Page 627 - Economia Azul - versão: inglês

Gas hydrates occur in permafrost re- progressively replace natural gas (GRAULS, estimates based on these seismic data have
gions (permanently frozen soils of polar Figure X2: BSR (Bottom- 2001), which could foster a new ener- sparked interest in the area (estimated at
regions), and as a result of the diagene- Simulating Reflector) – reflection gy revolution. According to Kvenvolden 780 tcf) (SAD et al. 1998).
sis of sediments from lakes and deep seas approximately parallel to seafloor (1993), 1 m³ of methane gas hydrate con- The confirmation of the existence of
(> 500 m water-blade), when appropriate reflection, with reversed polarity, tains 164 m³ of methane and 0.8 m³ of gas hydrates in Brazilian territory (Pelotas
conditions of pressure, temperature and presumably caused by the water when brought to the surface (STP). Basin) only occurred with the develop-
saturation of gas are found. The physi- contrast between overlapping This number he calls the hydrate expansion ment of the “CONEGAS Project: Origin,
cal-chemical equilibrium of these struc- sediments containing gas hydrate factor. On the other hand, Sloan (2003) occurrence and characterization of gas
tures can occur in the water column, at and underlying sediments states that if each cavity is filled with a gas hydrate deposits in the Rio Grande Cone,
saturated with free gas, due
the water-sediment interface and in the to the difference in densities. molecule, 1 m³ of hydrate contains 180 m³ Pelotas Basin”, (MILLER et al., 2015). Lat-
sediment pores, characterizing the gas Indicates the lower limit of the (Surface-Treating Pressure, STP) of meth- er, in 2015, an oceanic mission to the Foz
hydrate stability zone (GHSZ – Figure X2). gas hydrate stability zone, the ane. The conclusion is that hydrate-bearing do Amazonas basin confirmed the occur-
The catastrophic release of methane by GHSZ, where hydrocarbons are reservoirs contain more methane per m³ rence of this resource in the area (KETZER
the destabilization of such deposits due to trapped in a solid structure. when compared to the volume of free gas et al, 2018). Such projects were devel-
the global climate changes that have been in the same space (KVENVOLDEN, 1993). oped by the team from the Institute of
observed can present negative feedback in In Brazil, detailed studies on gas hy- Petroleum and Natural Resources at PU-
these processes, accelerating such chang- drates are still incipient, despite their enor- CRS over a decade. These discoveries in

es, as the instantaneous release of these mous potential given the large area of Bra- Brazilian territory have raised the need
gases increases the so-called greenhouse zilian ocean basins. The existence of gas for additional research to promote the
effect. Additionally, the destabilization hydrate deposits in the country was, until understanding of its forms of occurrence
of these deposits poses a geological risk, the beginning of this century, only based and the future use of this resource in oth-
due to their potential to cause landslides, on evidence or indirect markers, such as er sedimentary basins, in addition to the
earthquakes and tsunamis. the presence of the so-called BSR (Bottom known ones, the Pelotas and Foz do Am-
The origin of hydrocarbons for the for- Simulating Reflector) in seismic sections azonas basins (Figure X3).
mation of hydrates can be biogenic, result- (FONTANA, 1989; FONTANA; MUSSUME- In addition to their importance as an en-
ing from the action of methanogenic mi- CI, 1994; SAD et al., 1997 and 1998). This ergy resource, studies of gas hydrates also
croorganisms in sediments, thermogenic, marker consists of a seismic reflector par- provide important information about the
associated with the migration of gas from allel to the seafloor (Figure X2), normally Earth’s carbon cycle and climate change.
deep hydrocarbon fields, or mixed. The between 200 and 700 m depth, caused Small changes in ocean water temperature
most common gases that form hydrates are by the abrupt change in acoustic imped- conditions can, for example, cause the dis-
methane, butane, propane, and carbon di- ance at the base of the gas hydrate stabil- sociation and release of large amounts of
oxide (MILLER et al., 2015). ity zone (GHSZ) in the sedimentary mass, methane and carbon dioxide into the at-
Even though it is a little-known sub- depending on the existence of a zone with mosphere. The massive destabilization of
stance, methane hydrates are abundant in gas hydrates above and a zone with free the gas hydrate system in a given region
the world’s oceans. Conservative estimates gas below this reflector in the sediments can also trigger large mass wasting events
indicate that the energy resources associ- (MACKAY et al., 1994). In the Rio Grande with potential impact on subsea instal-
ated with gas hydrates can exceed all oth- Cone (RGC), in a thick sedimentary se- lations, such as oil platforms and subsea
er fossil fuels added together (COLLET et quence deposited during the Neogene, the communication cables, or even major ca-
al., 2009). Based on this enormous poten- Source: Authors elaboration, (2022) presence of BSR was continuously identi- tastrophes in coastal areas such as of tsu-
tial, it is expected that gas hydrates will fied in seismic surveys. Significant volume namis (MIENERT et al., 2010).

624 BLUE ECONOMY State of the Art of Gas Hydrate Occurrences 625