Central to the natural gas and fracking discussion in the past few years has been a lot of talk about unconventional gas and unconventional reserves. Should we produce them? How can we produce them safely? How can we do this most efficiently? To answer these questions, we may need to shift our attention from unconventional reserves to unconventional fluids.
As regulatory agencies crack down on fracking in many areas, the pressure to produce more with less water is shooting up. As a result, some of the most cutting edge technology in the field no longer involves hydraulic fracturing but is investigating fracturing with alternative fluids such as liquefied propane gas (LPG). During a recent meeting at the International Petroleum Conference, CEO of Shell Oil Peter Voser said he “told the R&D team to come back with the waterless fracture”4. A promising emerging technology for waterless fracturing is nitrogen gas fracking.
What is nitrogen gas fracking?
Like LPG fracking, nitrogen gas fracking involves switching out the working fluid in the fracturing process. Some or all of the fluid used in hydro-fracking is replaced by nitrogen gas which can fracture rock at high pressures much like water. While nitrogen (N2) is a gas at room temperature, it can be maintained in a liquid state through cooling and pressurization. Three main types of nitrogen gas fracking can be indentified based on the percentage and the state of nitrogen used in the fluid.
Pure nitrogen gas fracking
Pure nitrogen gas fracking uses nitrogen almost exclusively, with only negligible amounts of water present. In this case, the nitrogen is maintained in a gaseous state, meaning it is low density and compressible. Due to the compressibility, pure nitrogen gas fracking is ineffective at great depths. Its low density and viscosity also make it a poor proppant carrier. As a result, pure nitrogen gas fracking is an efficient method of production for only very specific types of formations such as coalbed methane, tight sands, and shales—all less than 5,000 ft. deep3.
Nitrogen foam fracking
Nitrogen foam fracking is a more widely used form of nitrogen gas fracking. Instead of pumping almost pure, compressible nitrogen gas into the rock formation, nitrogen is mixed with water and other additives and then cooled to form a denser foam-like liquid. Nitrogen foam fracking fluids are made up of somewhere between 53% and 95% nitrogen gas, with the percentage depending on proppant type and characteristics of the formation3.
The higher density and viscosity of nitrogen foam means it is a better proppant carrier and is capable of fracturing at greater depths than pure nitrogen gas fracking3. On the other hand, it is not a completely waterless technique.
Nitrogen energized fracking
Nitrogen energized fracking is carried out using a fluid made up of less than 53% nitrogen3. The remaining fraction of the fluid is again made up of water and small amounts of chemical additives. The smaller amount of nitrogen is used to energize the liquid phase fluid, increasing flowback and allowing less water to remain trapped in the ground during fracturing of low pressure formations3.
Nitrogen energized fracking can be used at even greater depths than either pure nitrogen gas or nitrogen foam. While it is not as water efficient as higher nitrogen content fluids, it is a vast improvement on standard hydro-fracking .
Nitrogen gas fracking: an environmentalist’s view
The obvious environmental advantage of nitrogen gas fracking techniques is the reduction in water use. In water tight and gas rich areas such as Texas, Colorado, Wyoming, and China, waterless or low water use fracking would be a boon to communities concerned with conserving drinking water. Lowering fracking water demand would also aid water dependent industries such as agriculture and brewing, that are currently losing the competition for limited resources.
More indirectly, reducing the amount of water in fracking fluid also reduces the amount of chemical additives used. Additives are soluble chemicals dissolved in the aqueous portion of the fracking fluid. Therefore, as the fraction of aqueous fluid is reduced, the total concentration of chemical additives—while already small—will be reduced even further.
Nitrogen gas also alleviates the environmental concerns involved with the produced water resultant of hydraulic fracturing. After nitrogen foam or liquid nitrogen is used to fracture a formation, it will return to a gaseous phase and rise to the surface, where it can be safely released into the atmosphere. This easy, environmentally safe method of disposal is unique, as nitrogen gas naturally makes up 78% of ambient air2.
Nitrogen gas fracking: an industrialist’s view
Nitrogen assisted fracking is extremely beneficial from a production standpoint as it reduces formation damage caused by water. When hydraulic fracturing is used to stimulate a well, inevitably some of the water pumped down the wellbore remains underground in the rock formation. This water may block gas flow through tiny channels in the rock, causing what is called “formation damage”. As nitrogen returns to a gaseous phase after fracturing, it rises back up the wellbore instead of remaining behind to cause blockages. This property is particularly applicable in water sensitive formations such as clay. Pumping water based fluid into a clay formation causes the clay to swell, trapping water that reduces profitable gas flow3.
Gas phase nitrogen can also help energize underground fluids3. When this fluid is water, nitrogen addition can help increase flowback and decrease formation damage. When this fluid is natural gas, nitrogen gas fracking becomes extremely useful in ensuring profitable gas flow from low pressure reservoirs.
Finally, reducing water use in fracking operations saves on the high cost of water. Water use is expensive at both ends of operations. Water for hydraulic fracturing must first be purchased. Purchase price is often elevated in areas with water shortages where competition is high, or where water must be shipped in from long distances. Then, after use, produced water must be disposed of. Disposal often requires transportation, underground injection, or various levels of water treatment—all of which add to costs. Nitrogen use either eliminates or significantly reduces water associated disposal costs as it can simply be released back into the atmosphere after use.
The main obstacle to nitrogen use in fracking is sticker shock. While infrastructure for hydraulic fracturing is abundant and available throughout industry, the tools needed for nitrogen gas fracking are not5. Many nitrogen fracking operations require specialized equipment to transport and pump nitrogen gas under the appropriate high pressures and low temperatures. All of this equipment must be purchased, representing a significant initial investment. In order to justify this expenditure, there must be a high certainty of the ability to significantly increase gas flux and lower water related costs.
Current use of nitrogen gas fracking
Various nitrogen gas fracking systems are currently in use as a specialty technology used to produce natural gas from shallow, water sensitive reservoirs or reservoirs in water poor regions. Nitrogen gas fracking has already been used to produce natural gas from the Montney and Devonian Shales and is being looked at as a prospective option for operations in dry regions like Texas and Tennessee3.
Companies are also beginning to look more seriously at nitrogen gas fracking and develop proprietary technologies and products. Notable among them is Baker Hughes, who has debuted a technology called VaporFracTM , a high nitrogen concentration foam, which is pressurized and cooled to almost -320⁰F6. VaporFracTM is marketed as a solution for water sensitive, low pressure reservoirs. Specialized light-weight proppants are used in order to overcome low viscosity challenges in a fluid that is over 90% nitrogen gas1. Benefits touted by Baker Hughes include lower proppant and fluid volumes, reduced formation damage, increased gas recovery, and easy flowback cleanup.
Widening the nitrogen niche
Much like LPG fracking, nitrogen gas fracking is currently seen as a niche technology for certain formation types. However, as hydraulic fracturing regulations and pressure from environmental groups expand, so could the nitrogen niche. As towns, states, and nations impose restrictions and even bans on hydraulic fracturing, unconventional fracturing fluids like nitrogen gas and LPG may see increasing demand as a way to skirt regulatory obstacles.
1) Baker Hughes. (2013). Vaporfrac fracturing fluid.
2) Harrison, S., & Miklos, E. (2013). Industrial gases support the natural gas production chain. Linde Gas,
3) Kothare, S. (n.d.). Economics and applicability of nitrogen for fracking. Air Products and Chemicals ,
4) Rassenfoss, S. (2013). In search of the waterless fracture.Journal of Petroleum Technology,
5) Waterless Fracking Coalition. (2013). High pressure nitrogen or carbon dioxide.