Offshore Topside Facilities Optimization
Authors: Mockridge J.I. , Akhtar N. 
Published: March 2010

Offshore topside facilities and supporting structure investments are generally substantial. Comprehensive front-end optimization studies are necessary to design the most cost-effective system which will be both flexible and efficient. This paper will discuss the development of an optimized topside facilities design for oil/gas production.

Process optimization is perhaps the biggest weight and space saving technique. The paper will describe the objectives and areas of process optimization, and the factors that dictate the design and selection of optimum operating conditions for oil and gas process systems.

When production is from two or more locations, centralized production and processing may reduce total investment costs. Discussions on the logical approach to determine the optimum development scenario are presented.

The topsides designer Vias various means of predicting space and maintaining weight control. These options are outlined and flares structures are given as an example. The potential of new technology for reducing weight and space of standard equipment is explored.

Introduction

Offshore topside facilities generally use a design based on the simplest useable process in order to minimize equipment and utility requirements. This is to reduce platform weight and space. A simple process design may not be the most efficient or flexible choice. A design is however, often based on limited data and must have flexibility for other than design conditions. Since offshore production facilities and supporting structures investments are substantial, comprehensive front-end optimization studies are necessary to design the most cost effective system which will be both flexible and efficient.

What is unique about offshore projects is their integrated nature; they are highly sensitive to the initial assumptions and decisions that are utilized to formulate the design.

Process Optimization

Process optimization is the primary weight and space saving technique. Typical offshore development plans start work on topside facilities process and utility design while the reservoir modelling is proceeding. Reservoir data such as: GOR, gas composition, produced water rate, etc., are known to change with time but design cannot proceed unless a basis can be established. Decisions must be made, and the uncertainties accounted for, by allowing for a design safety factor.

Processing the produced oil and gas offshore requires some or all of the following systems:separation of the gas, oil condensate, and water phases;heating/cooling for wax/hydrate prevention, stabilization, storage, etc.;gas conditioning to meet pipeline dewpoint requirements;produced water treatment;gas compression for injection/export; andseawater treatment/injection.

Commercial computer program packages are now available to simulate process design. These programs generally follow a building block approach and were originally developed for the chemical process industries but can very easily be adapted to simulate the oil/gas production process. The program is set to perform a heat and material balance for the desired process flow scheme to deliver the required stabilized crude or conditioned gas.

Optimization is achieved by multiple simulations with different temperatures, pressures, number of process units (e.g. separation stages, heaters, coolers) to fulfill the following major objectives: