Multi-isotopic Techniques to Trace Water-Rock Interaction in Petroleum Systems – A Case Study from the Northern Red Sea Basin, Saudi Arabia

Formation water from the Al Wajh Formation (Oligocene-Lower Miocene) and Adaffa Formation (Upper Cretaceous) was geochemically fingerprinted to constrain fluid migration pathways from surface infiltration toward the present position of the groundwater regime from the deep sedimentary column in the Northern Red Sea Basin. Multi-isotopic analyses on inorganic fluids were performed to assess potential flow pathways for the analogue migration of organic phases. Depleted strontium isotopic ratios (87Sr/86Sr = 0.707307 - 0.708012) of formation brines from the sedimentary sequence suggest the occurrence of hydrothermal interaction with the underlying igneous basement (87Sr/86Sr = 0.70292-0.70316), likely to be triggered by temperature-triggered hydrothermal reactions. Fluid migration must be structurally-controlled or by depositional hiatus of salt layers, as halite dissolution from the seal cap of Miocene evaporites (Mansiya Formation) has not been evidenced. Boron (11B) and iodine (129I/127I) isotopic fingerprints indicate: a) the contact of formation water to a clay-rich, organic-rich rock type, likely to be of Late Eocene and Late Cretaceous age; b) the potential release of adsorbed boron from clay minerals and biophyllic iodine from organic matter; and c) the subsequent migration of iodine-enriched formation water (from the organic source) to the present groundwater horizon at Al Wajh Formation.