New Revision of Drilling Riser Recommended Practice (API RP 16Q)

Abstract

Since the Recommended Practice for Design, Selection, Operation and Maintenance of Marine Drilling Riser Systems (API RP 16Q) was first issued in 1993, the focus on drilling operations in deep water has significantly increased. With that evolution comes the need to reassess the way we design and operate such risers to ensure the safety and integrity of drilling risers designed and operated in deepwater environments. Under the auspices of the DeepStar program, substantial work was commissioned in 1999 that lead to the drafting of guidelines to address several issues not addressed within the existing RP. In a subsequent Joint Industry Project sponsored by DeepStar and in collaboration with API, MCS International has brought forward this work to produce a major update of RP16Q and an associated Technical Report (API 16TR1). This paper describes the contents of the revised standard, in terms of the substantive changes from the 1st edition and the significant additions drafted to broaden its applicability to deepwater drilling risers. The revision of API RP 16Q, which is proposed for submission as an ISO Standard, incorporates the new guidelines developed under DeepStar and supplements this with additional guidelines to address other issues. Guidelines developed for DeepStar have been incorporated in the areas of riser analysis methodology, riser operations and riser integrity. Several additions to the existing RP16Q text cover analysis methodology associated with soil structure modelling, coupled analysis, drift-off analysis, weak point analysis and other issues. Additional guidelines have been included which relate to operational procedures and riser integrity issues and these are described by the paper. This first substantial revision of API RP 16Q provides the offshore industry with an improved recommended practice that has been substantially extended to address issues associated with the design and operation of deepwater marine drilling risers. Background DeepStar Phase IV Under the auspices of the DeepStar program, substantial work was commissioned during 1999 and 2000 by the DeepStar Drilling Committee 4502. The work was designed to address several issues associated with the design and operation of deepwater drilling risers that were not explicitly dealt with in the existing text of API RP16Q. The deliverables of this work were a set of guidelines and worked examples that provided sufficient detail to supplement the existing text of API RP16Q and provide additional guidance for deepwater drilling in water depths up to 10,000ft. This work, delivered by several contractors, lead to the drafting of "Deepwater Drilling Riser Methodologies, Operations and Integrity Guidelines" in February 2001 as an integrated collation of all of the Phase IV DeepStar work. The authors and the other contractors produced and issued several documents to DeepStar that supplement and sometimes complement the text of the existing API Drilling Riser Recommended Practice [RP16Q]. These guidelines were intended to ‘modernize’ the existing RP and bring it into the current era of ultra-deepwater drilling. A breakdown of the workscopes associated with the drafting of these guidelines is presented in Figure 1.

Top angle control and vibration reduction of flexible marine risers

“…4. The control action reduces the angle to a near zero magnitude which adheres to the recommendation in [4]. The riser profiles for controlled and uncontrolled responses under excitation were overlaid for different time instance and shown in Fig.…”

“…(4) and (5) represent zero deflection and a torque being applied at x = L respectively. Remark 1: The input torque τ (t) at the upper riser end can be modelled as a boundary condition (5) in relation to the dynamics of the system.…”

“…Another important consideration is the angle limit for the upper and lower end joints. The American Petroleum Institute recommends that the mean lower and upper joint angles be kept within two degrees in drilling operations [4]. Hence, vibration reduction to reduce bending stress and control of the riser angle magnitude within limits are desirable for preventing damage and improving lifespan.…”

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“…Li et al [6] studied the stability of a composite subsea wellhead, considering the effects of cement, waiting time, and riser joint end-resistance force. Kavanagh et al [12] highlighted the analysis guidelines for modeling approaches of underwater wellhead systems and nonlinear subsea shallow soils. Reinås et al [13] used a fully developed fatigue fracture approach based on finite element method (FEM) analysis to calculate the residual ultimate load capacity of a typical North Sea subsea wellhead.…”

“…The main function of the BOP is to shear the drill pipe and/or inner casing inside the riser main tube and close off the wall opening to prevent a blowout occurrence or to prepare for an emergency disconnect. The LFJ is capable of not only releasing bending moments caused by upper riser devices but also of Xingkun Zhou, Jinghao Chen, Numerical investigations on the effects of seabed shallow Zhengguang Ge, Tong Zhao, Wenhua Li. soils on a typical deepwater subsea wellhead system 4 limiting a certain rotation angle (usually 2 to 4 degrees) [12,14,26] to prevent excessive string bending during normal drilling operations.…”