Abstract
Two sectors, Itata and Valdivia, which are located in the Chilean margin were analysed by using seismic data with the main purpose to characterize the gas hydrate concentration. Strong lateral velocity variations are recognised, showing a maximum value in Valdivia offshore (2380 ms−1 above the BSR) and a minimum value in the Itata offshore (1380 m·s−1 below the BSR). In both of the sectors, the maximum hydrate concentration reaches 17% of total volume, while the maximum free gas concentration is located Valdivia offshore (0.6% of total volume) in correspondence of an uplift sector. In the Itata offshore, the geothermal gradient that is estimated is variable and ranges from 32 °C·km−1 to 87 °C·km−1, while in Valdivia offshore it is uniform and about 35 °C·km−1. When considering both sites, the highest hydrate concentration is located in the accretionary prism (Valdivia offshore) and highest free gas concentration is distributed upwards, which may be considered as a natural pathway for lateral fluid migration. The results that are presented here contribute to the global knowledge of the relationship between hydrate/free gas presence and tectonic features, such as faults and folds, and furnishes a piece of the regional hydrate potentiality Chile offshore.
Highlights
Many studies related to gas hydrate occurrences worldwide have been reported mainly to better characterize reservoirs, their potential as energy resource and the role gas hydrate can play in global climate change [1,2,3]
To determine the temperature at the bottom simulating reflector (BSR), we considered the gas hydrates dissociation temperature-pressure function proposed by [43,44]; knowing the pressure at the BSR the temperature is determined by the hydrate dissociation function
By comparing the background velocity with the velocity models, it is possible to recognise above the BSR a high velocity layer (1900–2380 m·s−1 ) that is associated to gas hydrate presence
Summary
Many studies related to gas hydrate occurrences worldwide have been reported mainly to better characterize reservoirs, their potential as energy resource and the role gas hydrate can play in global climate change [1,2,3]. Concerning the former, large amounts of methane gas can be trapped in form of gas hydrate being considered as an important greenhouse gas. Panel on Climate Change [4] For these reasons, in the last decades, several projects have been carried out to assess the global methane hydrate quantities. Few authors estimated 11,000 Gt of carbon in hydrate [5], while the last estimations are significantly lower [2,6,7,8]
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