Pressure characteristics in CO2 flooding experiments

Abstract

In the initial period of CO2 flooding, formation pressures of reservoirs do not increase noticeably. Physical simulation experiments were designed to study this phenomenon. In the 1-D infill-sand model, it was found that, under the same pressure conditions, the densities of distilled water, salt water and crude oil increased with CO2 dissolution, and then reached stability. By the volume decrease calculation of the liquid and the distilled water dissolution experiment, it was confirmed that the effects of CO2 dissolved in oil and water are the main reasons for any pressure decrease. In the 2-D sand plate model, injection pressure also decreased. By analyzing production PV (pore volume) and injection PV curves, it was found that the main reason for the pressure decrease is that the injected CO2 can flow into the minute pores that are unavailable to oil and water, and comparatively speaking, dissolution of CO2 can be neglected. The result is also proven by porosity calculations and CO2 flooding experiments using different production control methods and by using carbonate cores. 摘要: 在CO2驱油试验区的开发初期，地层压力并没有明显上升，为了查明其原因，开展一维填砂模型和二维砂岩模型物理模拟实验研究。一维填砂模型CO2驱替实验显示：在相同压力下，随着CO2溶解量的增加，蒸馏水、盐水和原油3种流体的密度均上升后趋于稳定。结合液体升压过程中的体积缩小量计算及蒸馏水溶解实验，确认CO2在油相和水相中因溶解而导致液相体积缩小效应是填砂模型中压力降低的主要原因。在二维砂岩模型CO2驱替实验过程中也存在压力降低现象，对产出液体积倍数与驱替体积倍数关系曲线分析后提出：CO2在渗流时能进入油、水所不能进入的微小孔隙从而导致注入压力降低，相对而言CO2在液相中的溶解效应可以忽略。孔隙度计算及不同生产控制方式下碳酸盐岩岩心的CO2驱替实验验证了分析结果。图4表2参15 Key words: pressure, CO2 flooding experiment, dissolution, micro-pores