Every day seems to bring news of another extreme weather event which might almost have been purposely designed to demonstrate the reality of man-made climate change, and most specifically the fact that the impacts are being felt in the here and now rather than some theoretical future.
Given that this is the case, the push for a net zero means of producing the energy the world needs has never been more urgent. This is why renewable sources of energy which make economic as well as ecological sense are sought after across the globe, with the understanding being that those countries which develop the technology of the future will not only find themselves at the forefront of efforts to protect the environment but also in a position of reaping huge economic benefits. All of which helps to explain the renewed focus on geothermal energy.
Geothermal energy occupies the unique position of being simultaneously one of the oldest technologies in the world and also one which is touted as offering the greenest possible future if delivered to sufficient scale.
Geothermal Energy
In simple terms, geothermal energy involves tapping into the heat which is trapped beneath the surface of the earth. In a country such as Iceland the presence of a range of geological factors such as the rift in the continental plates over which the country is located and a high concentration of volcanic activity makes it relatively simple to exploit this energy. This ease of access accounts for the fact that 25% of the country’s electricity production and 66% of its primary energy use is derived from geothermal sources.
The reference to geothermal energy being one of the oldest ‘technologies’ utilised by mankind is a nod to the fact that archaeological evidence points to human beings gathering to make use of natural hot springs – a basic and obvious form of geothermal activity – as long ago as 10,000 years.
The idea that it might offer the greenest possible energy source for the future is based upon the fact that a geothermal energy station, once up and running, can tap into a perpetual source of heat deep below the surface of the earth without having to burn any fuel to either use that heat directly or exploit it to generate electricity.
The issue which currently stands in the way of geothermal energy achieving a wide scale global take-up is, above all else, the expensive nature of the drilling process.
Geothermal Drilling
In geographical locations which offer pockets of what is known as ground source heat – fundamentally heat from the sun which is trapped in the fabric of the rocks themselves – the drilling involved often only has to go as deep as a maximum of 200 metres before tapping into the energy being sought.
In the vast majority of cases the drilling needs to be much deeper, however, in order to access deep wells of heat created by volcanic and magmatic systems heating igneous rocks, or hydrothermal systems involving high temperature water trapped at depth.
Accessing geothermal sources such as these can involve drilling as deep as 6000 metres or more, and it is in cases such as these that the front loaded nature of the capital required to create a geothermal energy plant makes it an investment which relatively few businesses or governments are willing to make.
Existing Technology
Estimates of the percentage of any geothermal project funding which needs to be spent on the actual drilling of the well (as opposed to the creation of the plant and technology needed to harness the power tapped into) vary, but a figure of 40% was given in a 2018 study into geothermal wells in Turkey into geothermal wells in Turkey, published by Stanford University.
Given that, at the time of the study, there were more than 1000 geothermal wells in Turkey – a country with geological conditions which make it ideal for shallower geothermal drilling – the estimate of 40% is likely to be on the lower side.
Indeed, a feasibility study completed by the Scottish Government in 2016 estimated that the relatively deep wells needed to be drilled in the country would push the cost of drilling up to 80% of the cost of any geothermal project.
The reasons why drilling contributes to such a large percentage of the cost of a geothermal energy project are multiple.
The first of these is time. Geothermal drilling, by its very nature, often involves drilling through the kind of igneous and metamorphic rocks which would be avoided when drilling for oil and gas. Materials of this kind slow the drilling down considerably, pushing the price up to an estimated €2,200 - €2,500 per metre, when compared with the average rate for a shale gas well of €900 per metre.
The longer the drilling takes, the longer the full drilling rig has to be operated around the clock, and this is before the wear and tear on materials is taken into account. The depth and nature of geothermal wells means that utilising the same kind of drill bits and techniques used for conventional drilling leads to greater degree of non-productive time, as the bits are worn or damaged by the stronger and more abrasive rock and drill pipe has to be pulled from the hole for rerunning.
Another factor which leads to the higher incidence of drill bit wear and tear is the intensely higher temperatures at which the bits are being expected to work, as well as seals and additional instrumentation which happen to be nearer to the bit.
Cutting the Costs of Geothermal Drilling
One fact which needs to be borne in mind when considering the expense of geothermal drilling is that the more complex projects not only require a deeper hole to be drilled, but also, in many cases, need two holes drilling in order to function.
This is to enable a process known as enhanced geothermal, in which water is injected into a well, forced through hot areas of rock, and then pumped back put of another well in its heated form in order to generate energy. The presence of two wells, it hardly needs saying, doubles the amount of drilling required.
Many of the suggestions for cutting the costs of geothermal drilling involve altering the drilling technology itself. Down the hole (DTH) hammer systems, for example, use shock to break the rock through the bit, greatly increasing the speed at which the bit progresses - sometimes to as much as 10m per hour.
Various projects are currently underway in different parts of the world with the intention of delivering new forms of drilling technology capable of speeding up the geothermal drilling process even further. These include the utilisation of a plasma arc capable of heating the rock in question to 6000°C and drilling through it without the physical contact required of a bit, or steel shot drilling, which is claimed to make it easier to drill the kind of horizontal shafts which aid wider and more complex exploration of geothermal fields.
Another option being explored by the EU Horizon 2020 program is the use of high pressure water jets and fluid driven hammers to prime the rock for drilling and increase the standard rate of progress from 1-2 metres per hour to as much as 10 metres per hour.
What many of these suggestions share – despite the potential they offer – is the fact that they are still currently in development or, as is the case with DTH hammer systems, still being modified to meet the specific challenges of geothermal drilling.
Costs of Produced Water Management
One solution which can help to cut the costs of any geothermal drilling project in the here and now is the utilisation of the on-site produced water treatment technology pioneered by Separo.
Even without utilising a suggestion such as that put forward by the EU Horizon 2020 program, a geothermal drilling project creates a huge amount of water – ranging from slop and formation water to any rain which falls as the well is being drilled – creates massive amounts of waste, all of which needs to be purified before it can be disposed of and/or recycled and utilised within the programme.
Our SepSORB® systems can be installed in a matter of days and, once in situ, are simple to run and maintain. The huge cost of constantly shipping produced water away from the site to be dealt with is immediately negated, while our expertise in wastewater treatments, dealing with all types of impurities – from sand and mud to saline and anything else which might be present – means that any drilling site can be certain of complying with all relevant environmental legislation at the same time as greatly reducing their own carbon footprint.
