Effective riser tension: Fact or fiction ///
The author, with 44 years of industry experience, analyses complex oilfield practices using elementary physics. When a conflict with these basics is evident, he points that out so that improved practices can be developed. This second article – following “Important basic facts regarding riser tension and mud weight,” World Oil, August 2001 – also deals with a complex subject – riser analysis – in an effort to dispel commonly held beliefs that do not comply with elementary physics.
Effective tension. The physical model: For more than 30 years, analysts have used, as a basis for fundamental forces on risers, the concept illustrated in the accompanying figure. The drawing shows: A) a straight riser loaded with heavy mud; B) the same riser with a slight displacement due to a temporary eddy current or temporary vessel excursion; and C) the same riser with a large displacement due to postulated internally generated forces from the hydrostatic pressure of the mud. Casual examination indicates that the side of the riser to the right is longer than the other side of the risers in the other two scenarios. Thus, it seems plausible that this longer side would have more area than the other side.
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