PLATFORM FOR OIL RECOVERY PREPAREDNESS

Abstract: The platform is intended for control of under water blow-outs and for prevention of oil spill. Existing techniques utilize various kinds of oil boomes which have appeared to be ineffective for under water blowouts. This platform is constituted by a semisubmersible steelstructure which main features are an enclosed pontoon (1), vertical side bulkheads (3), deck beam carriers (2) and deck hatch openings (5). The steel structure is kept in position by means of tugs or mooring wires and functions like and up/down turned "cup" where oil and gas can be accumulated internally in the "cup" and be discharged through a pipe system or hoses to a tanker kept in position near to the platform. The platform size and partly also its shape must be chosen to suit geographical, geophysical and climatical conditions in the planned blow out preparedness area. Besides positioning by means of tugs and mooring wires, the platform can be provided with propellers and dynamic positioning system. The platform can be used as an accomodation platform or for other applications when being in stand-by condition.

Description: DESCRIPTION. PLATFORM FOR OIL RECOVERY PREPARDNESS The platform is under normal condition intended for use as an accomodation platform, site workshop platform or similar, whereas in the case of an underwater blow out it can be used for control and recovery of oil and gas spill. When serving as an accomodation platform it can,* as an example, be located at an offshore construction " site. For recovery operations it will be evacuated and towed to the blow-out position. Here it can be positioned over an out-burst of oil and gas on the sea surface even if this is burning, in which case it will cause extinction of the fire, and the platform can be used for handling of a suitable ducting system for collection of oil and gas in the internal space of the platform. The main design features of the platform can be as in¬ dicated on the enclosed sketch fig. 1. The main buoy¬ ancy volume consist of a cylindrical pontoon, (1) , ar¬ ranged as a six angled polygone. Along the cylindri¬ cal pontoon's centerline are two parallell vertical bulkheads (3) , for the purpose of increasing vertical bending strength and provide means for stabilizing buoancy;; Main deck carrying beams (2) are arranged diametrically from each corner. The beams carry the pay load which may be placed within the dotted line (4) as well as the weight of the deck structure itself. In order to re¬ duce the effect of an enclosed air cushion during hea¬ ving,hatch openings are provided (5) . The openings are made equally in each of the triangular deck surfa- ces. With hatches closed and by blowing in air, there¬ by increasing the under deck pressure, the platform can be lifted in the water. Under transport this will strongly reduce drag and the platform can be selfpro- pelled by means of thrusters located for instance in the corners b, d and f where the b and d thruster can be used for propulsion and f thruster for steering. Dynamic positioning can be achieved conveniently with 3 compass-thrusters. Crane lifting gear with associ¬ ated wires through the centre of the platform offers a possibility for hoisting heavy equipment over the . sea bed without loss of stability. Normal draft "on location" will be midway between top of cylindrical pontoon (1) and top of vertical bulkheads (3) . This draft will give best movement characteristics in waves. Mooring forces will be higher than for conventional platform types. On the other hand the platform will to same extent act as a breakwater thereby leaving better possibilities for transfer of passengers by vessels on the lee side. This will be an alternative to helicopter transporta- tion. Lower height between water level and deck is also advantageous in this respect. Prime movers for electrical generators and thrusters can be placed in the cylindrical pontoon. This is favourable with respect to ..acoustical noise level in the accomodation area. Lifeboats can be located at the horizontal part of the main deck. Lowering can be arranged by a skid ar¬ rangement along the deck side. Under oil recovery actions an underwater ducting sys- tern can be lowered by means of wires through the platform centre or by means of wires symmetrically O PI arranged from thedeck beams. The platform is intended used for surface control of future underwater oil collection and ducting systems and as a surface reception reservoir for such systems. On smaller depths (approx. 50 ) it is assumed that a simple steel cylinder -set-down, over- a blow out point, thereby enclosing the oil and gas stream,may offer an effective duct up to the inner space of the platform, that is the space enclosed by the platform pontoon, side bulkheads and top deck structure. The oil being accumu¬ lated in this space can be discharged by means of a pipe system suitable for loading of tankers positioned near the platform, e.g. bow loader tankers. Due to the lagre volume of oil that can be kept within the platform before it tends to escape underneath the pontoon, long lasting interruptions of a discharging procedure will not cause oil spill trouble. The plat¬ form can be considered equivalent to a full loaded tanker with respect to fire and explosion hazard. The gas cushion pressure within the platform space has to be kept under control by means of a gas discharge pipe system. This may physically be the same pipe sys¬ tem being used for air cushion pressure control under transportation of the platform. in cases where the sea surface out-burst of oil and gas is burning, efficient extinction can be accomplished if the platform inner space is filled with inert gas be¬ fore towing over the fire. Exhaust gas form diesel engines belonging to the plat- form machinery can for this purpose be used as inert gas, as an alternative to inert gas produced on a near _ Oft.PI by support vessel and transferred via a- pipe/hose sys¬ tem. Under this phase of a recovery operation the plat¬ form deck can be oversprayed- by means of water monitors on an assisting fire fighting supply vessel, if this is necessary in order to avoid excessive heating of the steel structure. O P

Claims: PATENT CLAIM 1. Platform consisting of a semisubmersible movable steel structure provided with necessary towing, moo¬ ring and oil handling facilities characterized by a nearly ring or polygone shaped buoancy volume with a conveniantly chosen cross section shape and carry¬ ing a closed vented or partly open deck structure . 2, Platform as in claim 1, characterized by a super¬ structure intended for accomodation or storage fa¬ cilities. ° 3. Platform as in claim 1 characterized by provisions for fixation of concentrical telescope cylinders lo¬ cated vertically underneath the platform with the ability for lowering in the water. 4. Platform as in claim 1 and 3 characterized by a pipe 5 system arrangement for transfer of oil from the tele- scopical cylinder system to a pipe system internally in the platform with connections to a discharge line. 5. Platform as in claim 1, 2, 3 and/or 4 characterized by a closed deck and provided with a pipe system con- 0 nected to air blowers or inert gas blowers enabling the platform structure to be lifted on a cushion of air or inert gas for easying movement on the sea sur¬ face as well as providing means for effective extinc¬ tion of a surface fire. **-* 6. Platform as in claim 1, 2, 3 and/or 4 characterized by provisions for lowering of a pipe with slightly coned bottom end with facilities for attachement of wires providing possibility for positioning of the pipe over the blow out by means of tug boats while the pipe's top end is kept in position by fixation to a separate float body under water, at the water surface,or moored directly to the inner structure of the platform.

Inventors: AAGEDAL A
Applicants: AAGEDAL A
Application year: 1980
Main classification: B63B35
IPC codes: B63B35, E21B35, E21B43