Eliane Petersohn

Investigating Naturally Fractured Reservoirs in the Brazilian Pre-Salt Play

Eliane Petersohn

Eliane is an experienced geologist working for ANP (Agência Nacional do Petróleo, equivalent to the Norwegian Offshore Directorate) in Brazil for more than 15 years, currently on leave to do a Fulbright-funded PhD project at Stanford. There, she is working on the relationship between deformation structures (fractures, mostly) and fluid flow in the subset carbonate reservoirs offshore Brazil, employing a wealth of well and seismic data available through ANP.

Abstract:

Natural fracture networks significantly enhance reservoir permeability, facilitating fluid flow and optimizing production rates within carbonate reservoirs. However, these networks also introduce heterogeneity, creating complex flow pathways that can be challenging to characterize and quantify. Similarly, fault systems act as conduits or barriers to fluid flow, contributing to reservoir heterogeneity and potentially inducing fracturing. Understanding the interplay between these features is crucial for effective reservoir management. The Brazilian Pre-salt Province, characterized by naturally fractured carbonate reservoirs with exceptionally high production rates, exemplifies this challenge. While the high productivity is likely linked to interconnected fracture and fault systems, their complex nature and limitations in observation scale make characterization challenging. My research aims to unravel this complexity by investigating the relationship between fracture networks, fault systems, and their influence on reservoir property distribution. To achieve this, I propose an integrated approach encompassing 3D seismic interpretation, geomechanical modeling, and analysis of seismic and sonic anisotropy. Preliminary results from a strategically selected well in the Atapu field reveal valuable insights into fracture characteristics, including a consistent WSW-ENE strike orientation. However, a clear correlation between highly fractured intervals and permeability, porosity, or silica content was not observed. Notably, fractures do correlate with vuggy porosity estimated from the acoustic borehole image (BHI). Additionally, a fracture index, developed using random forest regression on well log responses and BHI-interpreted fracture intensity, demonstrates promising results in predicting fractured intervals.