Slickwater Question

I'm wondering about which is best for hydraulic fracturing, slickwater or gel? Is it that one is better then the other for particular rock formations? For example is it more common to use a gel frac in the Niobrara, and a slickwater frac in the Permian? (or vice versa).

What other pros and cons are there. How do the numbers add up on pricing, is one better for the machinery,equipment or environment?

Comments

  • edited April 16

    Frac Fluids 101

    Hi Johnny, Hydraulic fracturing is something that is widely misunderstood, and some would say that we get deliberately misinformed. Those against it paint a very dark picture, and those who's share values are influenced talk it up a little too much. As with most hotly contested issues, the truth is somewhere in between.

    While we wait for an expert to answer some of the specifics of your questions, I'd like to go over a few basics, so that anyone reading this who isn't a frac expert, can see the whole picture. By the time we get to 'a critical evaluation of high brine tolerant additives used in shale slickwater fracs', we'll all be on the same page!

    For the rest of this post, I'll post and answer a few common questions about the matter.

    How many different types of hydraulic fracturing fluids are there?

    There are mainly 3 different types of fracturing fluids in use today:

    1. Slickwater (also known as water frac)
    2. Closslinked gel
    3. Linear gel

    Any other types of fluid tend to be hybrids of these, although there are other ones that are in existence. (Gelled acid, gelled oil, gelled LPG, foamed oil with nitrogen/carbon dioxide).

    All have different properties, applications and benefits, none of the main 3 are better per-se, just better choices for particular jobs. In relation to Johnny's question when we compare gel to water, we need to consider that there are different types of each.

    Slickwater fluid is created by adding friction reducers, usually a polyacrylamide. This means that the fluid can be pumped almost twice as fast. (100 Bbls per minute instead of around 60 for plain water).

    Interestingly, gel fluid is the opposite, where the intention is to increase viscosity. The main ingredient for the gel is guar gum which is used a lot in our processed food.

    What gets added to the frac fluid, and why?

    This is a very important question, and just like with the food we eat, understanding the ingredients leads to better decisions. Here are a list of common ingredients, and why they get added:

    Water. Frac fluid is mostly made from water, just like most of nature, including our bodies, and the earth itself.

    A proppant gets added to the fluid so that the well stays open after being fractured. The most common material is sand, but sometimes man-made ceramics are used. Unlike a standard well bore that has casing and cement, a frac needs proppant. This is a reason why the fluid needs to be pumped hard, and made less viscous so that the sand can travel to its destination.

    (Frac fluid is around 98-99% water and sand, which is why we see constant news about frac sand and water supply concerns).

    Disinfectants are added to stop microbes from breaking down and denaturing the frack fluid. The disinfectants used are similar to the ones used in hospitals or in the public water supply.

    Surfactants are added to lower surface tension. Dispersants and emulsifiers are examples of surfactants, which make a liquid 'more slippery'. In this situation, the purpose is to keep the proppant suspended in the fluid allowing it to be pumped along with the flow.

    Thickeners might be a counter-intuitive thing to add with surfactants, but they help deliver the proppants by pushing them along the fractures.

    Scale inhibitors such as ethylene glycol are used help to prevent scaling on the inside of the well bore, tubing, or inside the well.

    Corrosion inhibitors help to protect the pumping equipment, fixtures and fittings in general.

    Hydrochloric acid is sometimes used in the beginning of the process to help reduce pressure and allow the fluid to break through more easily.

    Apart from the chemical differences, what are the practical ones (pros and cons)?

    The main difference is down to viscosity, which results in the ease and/or speed of flow rate. These fluids are pumped into the well, some need to go further distances, or through different equipment of formation structures.

    Slickwater

    Slickwater frac fluid has a low viscosity, so needs to be pumped at a higher pressure and is used for shallower wells where the water needs to travel shorter distances. This counts as a 'conventional' extraction method because it's been around for a very long time.

    The pros: Slickwater fluid contains relatively few chemicals, so it's more environmentally friendly. It's cheaper and easy to use even with a less experienced crew. Fewer chemicals means less residue which is good for the equipment, and the formation.

    The cons: Because of the low viscosity, the fluid needs to be pumped at a higher rate in order to deliver the proppant. This means that a lot of water is used and can lead to concerns about the reservoir and groundwater levels and pressure on the local water system in general. Millions of gallons of water is needed per fracing operation. Less proppant gets to the frac because its hard to add enough concentration, this leads to a thinner coating inside the well. The frac network will be less stable, conductive and interconnected.

    Gel

    Hydraulic Fracturing using crosslinked or linear gel is what is called an unconventional extraction method. This can be used deeper, more effectively, but has also lead to controversy.

    The pros: Frac gel is much more viscous and can carry up to 10 times more proppant, depending on the local situation. Because it carries more proppant, the finish to the fractured network is more robust and efficient. Gel is denser, leading to wider fractures and can penetrate deeper into the formation, rather than the slickwater tendency to go wide or vertical.

    The cons: Gel is a lot more expensive, due to the much higher concentrations of all the additives, both the proppant and any chemicals. This is mitigated against efficiency, so the costings must be looked at on the whole. Gel is more likely to damage the formation meaning more care and expertise is needed. Formation damage can ruin the well, but also lead to other unintended consequences.

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