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Unlocking the Impermeable Reservoir: Lessons from a 30-Year Reservoir Engineer
An Alphaxioms interview with Richard Joseph Holt, Principal Consultant in Reservoir Engineering at RESPEC. Context: Menengai East and Olkaria Central.
Every geothermal developer knows the moment.
The rig is gone and the money is spent. The well is drilled to depth, the temperature is there, and then the well will not flow. The heat is real, but the connection between the well and the reservoir is not.
Wells like this sit at the centre of one of the most important questions in geothermal development: what do you do with a tight reservoir? Walk away and drill again, or find a way to unlock what is already there?
To explore the question, Alphaxioms spoke with Richard Joseph Holt, Principal Consultant in Reservoir Engineering at RESPEC. Richard brings 30 years of global experience in geothermal energy.
We framed our questions around two settings, Menengai East and Olkaria Central, and asked him how to diagnose an impermeable reservoir, which stimulation route has the best odds in high-temperature volcanic systems, what risks must be managed, and where the next breakthrough might come from.
His answers were direct. On some points he was precise, and on others he was candid about what the industry has not yet settled. Both are valuable to anyone who develops, finances or engineers geothermal projects.
Start with the right question: impermeable, or poorly connected?
The first mistake in a tight well is treating every failure to flow as the same problem. Richard's opening point separates two situations that look identical from the surface: a reservoir that is truly impermeable, and one that is poorly connected.
His approach starts with two tight wells that will not flow naturally, and it is practical rather than exotic.
Step one: run a short injection test on each well to get the Injectivity Index for both wells. This gives a first measure of how readily each well accepts fluid.
Step two: inject for a longer period into one of the wells while leaving the other well idle, and measure the pressure in the idle well during the injection.
The logic of the second step is worth spelling out. A well that sits idle becomes an observation point. If pressure responds in the idle well while fluid goes into its neighbour, the two wells are in communication.
If nothing happens, the connection is weak or absent. The result tells the developer whether the problem is the rock itself or the pathways between wells.
That distinction shapes every decision that follows. Money spent stimulating a reservoir that is merely poorly connected is a different bet from money spent on rock that does not transmit fluid at all. Richard's method does not require a long list of instruments. It asks the wells themselves to say how they behave.
For developers working in fields like Menengai East and Olkaria Central, the lesson is to establish what you have before you decide what to do about it. Diagnosis comes first.
Which stimulation route? Hydraulic stimulation
We asked Richard a pointed question for high-temperature volcanic systems like these: which stimulation route has the best odds, hydraulic, thermal, chemical or closed-loop?
His answer was a single line: hydraulic stimulation.If the volcanic rock was a rare case where it contained significant carbonate, then acid stimulation may be worthwhile
There was no hedging and no ranking of runners-up. For developers weighing options, that clarity matters. The geothermal sector is full of promising concepts, and attention often goes to the newest one. Richard's view, drawn from three decades of work, is that for the situation we described, hydraulic stimulation has the best odds.
We did not ask him to defend this at length, and we do not add arguments on his behalf. What it gives readers is a reference point from a practitioner. If your project is a tight well in a high-temperature volcanic setting, hydraulic stimulation is where an experienced reservoir engineer would put his weight.
What would rule one out? The place of closed-loop
We also asked what would rule one of the routes out. Richard named one: closed-loop.
His position is specific. Rule out closed-loop for electricity generation. Use closed-loop only for HVAC, for making warm or hot water for greenhouses or industrial processes, or for heating buildings.
This distinction deserves attention because closed-loop systems attract a great deal of interest, and the conversation can blur two different questions: whether a technology works, and what it works for. Richard does not say closed-loop is without value. He says it belongs to a particular set of uses: heating and cooling buildings, warm water for greenhouses, and industrial process heat. For electricity generation, he rules it out.
Readers who evaluate projects will recognise the value of that boundary. A technology matched to the right application can be sound, and the same technology matched to the wrong one can waste capital. Richard's answer gives a clear line to work from.
Designing for risk from the beginning
We asked Richard how to manage induced seismicity, scaling and short-circuiting without damaging the reservoir. His answer separated the three risks by how well understood they are.
