The world can address greenhouse gas (GHG) emissions in different ways. The direct way is by reducing fossil fuel production, which generates 73% of global GHG.
This is the approach in Europe, perhaps because its energy companies do not have the success of a shale revolution to maintain. Europe has several examples of integrating renewables into its future.
In the US, companies have adopted less-direct approaches, including greening of operations, cleaning up of gas flaring and methane leaks, and carbon capture and storage.
Greening oilfield operations.
One indirect way for reducing GHG is by companies greening their own operations by using wind or solar electricity to pump frac jobs.
A frac pump has to inject frac fluid, mostly water and sand, under huge pressure, up to 10,000 pounds per square inch (psi), to crack up the rock deep underground to allow oil or gas easier inflow to the well. Typically, 250,000 – 350,000 gallons of diesel are used for each frac pumping treatment. But diesel is more expensive than natural gas and burns dirtier (twice as much GHG emissions).
High-pressure, high-volume conventional diesel-fueled combustion engines are being replaced in some cases by e-frac systems where electric pumps are driven by gas turbine generators that use CNG or LNG.
E-fracs are only 10% of the market now, but this stands to increase because of worldwide demand to lower GHG emissions. GHG reductions are typically 50% by using e-fracs.
Cost savings exist in fuel and pump engine repairs, but upfront costs are higher than a new diesel system.
A diesel fleet typically needs 20 pump-trailers at the wellsite while an e-frac system requires eight. A 95% reduction in frac pumping noise is an advantage too.
Using field-gas to pump fracs.
An alternative to e-frac pumps that use CNG or LNG is to capture and use associated gas, which is the name for gas that is produced along with crude oil. Normally, if this gas has its own pipeline it can be taken to processing facilities and sold on the market.
If not, such gas can be flared which is a wasted profit and contributes directly to GHG emissions.
Now a company called GTUIT, LLc, founded in 2011, has a mobile unit that transports gas processing equipment to a wellsite and converts associated gas into Tier-4 dual-fuel frac fleets, or into e-frac fleets powered by a gas turbine generator.
The process, called direct fuel conversion (DFC) has been used on over 125 frac jobs with frac fleets that use Tier-2 and Tier-4 dual-fuel pumping engines or all-gas engines.
Natural gas with liquids (NGLs) cannot be used with these frac fleets because it’s too rich in heavier hydrocarbons (C3+) which causes engine knocking, degradation, and too frequent maintenance — and too much downtime.
Compressed natural gas (CNG) can be used in dual-fuel engines but entails multiple steps and each step adds to overall costs and GHG emissions.
Typical frac fleets in the Permian basin have 15-20 frac pumps that require 3 MMcfd (million cubic feet per day) of fuel gas. The raw gas can be sourced efficiently from up to a mile away. NGLs that are separated in the processing truck can be sold on the market. Water removed from the raw gas is disposed at the well site.
Results were compared from three well pads in the Midland basin, part of the Permian. Each pad had 3 or 5 wells. The frac fleet consisted of 15 dual-fuel powered pumps.
The diesel volume that the associated gas replaced varied between 244,000 and 392,000 gallons. Hence big reductions in GHG emissions.
For the three pads, the fuel costs varied $3.37 – $3.73 / gallon for diesel versus $1.43 – $1.51 / gallon-equivalent for the DFC frac ops. The DFC process costs only about 42% of the diesel, because natural gas produced close to the wellsite is much cheaper than trucking in diesel.
The DFC process also results in savings compared with using CNG to pump the frac jobs. The CNG costs lie between the per-gallon costs of DFC gas and diesel.
The NGLs recovered from the 3 pads lay between 27,000 – 62,000 gallons. Hence good money was made when these NGLs were sold.
Amounts of CO2 emissions saved by the replaced diesel varied from 694 to 1116 tons. This doesn’t include CO2 emissions saved by not using trucks to transport the diesel or CNG (29 trucks would have been needed to transport the diesel, and 60 trucks for the CNG.)
Source: Forbes by