Combined miscible or near miscible gas and asp flooding for enhanced oil recovery

Abstract

A method for enhancing oil recovery by combining miscible or near miscible gas flooding with Alkaline-Surfactant-Polymer (ASP) flooding to produce an enhanced Water-Alternating-Gas (WAG) flooding method is described. The ASP flooding may include individual and combination injections of alkaline, surfactant and polymer. Carbon dioxide may be used as a flood gas. Numerical simulations show that the present method may provide better oil recovery when compared with separate ASP or CO₂ WAG flooding for different depositional environments, as a result of high micro and macro sweep efficiencies plus miscible gas flooding. A significant acceleration and improvement in recovery may be achieved with as small as a 10% pore volume ASP slug size.

Description

RELATED CASES[0001]This application is the U.S. National Stage patent application of International Application No. PCT / US10 / 048,496, filed on Sep. 10, 2010, which claims the benefit of U.S. Provisional Patent Application Ser. No. 61 / 248,348 filed on 2 Oct. 2009 entitled “Combined Miscible Gas And ASP Flooding For Enhanced Oil Recovery” by Brian F. Towler, the disclosure and teachings of which are hereby incorporated by reference herein.FIELD OF THE INVENTION[0002]The present invention relates generally to enhanced oil recovery and, more particularly, to enhanced oil recovery using miscible gas flooding in combination with Alkaline-Surfactant-Polymer (ASP) flooding in oil reservoirs to produce an enhanced Water-Alternating-Gas (WAG) process.BACKGROUND OF THE INVENTION[0003]Water, alternating with miscible gas flooding or Water-Alternating-Gas (WAG) floods has found significant application as an effective enhanced oil recovery method. Both miscible and immiscible injections have been ...

AI Technical Summary

Benefits of technology

[0025]Benefits and advantages of the present invention include, but are not limited to generating increased oil recovery by combining the ASP and WAG methods, both methods having revealed enhanced oil recovery separately, by taking advantage of high micro / macro scale sweep efficiencies and yet further improvements in recovery if miscible gas flooding is achieved.

Problems solved by technology

It has been found that the use of CO2 and other miscible gases, such as ethane, propane, and butane, as examples, generates multi-contact and first contact miscibility with oil at reasonable reservoir pressures while other miscible gases may not reach this point unless very high pressures are applied.

Although the microscopic sweep efficiency of carbon dioxide flooding is good, its macroscopic sweep efficiency is relatively poor due to phase segregation and unfavorable mobility ratio.

If an unfavorable mobility ratio is obtained; the gas will finger (or channel), causing early gas breakthrough and decreasing the sweep efficiency.

Usually, gas is found to give early breakthrough; this is caused not only by the mobility ratio but also by the reservoir heterogeneity and especially highly permeable layers, as well as premature breakthrough of the water phase.

Too much water will result in poor microscopic displacement, while too much gas will result in poor vertical, and possibly horizontal, sweep.

The higher recovery from CO2 injections may result from its miscibility in many oil formations.

Increasing the CO2 concentration may improve sweep efficiency, but it may destabilize asphaltenes, especially when the WAG ratio rises above 60%, leading to difficulties and disturbances in production.

WAG mobility control is not feasible in high or medium viscosity oil; however, it can be improved by using polymers to raise the aqueous phase viscosity.

However, such concentrations do not survive long in many reservoirs because of alkaline consumption by the rock, making propagation through the oil reservoir of such dilute alkaline solutions prohibitively slow.

Soaps are usually too lipophilic to produce low IFT at reservoir conditions.

However, oil production usually decreases more rapidly as salinity is increased to make a system over-optimum than when salinity is decreased to make the system under-optimum.

First, as in chemical flooding, over-optimum systems lose more surfactant to the rock than do under-optimum systems.

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