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Harnessing geothermal energy through Enhanced Geothermal Systems (EGS) offers a sustainable and renewable means of tapping the Earth's subsurface heat. However, in ultra-low permeability formations like those found in the Williston Basin, the effectiveness of conventional hydraulic fracturing techniques is limited. This study evaluates the potential of fishbone drilling technology as an alternative approach, focusing on the efficiency and engineering aspects of both methods in the context of geothermal reservoirs with extremely low permeability.

We carried out an extensive literature review, numerical simulations, and case studies to compare fishbone drilling and hydraulic fracturing in EGS applications. Fishbone drilling, which involves extending a single horizontal wellbore into multiple branching wellbores, shows several advantages in ultra-low permeability formations. This technique can effectively increase reservoir permeability and flow rates by accessing a larger volume of hot rock materials and creating an interconnected network of fractures, a challenge that hydraulic fracturing struggles to overcome in reservoirs with permeabilities as low as a few nanodarcies.

Our analysis reveals that fishbone drilling can maintain wellbore stability in impermeable formations, where hydraulic fracturing might face difficulties in generating sufficient fractures without compromising wellbore integrity. Moreover, fishbone drilling can enhance fracture connectivity and heat extraction rates compared to hydraulic fracturing, making it a more efficient method for developing ultra-low permeability geothermal environments.

Publication Date



Bismarck, ND


Enhanced Geothermal Systems (EGS), Ultra-low permeability formations, Fishbone drilling technology, Geothermal reservoirs, Wellbore stability, Heat extraction rates


Petroleum Engineering


Adapted from extended abstract based on oral presentation given at 2023 AAPG Rocky Mountain Section Meeting, Bismarck, North Dakota, June 4-6, 2023.

Comparing Fishbone Drilling and Hydraulic Fracturing in Ultra-Low Permeability Geothermal Reservoirs