Fly Ash-Based Proppants for Hydraulic Fracturing: Studies, Cases, Products, Capabilities, and Limitations

     Fly ash, or coal ash, is a waste product left over after the combustion of coal in power plants. It is typically stored in very large slurry ponds. In order to get the fly ash out for use, it needs to be dredged out of those ponds and conditioned for use. A device is shown below that classifies and thickens the ash. Before use, it also needs some separation into ideal particle sizes.  

     The use of fly ash as a proppant component began to be explored in earnest in the 2010s. I remember hearing a talk, I believe in 2014, that mentioned it as a possibility. According to a slide presentation at the Kentucky Oil & Gas Association (KOGA) meeting in 2024, the company Enhanced Solution Services (ESS), formerly Metis, began field trials in 2017 with fly-ash-based proppants. The presentation explores fly ash suitability as a standalone proppant. Some fly ash properties are given below. Particle sizes are up to five times smaller than frac sand. Proppants compress when induced fractures close, which reduces flow. If they crush, that creates finer particles which are much more likely to impede flow. Fly ash has good crush resistance but inadequate compressive strength, which limits its applicability.

 

     The fly ash is first separated into different particle sizes.

     The paper touts a hydraulic fracturing method known as Dar-Stim, which utilizes fly ash as a proppant. It has been tested for refracs of marginal wells and for stimulating new wells. About 25% of the tests were on horizontal or deviated wells, so most were on vertical wells.

     Fly ash as a proppant has sufficient rounding and sphericity, as well as acceptable crush resistance. It has smooth surfaces and low drag. It has no surface charges. It stays in suspension, which means its use requires much less pumping horsepower than pumping frac sand. However, the particles are much smaller than those of typical frac sand or ceramics.

     Dar-Stim has been tested across multiple formation types. Well production improvement post-frac has been very good. Most of the tests were in wells with pressure below hydrostatic pressure.

     It has a lower carbon footprint, requires fewer site personnel, uses less water, has much greater flowback recovery, and does not use polymer gels.

     A June 2025 study presented at the SPE Europe Energy Conference and Exhibition explored Class F fly ash proppants mixed with volcanic ash. It noted that the lightweight, low-density ash proppant mix with enhanced buoyancy and compressive strength has some advantages over sand. They explored different mix designs and binder-to-water ratios. They concluded that volcanic ash can offer higher strength and better structural integrity than class F fly ash. However, that compressive strength is still well below industry standards. Thus, for now, it is confined to lightweight proppant applications. The abstract is given below.

     A January 2025 paper published in the journal Materials also assessed the compressive strength of fly ash proppants. The study evaluated these proppants under harsh environmental conditions, including high temperature, high pressure, acidic, alkaline, saline, and crude oil environments. Some of these are typical in deep horizontal wells. The different environmental conditions were found to pose little to no difference in the compressive strength of the proppants. However, as the abstract below notes:

“The B20W25 sample demonstrated a compressive strength of 1181.19 psi (8.1 MPa), which, although resilient, remains below industry standards.”

     Unfortunately, this is far below the required minimum of 5000 psi for compressive strength. A typical sand proppant can withstand up to 5800 psi, and a ceramic proppant from 7000 psi to 15,000 psi.

    Below is the mix design, the composite-bound cubic and spherical samples, and the machine used to test compressive strength. I used a machine like this back in the late 80s when I worked for a short time as a concrete inspector in the construction and geotechnical industry. It was fun to smash the concrete cylinders!

     While the compressive strength of fly ash proppants remains far below industry requirements, the use of additives, different binders, and activators could bring it up to those standards.

“When further understanding has been developed, enhancing the fly ash alkaline-activated proppant with additives can be looked at to reach the industry standard. Other binding and activating materials/solutions also need to be investigated besides the alkaline activators. Furthermore, an exploration of varied proppant geometries and utilization techniques could yield significant enhancements in performance across multiple applications. In sum, this study lays a robust foundation for ongoing inquiry and advancement within the realm of proppant technology.”

     They suggest testing different types of fly ash, binders, and activators.

“The first actionable recommendation for future work is to test different types of fly ashes and binders as well as chemically analyzing the raw materials and synthesized products to understand further how a proppant compatible with industry standards can be made from fly ash. Although this study identified certain mechanical limitations, it provides a solid foundation for future investigations aimed at optimizing fly ash proppants. In summary, fly ash holds significant promise as a cost-effective and sustainable proppant material for hydraulic fracturing applications.”

     Superior Energy makes a fly ash proppant called EcoReach, which they describe below:

“EcoReach™ is a next-gen micro proppant sourced from coal combustion byproducts. It’s made up of perfectly spherical particles, over five times smaller than a grain of sand. These microscopic spheres glide without jamming, staying in suspension longer. They travel farther into the microfractures that conventional proppants can't reach. And they do so without damaging the reservoir or the environment, all while cutting operating costs.”   

    For now, fly ash can only be practically used alone in wells that don’t require high compressive strength. However, it can be blended with sand or ceramics, and more experiments with blending and recipes are likely to be developed as testing continues. As a waste product, it is cheaper to obtain than mined sand or manufactured ceramic proppants.  

References:

 

Use of Fly Ash as a Proppant in Fracking of Unconventional Oil & Gas Wells. Thomas Robl, Anne Oberlink, Robert Jewell, University of Kentucky Center for Applied Energy and Curtis Wilie, Jim Crenshaw, Enhanced Solutions Services. KOGA Annual Meeting 6/27/2024. Program Briefing

Developing Fly Ash Based Proppants and Evaluating Their Load Bearing Capacity for Hydraulic Fracturing Available to Purchase/ Raz Haydar; Sherif Fakher. Paper presented at the SPE Europe Energy Conference and Exhibition, Vienna, Austria, June 2025. Paper Number: SPE-225632-MS. Developing Fly  Ash Based Proppants and Evaluating Their Load Bearing Capacity for Hydraulic Fracturing | SPE Europec featured at EAGE Conference and Exhibition | OnePetro

Ecoreach. Smarter Proppant. Stronger Performance. Superior Energy. Wellsite Solutions. EcoReach™ Micro Proppant | Superior Energy Brands

Investigating and Evaluating Novel Fly Ash-Based Proppant Compressive Strength Under Various Environmental Conditions. Raz Haydar and Sherif Fakher. Materials 2025, 18(2), 399; Published: 16 January 2025. Investigating and Evaluating Novel Fly Ash-Based Proppant Compressive Strength Under Various Environmental Conditions

EcoReach: Smarter Stimulation for Production Enhancement. Superior Energy. EcoReach_Flyer_02.24.26