Natural hydrogen in the Monzón-1 well, Ebro basin, northern Spain – Geological Society of France publication

20th June 2022

Helios Aragon made an article and publication about natural hydrogen, published by the Geological Society of France.
Below is the detail of the article.

Christopher Atkinson¹, Christopher Matchette-Downes and Sandra Garcia-Curiel.

Introduction

Sixty years ago, Spain was amid an energy crisis. Totally reliant upon imported oil and with limited in-country alternatives an aggressive campaign of hydrocarbon exploration drilling was initiated throughout the country. Between 1954 and 1964 the finances of its national oil company were bolstered; state-of-the-art drilling equipment was purchased and together with several international partners multiple wells were drilled. One of the prospective areas chosen for exploration drilling was the Ebro Basin and the associated South Pyrenean foothills located in the northern part of the province of Aragón. It was here on March 7th, 1963, that Empresa Nacional de Petróleos de Aragón (“ENPASA”) spudded the Monzén-1 exploration well. The well drilled to a total depth (“TD”) of 3715 metres below ground level (“mBGL”) and encountered shows of methane in fractured Infra-Liassic carbonates which upon drill-stem testing failed to flow at commercial rates. Consequently, the well was plugged and abandoned as an exploration dry hole. Importantly, the well also encountered shows of hydrogen at two levels.

The deeper of the two, within the Triassic Bunter Sandstones, was significant enough to be specifically highlighted in the final well report. In 1963 hydrogen was of no interest but fast forward to today and this “dry hole” in Aragón could be a key component in the largest energy transition the world has ever seen.

Location, geological and structural setting

The Monzon-1 well was drilled just a few kilometres southeast of the town of Monzon in Huesca province, Aragón, Spain (Fig.1). Geologically, it is located at the juxtaposition of the Southern Pyrenean Thrust Belt and the Ebro Basin, to the south of the Pyrenean Mountains (Fig.1 and Munoz (1992)). It lies immediately south of a saltcored «triangular» zone of deformation known as the Barbastro Anticline (Fig. 1). The southernmost thrust sheets of the South Pyrenean deformation belt lie a few kilometres to the northeast of the well along the northern flank of the Barbastro Anticline (Fig. 1). The well penetrated an autochthonous sequence of Mesozoic to Tertiary deposits resting on basement which is typical for the Ebro Basin succession in this area (Fig. 2).

The Monzén-1 is drilled on a large basement-cored anticline and was defined using 2D seismic and gravity data interpretation at the northern limit of the Ebro basin (Fig.1).The well drilled through a very thick post-orogenic sequence of sandstones and conglomerates (molasse) down to 1402 mBGL, below which a thick interbedded sequence of halite, anhydrite siltstone and shale of Oligo-Miocene age was encountered (Fig. 2). A relatively thin, condensed interval of continental Eocene sandstones, siltstones and shales (the“Red Marls”or“Margosa Roja”) penetrated below 2268mBGL.

Fig. 1

Fig. 2

A highly-condensed interval of Lower Eocene shallow marine limestone was present between 2429 and 2446mBGL.The Eocene limestone rests unconformably upon Lower Jurassic (Infra-Lias-sic) carbonates. The entire Middle Jurassic to Palaeocene section was missing due to non-deposition and/or erosion along this unconformity. Below 2655mBGL, the well passed into Triassic strata, with UpperTriassic (“Keuper”) anhydritic and halitic mudstones present from 2655 to 2977mBGL, Middle Triassic (“Muschelkalk”) limestones, dolomites and evaporites between 2977 and 3415mBGL, and Lower Triassic (“Bunter”) halites/anhydrites, shales and porous sand stones below 3415mBGL (Fig. 2). The well TD is at 3715mBGL within Bunter Sandstone conglomerates although the well to seismic tie confirms pre-Mesozoic basement is just a few tens of metres below that depth. Figure 3 illustrates the location of the well on a modern reprocessed? vintage northeast-southwest oriented 2D seismic line. Note the presence below the Barbastro Anticline of a major, deep-seated basement inversion fault system which bounds the Monzon structure to the north.

Fig. 3

Hydrogen in the Monzon-1 well

The post-well geological and drilling reports of ENPASA reveal shows of “pure” hydrogen were recorded at two levels in the Monzon-1 well (ENPASA,1963 and Fig.4). The ﬁrst is a modest 0.4-1.2% Total Gas (TG) show encountered between 4oo-6oomBGL within coarse sandstones and microconglomerates of Tertiary age. The second, and much more significant, is a 25% TC show encountered between 3683-3714.6mBGL within the Triassic Bunter Sandstones (Fig.4). This signiﬁcant gas show is even more surprising given that EN PASA drilled the interval at significant overbalanced pressures with consequential mud loss into the formation (mud weight of1.4o kilogram/litre equivalent to 11.63 pounds per gallon -figure 4). Unfortunately, no actual drilling mud-log or detailed mud-log reports have survived in the archive for the Monzén-1 well.

