Abstract

Oil production rates in Minas fields have been declining over the past few years, and new methods of producing remaining reserves are needed. A detailed stratigraphic framework constructed from more than 1400 wells, however, has demonstrated significant reservoir heterogeneity. Production and injection data within this stratigraphic framework have identified "thief zones" throughout the main reservoir layers. These zones are particularly apparent in the coarse, more permeable lower sections of fining upward sequences. Injection water passes preferentially through these intervals. This results in high water flow, blocked oil withdrawal, and ineffective sweep of oil in the upper portion of sequences. These observations suggest that in situ profile modification (IPM) via polymer injection is a promising method for improving reservoir sweep efficiency.

By passed oil at the top of fining upward sequences is the main target for IPM implementation. To identify potential areas, a comprehensive study was conducted throughout Minas field. This review resulted in the selection of a high-graded area as determined by the distribution of vertical permeability variation, thickness of fining upward sequences, and interpreted wireline log facies. Cased-hole resistivit y logs were used to further identify and validate bypassed zones. A detailed review using seismic and log data was carried out to assess lateral reservoir continuity. Engineering data, such as spinner surveys, were utilized to confirm the production characteristics of potential well candidates. This integrated review process resulted in the identification of sands in several wells that met the necessary criteria for IPM.

This paper describes the integrated approach used to select candidates based on reservoir characterization work and the challenges of applying the IPM technique in Minas field. Furthermore, the viability of applying this technique to other oil fields will also be addressed.