Improving Recovery from a Mature Reservoir by Understanding the Stratigraphy, Eden-Yuturi Field, Oriente Basin, Ecuador

Abstract

The Eden Yuturi field, first exploited in 2002, is located in the northeast of the Oriente basin, Ecuador. The field was initially operated by Occidental Petroleum and has been operated by Petroamazonas EP (PAM) since 2006. From its peak production of 83.8 million B/D in August 2004, the field declined and now produces less than 30 million B/D, with a water cut of 92%. In 2014, PAM awarded an incremental production based service contract to the Kamana Services consortium, with the objective of reversing the field decline and increasing the recovery factor by optimizing production and applying enhanced oil recovery techniques.The Lower U in the Cretaceous Napo formation is one of the most important reservoirs in this mature field and has a cumulative oil production of 48.1 million barrels (as of July 2015) from 110 wells. The production is supported by a water drive mechanism and a strong aquifer.The major challenge for the consortium is to define an optimal field development plan that maximizes the current recovery factor of 34%. To achieve this goal, it is crucial to enhance the reservoir characterization by integrating all the available information from multiple disciplines and use this knowledge to understand the fluid dynamics in the reservoir.The sedimentary column of the Lower U is interpreted as fluvial at the base follow by tide-dominated estuarine tidal shelf deposits grading into lower shoreface deposits towards the top of the reservoir. This transition subdivides the reservoir column into different hydraulic units. However, the vertical stacking of these hydraulic units is not present across the whole field, and amalgamation has been observed in specific zones. The fluid dynamics changes inside the reservoir have a large impact on the waterdrive mechanism sweep efficiency, as identified in the pressure and production performance analysis of the reservoir across the area, and differences in pressure levels and water cuts trends are evident.Therefore, a proper stratigraphic characterization is the key to optimizing the field development strategy of the Lower U reservoir to improve the ultimate recovery factor.In this paper, we describe how the stratigraphic characterization has been performed and the final framework obtained by the multidisciplinary team, to be used for the optimized development strategy of the Lower U reservoir.