The most expensive mistake in geothermal is drilling before you understand the geology. A single exploration well can cost US$3 million to more than US$10 million, depending on depth and location. Yet the first production well in a new geothermal field succeeds only about 25% of the time. With additional geological analysis and follow-up drilling, success rates typically improve to 60–80%.

That is why geothermal exploration exists. Its purpose is not to find heat. Geologists already know the Earth gets hotter with depth. Its purpose is to identify where heat, permeability and water come together in sufficient quantities to support a commercial project. Everything that happens before drilling is an attempt to improve those odds.

Stage One: Regional Screening

Exploration begins at the largest possible scale. Scientists analyse satellite imagery, historical drilling records, volcanic activity, fault systems, geological maps and previous academic studies to eliminate areas that have little commercial potential.

The objective is simple. Reduce thousands of square kilometres into a handful of promising prospects. This stage also evaluates infrastructure, environmental constraints, grid access and electricity demand. A geothermal resource has little value if it cannot be economically connected to the market. At this point, they are searching for a region worth investigating.

Stage Two: Geological Mapping

Once a target area has been identified, geologists move into the field. They map faults, fractures, volcanic rocks and surface manifestations such as hot springs, fumaroles and altered minerals. These features reveal how heat moves through the Earth’s crust.

A geothermal reservoir is only commercially valuable if fluids can circulate through permeable rock. Fault systems often provide those pathways, making structural mapping one of the most important parts of exploration.  The surface is being used to understand something several kilometres below it.

Stage Three: Geochemical Analysis

Hot springs are more than tourist attractions. They are chemical reports from deep underground. Scientists collect water and gas samples to estimate reservoir temperature, fluid origin and chemical composition. Elements such as silica, sodium and potassium act as natural thermometers, allowing geochemists to estimate underground temperatures without drilling a well. Advanced geothermometers can predict whether reservoir temperatures exceed the threshold needed for commercial electricity generation.  Every water sample reduces uncertainty. Every laboratory result refines the geological model.

Stage Four: Geophysical Surveys

The next step is seeing beneath the surface without drilling. Geophysicists use magnetotelluric (MT), electrical resistivity, gravity and seismic surveys to create images of underground rock formations.

Among these methods, electrical resistivity surveys have become the industry’s most important exploration tool because geothermal reservoirs alter the electrical properties of surrounding rocks. Low-resistivity zones frequently indicate hot, fluid-filled formations buried kilometres underground. These surveys identify the conditions where steam is most likely to exist.

Stage Five: Exploratory Drilling

Only after geology, geochemistry and geophysics point to the same target does drilling begin. This is the industry’s moment of truth. Exploration wells provide the first direct measurements of temperature, pressure, permeability and fluid chemistry.

No surface survey can match the accuracy of drilling. It is also the most expensive exploration tool available. The exploration phase generally continues until at least one successful production-scale well confirms that the reservoir can sustain commercial energy production. Everything before drilling was a prediction. The well delivers the evidence.

Exploration Is About Probability

Many people imagine geothermal exploration as searching for underground heat. The industry thinks differently. Heat alone is not enough. A commercially viable geothermal reservoir requires four conditions to exist simultaneously:

Requirement	Why It Matters
High temperature	Provides usable energy for electricity generation.
Permeable rock	Allows geothermal fluids to circulate.
Sufficient water or steam	Transfers heat to the surface.
Sustainable reservoir size	Supports decades of continuous production.

Exploration is the process of proving that all four exist in the same place. That is why geothermal companies invest years before drilling their first commercial well. They are not trying to discover the Earth’s heat. They are trying to reduce the cost of being wrong.

Environmental Impact Assessment for Geothermal Projects

Every geothermal project begins with a geological question. Is there enough heat underground? Before drilling starts, another question becomes just as important. Can this project coexist with the environment above it? That is the purpose of an Environmental Impact Assessment (EIA).

Contrary to popular belief, an EIA is designed to identify environmental and social risks before they become engineering problems, legal disputes or financial liabilities. For geothermal developers, it is often the difference between a project that secures financing and one that spends years trapped in regulatory approval. 

Why Geothermal Projects Require an EIA

Geothermal energy is one of the world’s lowest-emission energy sources, but that does not mean its environmental footprint is zero. A utility-scale geothermal project involves exploration drilling, road construction, well pads, pipelines, steam gathering systems, power stations, cooling towers and transmission infrastructure. Each stage has the potential to affect ecosystems, groundwater, nearby communities and biodiversity if poorly managed. That is why most countries require an Environmental Impact Assessment before exploration drilling or power plant construction can begin. In Kenya, geothermal drilling and electricity generation projects are specifically listed under the Environmental Management and Coordination Act (EMCA) as activities requiring an EIA before implementation.

What Does an Environmental Impact Assessment Examine?

A geothermal EIA begins long before construction. Consultants establish baseline environmental conditions by collecting data on vegetation, wildlife, groundwater, air quality, noise levels, soil conditions, surface water, land use and nearby communities. This baseline becomes the reference point against which future project impacts are measured. 

The assessment then models how each phase of the project may affect the surrounding environment.

Typical issues include:

Assessment Area	What Is Evaluated
Air Quality	Steam emissions, hydrogen sulphide (H₂S), dust during construction
Water Resources	Groundwater protection, wastewater disposal, reinjection systems
Biodiversity	Vegetation clearance, wildlife habitats and protected ecosystems
Noise	Drilling rigs, steam venting and construction activities
Land Use	Roads, well pads, pipelines and permanent infrastructure
Community Impact	Land acquisition, employment, public safety and stakeholder concerns

Modern EIAs also evaluate cumulative impacts, climate resilience, emergency response plans and long-term monitoring requirements rather than focusing only on construction activities.

The Biggest Environmental Risks

Despite its environmental advantages, geothermal development presents several technical challenges. Hydrogen sulphide (H₂S), a naturally occurring gas found in some geothermal reservoirs, requires continuous monitoring because high concentrations can affect air quality. Poorly managed drilling operations may contaminate groundwater if wells are not properly cased and cemented. Reinjection systems must also be carefully designed to maintain reservoir pressure while preventing unintended impacts on surrounding groundwater systems. 

Another issue receiving increased attention is induced seismicity. Injecting or extracting fluids from deep underground reservoirs can trigger small seismic events. Most are too small to be felt, but they remain an important consideration during project planning and long-term reservoir management. 

Mitigation Is Built Into the Design

An Environmental Impact Assessment does more than identify problems. It prescribes solutions. Modern geothermal projects minimise environmental impacts through closed-loop reinjection systems, emissions control technologies, noise barriers, biodiversity management plans, stormwater controls, groundwater monitoring networks and continuous environmental reporting throughout the life of the project. These mitigation measures become legally binding commitments once a project receives approval. 

This is why environmental performance is no longer treated as a separate compliance exercise. It has become part of the engineering design.

The Real Value of an EIA

Many people think an Environmental Impact Assessment exists to protect nature. That is only half the story. It also protects the project. A geothermal plant is expected to operate for 30 to 50 years or more. During that time, environmental failures can lead to regulatory penalties, operational shutdowns, legal disputes and reputational damage that far exceed the cost of conducting a rigorous assessment.

The strongest geothermal projects are not the ones that pass an EIA. They are the ones designed around it from the very beginning.