The decision to develop a small (t100 million bbl) oil field in the U.K. sector of the central/northern North Sea requires a careful assessment of all aspects of the field-development plan-the reservoir model (reserves and production profile), capital and operating costs, and the current economic climate (oil price, interest rates, and tax regime). This paper describes the development of a knowledgebased software package that allows a "quick-look" assessment of the overall economics and risk profile associated with the development of small oil fields in this region. It is a modular system that uses a cost database, cost-adjustment algorithms, cash-flow analysis engine, and simulation procedures to integrate and analyze the impact of reservoir and production characteristics, costs [capital expenditures (Capex) and operating expenditures (Opex)], and economic factors on the decision to develop such a field. The production-system configurations considered by the system are (1) an unmanned wellhead platform tied back to a third-party platform for fluid processing/export; (2) a floating production, storage, and offloading system (FPSO) with oil export through a shuttle tanker and gas export through a tie-in to the existing North Sea gas pipeline infrastructure; and (3) a straight tieback from a group of subsea wells to a third-party platform for fluid processing/export.

The decision to develop a small (C 100 mmbbls) oilfield in the UK sector of the Central/Northern North Sea requires a careful assessment of all aspects of the field development plan:l the reservoir model (reserves and production profile)capital and operating costs, andl the current economic climate (oil price, interest rates, tax regime etc) This paper describes the development of a knowledge based software package that allows a 'quick look' assessment of the overall economics and risk profile associated with the development of small oilfields in this region. It is a modular system that uses a cost database, cost adjustment algorithms, cash flow analysis engine and simulation procedures to integrate and analyse the impact of reservoir and production characteristics, costs (capex and opex) and economic factors on the decision to develop such a field. The production system configurations considered by the system are:an unmanned wellhead platform tied back to a third party platform for fluid processing/export,an FPSO with oil export via a shuttle tanker and gas export via a tie-in to the existing North Sea gas pipeline infrastructure, anda straight tie-back from a group of subsea wells to a third party platform for fluid processing/export. INTRODUCTION It is generally agreed within the industry that it is extremely difficult to make generalised cost comparisons between alternative field development strategies. This is because the field characteristics vary so widely and have such a large and complex impact on the cost of development, and subsequent financial returns from the project. The software system described in this paper is designed to assist the engineer in this task. The region selected for analysis was the central and northern sectors of the UK sector of the North Sea. As of March 1995 (ref. I) this region has around 8.3 billion barrels of remainingrecoverable reserves. Of this total, 2.5 billion barrels are associated with fields that are either under development now or probably will be developed in the next 3 to 4 years. Unfortunately the majority of the undeveloped fields are quite small (typically around 30–40 million barrels) and geologically complex. System Architecture. The overall structure of the package is shown in Figure 1. The core of the system is the cashflow analysis 'engine'. This is a formatted spreadsheet whichallows a cashflow profile, NPV, NPVI and IRR for the project to be computed. This output is generated from the capex (with abandonment costs), opex, field production profile, and the appropriate tax rules and macroeconomic conditions, defined by the user. The spreadsheet is subsequently used to undertake sensitivity analysis, and generate spider diagrams for defined variables, and to allow Monte Carlo simulation for economic risk assessment.