Analysis of Riser Measurements in the North Sea

Abstract

Riser measurements in the field have provided a variety of data collected from several locations in the North Sea. Data were obtained by means of instrumented riser joints installed in both a 24-in. and a 16-in. drilling riser. Bending moments in the riser, riser tensions, motions of the semisubmersible, and wave heights were recorded simultaneously. The measurement program was aimed at verifying predictions from theoretical riser models in the typical regions of riser response; namely, the wave-active zone at the top, the "boundary layer" at the bottom, and the riser main section in between. In this paper attention is focused on the data obtained for riser response in the wave-active zone. Measured results are compared with theoretical predictions based on both analytical solution methods and numerical time-domain simulation techniques. In particular, the relationship between the standard deviation of riser bending response and significant wave height is discussed, as is the probabilistic nature of riser response. It is concluded that standard deviations of measured bending moment response agree well with theoretical results. The probability distributions of measured response were found to be non-Gaussian and consistent with theoretical predictions based on Morison-type wave loading.