# Hydrogen from Depleted/Depleting Hydrocarbon Reservoirs: A Reservoir Engineering Perspective
## 6 H\({}_{2}\) Generation in DORs
### Concept
They describe a so-called downhole gasification unit (DGU) to investigate the catalytic steam reforming of naphtha fraction cuts from Statfjord crude oil under high pressures and temperatures. Figure 5: Temperature and saturation profiles during dry ISC process. High H\({}_{2}\) conversion rates ranging from 35% to 69% (molar basis), considering the outlet gas composition and remaining gases being CO\({}_{2}\) and CO, are reported due to high P and T and favorable catalyst types, oil compositions, and steam/hydrocarbon ratios. Unfortunately, there is no information available on the material balance of the reactions. [PERSON] et al. studied, numerically, the in situ generation of H\({}_{2}\) by the gasification of bitumen from the heavy-oil and bitumen reservoirs in Alberta, Canada [16]. The required reactions were simulated with a reservoir simulator on a generic model by mimicking an ISC process and the authors estimated the H\({}_{2}\) amounts as a result of bitumen burning. Up to 1000 Sm\({}^{3}\) H\({}_{2}\) per m\({}^{3}\) of bitumen, which burned (approximately 0.1 kg H\({}_{2}\)/kg oil) as function of P and T, was reported. In an earlier ISC study on the combustion kinetics of Athabasca bitumen from 1D combustion tube experiments, no H\({}_{2}\) was recorded in the outflow gas composition [79]. In a related patent, the numerical estimation yield of 1 kg H\({}_{2}\) per 64 Sm\({}^{3}\)O\({}_{2}\) seemed to be overestimated compared to the yields obtained in the laboratory works [66]. [PERSON] et al. reported three dry ISC tests in a combustion tube carried out at 34.5 bars, with a pre-heating and ignition temperature of 95 \({}^{\circ}\)C and 350 \({}^{\circ}\)C, respectively, to investigate the performance of regenerated and reused catalysts on the upgrading potential of Athabasca bitumen [80]. Temperature profiles with peaks up to 800 \({}^{\circ}\)C were recorded. They emphasized that H\({}_{2}\) generation is due to WGS catalytic and thermal cracking reaching 10% of the total gas production at the outlet. An H\({}_{2}\) generation rate of approximately 1.5 g H\({}_{2}\) per kg of OOIP could be derived from the data provided. A list of the H\({}_{2}\) yields from various experimental ISC works is provided in Table 4. In the table, the proposed H\({}_{2}\) generation reactions, as well as the reported AR values, are also provided. Unfortunately, very few studies reporting H\({}_{2}\) generation have provided AR data; AR values reported in ISC laboratory work and field evaluations converge at 500 \(\pm\) 100 Sm\({}^{3}\)/m\({}^{3}\) or even higher [81]. Although it is postulated that H\({}_{2}\) occurs in a reservoir as a result of ISC, and this has been observed in laboratory works as stated above, most of the laboratory and numerical studies, as well as the field applications, do not refer to the H\({}_{2}\) production in the effluent gas composition, except, if rarely, as a trace [79; 82; 83; 84; 85; 86; 87; 88]. In the early attempts, the lack of analytics may have contributed to the low success rate. If any H\({}_{2}\) was recorded, it was mostly considered an indication of an inefficient process in situ such as low-temperature oxidation or channeling. Additionally, the low or non-existent H\({}_{2}\) observation in an outflow can be attributed to the incomplete and incorrect interpretation of the reactions occurring in the reservoir. It can be concluded that reactions (2) through (6) involve an interplay of various components, with H\({}_{2}\) being both co-generated and consumed during combustion. The rate of H\({}_{2}\) generation during ISC depends on many factors, the most important of which are the thermodynamic conditions, the oxygen content, and the type and quantity of catalyst and the oil.