Multi-stage stimulation, a transformative tool for geothermal energy?


Drilling rig at the site of a geothermal project, Saskatchewan / Canada (source: DEEP Corp.)

Stimulating geothermal wells in several stages could help expand and dramatically intensify geothermal development, according to an article by Mark McClure in the Journal of Petroleum Technology.

In a recent article by Mark McClure from ResFrac Corp. published in SPE’s Journal of Petroleum Technologies, it describes how multistage stimulation could help transform the geothermal energy industry as we know it today.

Describing the experience gained in the shale, he points out that the techniques applied there could be applied directly to geothermal energy and thus help create “hundreds or thousands of fluid fracture paths around horizontal or deviated geothermal wells”.

This is clearly part of a larger ongoing discussion of how technologies developed for oil and gas could help elevate the game and expand geothermal energy development to levels never seen before.

In the context of conventional geothermal energy, where the geothermal sector seeks to exploit existing hot water reservoirs, risks are often seen as a major obstacle to investment and development of these resources. Find the right temperature (sufficient for use, e.g. for power generation), water as a heat carrier to the surface, and sufficient water flow for surface use. To achieve profitability, according to the author, “geothermal wells must produce the equivalent of tens of thousands of barrels of water or steam per day to be economical, or to produce the energy equivalent of an oil well. or typical gas ”.

The geological parameters from hydrothermal systems therefore determine the level of production of geothermal wells. Essentially, this concerns the permeability of the rock to ensure sufficient flow and sufficiently heated water.

To increase permeability, hydraulic stimulation has been a key aspect of research and is seen as a key tool to help unlock the vast geothermal resources of the United States. The 2019 Us DOE GeoVision report describes development potential of up to 60 GWe, compared to around 3,700 MW of installed geothermal power generation capacity in the United States today.

In his article, the author describes the limited success of hydraulic stimulation so far and sees the main reason for this in “one-section open-hole” stimulation of conventional vertical wells. With this, one does not create enough flow paths on a larger scale, but only in localized dominant pathways. This does not create the capacity needed to “keep high flow rates”.

In the shale industry, a similar experience has led to multi-stage hydraulic fracturing along horizontal boreholes. This allowed the sector to mechanically isolate specific sections in a well. With this, it was possible to stimulate significantly more conductive fractures.

Moving from open-hole designs to “limited entry designs”, such as Mark McClure, engineers were able to “distribute the flow and force a large number of fractures to form”. This experience and know-how could now be applied directly to geothermal energy.

3D model by ResFrac Corp. (source: company)

The UtahFORGE geothermal R&D project funded by the US Department of Energy is working on the application of multistage stimulation in granite rock. Private sector players such as Fervo Energy (US) and the Canadian DEEP Earth Energy Production project are planning or executing multi-stage stimulation and essentially doing groundbreaking work that could raise the global level of geothermal energy.

Yet with all the new approaches to technology or their application to development, the author also describes some risks.

It describes the challenge of lack of field-scale experience and data on the durability of long-term fracture conductivity, rock cooling, and the possibility of shorting paths to develop between wells. injection and production. The higher temperatures of these systems also create challenges for operations with the need for rugged high temperature downhole tools and large diameter plugs for stimulation.

And of course, induced seismicity is a concern that in recent years has clearly been a challenge for supporters of EGS / geothermal well stimulation. Good practice protocols for induced seismicity are either under development, or in the case of the United States by the DOE already in place.

One aspect to consider and not mentioned in the article is the approach to public acceptance of geothermal stimulation activities. Clearly an important aspect for projects in more urban contexts, such as in Central Europe. Opposition to geothermal energy has increased dramatically in areas, where the stimulation has led to seismic events and created a challenge to gain public acceptance for geothermal energy.

For the full article, see the link below.

Source: Mark McClure, “Why multistage stimulation could transform the geothermal industry” in Petroleum Technology Journal (SPE), October 1, 2021

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