Methods for treatment and use of produced water

Abstract

Produced water is treated by raising the pH to a level that significantly increases silica solubility and breaks emulsions. So treated water is then de-oiled, filtered, and subjected to ion exchange chromatography to reduce water hardness prior to feeding into a steam generator to form an intermediate quality steam. If desired, the intermediate quality steam is directly used in SAGD, or separated into a high quality steam and condensate, which is further treated to obtain additional water that can then be used in the steam generator.

Description

[0001]This application claims the benefit of priority to copending U.S. provisional applications with Ser. Nos. 61 / 539,883, filed Sep. 27, 2011, and 61 / 621,145, filed Apr. 6, 2012.FIELD OF THE INVENTION[0002]The field of the invention is methods and use of treated produced water, especially as it relates to treatment and use for enhanced oil recovery (EOR) and steam assisted gravity drainage (SAGD).BACKGROUND[0003]Enhanced Oil Recovery (EOR) of heavy thick oil or Bitumen is often done by injecting steam into a formation, resulting in a combination of condensed steam and oil and / or melted bitumen that is later separated into the hydrocarbon product and “produced water”. For example, steam-based tar sands EOR, also known as steam assisted gravity drain (SAGD), requires about three barrels of water equivalent of steam to produce one barrel of liquid bitumen product. Such relatively high quantities of water demand can present significant challenges, especially where recovery and recycli...

AI Technical Summary

Benefits of technology

The patent describes a method for processing produced water to remove solids and emulsifiers, and to increase the solubility of silica. The water is then chemically broken into an emulsion and the solids removed using an ion exchange resin. The resulting water is alkalinized and can be used for injection into a formation. The method also includes steps of using intermediate quality steam for injection and processing the condensate to produce a purified water product. The technical effects of the patent include improved water quality for steam generation and reduced costs for water treatment and purification.

Problems solved by technology

Such relatively high quantities of water demand can present significant challenges, especially where recovery and recycling of the water is required.

Among other difficulties, produced water from SAGD has frequently high quantities of emulsions of liquid bitumen and dissolved solids, suspended solids, and free or floating oil, which requires significant treatment for production of usable water.

Unfortunately, de-oiling of produced water containing tight emulsions using commonly known industry practices (e.g., hydro cyclone, induced or dissolved gas flotation, etc.) are often not effective.

Consequently, most of the oily emulsion will pass through to the downstream units, which tends to undermine the effectiveness of filtration, lime softening, or ion exchange systems.

As a result, poor quality water is injected into the high pressure boiler for steam generation and leads in many cases to frequent and very expensive break downs.

However, such approach generally requires a large number of centrifuges, which is often cost prohibitive and consumes significant plot space.

However, such low pH will require neutralization or alkalinization prior to further treatment, and require large amounts of acid and caustic materials and special metallurgy.

Moreover, handling of large amounts of acid and base will increase safety hazards.

The removal of silica has been previously driven by process consideration and the removed silica has become a high volume hazardous waste product of SAGD operations that must be properly disposed of.

Moreover, many operators are generally opposed to the use of high silica water in SAGD due to concerns over silica deposition and precipitation in high-value equipment (e.g., once through steam generators and steam separators).

As a consequence, and due to the relatively high silica content of most produced water, operators tend to rely on expensive processing equipment for water treatment prior to steam generation, which presents a significant economic impact.

Worse yet, steam generation and particularly high-quality steam generation is energy intensive and further exacerbates the economic challenges with continuous SAGD.

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