Natural Hydrogen in the Pre-Salt of the Santos Basin: A Hypothesis

Natural hydrogen in the pre-salt layer of the Santos Basin: a hypothesis

Abstract

Occurrences of natural hydrogen (Nat H₂) are relatively common in surface and in other different geologic environments. Pionner studies have shown that Precambrian rocks, especially those Proterozoic, hold the most significant occurrences of Nat H₂. Nat H₂ can have different origins, e.g., radiolysis, reduction of the water, serpentinization, leaking from the mantle, associated with movements of large faults, decomposition of H₂S, and from overmature kerogen.  In this investigation is discussed the hypothesis of potential traps for Nat H₂ are associated by mounds in the pre-salt of the Santos Basin. Those mounds grown in response to the upward migration of deep fluids related to hydrothermal vents formed at the contact aureole of the shales of the Itapema Formation intruded by diabase sills. Such conditions favored the formation of Nat H₂ through water reduction under high temperature and in presence of minerals with iron, or other metal, leaking from the mantle, through the deep-seated faults, or even derived from the overmature petroleum kitchens.  Hydrogen systems are complete with the network for fluid migration (deep-seated faults), and deposition of reservoir rocks covered by efficient seal (evaporites). Hydrogen systems were controlled by the tectonic evolution of the Southeastern Brazil, principally the direction NW-SE, e.g., Cruzeiro do Sul tectonic belt. In the ongoing petroleum exploration, the attention to the presence of anomalies of hydrogen, as a secondary target in petroleum prospect, will reduce costs, and could bring extra reward to the exploration.