巴西桑托斯盆地高含CO2油气藏类型、特征及成因模式

桑托斯盆地盐下油气藏中CO₂分布广泛，局部摩尔分数极高，给勘探、开发都带来了巨大挑战。通过对典型油气藏解剖分析，并利用流体取样、闪蒸实验测试分析等资料，将盆内油气藏分为3类：类型Ⅰ，含CO₂溶解气的高气油比常规油藏；类型Ⅱ，CO₂气顶+油环型油气藏；类型Ⅲ，（含溶解烃）CO₂气藏。其中类型Ⅰ油藏和类型ⅢCO₂气藏中流体性质均匀、稳定，油-水界面、气-水界面清晰；类型Ⅱ气顶+油环型油气藏流体成分和性质不均匀、不稳定，流体界面复杂。物理热模拟实验表明盆内3种类型油气藏是地层条件下，超临界状态CO₂和烃类有限互溶，动态成藏过程不同阶段的产物。动态成藏过程中，CO₂对烃类进行抽提、萃取，烃类（原油）对CO₂进行溶解，两者相互作用存在一个动态平衡（范围）。烃类和CO₂相对量大小决定了最终的油气藏类型，温-压条件变化和油气藏开发可改变油气藏平衡状态，造成流体相态变化和3类油气藏间的相互转化。

Main Types,Characteristics and Genetic Model of Oil & Gas Reservoirs with High CO2 Content in Santos Basin,Brazil

Together with the encouraging oil and gas discoveries in the pre-salt section in Santos basin, the reservoirs are also characterized by a wide occurrence of CO₂ and high gas-oil ratio (GOR), which leads to a series of challenges both in oil & gas exploration and development. Based on the CO₂ content and fluid phases, the reservoirs currently discovered in Santos basin could be divided into three types:Type Ⅰ conventional oil reservoirs containing dissolved CO₂ with high GOR, type Ⅱ CO₂ gas cap + oil ring reservoirs and type Ⅲ CO₂ gas reservoirs (containing dissolved hydrocarbons). For type Ⅰ oil reservoir and type Ⅲ CO₂ gas reservoir, the fluid properties, such as GOR, API and CH₄ content are uniform, and oil-water contact and gas-water contact are easily defined. For type Ⅱ gas cap+oil ring reservoirs, its fluid properties are not uniform anymore and are very complex. The authors proposed an innovative geological model, dynamic dissolving-extracting between CO₂ and hydrocarbon. The three types of reservoirs are likely to be a mixture of two different endmembers, supercritical CO₂ and fluid hydrocarbon. The crude oil dissolves CO₂ while CO₂ extracts lighter components of hydrocarbon. There is a dynamic balance point or scale under certain pressure and temperature. If CO₂ volume is less than the balance points, the crude oil could dissolve it completely and the reservoir belongs to type Ⅰ. If the CO₂ volume is larger than that, a gas cap will appear, and the reservoir become type Ⅱ. In some situations, the CO₂ volume is very large while hydrocarbon is very limited, the type Ⅲ CO₂ gas reservoir will be developed. Therefore, the relative amount of hydrocarbon and CO₂ determine the fluid phases and types of reservoirs finally. Meanwhile, the reservoir types could also change with temperature, pressure, or tectonic movement. Because these factors could break such balance and result in phase change and transition.