Selecting Umbilicals for Control System Perfomance.
Authors: Kovit S. 
Published: October 2008

This paper provides qualitative discussions and quantitative performance estimates to define the relationship between the size, material and length of umbilical lines and the perfo rmance of common types of subsea production control systems.

Since performance is also a function of other parameters such as control fluid characteristics, platform and field geometries and the characteristics of the controlled functions; these are also considered in order to provide a more complete overview.

INTRODUCTION

Many new offshore projects require the consideration of greater depths, longer umbilicals and more controlled functions than those common in the past. Further, most companies are striving to reduce the time required to complete such projects, As a result, the preliminary selection of umbilicals has become more critical, but must often be accomplished without performing a detailed hydraulic analysis.

The performance estimates of this paper, in conjunction with the associated discussions are intended as an aid for such selections.

It should be noted, however, that this paper is not intended as an alternate to a detailed analysis during the final design phase of the project, since such an analysis is essentisl to insure that all of a specificproject's unique feawes and needs are fully addressed.

Further, it should be recognized that this paper is limited to only one aspect of umbilical selection, performance; but that other factors such as ease of deployment, fluid compatibility, impact on interfaces, etc., must also be considered during the selection process.

METHODS

If an empirical selection aid is to be used, it must incorporate a wide enough range of parameters ad their values to encompass most applications, but not include so much data that it becomes cumbersome to use.

Accordingly, the first step in the preparation of this paper was to identify the potentially critical parameters and the associated ranges of values which would encompass most applications.

The second step was to select the combinations of parameters and values for which performance estimates would be derived. Selection w based on both the sensitivity of performance (and thus umbilical selection) to variations within a parameter's range,' and also the frequency with which specific values within the range may occur. (Sensitively was based on analysis, and frequency of occurrence was based on experience.) Specific reasons for data point selections are discussed in greater detail in subsequent paragraphs.

Finally, quantitative performance estimates for the selected combinations of parameter values were derived. All of the quantitative performance estimates presented in this paper were derived byanalysis using proprietary methods and programs. number of representative estimates were then selected and reestimated using a commerciallyavailable program.

(A total of 13 estimates were compared. One varied by 41% two by 15 to 250A, and the remaining nine by less than 15%.)

PARAMETERS AND VALVE RANGES; GENERAL

System Type

Virtually all production control systems deployed in recent years have been of the Direct Hydraulic, Piloted Hydraulic or Electro hydraulic types. Accordingly, this paper was limited to these threetypes of systems.