although having good oil deposit, have poor exploration potential due to poor upward migration caused by weak tectonic activities and undeveloped fractures. Moreover, the basin structural model allowed detailed analysis of the tectonic styles and fractures, resulted from the superposed rifts and their controlling effects on hydrocarbon accumulation in the basin, so as to optimize exploration targeting. Application of the structure model has made breakthroughs in the exploration of the upper Paleogene and lower Cretaceous assemblages.

Key words: rift basin, Termit Basin, basin tectonic modeling, 3D visualization