Miscible Displacement In the Weyburn Reservoir: A Laboratory Study

Abstract

Most Saskatchewan light and medium oil (LMO) reservoirs have reached their economic limit of production under current technology (primary and secondary recovery methods). The successful development of me miscible displacement process using CO ₂ and hydrocarbon gases will lead to a significant increase in Saskatchewan LMO reserves and substantially extend the production life of these pools.

A laboratory study was conducted to evaluate the applicability of various solvents (including the potential source of CO ₂ extracted from flue gas) for the recovery of oil from a southeast Saskatchewan reservoir (Weybum). The physical, chemical, and phase behaviour (PVT) properties of the dead oil, reservoir fluid, and reservoir fluid with CO ₂ were determined.br/>
Slim tube tests were conducted for the Weyburn reservoir fluid with pure Cal, with wellhead gas from the Steelman gas plant, and with two impure CO ₂ gases (one containing 9.9. mol CH ₄ and the other containing 5.1 mol % Ni 5.1 mol % CH ₄ in CO ₂ as contaminants) at various pressures and the reservoir temperature of 59 ºC. The tests were also carried out to determine the maximum amount of impurities in CO ₂ that can be tolerated for the miscible process.

The minimum miscibility pressures (MMP) determined for the above four systems demonstrated that the miscible displacement process using pure CO ₂ or impure CO ₂ containing up to 9.9 mol % CH ₄ (contaminant) as a solvent is a promising enhanced oil recovery (EOR) technique for southeast Saskatchewan reservoirs. The MMPs' for these two systems are below the estimated reservoir fracture pressure. Carbon dioxide contaminated with 5.1 mol % N2 from flue gas and 5.1 mol % CH ₄ from the reservoir during recycling would require further purification to lower the MMP to an acceptable level. The wellhead gas from the Steelman gas plant is not a suitable EOR agent for the Weybum reservoir.

Rising bubble (RBA) tests on the four reservoir fluid/solvent systems were conducted and the MMPs obtained from these systems were in good agreement with those obtained from slim tube experiments. The RBA test is much faster than the slim tube technique, requires only a small amount of fluids, and also allows direct visual observation of miscibility (vapourizing-gasdrive) development. The technique is thus considered to be superior to slim tube tests.

Introduction

Most Saskatchewan light and medium oil (LMO) reservoirs have reached their economic limit of production Under current technology (primary and secondary recovery methods) ⁽¹⁾. The successful development of the miscible displacement process using CO ₂ and hydrocarbon gases will lead to significant increase in Saskatchewan LMO reserves and substantially extend the production life of these pools ⁽²⁾.
Current industry interest in CO ₂ and hydrocarbon miscible flooding is high, as evidenced by the high level of activity in field testing worldwide ⁽³⁾. In spite of a general slowdown in enhanced oil recovery (EOR) during the last two years (the number of active US EOR projects decreased from 366 in 1988 to 295 in 1990s, oil production from the miscible projects showed a 113% increase by 49% (over the same period in 1988).