Alternating sagd injections

Abstract

Methods produce heavy oil with steam assisted gravity drainage. Such methods alternate a traditional steam injection with an injection of a steam-plus-non-condensable gas (such as CO2 or CO2-plus-diluent) mixture. The CO2 / diluent mixture is soluble in bitumen, leading to a reduction in viscosity of the heavy oil. Additionally, the steam-only injection reduces the accumulation of vapor NCG along the edge of the steam chamber, leading to improved thermal efficiency.

Description

PRIOR RELATED APPLICATIONS[0001]This application is a non-provisional application which claims benefit under 35 USC §119(e) to U.S. Provisional Application Ser. No. 61 / 897,555 filed Oct. 30, 2013, entitled “ALTERNATING SAGD INJECTIONS,” which is incorporated herein in its entirety.FEDERALLY SPONSORED RESEARCH STATEMENT[0002]Not applicable.FIELD OF THE DISCLOSURE[0003]The disclosure generally relates to methods for improving hydrocarbon recovery utilizing alternating steam and steam-plus-additive injections.BACKGROUND OF THE DISCLOSURE[0004]Canada and Venezuela have some of the largest deposits of a thick, heavy oil called “bitumen.” Bitumen is especially difficult to recover because it is wrapped around sand and clay, forming what is call “oil sands.” Furthermore, the viscosity of bitumen in a native reservoir is high—often in excess of 1,000,000 cP. It will not flow without being stimulated by methods such as the addition of solvent and / or heat.[0005]Many approaches to recovering h...

AI Technical Summary

Benefits of technology

This patent is about a better way to recover oil from underground. It involves using a combination of steam and a non-condensable gas (NCG) like CO2, along with a diluent, to improve the process. The improvement involves a cyclic use of steam injections after each co-injection. This helps to prevent the NCG from accumulating along the edges of the steam chamber, which can decrease oil production and increase water consumption. By reducing the accumulation of NCG, the improved method leads to increased oil production with less water and energy consumption.

Problems solved by technology

Canada and Venezuela have some of the largest deposits of a thick, heavy oil called “bitumen.” Bitumen is especially difficult to recover because it is wrapped around sand and clay, forming what is call “oil sands.” Furthermore, the viscosity of bitumen in a native reservoir is high—often in excess of 1,000,000 cP.

However, this 3 to 5 month startup time increases the overall cost of SAGD because of the amount of steam required and the delay before oil production can begin.

Decision makers may limit projects available for SAGD production because of this added cost.

The process is relatively insensitive to shale streaks and other vertical barriers to steam and fluid flow because, as the rock is heated, differential thermal expansion causes fractures in it, allowing steam and fluids to flow through.

Although quite successful, SAGD does require enormous amounts of water in order to generate a barrel of oil.

In addition to using a precious resource, additional costs are added to convert those barrels of water to high quality steam for down-hole injection.

However, much research has to be done before ES-SAGD becomes an economically viable alternative to SAGD.

Research has shown, however, that the disadvantage of co-injecting CO2 or other solvents with steam is the accumulation of the non-condensable gas in the upper part of the steam chamber, thus inhibiting steam chamber growth.

In addition to lower hydrocarbon recovery, an accumulation of CO2 and solvents along the steam chamber has adverse effects on reduced energy consumption.

First, the accumulated CO2 / solvent acts as a thermal insulting blanket and impairs the transport of heat from steam to bitumen.

Second, due to the partial pressure effect, the temperature of the drainage interface decreases and the oil that drains along the boundary becomes less mobile.

Third, the gas saturation increases as a direct result of gaseous CO2 / solvent accumulation at the drainage interface, which decreases the effective permeability to oil.

Images