超临界蒸汽开发特稠油提高采收率机理实验研究

超临界蒸汽技术可将油田采出污水作为燃料，且产生的超临界蒸汽具有更高的热晗值，采用该技术开发海上特稠油具有广阔前景，但目前超临界蒸汽开发特稠油的增产机理尚不明确。以渤海油田LD5-2N典型特稠油油藏为例，利用新建立的超临界蒸汽驱实验装置模拟超临界蒸汽开发稠油过程，开展了超临界蒸汽开发特稠油的增产机理研究，分析了超临界条件下原油物性及储层物性变化规律，研究发现:超临界蒸汽驱技术可大幅度提高采收率，其增产机理主要体现在蒸汽具有更高的热晗值可大幅度降低原油黏度，具有高溶解性可产生近似混相驱的效果，具有高扩散性更容易进入岩心微孔结构。超临界蒸汽驱的驱油效率提高率可达94%；超临界条件下特稠油中的沥青质与胶质组分会发生热裂解反应使原油黏度进一步降低30%左右；岩石会发生溶蚀可增大储层孔隙度和渗透率，渗透率的最大增加幅度可达21.7%。研究成果为海上特稠油油藏采用超临界蒸汽开发提供了理论依据。

Experimental study on the EOR mechanisms of developing extra heavy oil by supercritical steam

Supercritical steam technique can take the oilfield produced water as the fuel and its generated supercritical steam has higher enthalpy, so its application prospect to develop offshore extra heavy oil is promising. So far, however, the stimulation mechanisms of developing extra heavy oil by supercritical steam hasn’t been clarified. The development process of heavy oil by supercritical steam was simulated with the LD5-2N typical extra heavy oil reservoir of the Bohai Oilfield as the example, by using the newly established experimental device of supercritical steam flooding. Then, the stimulation mechanisms of developing extra heavy oil by supercritical steam were studied and the change laws of the physical properties of crude oil and reservoir under supercritical condition were analyzed. It is indicated that the supercritical steam technique can enhance the recovery factor greatly and its stimulation mechanisms are embodied as higher enthalpy to reduce oil viscosity significantly, high solubility to produce the similar effects to miscible flooding and high diffusibility to move into the micropore structures in cores more easily. The oil displacement efficiency of supercritical steam flooding can reach 94%. Under the supercritical condition, asphaltenic and colloidal compositions in extra heavy oil undergo thermal cracking reaction, which decreases the oil viscosity by 30% further. Rock dissolution can happen, which leads to the increase of reservoir porosity and permeability. And the maximum increase amplitude of the permeability is up to 21.7%. The research results provide the theoretical basis for the development of offshore extra heavy oil reservoirs by supercritical steam.