The truth about diesel, dual-fuel, and electric hydraulic fracturing emissions

US Well Services (USWS) seeks to foster environmental stewardship in the oil and gas industry by reducing hydraulic fracturing emissions. As a provider of both conventional and electric frac technologies, USWS has the data to prove which technology has the lowest impact. And here’s what the data show: by utilizing natural gas turbines and electric motors, electric frac technologies like USWS’s CleanFleet® has a smaller environmental footprint than conventional diesel or dual-fuel completion equipment.

Approach

To ensure equivalency, this analysis normalizes hydraulic fracturing technologies by output, as measured in hydraulic horsepower (hhp). After all, comparing the technologies under different loads would skew the results in favor of technologies providing lower output.

We assume a 48-hour, 13-stage load cycle based on measurements collected on real USWS fleets operating in Texas. Each powered stage took 18,013 hhp and 159 minutes on average; idle time between stages averaged 58 minutes and 2,920 hhp for the diesel fleets or 175 hhp for electric fleets.

Following IPCC guidelines, USWS utilizes OEM specifications paired with historical load cycle data and direct measurements throughout our fleets’ load cycles to determine our emissions.

Results

Over the assumed 48-hour load cycle, USWS’s CleanFleet® fleets clearly outperform both diesel and dual-fuel [i.e., dynamic-gas blending (DGB)] fleets (see figure, next page): Compared to conventional Tier IV diesel, CleanFleet® reduces pump-related CO2e by 32% and NO2 by 28%. Similarly, CleanFleet® cuts pump-related CO2e by 27% and NO2 by 31% compared to a Tier IV DGB engine using 75% natural gas and 25% diesel.

Pump-Related Emissions

Chart comparing emissions

Per the conservation of mass, the same quantity of carbon going into a CleanFleet® turbine as natural gas must come out; hence, reducing CO2 output increases CO emissions. While lethal in nonventilated environments, CO has a short lifetime in the atmosphere and a weak, indirect effect on global warming, making atmospheric CO emissions preferable to CO2 emissions.

However, the biggest emissions reduction comes from utilizing field gas that would otherwise be flared. Assuming a diesel operation would flare the same quantity of natural gas as a CleanFleet® consumes over our 48-hour load cycle with a 98% flare efficiency,3 CleanFleet® reduces CO2e by 62% and NO2 by 33%. Similarly, CleanFleet® cuts CO2e by 61% and NO2 by 36% compared to a Tier IV DGB engine using 75% natural gas, 25% diesel, and flaring the remaining gas.

Comparing Emission Calculation Methods


The most commonly used methods for assessing GHG emissions are:

  1. Using the carbon content of the fuel per “The Greenhouse Gas Protocol: A Corporate Accounting and Reporting Standard”
  2. Applying generic fuel emissions factors published by the US EPA’s “Center for Corporate Climate Leadership”
  3. Employing equipment-specific emissions factors per the US EPA’s “Compilation of Air Pollutant Emission Factors”
  4. Calculating emissions using OEM performance and emissions specifications together with the equipment load profile
  5. Direct measurement throughout the load cycle

Many corporate entities prefer the first three methodologies because they simply multiply fuel receipts by a factor pulled from a table. However, these methods ignore the condition and efficiency of the prime mover — factors that affect its emissions.

For example, consider two diesel pumps: one Tier II, one Tier IV. Tier IV engines require significant emissions reductions compared to Tier II.5 To achieve these results, Tier IV engines utilize advanced engine designs to ensure more complete combustion, and thereby, to reduce emissions. Yet, the first three methodologies result in identical or worse CO2e emissions for Tier IV engines over the assumed 48- hour load cycle, as shown below.

That’s why the Intergovernmental Panel on Climate Change (IPCC) advises using the most accurate emissions determination method for which organizations have or can generate the data — i.e., direct measurements first, then emissions models, and generic emissions factors last.

Chart comparing emissions

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Our Commitment

At US Well Services, environmental stewardship is not just a mantra; every operational decision considers our three core values:

Illustration representing Cleaner Communities

Cleaner Communities

Illustration representing Continuous Improvement

Continuous Improvement

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Waste Reduction

To ensure we achieve our ideals, USWS researches best practices and performs ongoing audits of our processes to guarantee the efficiency, effectiveness, and sustainability of our operations.

In 2013, a goal to reduce the noise and emissions produced by our conventional fleets led to the creation of CleanFleet®, the industry’s pioneering fully electric, mobile hydraulic fracturing fleet. Over the past six years, USWS has completed over 12,000 pumping stages with CleanFleet® — more than any other pressure pumping company utilizing electric frac equipment — and over 54,000 pumping stages with our conventional, diesel-powered fleets.

With 30 patents granted and 104 more pending, USWS is committed to mitigating the environmental impact of hydraulic fracturing, and we will continue to innovate new technologies as we push towards this goal.