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.

The Caesar-Tonga development in the Green Canyon Area in the Gulf of Mexico was the first application of steel lazy wave risers in the Gulf of Mexico, and it was the first such application tied back to a spar platform. Anadarko and co-owners completed the project on an aggressive schedule in which detailed design, procurement and preparation of the installation program progressed concurrently. Anadarko contracted Technip to perform the analysis and detailed design of these riser systems and, in light of the procurement schedule, the design team was required to refine the riser configuration and sizing early in the design program. This paper describes the strategy and methods employed in this successful riser design. The utilization of the steel lazy wave riser configuration was an enabling technology for tie-back of a high pressure subsea development to an existing host facility with vertical I-tubes rather than pull tubes. The design optimization process required due consideration for internal pressure, extreme storm, currents, wave fatigue, clashing, and installation loads. The complex configuration required several design iterations to satisfy the competing design requirements. A collaborative team environment was established with closely managed interfaces to progress the detailed design, procurement, fabrication and installation elements of this technologically challenging project. This technology may be used to enable tie-back of other high pressure subsea systems to deepwater floating hosts in the Gulf of Mexico. Introduction The Caesar-Tonga field development consists of four subsea wells tied back to the Constitution platform in the Green Canyon area. A dual flowline system links two drill centers to the host processing facility. The platform riser arrival configuration, combined with the high pressure requirements for the flowlines, created a major technical challenge for the project team. The team utilized steel lazy wave risers to bring the well contents from the seafloor to the host facility. This paper provides an overview of the design parameters, procurement program, and the installation campaign for the Caesar-Tonga riser systems. The Anadarko-operated Caesar project is a partnership among Anadarko, Shell, Statoil and Chevron for the development and production of reserves in the Caesar Unit. This unit was formed to combine the Caesar and the Tonga discoveries and includes Green Canyon Area Blocks 683, 726, 727, and 770. The Caesar-Tonga development is a unit formed to exploit several Miocene horizons. The initial discovery, Caesar, was made in Green Canyon Block 683 in 2006. The Tonga discovery occurred the following year in Block 726. The owners estimate that the field holds from 200 to 400 million barrels of oil equivalent. The project was sanctioned in 2009 and first production was achieved in March of 2012. These reserves will be produced through a subsea system that ties back to the Constitution spar. The dual flowlines are rated for a pressure of 12,700 psi. A pipe-in-pipe design was used to meet flow assurance requirements. Anadarko utilized their standard 15K trees and controls in this project. A depiction of the Caesar-Tonga Development is shown in Figure 1.

The decision to run fairings on drilling risers is critical in terms of the additional cost to run fairings versus downtime cost from suspended operations due to current conditions causing excessive flex-joint angles. Making an informed decision, enhanced by actual predicted current conditions for a drilling program, is a valuable capability in planning to maximize drilling uptime and minimize downtime costs.This paper presents an innovative model which has been developed as a rational decision tool for determining the fairing requirements to mitigate predicted loop current events for proposed drilling programs in the Gulf of Mexico.

Offshore production risers are generally designed considering a large margin of conservatism to account for the uncertainty in the design parameters and to ensure robust design. As the Oil & Gas Industry is advancing toward ultra-deepwater there may be a necessity to adopt new technologies and riser configurations to develop the field. Project teams may elect to quantify the degree of conservatism in the designs as an additional measure to improve confidence in the safe and reliable service over the life of the field. Such validation provides confidence in the design performed based on theoretical concepts and software predictions.This paper presents a novel approach that has been undertaken to validate the design of the Caesar-Tonga Steel Lazy Wave Risers (SLWR) tied back to the Anadarko Petroleum Company (APC) operated Constitution Spar located in the Green Canyon Area of the Gulf of Mexico. These risers represent the first application of the steel lazy wave riser technology in the Gulf of Mexico, and it was the first such application tied back to a spar platform.The procedure is based on the monitoring of motion and strain data measured at critical locations along the risers. The measured data is post-processed to identify significant riser motion events that occurred during the observation period. Met-ocean data during this time period is also evaluated to correlate back to the riser motion events. Vessel motions and current data corresponding to these identified events are used to drive a Finite Element (FE) model of the riser, and the corresponding riser motions and strains are calculated. The calculated motions and strains are compared with measured motions and strains to provide confidence in the design methodologies. The procedure as well as the results of the comparison between predicted performance and measured performance is discussed in detail in the paper. The procedure can be applied for design validation and performance and integrity assessment of newly-built or existing risers.