- Waterless stimulation technology developed in 2012 by ecorpStim R&D team in Houston, Texas (United States).
- PPS does not require any chemical additive whatsoever. Only pure regular propane is used with inert proppant (sand or ceramics).
- Propane is a component of natural gas. Thus, all substances injected in the subsoil are already there naturally.
- Almost all of the injected propane (from 95 and 100%) flows back in the form of a gas, due to natural phenomenon of pressure.
- The recovered propane can then be re-used for subsequent stimulation operations, or re-injected in pipelines with the rest of the extracted gas.
What is Pure Propane Stimulation ?
Developed in 2012 by ecorpStim R&D teams in Houston (USA), Pure Propane Stimulation or PPS is a technology for extracting unconventional hydrocarbons, which uses not a single drop of water and no chemical additives.
Instead of the water-based stimulation fluid used in traditional hydraulic fracturing, PPS uses a naturally occurring component of conventional and unconventional hydrocarbon production, namely propane gas.
Concept: replacing water with a reusable gas
To free the gas or oil trapped in shale formations, the well must be “stimulated”. By opposition to the hydraulic fracturing technique which uses water as a fracturing fluid, the technology developed by ecorpStim uses a component of natural gas: propane.
Carried under liquid form, the propane is injected with simple sand (or ceramics), a proppant that maintains open the gaps created and enables the trapped hydrocarbons to escape.
The injected propane turns to a gaseous form under the effect of reduced pressure and higher temperature and flows back into the well, followed by the natural gas or oil.
The specific gravity of propane is two times lower and its viscosity eight times lower than that of water, which makes the transport of the proppant into the fractures challenging. This is the reason why the Canadian company, GasFrac, had chosen to jellify the propane, by adding a number of chemical thickeners, to resolve this issue.
At ecorpStim, our objective is to remove all chemical additives from the stimulation fluids that we use. We have therefore thought completely out of the box, and instead of trying to act on the viscosity of the propane, we have focused on the specific gravity and size of the proppants, which is a completely new paradigm: for those who are familiar with Stokes law (used to determine the drag force exerted on spherical very small particles in a viscous fluid), we have worked on the numerator instead of the denominator.
With this objective, we have developed light glass and carbon fullerene microbeads with our research consortium. It is completely feasible to transport such proppants in the propane into the micro-fractures network. Pure propane stimulation used in combination with non-toxic man-made proppants of suitable specific gravity, geometry, dimensions and crush strength is therefore a very attractive alternative to replace standard hydraulic fracturing in the long term.
Gelled propane, as developed by the Canadian company GasFrac, had several drawbacks.
Gelled propane requests the use of chemical additives, such as Iron Sulfate, Magnesium Oxide, Alkyl Phosphate Esters and Phosphoric Acid, among other diluents and additives, as disclosed by the company in the Frac Focus database. These reagents are reactive downhole / downstream and also lose viscosity at reservoir temperatures. Some of these additives are left behind as gel residues and interact with the naturally occurring chemical components downhole. The proppant is poorly transported and therefore the effective length of the fractures is shorter, leading to a lower cumulative production.
Altogether, in addition to environmental and safety potential issues, gelled propane for the stimulation of shale had disappointing results in terms of production, as shown by the results of the 90 days production test done by GasFrac in the Utica just before the company was liquidated in April 2015 (the Colombus Business Journal – May 12th 2015).
The ecorpStim proposition which consists in stimulating shale with pure propane, completely eliminates the issues related with the use of chemical additives. Pure propane used in combination with non-toxic man-made proppants of suitable specific gravity, geometry, dimensions and crush strength is a real compelling improvement to gelled propane.
Propane (LGP) is one of the most used and most versatile energy sources around the globe. It is widely used in everyday life since 1911, as a fuel for residential heating. The safety of this domestic and industrial usage is strictly regulated and has been well established for many decades.
In addition, propane:
- Disperses immediately into the air under normal temperature and pressure (i.e. outdoors or in an enclosed place with even modest ventilation).
- Has a very low flammability rating. In contrast with gasoline’s ignition temperature of 430 to 500 degrees F, propane will not ignite until the air reaches at least 940 degrees F.
In conclusion, the flammability of propane in the Pure Propane Stimulation process is an industrial risk, which is handled and managed as in many other industrial sectors. eCORP which has been using propane over the past decades since 1978 (for EOR, storage and conventional operations), has put in place strong security protocols which have resulted in zero accidents or operating incidents.