Production Optimization in the Campos Basin: A Case for Robustness in Waterflooding

Abstract

This article, written by Editorial Manager Adam Wilson, contains highlights of paper OTC 22560, ’Production Optimization in a Campos Basin Reservoir: A Case for Applying Robustness Measures to a Waterflood Project from Subsurface and Operational Design to Execution,’ by Ozan Arslan, SPE, Kyle Koerner, SPE, Stephen Knapp, Nate Biddle, Alwin Bok, SPE, and Paulo Chaves, BP, prepared for the 2011 Offshore Technology Conference Brasil, Rio de Janeiro, 4-6 October. The paper has not been peer reviewed. A successful cross-discipline workflow used in a Campos basin multiproducer-system waterflood program encompassed subsurface characterization, well planning, data acquisition, well controls, and surveillance to support efficient oil recovery. Drilling from a central platform, extended-reach wells were necessary to access a structured series of near-shore, laterally amalgamated channel sands separated by variable barriers posing significant subsurface-modeling, well-design, and drilling challenges. A cross-discipline-team approach employed robustness measures to find a near-optimal solution with controlled risk management. Introduction The Polvo complex is a system of clastic (Upper Cretaceous) and Macae carbonate (Lower Cretaceous) reservoirs in the Campos basin with 18–22°API oil. The clastics have been on production for 3 years with natural waterdrive and water injection. Development drilling started in mid-2008 for the Cretaceous sand system (CSS) where wells were completed with openhole gravel packs and electrical submersible pumps. Robust waterflood design and execution require a proactive, risk-minimizing reservoir-management strategy. The team used a cross-discipline workflow to achieve a near-optimal performance in the Polvo C_3 reservoir (Fig. 1). The workflow ensured the communication of constraints and raised potential decision points for Reservoir characterization Numerical modeling and uncertainty assessment Well planning (constraints and data acquisition) Well completion (integrity and sustained injectivity) Operational issues and surveillance tactics Remediation and optimization Robustness of proposed solutions is particularly critical in terms of reservoir characterization where certain geological outcomes, such as fault transmissibility or sand/sand connectivity, can be discrete in nature (sealing or not sealing). Therefore, capturing key geological assumptions in the CSS and communicating the critical decision points and possible outcomes across the team played pivotal roles in the workflow. Reservoir Characterization and Waterflood Design Detailed descriptions from core data indicated that channels and lagoons are the primary depositional environments for these reservoirs. Analysis of all the data collected on the CSS reservoirs suggested uniform layering, where each sand-prone layer exhibits a high degree of internal lateral continuity. Each sand-prone interval is capped by a shale layer interpreted as a sea-level rise shifting the reservoir facies northwest. The vertical rise in sea level coupled with the local dip on the Macae surface will control the lateral offset distance of reservoir facies from layer to layer, which, in turn, affects the local vertical communication between reservoir layers. The expectation is that there will be vertical permeability barriers, at least locally.