Integration of Prudhoe Bay Surface Pipeline Network and Full Field Reservoir Models
Authors: Litvak M.L. , Clark A.J. , Fairchild J.W. , Fossum M.P. , Macdonald C.J. , Wood A.R.O. 
Published: December 2007

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An integrated reservoir, well tubing string, and surface pipeline network model of the Prudhoe Bay oil field has been constructed. The integrated model incorporates a new procedure for the simultaneous solution of the reservoir and surface pipeline network flow equations. It also includes an optimization technique to allocate well production rates. As a result of the effectiveness of the developed procedures, the new technology for integrated reservoir and surface facility modeling has been successfully applied to a facility optimization study of the giant Prudhoe Bay oil field.

Introduction

Business Motivation. Production from the Prudhoe Bay oil field is on decline. For this reason, optimal usage of the surface facilities is a major factor in reducing production costs. Along with other measures, production costs for Prudhoe Bay can be reduced by–defining the optimum surface facility structure and operating conditions (optimum number of separator stages and their connections, optimum separator pressure, etc.);–using any excess capacity in the Prudhoe Bay surface facilities to process third party fluid production from satellite oil fields.

However, changes to the surface facility system will impact production from Prudhoe Bay wells. For example, tubinghead pressures for some Prudhoe Bay wells will increase if production from the satellite fields is conveyed to the separators via the existing surface pipeline network system. In this case, production rates for these wells would be reduced.

Tools. Integrated compositional models of–the reservoir,–well tubing strings,–the surface pipeline network system,–separator banks, and central gas facility

are constructed to evaluate the impact of facility modifications on well production profiles.

The compositional reservoir model and its history matching will be described in a separate paper. The integration of the central gas facility and reservoir models is presented in Reference 1. In this paper, we describe the well tubing string and surface pipeline network models and their integration with the reservoir model.

Model Objectives. The integrated reservoir and surface pipeline network model provides the capability to–allocate production well rates in a reservoir simulation from pressure constraints at the separator banks and from surface facility limits,–define optimum well assignments to high or low pressure flowline and separation systems–determine the impact of surface facility changes on a production profile.

Normally, tubinghead pressure or bottomhole pressure is used for the well rate allocation in reservoir simulations. However, well tubinghead (or bottomhole) pressures change in time as a result of well gas-oil ratio and water cut variations, and these changes are difficult to predict.

Challenges. Construction of an integrated model of the reservoir and surface pipeline network system for the Prudhoe Bay oil field is a very challenging and difficult problem for the following reasons:

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