Recently the offshore industry has shown an increased interest in developing a competitive Dry Tree Semi (DTS) concept. Several DTS designs have been proposed by floater designers and many of them have been evaluated by Operators and Classification Societies. So far, no DTS has been selected as host platform for a deepwater field development project. A Dry Tree Semi can be utilized for both drilling and production, eliminating the cost of the MODU which can run at approximately USD 500,000 per day and higher for ultra deepwater fields. Once a discovery is made, the field is no longer dependent on the MODU market for drilling access. The DTS concept increases the potential for deepwater development, especially for marginal fields. The result is increased reserves and productions in the Gulf of Mexico. It is essential to ensure that proper qualification of the concepts and all systems/components with novel technology has been carried out, in order to establish the foundation for a safe and successful project implementation, and reduces potential risk on personnel, environment and property. This paper provides an overview of the current technology and the concepts needed to be matured in order to make the project ready from operators and Classification Societies perspectives. The paper will discuss the key technical challenges of the DTS concept in general and how to make this technology ready to implement. Key technical issues discussed in this paper are global performance of the floater, riser system and responses, tensioner capabilities as well as technology qualifications. The paper will make relevant comparisons with other competing floating systems like TLPs, FPSOs and spar units. The methodology recommended to be utilized for the evaluation of the DTS technology is based on Chevron's Project Development & Execution Process. Within this process there is a Technology Selection workshop where the necessary technologies for the project are identified and determined as, enabling or enhancing, engineering or technology, and " proven technology?? or " new technology??. The " new technologies?? are then evaluated through the Technology Qualification Process. The Chevron's TQ Process was co-developed with DNV and is based on DNV-RP-A203 " Qualification Procedures for New Technology??.
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Wind energy is one of the key renewable energy sources that will make a significant contribution towards the goals of clean energy around the world. The offshore wind energy industry is in a period of rapid growth, which results in a massive demand on the current supply chain. The large scale development demands specific installation and maintenance vessels. Various wind turbine installation vessels are being designed or constructed with a combination of new and existing technologies. There are specific challenges and design considerations related to this kind of vessels. Understanding the critical design parameters and considerations for various design concepts of WTI units are important for proper selection of design and technical standards in order to ensure a safe and robust design. The industry needs new design standards developed with synergy from well established offshore/maritime practices to provide guidance for this new vessel type to meet the high energy demand and to ensure high safety standards in the offshore wind energy sector. The paper first presents examples of various types of Wind Turbine Installation vessels that currently are being developed and then describe how DNV rules and standards address the specific challenges and critical elements for these various types of WTI units to ensure a safe and robust design. The paper then goes on to describes some of the key parameters and methodologies by which selection of these various design concepts can be carried out for a particular project/application.
The objective of this paper is to share lessons learned with the industry from a recent accident and provide a recommended procedure for evaluating airgap and possible horizontal wave impact loads for column-stabilized units operating in harsh environments. On 30 December 2015, when operating on the Troll field, a column-stabilized drilling unit, COSL Innovator, was hit by a steep wave that impacted directly on the forward port side of the deck box. This resulted in several damaged windows, one fatality, four injuries and structural damages to the front of the deck box. Following the accident, there is increased attention and concerns raised by some regulatory bodies for safe operation of semi-submersibles in harsh environment. In order to evaluate the adequacy of Class rule requirements and pertinent industrial design practices, DNV GL has investigated and analyzed the circumstances surrounding the accident. The conclusion from this work is that there is a need for improved guidelines for calculating horizontal wave impact loads on deck box structure if a column-stabilized unit is designed to operate with a negative airgap, together with improved methods for calculating the airgap with a prescribed annual probability of occurrence. DNV GL has developed "Offshore Technical Guidelines" (OTGs) that can be used to document compliance with classification rules stipulated in DNVGL-OS-C103 [1]. Development of these guidelines has brought a deeper understanding with respect to airgap and associated horizontal wave impact loads on column-stabilized units. This paper discusses the technical challenges related to airgap prediction and wave impact load calculation, provides the technical background and insight of recently released Offshore Technology Guidance OTG-13 [2] and OTG-14 [3], and suggests a way forward.
With Pre-salt area being a massive new offshore oil frontier, there is a high demand for deepwater floaters for both drilling and production. There are some unique challenges related to the ultra-deepwater (water depth beyond 1500m) and the Brazilian environment for the pre-salt area. Various floater concepts have been evaluated with specific focus for Offshore Brazil applications.This paper provides an overview of the current technology related to dry tree solutions as well as discussion of the pros and cons of various concepts. The paper also discusses some new concepts emerging in the industry attractive for Offshore Brazil.A dry tree solution has the advantage of direct access into reservoirs from the floaters. This allows the operators to drill, complete and workover the well directly from the same hosting unit. The result could be increased reserves and productions in Offshore Brazil as well as significant cost reduction. Proper validation of the concepts and technology qualification of all the systems/components associated with novel technology, establish the basis for a safe and successful project implementation while reducing potential risk to personnel, environment and property.DNV has established processes to systematically evaluate new concepts and new technologies, e.g. Approval in Principle (AiP) and Technology Qualification (TQ). A brief introduction to these processes is included in the paper and how they support the development of these new concepts.
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