By1963 most global exploration wells would have been drilled with some form of gas monitoring equipment which would have used a gas chromatogram equipped with either a Flame Ionisation Detector (FID) or a Thermal Conductivity Detector (TCD). In the case of an FID system ditch gas during drilling would have been carried through the chromatogram using an “inert” carrier gas.TG measured by FID is the total amount of flammable gas seen in the mud and it is usually accompanied by some form of compositional analysis. The most common carrier gases used for FID are helium or hydrogen. Helium carrier gas is not recorded by an FID. However, hydrogen carrier gas has an obvious and almost immediate FID response and this peak is therefore normally ignored or overridden by hydrocarbon gases. In 1963 most FID chromatographs would have made no separation between methane and hydrogen.

Hydrogen is the carrier gas of choice as it is cheaper than helium and it can be made at the rig-site via electrolysis. Therefore, both in the TG and compositional analysis it is usually the hydrocarbon responses that are recorded, thus allowing the routine measurement of methane, ethane, etc. These are the normal components of interest in an oil and gas exploration well. In order to record the presence of hydrogen in the Monzén-1 well, it is likely that mud gas monitoring was achieved using a TCD system. This system would have probably used helium as the carrier gas and it would have measured all of the combustible gas in the mud including hydrogen. Unfortunately, we do not know which system was used at Monzén-1 and all the well summary log denotes is that the hydrogen shows are associated with measurement via a “Prakla” device (Fig.4).

Research to date regarding what a Prakla device is has proved inconclusive. Importantly, the TCD will also measure any other gases present such as nitrogen, carbon dioxide, etc. but the Bunter level in the Monzon well only “H2″ (hydrogen) is recorded.

Any TG show of 25% as seen in Monzén-1 is a very impressive gas show and warrants closer scrutiny. Interestingly, an analogous mud-log response to that observe in Monzén-1 and which was also interpreted as pure hydrogen has been observed by the authors in another exploration well (Fig. 5).

Fig. 4

Fig. 5

This well drilled in 1980 has a detailed mud-log and was interpreted by the Exploration Logging (“EXLOG”) crew as intersecting significant shows of hydrogen between 3230-3600 feet with a maximum of 200 gas units recorded at 3480 feet (Fig. 5). At this level both the Petroleum Vapour (PV) reading (gas which burns at a lower temperature) and the TG reading were the same. This evidence together with the chromatograph response strongly suggested to EXLOG that the gas being recorded was hydrogen.

This was further collaborated by the blender gas which was very similar to that being recorded from the mud flow line. Both the Operator and the EXLOG crew concluded that the mud logging equipment was functioning correctly (checked frequently via carbide tests) and that the flammable gas being recorded was without doubt pure hydrogen. As was most likely the case at Monzon-1 the presence of hydrogen in the mud caused controversy at the well site and EXLOG provided the following commentary with regards the effect of hydrogen on gas detectors:

Ditch gas and Microgas detectors give equal readings of TG and PV. Methane only registers on TG.
Using a detector voltage of 0.5 volts D.C. hydrogen will give a reading of approximately 25% of theTG (2.8 volts DC.) or PV (1.5 volts D.C.) readings.
There is no separation in the readout of the standard EXLOG chromatograph between methane and hydrogen. Hydrogen gives approximately half the response of TG = 200ppm methane,1 unit of TG =100ppm of hydrogen using methane calibration figure. It is this difference which allows methane to be determined above a hydrogen background if present.

In other words, if only hydrogen were present, 1 TC. unit of hydrogen gas would result in a TC detector volt ge of ~0.35 volts and a hot wire PV reading of ~o.375 volts, i.e. very close. Thus, if only hydrogen is present then the TG and PV readings with be more or less the same, which is what was observed. This fact, coupled with the absence of other gas components supports pure hydrogen presence which is what appears to have been the situation at Monzon-1.

It should be stated that In addition to a purely natural origin, it is feasible the hydrogen in Monzon-1 could have been generated artificially during the drilling process by a combination of drill-bit metamorphosis and/or mud motor failure (Keller and Rowe, 2017). While there is no way of categorically ruling out artificial gene ration the detailed drilling report for the well makes no mention of abnormal drill-bit wear nor mud motor failure during drilling of the Bunter interval despite there being mud losses into the formation (Fig.4). For info: nowadays, H2 measurements are routinely used by drillers to help assess drill bit wear status downhole. It is concluded therefore that the hydrogen encountered in the well is natural in origin.

