Study of biodegradation processes along the Carnaubais trend, Potiguar Basin (Brazil) - Part 1

The aim of this study is to estimate hydrocarbon losses in natural reservoirs due to biodegradation processes. A series of 12 non-biodegraded and biodegraded oils were selected in the Potiguar Basin (Brazil). Most biodegraded reservoir oils are located in the southwestern part of the basin (onshore), within the Cretaceous sandstones of the Açu units that occur at shallow depths (<1000 m). Deeper reservoirs, containing non-biodegraded but mature oils, are located in the northeastern area of the basin. Based on the chemical alteration of the saturates and aromatics observed in biodegraded oils, tentative estimates of absolute losses were calculated for the light hydrocarbons (saturates and aromatics) and for the heavy fractions such as C14+ linear and cyclo-alkanes and C14+ aromatics. Together with the estimation of losses on global classes, molecular studies clearly show that biodegradation scales based on saturated and aromatic biomarkers can be used as such but do not reflect the loss percentage by biodegradation on global classes.