Daumic

With the search for oil and gas in the North Sea, significant coal deposits were discovered in this sea (1). The localization of these deposits in a sea-bed prohibits a traditional exploitation by mine. In situ combustion was considered with an aim of generating a combustible gas mixture easier to extract. But this technique was too polluting. There is perhaps another resource to consider: the methane adsorbed in the pores of coal. This type of gas is called CBM for Coal Bed Methane (2). Several data could promise a significant and exploitable gas resource: - the amount of coal present under the North Sea seems significant; the amount of adsorbed methane should be in proportion, - part of these offshore coal deposits are sufficiently close to the coasts of England to be accessible by terrestrial drillings, - the technique of horizontal drilling, already used to recover shale gas, can be employed here to extract gas from coal, - coal is a porous rock, therefore the extraction of gas does not require hydraulic fracturing. (1) https://deepresource.wordpress.com/2018/12/18/north-sea-ucg/ (2) https://en.wikipedia.org/wiki/Coalbed_methane#

Perhaps the mining of shale deposits isn’t the enemy of energy transition. Since 2005, hydraulic fracturing has permit the exploitation of gas and oil confined in shale deposits. These shale deposits produce gas and light liquid hydrocarbons. Some studies have shown the possibility to extract heavy hydrocarbon molecules like paraffin from shale deposits by using supercritical carbon dioxide (1). This fluid is also ideal for the heat extraction from the deep deposit: its high density facilitates the heat transport and its low viscosity eases the circulation in small cracks of the fractured zone. The use of supercritical CO2 on depleted shale wells can associate the extraction of heavy hydrocarbons and geothermal heat. The extraction of heavy hydrocarbons can last some years like the classical extraction of gas and light hydrocarbons in shale deposits. By contrast, the heat extraction can last a very long time. The first test of this heat extraction could be made by the Pittsburgh town in Pennsylvania. This town is surrounded by many wells extracting gas from Marcellus shale deposit (2). This town has also maintained an urban heating network (3). The geothermal heat extracted from the wells located around the town could feed the urban heating network. The geothermal energy has a good reputation as a stable renewable energy but its development is blocked by its high investment cost. If we can associate geothermal energy and hydrocarbon production, the investment cost can be reduced. (1) https://www.researchgate.net/publication/283619903_Extraction_of_Hydrocarbons_from_High_Maturity_Marcellus_Shale_Using_Supercritical_Carbon_Dioxide (2) https://www.fractracker.org/map/us/pennsylvania/pa-shale-viewer/ (3) https://apps.pittsburghpa.gov/mayorpeduto/District_Energy_in_Pittsburgh_DOE_Power_Point_AL.pdf

Unsupported optimism : this comment can be applied on high temperature geothermy. This sort of renewable energy is a promise never realised because its costs are too high. The extraction of gold or other high value metals in deep wells can help the financing of geothermy. Yes, it is speculative. Why not ? In hydrothermal deposits, gold is more often associated with molybdenum or platinum than zinc.

If gold mining by fracking is possible, the gold value can amortize quickly the high cost of drilling and fracturing. After the gold extraction, the drills and fractured zone remain for another use, like geothermal energy. T Finally, the great value of gold can facilitate the development of geothermal energy.

I have a preference for the first method. As you noticed, this method permit to choose precisely the zone of interest.

The great part of the ore is made of silicate that is not dissolved by pyridinethiol. If pyridinethiol extracts other transition metals like zinc, it is not a bad thing, it can add a value to the extraction.

The use of pyridinethiol is for chelating gold and not for dissolving ore.

In few years hydraulic fracturing has revolutionized the world of energy by the production of shale gas and shale oil. It is perhaps possible that fracking can reach another resource in the depth of the Earth: gold. A new theory established by geochemists (1) describes a transport of gold by trisulphide ion in hydrothermal deposit. Trisulphide ion chelates gold and facilitates its transport towards the ground surface by water. But the stability of trisulphide ion depends of temperature and pressure. Trisulphide ion decays at a depth of some kilometres and leaves a first deposit of gold. According to this theory, a second transport by chloride and sulphide ions explains the gold deposits near the surface. We can imagine a deep gold deposit under each hydrothermal gold deposit. The deep gold deposits are probably more massive than the upper deposits because the transport by trisulphide ion is more efficient than the transport by chloride and sulphide ions. These deep gold deposits are not accessible by classical process of mining. These deep deposits are perhaps accessible by hydraulic fracturing. A depth of some kilometres is not a problem. The shale oil deposits of Permian Basin exploited in Texas by fracking have an equivalent depth of some kilometres. How can we extract gold? Perhaps by the following process: - two vertical wells to reach the deep layer of deposit, - horizontal drill between the vertical wells with a hydraulic fracturing, - circulation of water with gold chelatant in the fractured zone, for example pyridinethiol (2). If this process works, gold extraction by fracking can be the beginning of a new chapter of fracking industry: the deep mining. (1) Sulfur radical species form gold deposits on Earth (https://www.pnas.org/content/112/44/13484) (2) Pyridinethiol‐Assisted Dissolution of Elemental Gold in Organic Solutions https://onlinelibrary.wiley.com/doi/abs/10.1002/anie.201810447

