Offshore operations well control

The basic principles of rotary drilling defined for onshore operations are also applicable to offshore operations. The primary difference offshore is that a stable, self-contained platform must be provided for the drilling equipment. Communication with a well through possibly thousands of feet of water provides for mechanical as well as procedural differences, primarily in well control. Onshore technology can be applied to offshore operations in many instances on bottom-supported rigs, but the use of floating vessels has resulted in the development of new technology tailored to the offshore environment. 

Offshore, well control equipment and associated operations present some differences from that seen and used onshore. In some instances onshore equipment can be employed, but the offshore environment generally dictates a modification of equipment and procedures. There are several different well configurations used offshore, often on the same well at different drilling intervals, and each configuration has specific well control procedures that should be followed. A well may be equipped with a surface blowout preventer stack a subsea blowout preventer stack, riser and diverter system a riser and diverter system with no blowout preventer a diverter only or a riserless system with no well control equipment. 

In the oil and gas industry, the term abandonment generally refers to the activities undertaken to remove the structures used to sustain oil and gas production after the production is ceased. The structures range from a few tonnes of steel on the seabed to a complete platform constructed from around 30000 tonnes of steel framework. The task of removal requires extremely detailed and careful planning as well as substantial resources. Explosives are very efficient tools for cutting steel underwater and have been the preferred choice of many offshore operators for over 40 years. Also explosives offer the flexibility of a single controlled cut or multiple simultaneous cuts for remote and safe toppling of very large structures [129]. 

Two articles by investigative reporters at the Wall Street Journal (WSJ) indicate the potential value of a more thorough approach to comparative analysis of performance indicators. The first, published shortly after the Macondo accident, found that for each 100 million hours worked offshore during the years between 2004 and 2009, U.S. operations incurred 4.84 worker fatalities, more than 4 times the European rate of 1.07 fatalities, and experienced 5 major losses of well control in 2007-2008, whereas 5 other major countries (Norway, United Kingdom, Australia, Canada, and the Netherlands), with about half as much drilling activities, reported no such incidents. ... 

RP T-6 Training and Quaiifications of Personnel in Well Control Equipment and Techniques for Completion and Workover Operations on Offshore Locations... 

A guide to the integrity, workplace environment and miscellaneous aspects of the Offshore Installations and Wells (Design and Construction, etc) Regulations 1996 Control of substances hazardous to health m fumigation operations... 

In harsh operational conditions environmental factors can affect the performance of DP which can lead to loss of the position control abiUty. For a Mobile Offshore Drilling Unit (MODU), loss of position without safe disconnection could result in critical damage not only to the well, but also to the subsea equipment. For an Offshore Support Vessel (OSV), loss of position could lead to colhsion with the nearby installation during operation or to damage to the subsea fadhties. In order to increase the safety and reliabiUty of a DP system, it is important to identify and quantify all influence factors and the way that they can affect the DP performance. For example bad weather condition is an effective factor on the position reference sensor or the local position reference system. Such operational conditions can vary from place to place and may have a dynamic nature in a specific location. Moreover, it is important to investigate safe recovery back to position, safe disconnection and reconnection when the loss of position is outside the safe operational range. 

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