Prudhoe Bay E-Field Production Optimization System Based on Integrated Reservoir and Facility Simulation

Abstract

Abstract This paper describes the E-field production optimization system (EFOS), recently developed for the Prudhoe Bay oil field in Alaska. EFOS is based on an integrated compositional model of the reservoir and surface facilities. A commercial reservoir and surface facility simulator is used for integrated fluid flow modeling in the reservoir, well tubing strings, surface pipeline network system and surface separation facilities. EFOS is designed as an operational tool for short-term field production optimization and debottlenecking studies as opposed to a tool for long-term reservoir modeling studies. While full reservoir modeling capability is an option, and is a valid approach to daily optimization for small fields, it is not a practical approach at Prudhoe Bay where there are over 800 producing wells. To facilitate a practical alternative, an option was developed to use well inflow performance curves to predict well performance as opposed to running the full reservoir model. EFOS consists of the following major components: automatic data preparation, automatic model tuning to match available field production data, production optimization, and a user-friendly interface. Procedures were developed for automatic data collection and creation of simulator input data sets from data gathered by existing process control systems. In the tuning phase, simulation parameters are automatically adjusted within physically justifiable ranges to match field measurements of well production rates, well tubinghead pressures, and flowline pressures at the specified simulation time. To optimize production, robust mixed integer optimization algorithms are applied. Well production rates, well allocations to separator trains and, optionally, gas lift rates are selected that maximize field oil production subject to reservoir and facility constraints. The selected objective function is maximized in each simulation time step. The foreground user-friendly interface is an integral part of one of the Prudhoe Bay process control system databases, with the reservoir simulator running in the background. The interface between the two systems is enabled through a new interactive mode of reservoir simulator operation. Some examples of the EFOS application are described which also outline the system efficiency. EFOS is based on commercial software permitting its application in a large variety of oil and gas fields. Introduction Business Motivation. Production from the Prudhoe Bay oil field is on decline. At ambient temperatures above about 0 degrees Fahrenheit (°F), gas compression capacity is the major bottleneck to production. For example, field gas compression capacity is reduced by 1.2 bcf/d when the ambient temperature is 40°F compared to an ambient of 0°F. This equates to an approximate reduction in oil rate of 1000 bopd per °F increase in temperature. Between 40 and 60°F this increases to a reduction of approximately 3500 bopd per °F. A secondary constraint to production is fluid velocity in the flowlines. For these reasons, the optimum allocation of well production rates, subject to the current facility constraints, is an important factor for oil production acceleration. Business Motivation. Production from the Prudhoe Bay oil field is on decline. At ambient temperatures above about 0 degrees Fahrenheit (°F), gas compression capacity is the major bottleneck to production. For example, field gas compression capacity is reduced by 1.2 bcf/d when the ambient temperature is 40°F compared to an ambient of 0°F. This equates to an approximate reduction in oil rate of 1000 bopd per °F increase in temperature. Between 40 and 60°F this increases to a reduction of approximately 3500 bopd per °F. A secondary constraint to production is fluid velocity in the flowlines. For these reasons, the optimum allocation of well production rates, subject to the current facility constraints, is an important factor for oil production acceleration.