Table 2
H2-rich zone description based on available well log information from eight exploratory wells. *H2 zone thickness not estimated due to low neutron reads. **We show the original values in ppm, but they could not correspond to the exactly H2 amount in the zone, because they correspond to isotube or isojar samples, which do not have the same reliability as cylinder samples. To emphasize the cylinder well test data, additional layers with reported H2 in the PTRA-1, PTRA-2, and PTRA 5 datasets were not listed in the table due to their unreliable origin (isojar samples).
| Well | Range of depth with H2 (meters deep) | Main lithotype | Sequence/Lithostratigraphy | H2 amounts (max) | Reservoir properties |
|---|---|---|---|---|---|
| PTRA-1 | 860 to 912 (Cylinder – well test) | Siltstone and shale | Sete Lagoas Fm | 41.1% | Pores closed and fractures filled with calcite. Drill stem tests indicate a reservoir with very low permeability, final static pressure around 14.4 MPa (about 2090 psi) and not depleted. |
| PTRA-2 | 1790 to 1930 (Cylinder – well test) | Siltstone and calcarenite | Sete Lagoas Fm | 1.0% | Microfractures filled with calcite. Well tests suggest a reservoir with a low permeability of 0.00784 mD and final static pressure of 170,78 gf/cm2, approximately 2430 psi. |
| PTRA-5 | 348 to 509 (Cylinder – well test) | Siltstone and shale | Sete Lagoas Fm | 32.8% | Fractures filled with pyrite. Final static pressure measure during the wireline formation test: 4.9 MPa, approximately 722 psi. |
| PTRA-6 | 900 to 1008 | Arenite and phyllite | Macaúbas and Espinhaço Sequences | 36,100 ppm** | Presence of veins on arenite and foliation on phyllite. |
| PTRA-10 | 1203 to 1311 | Calcarenite | Macaúbas Sequence | 67,300 ppm** | Presence of fractures. Drill stem tests indicate a reservoir with very low permeability and final static pressure of 13.7 MPa, approximately 1984 psi. |
| PTRA-12 | 2450 to 2950, 3565 to 3850 | Calcilutite and calcarenite, marl and dolomite | Sete Lagoas Fm, Macaúbas and Paranoá Sequences | 229,800 ppm** | No primary porosity. Presence of fractures. |
| PTRA-13 | 954, 1670 to 2604, 2712 to 2784 | Shale, claystone and arenite | Bambuí Grp, Sete Lagoas Fm and Paranoá Sequence | 244,600 ppm** | Presence of four types of microfractures: opened, cemented, filled with calcite, and with quartz. |
| PTRA-14 | 1779 to 1929 (Cylinder – well test) | Siltstone and calcilutite | Bambuí Sequence and Sete Lagoas Fm | 0.2% | Microfractures and stylolites, showing porosity lower than 1% (based on petrography analysis). Drill stem tests indicate a reservoir with very low permeability and final static pressure of 14.3 MPa, about 2076 psi). |
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