河南济源凹陷邓2井油藏成因分析

A Genetic Model for the Deng-2 Oil Pool in the Jiyuan Depression, Henan Province

济源凹陷是河南省油气勘探前沿区 ,由于构造活动和油气成藏条件比较复杂 ,仅在邓 2井发现了下第三系油藏。作者通过对该井砂岩储层的气液包裹体均一温度、包裹体内外生物标志物组成等分析 ,提出该油藏成藏温度为 75℃左右 ,成藏深度为 2 2 0 0m左右 (现今深度为 690m左右 )。该油藏的原油遭受了比较严重的生物降解作用 ,而成藏前原油只有轻微的生物降解作用。结合圈闭发育史分析 ,认为这是一个中生代原生油藏被破坏后 。

The Jiyuan Depression is a frontier area of oil and gas exploration in the Henan Province. Because tectonics and petroleum geology are very complicated in the Depression, only a small oil field, i.e. the well Deng-2 oil pool, has been found in the Lower Tertiary. However, controversy exists over the genetics of this oil pool. Some geologists believe it is a primary oil pool while the others consider it as a secondary pool reformed from the Mesozoic oil pools. In this paper, well will first present results of a series of geochemical experments on organic/salt-water inclusions and biomarkers in the oil-bearing/bare sandstones from the well Deng-2, which included measurements of homogenization temperature of hydrocarbon/gas-liquid inclusions and GC-MS analysis of biomarkers within and outside the inclusions, and then propose new genetic model for the Deng-2 reservoir. The Deng-2 oil-pool was formed at about 75℃ corresponding to a depth near 2200m with a present burial depth about 690m. Although the oil in the reservoir is biodegraded heavily now, the biomarkers inside the inclusions show little biodegraded features, which represent watering and biodegrading process accompanied with the reservoir evolution. Investigation on the structure evolution of the Deng-2 trap suggests that the Tertiary reservoir of Deng-2 is a secondary reservoir and its oil was migrated from the previously existed Mesozoic reservoirs below. Based on measurements of the maximum homogenization temperatures of gas-liquid inclusions in oil-bearing sandstones, we believe that the Eocene oil pool of Deng-2 was charged at about 2200m depth in the Late Oligocene. Studies also revealed that the hydrocarbons in the oils of sandstone pores in the Eocene reservoir of Deng-2 are characterized by heavy biodegradation, but those in the inclusions of the sandstones are lightly biodegraded, indicating that the Eocene oil pool of Deng-2 is a secondary oil pool formed in a bacterial living environment in the Late Oligocene and the oil in the pores of sandstone has undergone much longer biodegradation than that in the inclusions because of the tectonic uplift. The Eocene oil in the Deng-2 oil-pool was migrated from a primary Mesozoic oil pool by faults around the Deng-2 trap. The results of this study are important to understand the oil distribution in the Eocene reservoirs in the Jiyuan Depression, and to exploring oil in the faulted traps of the Eocene.