Effect of Miscibility Condition for CO2 Flooding on Gravity Drainage in 2D Vertical System

Joohyung Kim

doi:10.4172/2157-7463.1000177

Abstract

In CO2 flooding process, gravity drainage and miscibility condition are the main factors on the efficiency of oil recovery. In this study, we observed oil recovery for different miscibility conditions in vertical oil reservoir. This was investigated in two dimensional vertical sandstone slab, where unstable gravity drainage phenomena can be formed. CO2 is injected at bottom into 100% saturated with oil and production port is open at top of the system. We have performed a series of experiments using continuous CO2 flooding for immiscible and near-miscible conditions. From the experimental results, oil recovery at near-miscible condition is 3.77 times greater than at immiscible condition, particularly in vertical system. It indicated that applying the immiscible CO2 flooding is ineffective because of gravity override of CO2 and generation of CO2 channel at upper side in vertical reservoir. Meanwhile, the results revealed that oil recovery increases considerably once miscibility is reached at outlet. That is, miscibility condition is found to be a sensitive factor on oil recovery particularly in vertical oil reservoir.

Highlights

In CO2 injection process, the densities and viscosities of oil and CO2 are the main variables determining the gravity drainage that can cause early CO2 breakthrough
In order to investigate the oil recovery performance by the continuous CO2 flooding process, we conducted the experiments for Immiscible (IMS) and Near-Miscible (NMS) conditions in vertical
We discussed an experimental study of CO2 injection process to examine the influence of gravity drainage on the oil recovery for the vertical oil reservoir

Summary

Introduction

In CO2 injection process, the densities and viscosities of oil and CO2 are the main variables determining the gravity drainage that can cause early CO2 breakthrough. Several researchers showed the importance of miscibility condition and gravity drainage effect on the oil recovery during CO2 injection. Asghari et al [1] and Torabi et al [2] conducted experiments and simulation study considered miscibility condition in fractured system. They showed the oil recovery may decrease far above the miscibility. Trivedi et al [3,4] conducted experimental work about effect of CO2 injection rate at various miscibility conditions in fractured reservoir. A series of CO2 injection experiments have been conducted at immiscible and near-miscible conditions in two dimensional vertical sandstone plates. The CO2 (purity 99.999%) was injected constantly at 20 ml/hr as a solvent at immiscible and near-miscible reservoir conditions of 600 psig and 1,000 psig at 35°C

Results and Discussion

20 Injection at Bottom Production at Top

Conclusion