The rock formation in north-western Türkiye could have generated around 269 mln tons of native hydrogen throughout its geological history, of which some 13.5 mln tons is potentially recoverable. This finding was reported recently by a Çanakkale Onsekyz Mart University researcher who was the first to estimate naturally occurring hydrogen volume in the Biga Peninsula. It is not about explored reserves yet but rather about the amount of hydrogen that local rock could have potentially produced.
The author points to serpentinization, a natural chemical reaction between water and iron-rich minerals, as the main source of H2. As water penetrates fractured rock it reacts primarily with olivine and pyroxenes. The ferrous iron contained in those minerals oxidizes into magnetite, and some hydrogen is released from water as molecular H2. Hydrogen can thus emerge naturally within the rock without exposure to organic matter.
The research focused on two particular rock formations, Denizgören and Tozlu, the former found to be the more promising. Denizgören is a belt 2 to 5 km wide stretching approximately 50 km. Its mineral mass is 70 to 90 percent serpentinized, meaning that most of it has already reacted with water. Moreover, serpentinization here occurred at about 300-500°C, partially coinciding with the temperature range of 200-400°C which is most conducive to the formation of natural hydrogen, with peak H2 output occurring at about 315°C.
The Turkish researcher used two methods to estimate the amount of H2 produced. First, he applied laboratory test findings that demonstrate how much hydrogen can emerge through serpentinization per mass unit of rock. For Denizgören, the estimated output was around 245 mln tons of H2. Second, he proceeded from the implied iron content in the rock and calculated the amount of hydrogen that could have emerged from oxidation. The result was close to 288 mln tons. He then accepted the average of both estimates (approximately 267 mln tons) as the basic estimator.
Tozlu’s potential was found to be much lower, at 2.5 mln tons, as a consequence of its geological history. In the past the rock here was heated to some 675-880°C. At such temperatures antigorite, one of the minerals that form through serpentinization, disintegrates, meaning that a major part of serpentinites involved in H2 formation processes was destroyed. At Denizgören, the much lower temperatures were closer to serpentinization conditions, the formation thus holding almost the entire estimated volume of H2.
However, the 269 mln ton figure shall be interpreted not as the formation reserve but rather as an estimate of the amount of hydrogen that Denizgören and Tozlu rock could have produced over geologic time. Much of it may have long escaped through faults to the surface. Indeed, so far there have been no discoveries of solid, impermeable strata or other geological traps above Denizgören that could seal H2 underground. The researcher thus applied the 5% recovery factor, leading to the estimate of about 13.5 mln tons of potentially recoverable hydrogen. But even this figure can be questionable as the author selected it as a conservative estimate, an approach he adopted from petrochemical studies.
The calculation itself also remains preliminary. In particular, no direct measurement of iron content has been taken so far for Denizgören, so the author used data from comparable rock units in other regions. Also, there is no certainty as to the formation size deeper underground. Added up, those key uncertainties may prompt either upward or downward adjustment of the estimate, and for Denizgören the research points to the range of 74-571 mln tons of H2.
Therefore, the research does not definitely conclude the existence of a large deposit of hydrogen in the Biga Peninsula, but rather points to exploration prospects in the region. According to the author, the next step should involve measurement of H2 concentrations in soil gas and ground water, elemental composition analysis of the local rock, and exploration of faults. Those operations will help understand whether hydrogen is still being generated, where it migrates, and whether there are underground traps where gas can accumulate in commercial quantities.
