Hugh Banon

Effect of Moonpool Hydrodynamics on Spar Heave

A Spar is a deep draft platform for oil and gas production and drilling operations. One of the features of the Spar platform is the presence of a moonpool (or centerwell) inside the cylindrical hull structure. A unique aspect of the moonpool in Spars is the presence of partial closure plates at the bottom. The seawater goes in and out of the moonpool though these bottom closure (or guide) plates. Depending on the design of a Spar (e.g., the number of risers), typical period of moonpool vertical oscillation can be close to the peak of extreme seastate spectra. The Spar heave motion is thus coupled with the moonpool water oscillation and presents itself as a two oscillator problem. The complex behavior of moonpool and Spar heave interaction is largely ignored in current practice, via conservative assumptions (this is also due to lack of a mathematical model). A new model describing this interaction between moonpool water oscillation and the Spar heave has been developed in this paper. The results of the new model highlight the importance of the moonpool hydrodynamics in predicting the heave motions of Spars.Copyright

Determination of Riser Tensioner Properties From Full-Scale Data

Tensioners are used for supporting various kinds of production and drilling risers on offshore platforms. All permanent production facilities (such as TLP’s and Spar’s) have employed tensioners to support their dry tree production risers. The key design parameters for the tensioners design are stiffness, stroke and friction properties. Full scale onshore testing of production riser tensioners to determine tensioner properties is difficult due to the magnitude of the loads and pressures required for typical deepwater risers, thus designers frequently rely on theoretical values or small scale tests. This paper presents a determination of riser tensioner properties from full scale offshore observations made on the Holstein Spar production facility during 2005 hurricance season. The paper presents a model for the tensioner system that relates the properties needed by platform and riser designers to the physical tensioner systems. The methodology and results from extraction of parameters from the full scale data is presented. The results presented in this paper will provide a better insight to the designers of such systems.Copyright

TLP Reliability Study Based on the Limit State of Tendon Unlatching

The tendons of a tension leg platform are critical structural components in maintaining the system integrity. A common tendon design limit is associated with the minimum tendon tension. Most TLP reliability studies in the past defined the minimum-tension limit state as the loss of tendon tension. However, studies have shown that temporary tension loss at a corner of a TLP will not necessarily jeopardize the system integrity if the tendon is allowed to stroke down during a loss of tension event. Hence, we define the limit state associated with minimum tension event as the down-stroke where the tendon unlatches itself. An approximate method is proposed in this study to evaluate the probability of tendon unlatching. Sensitivities to the key assumptions are also investigated.© 2005 ASME