Since some years, there is a great hope in the development of EGS (enhanced geothermal system) (1). EGS combines hydraulic fracturing and deep well to extract the heat of hot rocks. The interest of EGS is it could be located everywhere on Earth. The development of EGS is currently slowed by some problems, particularly its high cost of investment. In cases in which the hot reservoir is in basalt layer, this cost could be reduced by limewater injection: - the sale of hydrogen produced during some years could amortize quickly the cost of the well, - as we see before, the swelling during the reaction between limewater and basalt generates fracturing ; this induced fracturing could reduce the use of high pressure for mechanical fracturing. (1) https://en.wikipedia.org/wiki/Enhanced_geothermal_system

The planet has plenty of water in oceans and plenty of basalt in upper crust of Earth. That is a good potential of production of hydrogen. The combination of this hydrogen with atmospheric oxygen produces energy and water. The consumed oxygen is replaced by photosynthesis. The results of the whole operation is the inclusion of oxygen in basalt accompanying the oxidation of Fe2+.

Hydrogen produced by electrolysis is not an a primary energy, it is an energy carrier. This production needs another power source. Hydrogen produced by water oxidation of basalt is a primary energy, a sort of fossil energy without CO2 emission.

Yes, temperature and pressure are provided freely by Earth with the following gradients: - 30°C / km - 30 MPa / km

The experiment has already been made. In his thesis, Mr Malvoisin describes the production of hydrogen by a treatment of a steel slag. The FeO contained in the slag has been oxidized by water in a furnace at 200°C / 50 MPa. This experiment (1) on the slag continues for the purpose of the production of nanoparticles of magnetite. Despite its high purity, the hydrogen produced in this condition is too expensive. (1) https://www.linksium.fr/projet/hymagin/

Good remark. I forgot to consider the effect of temperature on the Nernst equation. The effect of pH on the potential of reaction (Fe2+ + H+ > Fe3+ + ½ H2) is expressed by: E = E0 – 0.06 pH But the factor 0.06 is really the result of (R.T.ln(10)/F) at ambient temperature (see the web page (1)). The reaction doesn’t occur at ambient temperature. According to the thesis of Mr Malvoisin (2), 150°C is a better temperature to obtain a good kinetic for the reaction. At this temperature, the value of the factor (R.T.ln(10)/F) is 0.084. So the effect of pH on the potential of reaction at 150°C is expressed by: E = E0 – 0.084 pH pH Potential at 150°C 0 0,771 1 0,687 2 0,603 3 0,519 4 0,435 5 0,351 6 0,267 7 0,183 8 0,099 9 0,015 10 -0,069 11 -0,153 12 -0,237 13 -0,321 14 -0,405 According to the precedent chart, the reaction becomes possible between pH 9 and pH 10 at 150°C. (1) https://fr.wikipedia.org/wiki/Équation_de_Nernst (2) https://tel.archives-ouvertes.fr/file/index/docid/934238/filename/33513_MALVOISIN_2013_archivage.pdf

It is not necessary to reach this pH of 14. At pH 12, the potential of the reaction is zero. That means the reaction is equilibrated: Fe2+ + H+ < > Fe3+ + ½ H2 In water at this pH 12, Fe2+ and Fe3+ are not soluble and thus remain fixed in the rock. The hydrogen produced is soluble in hot water. If limewater is put into circulation in the well, we can extract the hydrogen. The removing of H2 of the well displaces the reaction on its right wing and thus permits the continuation of the ferrous oxidation. ( Fe2+ + H+ > Fe3+ + 1/2 H2 ) is a simplified writing of the reaction. The real reaction is : 3 FeO + H2O > Fe3O4 + H2 ___________ The formula ( E = E0 - 0.06 pH ) is developped from Nernst law to see the effect of pH on the potential. The formula is obtained by considering the concentrations of Fe2+ and Fe3+ equal. You can see (but french text): http://www.chimie-briere.com/pcemoxred/OXYDO.htm