Risk Mapping

Subsurface risk is a major driver in geothermal decision-making

Geothermal projects require significant upfront investment, so understanding where subsurface risks lie — and how certain we are about them — is critical.

At PanTerra, we have developed a method that visualises key subsurface risks, together with the level of confidence in those risks, within a single map view.  By “risk”, we refer to the likelihood of unsuccessful development of a geothermal system. The resulting map enables decision-makers to quickly assess whether a location is expected to be high-risk and whether that assessment is supported by sufficient subsurface data.

A structured, regional approach

We map subsurface risk and uncertainty at a regional scale using three components that strongly influence geothermal success:

1. Geological complexity – structural factors (such as faults) that may affect drilling and system performance.
2. Reservoir presence – the likelihood of encountering a viable reservoir interval of sufficient thickness.
3. Data confidence – the extent to which interpretations are supported by available subsurface data (seismic and well data).

Each component is assessed separately using criteria tailored to the geological context of the study area, including proximity to faults, reservoir thickness, and the type, density, and quality of subsurface data. Mapping these elements individually ensures transparency, allowing users to clearly see what drives the outcome.

Bringing it together: risk versus uncertainty

The three components are then integrated into a single risk-versus-uncertainty map:

• Colour indicates the level of risk (for example, from low to high probability of unsuccessful development).
• Shading indicates the level of confidence (i.e. how strongly the interpretation is supported by data).

This approach enables users to distinguish between areas with similar risk levels but different levels of certainty—an important distinction when prioritising investments.

Example: high potential, complex structure, uneven data coverage

Consider a promising geothermal region with a sufficiently thick reservoir interval, but strong structural complexity due to extensive faulting. If only a limited area is covered by high-quality 3D seismic, while most of the region relies on digitally processed 2D lines and some areas on analogue 2D, the ability to interpret fault presence and geometry will vary significantly across the region.

In such a case, areas near faults may be mapped as high risk (e.g., red). However, where seismic coverage is limited or of lower quality, confidence in the risk estimate decreases. This result in medium confidence across most of the area, and low confidence in the least constrained zones.

Why this matters

This type of mapping is particularly valuable during the early stages of geothermal assessment, when decisions must be made with limited data. It provides a consistent basis for regional screening, helps identify more favourable versus more challenging areas, and highlights where targeted data acquisition could most effectively reduce uncertainty.

Figure: Workflow for regional subsurface risk mapping.

Layers for (A) fault‑related geological complexity, (B) reservoir presence, and (C) data confidence are combined into (D) a total risk map, displayed using the risk‑versus‑certainty scheme (colour = risk severity; shading = confidence).