Midstream solutions for water and energy

Sour Water Sweetening for Beneficial ReUse and Enhanced Oil Recovery

H2S in water is a problem that is common to municipal utility systems and oil & gas production. Treatment options include amine sweeteners, aeration (gas stripping), oxidation, membrane treatment, microbiological filtration and/or ion exchange.     Aeration and oxidation have recently emerged as common methods for treatment of produced water and flowback - each has its unique challenges.

Historically, aeration has been most commonly applied using either tray, packed tower, diffused air or spray-nozzle methods. However, the equilibrium of sulfide species in water (between H2S and HS-) is highly dependent upon pH.  As such, water must normally be treated with acid to lower the pH in order to increase the amount of H2S available for gas stripping.  Stripping gas can be either incinerated or re-processed within the sour gas recovery stream to recover valuable energy content.

Encana's award-winning d-70-K Debolt Water Treatment Plant utilizes a 5-stage aeration scheme employed HCl injection, inlet separator, stripping tower, degassing tank and scavenger polish (acrolein).  The end-product is suitable for hydraulic fracturing reuse: the acrolein scavenger creates a soluble, irreversible liquid product with non-detectable levels of H2S.

More recently, producers have utilized oxidizers to handle flowback and produced water associated with tight oil and gas fracturing and production.  In particular, service providers have developed ozone, chlorine dioxide and hydrogen peroxide systems for deployment in the Marcellus and Eagleford plays.  Media-based solutions (potassium permanganate, filtration or ion exchange) are more susceptible to fouling, particularly when the sulfide species are "oil-wet" and require a more aggressive oxidizer to "break through" the hydrocarbon barrier.

Oxidizer-based systems require careful consideration of oxidizer supply-chain logistics, operational simplicity, energy-efficiency and OH&S needs of the end-user. We are currently working on new applications for both aeration and oxidizer solutions with an focus on driving down the overall cost of service to achieve a better balance between CAPEX, OPEX and environmental footprint.

Montney Tight Gas Fairway - Solving the Water Disposal Riddle

The Montney Tight Gas Fairway (MTGF)  exists in the same region as the tight gas deep basin for many other formations.  Disposal formations (that may be prolific producers to the east) become too tight within the MTGF.  Other candidates are limited to specific geologic anomalies – such as the Leduc reefs or Debolt faults.  Wells drilled into these formations outside of these anomalies are not productive enough.

Existing injection wells within the Montney Tight gas fairway are generally for pressure maintenance with marginal disposal capacity. While useful for secondary recovery, there are not economically viable without the benefit of oil recovery.  In many cases these secondary recovery schemes exist on geological sweet spots with higher porosity and permeability that are limited in aerial extent.

Within the Montney tight gas fairway there are simply none of the hugely prolific disposal wells found elsewhere.  Whereas there are single wells in the Edmonton/Ft. Saskatchewan area capable of taking > 100,000 m3/month, a prolific MTGF well might take only 10,000 m3 per month. Immediately east of the MTGF, a prolific well might take approximately 30,000 m3/ per month.  Compounding the problem of the low quality of many potential candidate formations is the fact that the Fairway exists along the edge of the deformation front. This means that the drilling depth to candidate formations can be significantly deeper. For example, a Leduc formation disposal well in the Kaybob area can be found at 2,600m depth and easily accept >25,000 m3 per month.  In the Kakwa/Gold Creek area in the MTGF, a Leduc well would be completed at >3600m depth and accommodate <20,000 m3 per month.

Finally, the Montney is sour across some of the fairway, particularly in the deepest parts of the basin on the Alberta side.  This complicates water disposal, as it either limits potential disposal formations or requires treatment to remove H2S.

These factors are driving up disposal costs to uneconomic levels. As such, our Water Hub designs are incorporating higher water reuse strategies, sour water sweetening/reuse and evaporator systems to reduce disposal volumes.  With careful planning and technology selection, we are driving down the cost of water disposal and improving economics.

K'nowbe Montney Disposal Cumulative.pdf (940.2KB)