Refinery complexity quantifies the sophistication and capital intensity of a refinery and has found widespread application in facility classification, cost estimation, sales price models, and other uses. Despite the ubiquity and widespread use of refining complexity, however, surprisingly little material has been written on its applications. The purpose of this review is to describe the primary applications of refinery complexity and some recent extensions. A secondary purpose of this review is to provide a framework that unifies complexity applications and suggests avenues for future research. Examples illustrate the applications considered.

Hydrocarbons are produced offshore in more than 50 countries and contributed about a quarter of world production c.2020, slightly more for crude oil and slightly less for natural gas. All oil and gas projects involve technical, environmental, economic, and financial challenges, but offshore projects are especially sensitive to these factors and often require advanced engineering and innovative technologies to commercialise. Offshore projects may be put on-hold for many years due to technology gaps or technology too expensive to implement. In this review, highlights of the world’s deepest, largest, longest, tallest, heaviest, most complex, most difficult, and most expensive wells, structures, pipelines, and subsea equipment are presented in offshore development and decommissioning projects. Key engineering considerations and technology innovations are described. The perspective of this review is broad and aimed toward the general non-specialist reader bringing many topics together for the first time.