On scaling, he was brief: it can be handled with inhibitors. That is a risk with a known response.
On the other two, he was more cautious. Induced seismicity and short-circuiting, he said, are not settled in practice. That is an unusually frank statement from a senior practitioner. Experienced engineers have the standing to say where the industry's knowledge runs out, and Richard used it.
He then gave a design principle: short-circuiting and induced seismicity need to be included in the design of the project, not just dealt with later.
For project developers, this is perhaps the most actionable point in the interview. The common pattern in complex projects is to treat risks that are hard to quantify as problems for the operating phase. Richard's position reverses that. If a risk is not settled in practice, it cannot be left until it appears. It has to be part of the plan from the start, which means it affects the layout, the budget and the decisions made before any stimulation begins.
The same point matters for investors and lenders. A project that treats seismicity and short-circuiting as design questions is a project that has asked the right questions early. A project that postpones them has not removed the risk, only moved it to a later and more expensive moment.
The bankability question and an honest answer
We asked what stimulation success rate would make unlocking tight wells more bankable than drilling new ones. It is the question financiers care about most, because it turns an engineering approach into an investment case.
Richard answered plainly: he does not know, and the answer would be site-specific.
That answer is worth more than a confident number would have been. There is a strong temptation in the industry to offer a benchmark: a success rate above which stimulation beats new drilling. A figure like that would travel quickly through presentations and investment memos. But if the true answer depends on the site, a universal figure would mislead.
The implication for developers and financiers is that no shortcut exists. Each field has to build its own case with its own data. A well in Menengai East and a well in Olkaria Central should not be assumed to carry the same odds, and neither should be judged on the experience of a project elsewhere.
It is also a reminder of where Alphaxioms sees its role. Bankability follows from evidence, and evidence is gathered site by site. A platform that connects developers, investors and technical experts is useful because the answers sit with the people who have worked on the specific reservoir.
The pilot he would run: deep, superhot, and built to last
Finally, we asked Richard to look forward. If he could run one pilot at either field in the next two years, what would it test, and what would success look like?
He chose Olkaria, and he chose depth. His pilot would be deep drilling to around 4,000 to 5,000 m, which may reveal what he called a "superhot reservoir".
He then defined success in three parts:
Output: a deep well producing 25 to 50 MW
Temperature: 400°C fluid
Materials: materials that keep the well open and do not fail
The third element deserves a second look. A discussion of superhot resources usually leads with temperature and megawatts, which are the headline figures. Richard's definition includes the well itself. Success is a well that produces and also stays open and intact. A deep, hot well that cannot survive its own conditions is not a success by his measure.
This is a good example of how an experienced engineer defines a result. The target is a working asset over time, with the hardware able to carry it, rather than a single impressive number.
What this means for the people building geothermal
Taking Richard's answers together, a coherent approach emerges for anyone facing a tight reservoir.
Diagnose before you act. Injection tests and pressure monitoring in an idle neighbouring well show whether you have impermeable rock or a connection problem.
Choose the route that fits. For high-temperature volcanic systems, Richard's pick is hydraulic stimulation. Closed-loop has its place in heating and industrial uses, but not in electricity generation.
Put the hard risks in the design. Scaling can be handled with inhibitors. Induced seismicity and short-circuiting are not settled in practice, and they belong in the project plan from the start.
Build the case site by site. There is no universal success rate that makes stimulation bankable.
The answer is specific to each field.
Keep an eye on the frontier. Deep drilling at Olkaria, to 4,000 to 5,000 m, may reveal a superhot reservoir. Success would mean a 25 to 50 MW well, 400°C fluid, and materials that hold the well open.
Closing
Richard's contribution lies in his clarity about what is known, what is not, and where the next step lies. He names hydraulic stimulation as the best route for the setting we described, draws a clear line around closed-loop, and says plainly that two of the largest risks are still open questions. He also declines to give a number he cannot stand behind.
For developers, investors and engineers following this space, that candour is a useful guide. Alphaxioms thanks Richard Joseph Holt for his time and insight.
Alphaxioms is a global geothermal intelligence and deal facilitation platform.
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