API RP 95F:2006 pdf download
API RP 95F:2006 pdf download.lnterim Guidance for Gulf of Mexico MODU Mooring Practice-2006 Hurricane Season.
4 Mooring Design Criteria
4.1 CURRENT DESIGN CRITERIA
API RP 2SK 3rd Edition (2005) provides the basis for mooring design in the Gulf of Mexico for both MODUs and permanent installations. Appendix I contains a listing of key MODU mooring design parameters extracted from API RP 2SK.
4.2 RECOMMENDED MODIFICATIONS FOR GULF OF MEXICO MODU MOORINGS
4.2.1 Design Environment Return Period
For operations during the hurricane season. the design environment return period should be established from the following principIes:
• The return period should not he less than 10 years for the design of any mooring system based on site-specific metocean study
• A minimum 1-minute wind speed of M knots shall be used even if site-specific studies indicate a lower value
• In the absense of site-specific data, the environmental parameters presented in Section II shall he used
• Data used in prepairing site-specific metocean parameters shall he inclusive of weather information for the period 1950 through 2005
• A site specific assessment as described in Section 5 shall be conducted for the specific drilling operation and loaction. Mitigation strategies should be considered during the design of the mooring system
4.2.2 Anchor Capacity
Anchor holding capacity (for all types of anchors) shall he considered in the design of the mooring system. Anchor selection should be based upon capacity, availablity, and protential to minmize damage to subsea infrastructure should an anchor failure occur in condition such as:
• A marine installation such as a pipeline, which lies in the dragging path between the anchor and the MODU
• A mooring line that crosses another mooring line
• Density or importance of seafloor or water column infrastructure merits a higher safety margin
Unless site-specific soil data is available, upper and lower bound soil conditions shall be considered.
5 Site-Specific Assessment
5.1 ASSESSMENT
The probablity and consequences of a MODU losing station when operating at any location within the US Gulf of Mexico should be assessed. The intent of the assessment process is to identify the characteristics of the area near the drilling operation, options related to mooring component selection and mooring system design, and mitigation opportunities prior to the finalization of the design, installation, and operation of the mooring system. The resulting mooring system should lead to an acceptable risk scenario through minimization of potential consequences due to the loss of function in a mooring component or mooring system or the reduction in the probablity that a mooring component or the mooring system will lose function for a given MODU and operation.
In performing the assessment. one souce of infrastructure information is the Gulf of Mexico infrastructure map maintained by the Minderals Management Service.
5.2 ASSESSMENT REQUIREMENT
Risk is defined as:
Risk = [Probability of an adverse effect occurring] x [The consequences associated with that event]
The risk can be reduced either by reducing the probability of experiencing an incident, or by reducing the consequences of that incident should it occur. A fundamental part of reducing the risk associated with MODU operations is to ensure that all parties have a clear understanding of their “Risk Exposure.” These Guidelines contain two alternative approaches for assessing the mooring functionality and operation of any MODU location within the Gulf of Mexico.
5.2.1 Checklist Approach
The checklist approach is a simple evaluation methodology that allows the stakeholders to assess, on a relative basis, a level of risk the well operations represent. The intent of this approach is to be more conservative by comparison to a rigorous analysis. However, the checklist can bc completed with the routinely available information and data that would be expected to be available to the Operator and Drilling Contractor.
An example checklist approach is included in Appendix II. The data portion within the checklist describes the attributes of the location and the drilling vessel mooring system. These include, for example, the local surface and subsea infrastructure, the general location, the type of mooring system to be used, and the months that the drilling operation is planned.
