隐伏砂岩透镜体成藏动力学机制与基本模式

Mechanism and basic modes of petroleum accumulation dynamics in subtle sand lens reservoir

庞雄奇 陈冬霞 姜振学 张俊 李素梅

Pang Xiongqi Chen Dongxia Jiang Zhenxue Zhang Jun Li Sumei

隐伏砂岩透镜体聚集油气的主要动力包括砂、泥岩接触面上的毛细管压力差、生烃泥岩与砂体之间的烃浓度差引起的扩散力和泥岩内干酪根生成油气产生的体积膨胀力等;聚集油气的阻力主要包括油气进入砂岩体后遇到的毛细管力和油气将水挤出砂岩体外遇到的阻力.聚集油气的动力大于阻力是形成砂岩透镜体油气藏的基本条件.砂岩透镜体成藏受砂体孔渗及围岩含油气饱和度等因素的制约.围岩生成的油气进入到砂岩透镜体内的临界地质条件是围岩中的含油气饱和度超过5%～10%;砂岩体聚集油气的临界地质条件是孔隙度超过10%或渗透率超过1×10～2×10μm.地史过程中砂岩透镜体成藏分为3个阶段.第一阶段为成藏条件准备阶段,此阶段油气没有大量生成,围岩微孔隙中强大的毛细管力是分散油滴运聚的阻力;第二阶段为油气运聚成藏阶段,此阶段油气已大量生成,围岩与砂体之间的毛细管力差是油气通过有机网络不断聚集成藏的主要动力;第三阶段为油气聚集后的保存阶段,此阶段油气已不再大量生成,围岩与砂体之间的毛细管力差不能克服油气聚集过程中的阻力.根据成藏动力学机制与控油气作用特点可以预测砂体的含油气性大小与变化规律.

The major driving forces for hydrocarbon accumulation in subtle sand lens reservoirs includes differential capillary pressure on sand-shale boundary,diffusive force triggered by differential hydrocarbon concentration between source beds and sandbodies,and volume expansion caused by kerogen generating hydrocarbons;while the dominant forces that prevent hydrocarbons from pooling include capillary pressure the hydrocarbons faced when entering sandstones and resistance occurred when displacing water in sandstones.For hydrocarbons to accumulate in sandstones,the driving forces must be stronger than the resistances.Apart form that,the porosity and permeability of sandbodies and the hydrocarbon saturation of sourrouding rocks also control the accumulation of hydrocarbons in sandstones.The critical geologic condition for the hydrocarbons generated by the surrounding source rocks entering sandbodies is that hydrocarbon saturation of the surrounding source rocks exceeds 5%-10%,and while that for the hydrocarbons to accumulate in the sandbodies is that the porosity and permeability of sandstones are higher than 5%-10% and 1×10-2×10μm respectively.The accumulation of hydrocarbons in sand lens reservoirs can be divided into three stages.The first is preparation stage when no large quantity of hydrocarbons are generated by the source rocks and the strong capillary pressure in the micro pores of these rocks prevents the migration of dispersed oil drops.The second is migration and pooling stage when large amount of hydrocarbons are generated and accumulate in the reservoirs with the differential capillary pressure between the surrounding rocks and sandstones as the main driving force.The third is preservation stage when the hydrocarbon no longer generated in large amount and the differential capillary pressure between the surrounding rocks and sandstones is weaker than the resistant forces.The reservoiring dynamics and controls on hydrocarbon accumulation can be used to predict the hydrocarbon abundance and changing patterns.

10.11743/ogg20070213