Isotopic monitoring of steam injection used to stimulate production in heavy oil fields in the Potiguar Basin, Brazil

Abstract

The Alto do Rodrigues, Estreito and Salina Cristal, Potiguar Basin oil fields, Brazil, produce heavy oils which are derived from distinct production intervals. Steam injection is used to stimulate production, with the steam generated using water transferred by pipe from the Açu River. This work investigates the physicochemical and isotopic characteristics of the surface waters of the region, the water introduced as steam, and the water produced in the wells of the oil fields, in order to determine the contributions of the various intervals to well production, as well as the influence of injected steam as a recuperation method. The isotopic compositions were characterized, including the water introduced as steam (δ2H = 3‰ and δ18O = 0.5‰), the formation water in the reservoir (–25‰ < δ2H < –18‰ and –4.1‰ < δ18O < –2.6‰), and the water produced from wells with specific or combined production intervals in the Açu reservoir. The results help to determine the differential participation of the various production intervals in wells with combined production, as well as the isotopic and energetic influence of the injected steam in wells adjacent to the injection wells. Finally, it was possible to identify the effects of oil biodegradation, as evidenced by high concentrations of dissolved inorganic carbon (DIC) enriched with 13C.