原油裂解动力学及其相变特征和意义--以柴达木盆地北缘伊深1井为例

Kinetics of oil cracking and the meaning of its phase transition characteristics:Taking Well YS1 in northern Qaidam Basin as an example

为了研究柴达木盆地北缘(柴北缘)原油裂解及其相态演化历史,应用黄金管封闭体系高压釜模拟实验,对柴北缘马北106井古近系储层中原油进行了热模拟生气实验。通过对各演化阶段的流体组分精确定量,建立了原油裂解过程中的相态演化模型,同时根据化学动力学原理,计算获取了原油裂解成气的动力学参数。以此为基础,对柴北缘伊北生烃凹陷的原油裂解和相态演化史进行了重建。研究表明,独立相原油地下保存温度上限受到热演化程度和地层温度、压力的双重控制。原油裂解过程中的流体临界压力表现出明显的"稳定"(Easy%RO<1.08%)、"升高"(1.08%<Easy%RO<2.05%)、"降低"(Easy%RO>2.05%)3个阶段变化特征。柴北缘伊北生烃凹陷原油裂解从距今约20Ma开始,现已基本完全裂解,其流体相态在N^2_2—Q_(1+2)期间由液相转变为气相,油气运移过程中在埋深浅于1 500m时发生气液分异,伊北凹陷及其周缘勘探方向为深部找气、浅部找油,中心找气、周缘找油。

In order to study the history of oil cracking and phase evolution in the northern margin of the Qaidam Basin（North Qaidam）,the pressurized sealed gold tube pyrolysis experiments was conducted on Tertiary reservoir crude oil from Well MB106 in North Qaidam.The pyrolysis products of oil were accurate quantification and a model of phase evolution of oil cracking was established.According to the principles of chemical kinetics,the kinetic parameters of oil cracking to gas were calculated.On this basis,we reconstructed the history of oil cracking and phase evolution of Yibei Depression in the North Qaidam.Research shows that the upper temperature limit of independent oil phase appeared underground is controlled by thermal maturity and formation pressure.With the increase of maturity,the critical pressure of generated fluid show a variation of three stages,i.e.,Ⅰstabilizing（Easy%RO1.08%）,Ⅱicreasing（1.08%Easy%RO2.05%）,Ⅲ decreasing（Easy%RO2.05%）.The oil cracking of Yibei Depression started about 20 Ma ago and it＇s almost cracked completely now.The fluid phase changed from oil phase to gas phase during N-2_2-Q_（1＋2）.Oil and gas phase differentiation would occur when the depth was shallower than 1 500 m.The exploration direction of Yibei Depression and its peripheral edge in the future should comply with a rule that the gas exploration should focus on the deep and center of depression,the oil exploration should focus on shallow and periphery.