油藏CO2驱及封存过程中地化反应特征及埋存效率

Geochemical reactions and CO2 storage efficiency during CO2 EOR process and subsequent storage

关键词:  高温油藏  CO₂驱  CO₂埋存  地化反应  埋存效率

Key words:  high-temperature oil reservoir  CO₂ displacement  CO₂ storage  geochemical reactions  storage efficiency

摘要:

油藏CO₂驱过程中，CO₂与地层水和岩石矿物发生化学反应，影响地层物性和CO₂的埋存形式。基于吉林油田某高温油藏的地层及流体性质，建立考虑地层水蒸发、水中CO₂溶解扩散、CO₂-地层水-岩石地化反应和孔渗关系的CO₂驱及埋存综合模拟模型，分析不同阶段的地化反应特征和CO₂埋存形式，研究CO₂注入方式对提高采收率和埋存效率的影响。结果表明：在CO₂驱油阶段，地化反应对储层孔隙度和渗透率产生定影响，但对采收率的影响较小，CO₂主要以构造形式埋存于油藏内；在后续埋存阶段，气态CO₂通过地化反应不断转化为矿物形式，造成地层压力下降；水气交替注入方式可提高原油最终采收率和CO₂次埋存效率，应为首选注入方式；对于其CO₂埋存量的不足，可在CO₂驱后注入定的CO₂进行补充，同时起到维持地层压力的作用。

Abstract:

Geochemical reactions among CO₂-fromation water-rocks can occur and affect the physical properties of the reservoir and the CO₂ trapping mechanisms during CO₂ EOR process. In this paper, based on the properties of the reservoir and fluids in a typical high-temperature oil reservoir in Jilin Oilfield, a comprehensive model was established to simulate the CO₂ EOR and the subsequent storage, processes, in which formation water evaporation, dissolution and diffusion of CO₂ in water, CO₂-water-rock geochemical reactions and variations of porosity and permeability were considered. The geochemical reactions and various CO₂ trapping forms in different stages were analyzed using the model, and the influences of different CO₂ injection methods on EOR and CO₂ storage were evaluated. The results show that, though the geochemical reactions can change reservoir porosity and permeability, their effect is not significant and most of the injected CO₂ can be trapped as supercritical gas during CO₂ EOR process. During CO₂ storage, gaseous CO₂ can be continuously converted into mineral forms due to geochemical reactions, which results in a reduction of reservoir pressure. A WAG (water alternative gas injection) method can be applied to enhance oil recovery and increase CO₂ storage efficiency. Further injection of CO₂ after CO₂ EOR process can increase the CO₂ storage capacity, and simultaneously maintain the reservoir pressure.