SAGD water treatment system and method

Abstract

A method and system for treating a water stream which contains Fouling Organics, where the water stream is recovered from an underground hydrocarbon-containing formation during SAGD oil recovery operations conducted on said formation. The method comprises injecting an oxidizing agent, preferably air, into the water stream when first recovered from the underground formation, and using a porous membrane to separate oxidized Fouling Organics and / or filter separable compounds formed due to injection of the oxidizing agent into the water stream, prior to transferring the water stream to a boiler for re-heating the water stream and turning same to steam for re-injection into said formation.

Description

FIELD OF THE INVENTION[0001]The present invention relates to a method and system for treating water recovered from Steam Assisted Gravity Drainage (SAGD) operations prior to supply of such water to a boiler, and more particularly to a method and system for treating produced water or recycled boiler blowdown water being supplied to a boiler wherein such boiler is part of a system for supplying steam in a SAGD operation to an underground hydrocarbon-containing formation and recovering produced water and hydrocarbons from such underground formation.BACKGROUND OF THE INVENTION[0002]In Steam-Assisted Gravity Drainage (SAGD) oil recovery operations, 98% or greater quality steam is typically injected into a hydrocarbon-containing underground formation to heat viscous oil in the formation and render it mobile, so that it flows downwardly through the formation to horizontal collector wells where it is collected and thereafter pumped (produced) to surface.[0003]Typically, water that is produc...

AI Technical Summary

Benefits of technology

The patent text describes a need for a process to reduce methanol and other organics in boiler feedwater to prevent fouling in oil recovery operations. The invention proposes a method and system to achieve this through filtering and altering the surface structure of the organics to reduce their affinity to membrane surfaces. The use of oxygen or air as an oxidizing agent may result in the need for deoxygenation and deaeration of the water, which can be achieved using known methods. The technical effects include reducing fouling, increasing blow-down recycle volumes, and lowering disposal quantities, leading to cost savings.

Problems solved by technology

Such water, in whatever form, is typically desired to be re-utilized for producing steam and re-injected downhole as steam in a closed-loop system, because sources of additional (surface) water may be severely restricted due to legal regulations, or as a result of water being in scarce supply at surface.

Produced oil in a SAGD oil recovery process is typically separated from the produced water by common de-oiler or oil separation devices, to the extent possible, which may be very difficult particularly if the produced fluids contain water-in-oil or oil-in-water emulsions.

However, such devices work poorly for predominantly water mixtures, namely “oil-in-water” emulsions, which de-oilers have difficulty separating the oil from the water.

Such contaminants have a very detrimental effect on boilers, as such compounds tend to coat or form compounds on the interior of heating tubes within such boilers, thereby reducing the ability of the boiler to heat water efficiently in such boiler tubes or lead to hot spots and tube failures.

In addition, impurities such as Fouling Organics present in such water in emulsion format, may be unstable, and upon heating of any emulsion and removal of the water component, remain in the boiler causing aforementioned fouling of the boiler.

Even if Fouling Organics were to pass into vapour with the steam and thereby not cause boiler fouling (typically, upon heating, such Fouling Organics may alternatively form coke, depending on temperatures reached in the boiler, likewise fouling the boiler) after being injected downhole into the underground formation such asphaltenes Fouling Organics may form a separate phase which plugs not only oil-bearing rock in the underground formation, but may also detrimentally plug injector well bores and flow lines, resulting in costly repair work to the horizontal steam injector wells, and horizontal production wells, to repair plugged production lines and steam injection piping.

Disadvantageously, however, as Fouling Organics comprise organic compounds and such process is typically directed at removing inorganic compounds, the WLS process is ineffective with respect to eliminating fouling of boilers due to Fouling Organics within the boiler feed water.

Membranes or filters have been attempted to be used in the prior art systems to remove Fouling Organics from boiler feed water, but have generally met with poor success, becoming easily clogged and requiring frequent maintenance and cleaning, and typically are unable to effectively filter Fouling Organics from water when such Fouling Organics are present in an “oil-in-water” reverse emulsion.

Disadvantageously, however, such prior art method requires the use of expensive evaporators.

Such chemical treatment processes typically require continuous treatment of the boiler inlet feed stream with such chemicals, and such becomes expensive.

Each of the foregoing prior art methods and systems adds substantial expense and complexity to the feed water treatment system, and are unsatisfactory for such reasons.

If such water is disposed, the SAGD water utilization system is not a closed loop system, and water is being wasted.

Alternatively, if such boiler blowdown water is recycled back to the boiler inlet, typically this results in concentrating the impurities and Fouling Organics 1Registered US trademark 3423991 of Debasish Mukhopadhyay, licensed for use by General Electric Company in the boiler feedwater, eventually resulting in boiler fouling due to the concentration of impurities.

However, as noted above, drum boilers are more susceptible to fouling, and for such reason cannot be used where Fouling Organics are present in boiler feedwater.

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