Increasing Confidence in Production Forecasting Through Risk-Based Integrated Asset Modeling: Captain Field Case Study
Authors: Denney Dennis 
Published: February 2015

This article, written by Technology Editor Dennis Denney, contains highlights of paper SPE 99937, "Increasing Confidence in Production Forecasting Through Risk-Based Integrated Asset Modeling: Captain Field Case Study," by L.M. Wickens, SPE, RPS Energy, and G. De Jonge, SPE, Chevron Upstream Europe, prepared for the 2006 SPE Europec/EAGE Annual Conference and Exhibition, Vienna, 12-15 June.
To assist probabilistic forecasting and decision making for the Captain North Sea heavy-oil asset, Chevron developed an integrated asset model (IAM). This model includes probabilistic predictions of facilities performance and production, enabling decision-risk analysis for strategic and operational decisions. The IAM includes risk-based oil-, gas-, and water-production forecasts and cash flows. These forecasts take full account of facilities constraints and uncertainties in reservoir and operational parameters through links to decision-risk-analysis software.

Introduction
The Captain field is a phased development comprising Areas A and B. The field produces high-viscosity oil, with separation taking place on a floating production, storage, and offloading vessel. Critical processing interdependencies, single-train separation with limited redundancy, and gas- and water-handling constraints require facilities downtime with significant effect on production projections. The five producing areas in the field produce from three reservoir units: upper Captain sand (UCS), lower Captain sand (LCS), and the Ross (R). Production consists of the three fluid phases—oil, water, and gas. Produced gas includes gas-cap (GC) and solution gas. Electrical or hydraulic submersible pumps provide artificial lift in every well. All produced water from the field is reinjected into the reservoir, with a portion of it used to power the hydraulic submersible pumps. The dynamic subsurface behavior is simulated with four separate reservoir-simulation models.Area-A UCS plus Area-B GC.Area-A LCS.Area-B eastern extension (EE).Ross.
Key to the Captain IAM approach is that a wide range of different reservoir simulations, time dependencies, and production rates from each well can be reconstructed adequately from a two-parameter response surface that itself is not a function of time. This response surface is the phase rate tabulated as a function of total reservoir rate and cumulative production.
To investigate this assumption, a response surface for one of the Captain reservoirs was constructed and then used to predict well behavior during different well choke-back scenarios. This response-surface approach can be used to forecast strategies not covered in simulation runs. The IAM has facilitated estimating the effect of uncertainties in reservoir or operational parameters and linking to decision-risk-analysis software. The IAM analysis tool has been used to help with the following.Completing the second development phase.Selecting a concept for a third development phase.Providing credible probabilistic production forecasts.Developing operational and debottlenecking decisions.