| This paper studied the most important enrichment of oil and gas basin of South America and even the whole world, Llanos Basin. The structural location of Llanos Basin is in the northern part of South America. The basin extends west to the east Cordillera mountain organics belt, east to the Guiana Shield, and south to the Vaupes uplift. Its northern border is Arauca uplift which is also the boundary of Llanos Basin and the Barinas uplift. Llanos Basin spreads about 23.5×104km2 in Columbia.By means of summarizing the former study, this paper described and devised the of Llanos into three periods: Paleozoic passive continental margin, Mesozoic bask-arc rift, and Cenozoic foreland basin. Meanwhile, on the base of studying the tectonic evolution process intensively, with the guidance of P.R.Vial sequence stratigraphy, by using drilling, logging, and seismic data analyzation as technological means, the sequence stratigraphic framework is built. Five secondary sequences are recognized in Cenozoic strata. Multiple sets of hydrocarbon source rocks were developed in the basin, mainly Paleozoic mudstone, upper cretaceous Gacheta The deep- shallow sea facies shale and Paleogene coal-bearing mudstone. With the distribution characteristics and the maturity of organic matters analyzed,this paper described the Hydrocarbon generation status in detail. Among all the source rocks, Gacheta contributes the most to the hydrocarbon accumulation. The hydrocarbon kitchen inside the basin locates in the basin’s western margin and in the eastern Cordillera. After analyzing the reservoir physical property and developmental capacity, the plain distributive characteristics and favorable positions are confirmed. Multiple sets of cap rocks were developed in the basin, among which, the Leon group is the main one. Through analyzing logging curves of typical wells in the basin, we confirmed that the basin has a good sealing condition. There are plenty types of traps in the basin, structural traps,structural-stratigraphic traps, stratigraphic traps and hydrodynamic traps are all often found. Besides, traps in different structural belts are usually different.Guided by the petroleum geology, this paper has described the accumulation characteristics of four main hydrocarbon-rich areas in the basin. The evaluate result shows that: the western basin was highly affected by tectonism, therefore large structural traps were mainly developed; on the opposite, small stratigraphic traps were mainly developed in the eastern basin, and no hydrodynamic trap was found.The hydrocarbon kitchens of the oil fields are usually not inside the field, the hydrocarbon fluid comes mostly from the west margin of the basin and the east-Cordillera mountain areas. On this base, considering of Basin tectonic evolution and sedimentation effect, the oil and gas reservoir formation characteristics are revealed;the hydrocarbon accumulation patterns are built. The main features of the basin accumulation includes: long distance migration, complex hydrocarbon recourse, migration through faults and sand bodies, hydrocarbon continually accumulation, and ladder accumulation model.On the basic of accumulation patterns built, zones were marked out according to the extent of tectonic affecting. And then, hydrocarbon accumulation favorable area was determined according to the sand body development degree. In result, in total 6 explore target blocks of 3 kinds were selected. This research result hangs an important guiding significance to the future deepened exploration and development of Llanos Basin. |
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