Mitigating risks of methane accumulations in geothermal projects within Switzerland’s Molasse basin

15 March 2024

Methane accumulations are common in the shallow subsurface and can be found when drilling boreholes throughout the Molasse Basin, extending from Geneva to Zurich. Such accumulations pose significant risks during geothermal drilling, potentially leading to atmospheric release or necessitating flaring, resulting in CO2 emissions.

Assessing shallow gas risks is imperative before initiating drilling operations to address these challenges.

The prevalent industry method for identifying these potential pockets focuses on screening seismic data for specific indicators—bright and flat spots indicative of shallow gas pockets (see illustration). The presence of natural gas significantly alters the density and, consequently, the acoustic impedance of sedimentary layers, facilitating the detection of gas pockets through seismic reflection data. A thin gas layer typically manifests as a bright, flat spot on a seismic image. Implementing this screening process around planned well locations is critical.

Following the industry standards, if the operator does not have a modern high-resolution survey covering the drilling location, Ad Terra recommends conducting a high-resolution 2D seismic reflection survey to minimise drilling risks and avert potential gas blowouts upon selecting a drilling location. This survey targets the uppermost 500 meters below the surface, employing a low ground force approach and leveraging a broad frequency spectrum, ranging from up to 250 Hz for high resolution to 500 Hz for ultra-high-resolution assessments.

This strategic approach underscores the intersection of advanced seismic technology and rigorous scientific methodology, ensuring safer and more environmentally conscious geothermal energy extraction within the Molasse Basin.

When assessed properly shallow hazards represent a limited risk.

Do not hesitate to contact Ad Terra Consultancy if you need support conducting such operations and analysis.

See also

Geothermal Structural Study

The study we performed for the Geneva Geothermal project aims to locate and identify the geometries of the tectonic structures in the Geneva Basin and in the adjacent Jura fold-and-thrust belt.

Maximising Productivity on a Limestone Reservoir

Complex oil and gas fields need innovative technological solutions to maximise productivity. In addition, highly volatile fluid conditions require accurate modelling techniques to evaluate reservoir behaviour under high GOR and predict well production for different scenarios. Hydraulic fractures have been evaluated for a full field model along with other completion designs and presented to the client as part of potential field development options.

CCUS in Switzerland

This study summarises the results of our first-order conceptual feasibility study. We investigated the concept of injecting and circulating CO2 for geothermal energy production from potential CO2 storage formations in Switzerland.