Characteristics Of The Oil And Gas Accumulation In The Tertiary, NGE Project, Llanos Basin, Columbia

By using Sedimentary Petrology, Petroleum Geology, Accumulation Dynamics and other research methods, not only the elements of the oil and gas accumulation in macro scale, but also the four blocks’characteristics of oil and gas accumulation in micro scale are analyzed, which are based on the predecessors’research results and Llanos basin’s existing material such as geological, logging, and seismic data. Finally, the favorable targets, of the four blocks in the research area are selected. The main achievements made in this paper are as follows.(1) The structure strength and its style of Llanos Basin are obvious asymmetry. Near the orogenic belt, basin often formed fold-thrust zone which is caused by the intensity deformation. In the middle part of the basin, it often formed foredeep sag which is under the footwall of the thrust belt. To the east direction, the basin gradually extended to craton, and fin formed stable foreland slopes and front uplift.(2) There are mainly three types of hydrocarbon source rocks, the most important one is the Upper Cretaceous Gacheta Group Shale which is fromed of bathyal-neritic facies. The carbon shale in the paleogene system and the black shale in the devonian and carboniferous system are the secondary type of hydrocarbon source rocks. In the sedimentary center and uplifted belt of the Cordillera, the types of the organic matters are mainly type Ⅰ and type Ⅱ1. The rock pyrolysis experiments show that the western sedimentary center has the maximum hydrocarbon-generating potential and this tendence gradually reduces from the west to the east.(3) Llanos Basin not only has good reservoir and cap conditions, but also has multiple sets of source-reservoir-seal assemblages. The reservoir sandstone is mainly in medium-size, and the packsand take the second place, belonging to high pore and high permeability type reservoir which promises a good reservoir physical property. The cap rock conditions is also superior in Llanos Basin, which both developed the regional caprocks such as shale in Leon Formation and local caprocks such as mudstone in C2, C4, C6Segment.(4) Generally speaking, the fault seal property gradually becomes poorer from the west to the east in Llanos Basin. The fault seal property is intimately related to reservoir distribution. In the meantime, the lithology juxtaposition relationship of the two sides of the fault is one of the controling elements of oil and gas accumulation. However,, the fault seal ability index is not the only standard to judge the oil and gas accumulation.(5) The migration of oil and gas began in the late Eocene, and mainly happened after the Miocene. The main period for hydrocarbon accumulation also occurred in the Miocene. The oil and gas generating from the source rocks in the west of the basin migrated to the esat part of the basin along the basin slope. The main type of trap in this area is structural-dominant trap, such as anticline, fault-anticline and fault-nose trap, which has long and narrow shape, low amplitude, less area and small scale(6) The regulations of the hydrocarbon accumulation in the research area is concluded as that’the haydrocarbon generated in the far-away souce rocks migrated in a comprehensive passage system; the hydrocarbon accumulated through the shading of the fsults.’Which means the source rocks are far away from the research area and the fault, unconformity and high quality sand are all favourable passage systems for the oil and gas migration. Meanwhile, the oil and gas has been screened by fault in updip direction of reservoir, and then formed anticline, fault-anticline and fault-nose oil reservoirs. The main controling factors of hydricarbib accumulation are as follows:the gathering of the oil and gas is controlled by the hydrocarbon generation centers; the accumulation of of oil and gas is controlled by the seal of fault and cap; the reservoir type is controlled by sets of reservoir-seal assemblages; the scale of the eservoir is controlled by trap size.(7) After the comprehensive evaluation research, it is conluded that the traps of DPI, DP2and DP3are the most favourable targets for exploration which have excellent hydrocarbon accumulation conditions, such as large areas, and high closures. The CP4and CP3traps are similar to the reservoirs that have already been found.As a result, they also show great resource potential, and would be the optional exploration objects.