Potential source of hydrogen

Assuming the hydrogen is natural then where would be its likely source? The most obvious answer is it has originated from the deep crust as is the case with the impressive hydrogen emanations recorded on the northern side of the Pyrenees where they are concentrated between the North Pyrenean Fault and the Frontal North Pyrenean Thrust Front (Fig.1 and Lefeuvre et al., 2021).
Assuming a similar deep crustal source for Monzon then the most obvious conduit would be the basement inversion fault system which lies a few kilometres to the or the northeast of the well (Fig. 3). Interestingly, given the strongly asymmetrical nature? (Fig. 6) of the Pyrenees then the location of Monzon-1 in the South Pyrenees is almost identical geologically to that where the hydrogen emanations are recorded in the North Pyrenees (Fig. 6). In both cases hydrogen is seen in association with crustal scale faults and at the termination of later Tertiary aged compressional thrusting. The big difference between the southern side of the Pyrenees and the north is that there is much more cover of the basement geology in the south by later Mesozoic and Tertiary rocks. Importantly, as observed in the Monzon-1 well, these cover rocks contain many excellent seals such as the halite/anhydrite bearing Bunter shales, Muschelkalk carbonates, Keu per shales, Infra Liassic evaporites and the thick, halite and evaporitic shales of Tertiary age comprising the core of the Barbas tro Anticline (Fig. 2). In total the combined thickness of pure evaporites measured vertically above the Bunter Sandstone in the Monzén-1 well reaches in excess of 1000 metres.

Towards an exploration strategy for natural or“gold” hydrogen

The presence of natural molecular hydrogen found as a gas in the subsurface has been documented in many locations throughout the world (Zgonnik, 2021). In deference to man-made “green” hydrogen produced via zero emission electrolysis of water naturally occurring hydrogen gas in the sub-surface has been termed either“white” or “gold” hydrogen (Gluyas, 2021; Ball and Czado, 2022).

Given the extremely lightweight and highly reactive nature of hydrogen, its occurrence as a free molecule in nature is rare and requires specific subsurface conditions to be met:

A source of natural hydrogen generation (biogenic, chemical, or radioactive)
a reservoir rock,
an impermeable"cap rock or seal” to prevent hydrogen leakage via diffusion
the absence of oxygen as this will react with the hydrogen creating water and leaving no trace hydrogen gas was ever present.

The gold hydrogen recorded at the Bunter Sandstone level in the Monzón-1 well conforms perfectly to all the above criteria. The major inversion fault setting up the northern bounding limb of the Monzón structure provides a perfect conduit for deep crustal generated hydrogen gas to migrate upwards into the basement defined structure. Here the hydrogen accumulates in the porous and trapped by a thick sequence (>200 metres) of evaporitic Bunter shales. The depth of the Monzén Bunter reservoir at over 3,500 metres Is well below the reach of aerobic processes limiting any oxidation reactions which could consume the free hydrogen molecules.

Conclusion

Significant hydrogen gas shows were documented in 1963 from the Triassic Bunter Sandstone interval Monzon-1 exploration well. The Bunter Sandstone on a well-defined basement closure and is sealed by thick sequence of evaporite bearing Bunter shales at a greater than 3500 mBGL.The geology documented Monzon-1 well perfectly matches the sub-surface conditions thought to be required for the entrapment concentration of natural gold hydrogen. The well was tested at the Bunter level the time of drilling leaving the intriguing conclusion that an accumulation of gold hydrogen awaits re-discovery.

Acknowledgements

The authors would like to acknowledge the insistence of our geophysical consultant the late Muharrem ‘Joe’ Boztas to re-look at the Monzon-1 well. Joe’s enthusiasm was inspirational and he is thanked enormously for his vision and persistence.

Bibliographic

Ball, PJ., and Czado, K., 2022. Natural hydrogenzthe new frontier, Geoscientist, Online Resource, accessed 05/04/2022, https://geoscientist.0n|ine/sections/unearthed/natural-hydrogen-the-new-frontier/
Burgess, K., 2021. British scientists lead the way in hydrogen ‘gold rush’ The Times online, https://www.thetimes.co.uk/article/british-scientists-lead-the-way-in-hydrogen-gold-rush-frj2v8hts
ENPASA,1963. Informe de Actividad del Sondeo de Exploracion de Monzon (Mn-1) perimetro de Huesca-Lerida, Resultados Geologicos,14pp
Keller, RJ. and MD. Rowe, 2017. Hydrogen and Helium Detection for Drilling a Lower Cost Well, Society of Petroleum Engineers Paper 187491-MS, 8pp.
Lefeuvre N., L.Truche, F-V. Donz, M. Ducoux, G. Barr, R-A. Fakoury, S. Calassou, E. C. Gaucher., 2021. Native H2 exploration in western Pyrenean foothills, Research Gate Publication 351795593-
Munoz, IA, 1992. Evolution of a Continental Collision Belt, ECORS-Pyrenees Crustal balanced Cross Section, in: McClay, K. (ed.),Thrust Tectonics, Publ.Chapman & Hall, London, pp235-246.
Munoz, IA, 2002. The Pyrenees. In: Gibbons, W., Moreno, T. (eds). The Geology of Spain. The Geological Society of London, 370-385.
Pritchard, R., 2011.Aragon,Abiego, Peraltilla, Barbastro & Binéfar Permits, Serica Energia Ibérica S.L. Relinquishment Report, 51pp.
Zgonnik V., 2020. The occurrence and geoscience of natural hydrogen: A comprehensive review, Earth Science Reviews, 203,103140, 51pp.