Automatic GPS subsidence measurements at offshore oil and gas production platforms, Ekofisk, North Sea

A fully automatic procedure is used to measure subsidence of oil and gas production platforms in almost real time. The procedure gives reliable measurements of the magnitude and rate of platform subsidence. These measurements are essential in determining platform safety, planning remedial work, and verifying subsidence models. Automatic GPS (global positioning system) satellite-based subsidence measurements are made continuously on platforms in the Ekofisk field area of the North Sea. Subsidence measurement systems base on GPS satellites are much cheaper to install and maintain than systems based on sea-bed pressure gauges. In addition, GPS based measurements are not subject to gauge drift. GPS measurements were coupled to oceanographic quantities, such as the platform deck clearance, leading to less complex offshore survey procedures.