The Research On The Geological Conditions And The Main Controlling Factors Of The Oil And Gas Accumulation In Central Llanos Basin, South America

This paper is based on the previous studies of the Llanos basin and the geological data of drilling, logging and related geochemical. From the macro-perspective and the micro-perspective, the geological conditions and the main controlling factors of oil and gas accumulation of the central Llanos basin are analyzed and studied. From the macro-perspective, under the guidance of the sedimentary petrology, petroleum geology, organic geochemistry and analysis of oil and gas basins and other related theory, the geological conditions of oil and gas accumulation are studied. From the micro-perspective, the means of the analysis of Rock-Evaluation and the crude oil compounds with the help of a variety of biomarker parameters are applied in the study of the characteristics of the petroleum system are. Based on the comprehensive analysis of the characteristics of 3 blocks in the basis, the summarization of the main controlling factors of the oil and gas accumulation in the study area is carried out. This paper made the following main results:(1) The study area consists of two sets of source rock: the source rocks of the Gacheta Formation of Upper Crataceous was deposited in an environment of few terrestrial organic matters, saline water and the weak oxidation-reduction, the kerogen type of the Gacheta Formation is sapropel-humic type kerogen, and the source rocks of the Los Cuervos Formation of The Paleocene to Eocene was deposited in an environment of high terrestrial organic matters, brackish water and the oxidation, the kerogen type of the Los Cuervos Formation are sapropel- humic type kerogen and humic type kerogen. And the degree of its maturity of the two stratum are both in a low-middle level but it possesse a high hydrocarbon potential.(2) The study area has good reservoir condition. The main reservoirs of the study area include the Guadalupe Formation of the upper Cretaceous, the Mirador Formation of the Eocene and the C7 member of the Carbonera Formation of the Oligocene. The reservoirs are mainly consist of medium to coarse grained quartz sandstone, some are fine quartz. The reservoirs of the study area are mainly clastic-rock reservoirs with medium to high porosity and medium to high permeability. The study area has very favorable seal condition. There are 5 sets of cap rock found in the basin. They are the local cap rock of the C8, C6, C4, C2 member of the Carbonera Formation of Oligocene and Miocene, and the regional cap rock of the Leon Formation of the Miocene.(3) The study area is strongly affected by tectonization. The main trap types are anticline and faulted anticline structure. In the study area, the fault-related traps are found in the up-thrown block of the fault. The traps in the study area are featured by long shaping, low amplitude, large closed area and large size, and a distribution of along the faults. The migration events of oil and gas are mainly occurred at about 8Ma, the Miocene. The accumulation events of oil and gas began after the Miocene.(4) The study of oil components and biomarker parameters from 9 wells in the central Llanos basin showed that, the crude oil in the study area can be divided into the following 3 families: family A, the Cretaceous source rocks origin oil, family B, the Tertiary source rocks origin oil, family C, the mixed oil. The result of the oil-source correlation of the study area located 5 sets of matching source rock and reservoir combination. They are as fellows. The Gacheta Formation- the Guadalupe Formation, the Gacheta Formation- Mirador Formation, the Gacheta Formation- the C7 member of the Carbonera Formation, the Los Cuervos Formation- Mirador Formation, Los Cuervos Formation- the C7 member of the Carbonera Formation.(5) The petroleum system of the study area is characterized by ?late stage accumulation‘. Hydrocarbon kitchen is located in the area including the western part of the basin and the eastern Cordillera. The oil accumulation is featured by long distance migration and mixed charging. The normal source-reservoir-cap assemblage in the study area is generally ?old source rock and young reservoirs‘. The late occurrence of trap formation and oil and gas migration of enabled the traps and the fluid to form a good distribution in time and space. The large mounts of faults and sand body provide a stereoscopic translocation system for the migration of oil and gas. The main controlling factors of hydrocarbon accumulation are as follows: the source rock controls the accumulation of the oil and gas. The sizes of traps control the reservoir scale. The fault sealing controls the distribution accumulation of the oil and gas. The translocation system controls the location of the producing reservoirs.This study is aimed at the research of the geological conditions and main controlling factors of oil and gas accumulation of the central Llanos basin. The results from it will have a certain reference for the selection of favorable exploration area in the future, and also will provide theoretical reference and methods for the study the geological conditions and main controlling factors of oil and gas accumulation of other area.Indeed, as the study area located in foreign countries, there are some deficiencies in the collection of research data, such as, the collection and analysis the data of tested samples. The further improvement can be carried out in aspect such as, the description of a typical field.