A Novel Based Approach to Offshore Rig Positioning
Authors: Salman Mohamed , Fahmy Fadi 
Published: November 2012

Geoscientists routinely produce reports addressing the impact of proposed, platforms, rigs & barges in general on historical & prehistoric archaeological sites. These reports identify any conditions at the seabed or in the foundation zone where hazardous subsurface features or unstable soil conditions exist & provide guidelines regarding platform & drill site placements.

The principal aim is to reveal the general near-surface geological structure & indicate reflectors which may represent a change in soil characteristics &/or stratigraphy. This requires the correlation of seismic data with soil borings in the vicinity.

Accurate site surveying is crucial for proper rig positioning & to avoid Non-Productive Time. Mishaps with inaccurate rig positioning can cause disastrous consequences on the platform & impact the costs, more importantly, the lives of many.

This paper attempts to have a more sophisticated analysis on the rig move & rig positioning to ensure a 100% safe spud-in operation at all times. It uses qualitative risk based analysis on all the factors involved in the rig positioning which is a new creative approach that has never been done or thought of before.

During planning the positioning of an offshore rig on a high risk, high reward Gas tower many concerns were addressed. Some of the challenges were namely: a remote location but with close proximity to a residential island, movement history records are incomplete & future unconventional requirements need to be done. Furthermore, the particular area of this field is notorious for having numerous pin holes & punch-through woes due to historical barge/rig movements & due the soil being very muddy. Filling it up with sand bags is simply not a viable solution. To safely administer the rig positioning, several steps were taken to ensure a thorough and flawless approach:

Reviewing the various methods used for positioning a Platform &/or Rig on a new well location, making it ready for operation & performing accurate spud-in with Zero risk. Conducting feasibility studies, including optional checks for punch-through resistance and fatigue; such studies have resulted in a "Statement of Compliance Assessment" for specific locations & led to the idea of issuing preliminary "Certificate of Approval" Researching historical vessel movements that may have foundered in the area of interest conducted Scrutinizing advanced methods of rig surveying/positioning that allowed ADMA to develop a customized strategy & implement procedures to prepare these moves & guarantee Operation Safely & Quality delivery. This ultimately saved a huge amount of rig time & ample amounts of money. Writing up guidelines for sea-bed & sub sea-bed requirements to assess the suitability for locations. Reconnaissance of soil conditions is required in order to begin to establish design criteria for the following types of mobile rig and drilling operations: ✓ Jack-up rigs ✓ Anchoring of jack-ups for stand-off locations ✓ Conductor / casing setting for any rig type ✓ Initial spudding of drilling equipment, including guide-base stability, from any rig type ✓ Top-hole drilling

The normal & standard alignment of rig-tower orientation was not accepted by the contractor or the Insurance Company. It was maintained that with the current existing challenges, it is not possible to position the rig center to centre.

A detailed risk assessment, scaled orientation diagrams, diver's surveys, rig suitability assessment for positioning including

water depth, spud-can capacity, leg penetration/punch-through analysis, cantilever's relative positioning & reach have been done & examined. Conflicting records of diver's surveys with varying pin-hole numbers & relative orientations have prompted narrowing down the uncertainty and minimizing the magnitude of errors. Side Scan surveys, bathymetry surveys & sub bottom profiler have been acquired which greatly assisted in providing logical rationale behind the contradicting diver's survey reports. The safe & correct alignment between the rig & the tower had to be done at a relative 45deg angle to ensure all pinholes are avoided & the spud-in is done flawlessly & efficiently.