What's new in production: Things go better with Coke

LEONARD KALFAYAN, CONTRIBUTING EDITOR 

Coke (Coca-Cola) was invented in 1886 by Dr. John Stith Pemberton, a pharmacist in Atlanta, Georgia. I doubt many know how far back in history the development of Coke goes, especially as new versions have emerged over the years, including in the most recent years. It's impossible to list every single variation and flavor, as there are literally hundreds across over 200 countries, with many regional, short-lived, or test-market items.   

We see something similar with oilfield products, not to such an extent as Coke, the drink, but specialty products purported to be new are not much more than rebranded, reformulated or reconfigured old ideas or developments.   

One that has always stood out to me was the emergence of lightweight proppants with specific gravities of about 1.25 in the early 2000s–for example, resin-impregnated walnut hulls. Brilliant idea? Walnut hulls were first introduced in the industry in 1947, but I doubt many would remember or even know that. And there have been a number of different lightweight proppant materials introduced, especially in recent years. Many are based on forgotten ideas, as well as on the application of materials historically established for other applications, but found to be useful as fracturing proppants.   

Fig. 1. Petroleum coke.

So, it struck me when I recently read about ExxonMobil’s pronouncements of a new lightweight proppant development–coke, or petroleum coke, a refinery byproduct, known commonly as petcoke–and the significantly increased production response from multi-stage hydraulic fracturing in horizontal wells in the Permian region when mixing petcoke in with conventional sand proppant, Fig 1.   

Is petcoke a new idea? It is not. Reading about this “new development” reminded me of my old friend and colleague, John Smith, with the Union Oil Company of California (Unocal), who suggested back in the 1980s to use petcoke as a proppant in hydraulic fracturing. This was especially attractive, given that at the time, the company produced petcoke at certain company refineries. So, it represented a low-cost proppant option. It seemed like a very good idea. We tested its strength, and it had the properties desirable and required to serve as a fracturing proppant in applications at the time. But the idea did not get the support needed to commercialize it. 

But, even with that earlier idea regarding petcoke as a proppant, the first documented consideration of petcoke as a proppant in oil and gas well hydraulic fracturing actually dates to 1972, based on U.S. Patent US3664420A, titled "Hydraulic fracturing using petroleum coke." This patent was issued on May 23, 1972, to inventors John W. Graham, Othar M. Kiel, William M. Terry, and others, assigned to Esso Production Research Company (an affiliate of what became ExxonMobil's research arm). 

So, even within ExxonMobil, the idea is not new. But that is not to say the application does not have merit, especially when blended with traditional sand proppant, but not a full replacement.  

Key properties of petcoke as a proppant. What makes petcoke viable as a lightweight proppant additive? The same reasons lightweight proppants have merit: 

• Petcoke has a relatively low specific gravity, roughly 1.4 to 1.7. That is not as low as some commercial lightweight proppants, but still significantly lower than conventional sands, which have specific gravities of around 2.65. The lighter the proppant, the further it will travel into propagated fractures, improving fracture area. This can lead to greater fracture drainage, greater production rates, and greater hydrocarbon recovery. 

• Petcoke has rough surface texture. The irregularity of its surfaces provides multiple points of contact with fracture walls, which can reduce proppant embedment. That, in turn, can help to maintain fracture conductivity. 

• Petcoke crush strength is sufficient for most applications, and it can be resin-coated to enhance strength (as was done with walnut hulls). The crush strength of conventional sand in deeper onshore well applications is questionable, though, but typically avoided as a concern.  

• Petcoke is chemically inert to fracturing fluids and rock formations. It is also inert to acids, especially hydrofluoric (HF) acid, which is not commonly used in onshore fracturing, but it is in offshore frac pack completions.  

• Petcoke has relatively high porosity, which varies for produced petcokes, but enough to enable better fluid flow through proppant particles, which is not the case with sand. In coalbed methane applications, for example, this can improve gas flow through the proppant pack. 

• Low cost and availability. As a byproduct of oil refining, petcoke can be a much lower cost alternative to other lightweight proppant offerings. However, that may only pertain to companies such as ExxonMobil that produce the petcoke themselves. Shipping can add cost, too, since refineries are not typically located close to the areas where lightweight proppant would be delivered to well sites. But, the overall cost may still be significantly lower than other options, which are hindered by their costs. 

The reader, who is involved in hydraulic fracturing applications, is encouraged to look into lightweight and alternative proppant or proppant additive technologies. But do not be fooled by pronouncements of offerings purported as new developments. That is not to take away from such technologies entering the marketplace, but as a matter of principle. It is best to realize historical context and accuracy in advertising.