Abstract :
As a result of Mobile Offshore Drilling Unit (MODU) temporary mooring failures during mainly hurricanes Ivan in 2004 and Katrina and Rita in 2005, the need for new and improved anchor technology is ever so present. Currently, self-deployed high holding capacity (HHC) drag embedment anchors are widely used for catenary mooring systems. The majority of these mooring systems that failed during the storms were a result of anchor slip due to either high uplift or out of plane loading scenarios. Drag embedment vertically loaded anchors (VLA) require substantial vessel bollard pull and storage capacity for the installation wire. The suction caisson is currently the anchor of choice for a taut-leg system due to installation experience and the ability to accurately calculate holding capacity [1]. Still, localized structural failure can occur on suction piles due to out of plane loading. Suction pile fabrication and installation logistical costs are among the foremost reasons for new interest in a more efficient anchoring solution. The offshore industry is seeking a relatively small sized anchor that offers high capacity, high uplift, and genuine out of plane loading capabilities with reduced overall installation time. Reducing risk to subsea assets and improving the reliability of the mooring system is a core objective. Typically, in the case of a mooring failure, the probability of dragging anchors over pipelines is higher than the probability of a MODU colliding with another surface facility. Therefore, the mooring failure needs to occur at the rig side of each mooring leg before exceeding the anchor\´s capacity. To accomplish this mission, the anchor must be capable of maintaining sufficient capacity at high uplifts with any pull direction 360deg around the foundation. This paper will present the newly developed OMNI-Max Anchor. The OMNI-Max is a multi-directional, self-inserting, gravity-installed anchor. The OMNI-Max Anchor features an extended, swiveling mooring attach- ment arm that forces the anchor to "key" itself and dive deeper into stronger soils to find the required capacity. The OMNI-Max is installed under its own weight when released from a pre-determined height above the seafloor. The objective of this paper is to present an overall summary of the developmental steps of the OMNI-Max Anchor including laboratory testing data, full scale field testing data, and current behavioral prediction capabilities. Another conflicting topic in industry at the moment is the ability to place synthetic mooring components in the mud. During the full scale OMNI-Max Anchor field testing, two different High Modulus Polyethylene (HMPE) rope constructions, one of which saw significant normal progression under the mud-line while under load were analyzed. Visual inspection results suggest that with the proper construction and filter barriers in place, synthetic moorings in the mud can be an acceptable practice. The main topics regarding the development of the OMNI- Max Anchor offered in this paper are as follows. ldr Anchor Purpose / Function ldr Anchor Features / Advantages ldr Installation / Recovery Methodology ldr Laboratory Testing ldr Behavioral Predictions ldr Field Testing ldr Mud-Rope Technology.
Keywords :
marine vehicles; oceanographic techniques; offshore installations; HMPE rope constructions; High Modulus Polyethylene; MODU temporary mooring failures; Mobile Offshore Drilling Unit; OMNI-Max; anchor development; anchor slip; anchor technology; catenary mooring systems; high drag embedment anchors; hurricane Ivan; hurricane Katrina; hurricane Rita; mud; offshore industry; storms; suction caisson; suction pile; swiveling mooring; vertically loaded anchors; vessel bollard pull; Costs; Drilling; Fabrication; Hurricanes; Laboratories; Pipelines; Storms; Testing; US Department of Transportation; Wire;
