Assessment and Ranking of EOR Strategies for Giant Extra-Heavy Oil Fields

Abstract

Abstract This paper presents an integral methodology to evaluate and rank Enhanced Oil Recovery (EOR) strategies for heavy oil fields, together with preliminary results for a real case study in the Orinoco Oil Belt (OOB) where thermal EOR processes are planned to be used in a very large scale. The decisions around EOR deployment are diverse, including EOR process selection, wells placement, injection conditions and scheduling. Typical decision parameters are: incremental oil recovery, Net Present Value, injection cost and environmental impact. Full field incremental recovery and injection requirements are estimated from reservoir simulation using a sectoring approach and taking into consideration the project development plan. Injection cost is highly dependent on the EOR process to be applied, as well as on specific project constraints, such as location or resources and infrastructure availability. The decision workflow uses the previously estimated full field production and injection profiles to size the surface facilities for each particular comparison case, and estimate the respective associated costs. Incremental drilling and completion costs for the EOR operations are also considered within the methodology. Environmental impact is assessed by estimating CO2 and H2S emissions, as well as energy and fresh water demands. The automation of the workflow allows the fast but meaningful assessment of hundreds of alternative strategies, including variations on EOR process conditions, surface facility configurations, deployment schedules and geological or commercial scenarios. This workflow has been applied to a field in the OOB to support the decisions about EOR deployment strategy to be taken during the project conceptualization phase. The main objective was to identify the EOR process that could provide the best incremental recovery without infringing any project constraint, primarily target production plateau and fuel and fresh water availability, and, at the same time, minimizing cost and environmental impact. Being an extra-heavy oil field, thermal EOR processes were considered, more particularly: Cyclic Steam Stimulation (CSS), Steam Flooding (SF), Steam-Assisted Gravity Drainage (SAGD) and Horizontal Alternating Steam Drive (HASD). About one thousand cases were evaluated under uncertainty using information from different domains: geology, reservoir, wells, facilities, HSE and commercial. The comparison results provided very useful insights on the advantages, risks and drawbacks of each EOR strategy, and set the basis for a high quality decision.