Offshore fixed platforms
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The document discusses various types of offshore structures used in oil and gas production, including both floating and fixed structures. It describes jack-up rigs, drillships, semi-submersibles, tension leg platforms, SPAR platforms, FPSOs, jacketed platforms, compliant towers, and concrete gravity structures. Each structure type is suited for different water depths, from shallow to deep water. The document also provides details on properties, uses and advantages of different offshore structure types.
Offshore fixed platforms
- 1. SLBS ENGINEERING COLLEGE NAME – DEEPAK SOLANKI ROLL NO – 14ESLPE010 YEAR – IV YEAR SUBMITTED TO Dr. R.K. BAWA (ACADEMIC DIRECTOR)
- 2. CONTENTS 1. INTRODUCTION 2. OFFSHORE MOBILE DRILLING UNITS 3. PRODUCTION STRUCTURE 4. FIXED PLATFORMS 5. FLOATING PLATFORMS
- 3. INTRODUCTION TO OFFSHORE STRUCTURES & FIXED PRODUCTION PLATFORMS 3
- 4. OFFSHORE MOBILE DRILLING UNITS 4 Broadly classified into two types: 1. Shallow water drilling units: Self Elevating Jack-ups Drilling Barges 2. Deepwater drilling units: DrillShips Semi Submersibles
- 5. OFFSHORE PRODUCTION STRUCTURES 5 Broadly classified into two types: 1. Fixed structures that extend to the sea-bed: Fixed Steel (Jacket) Structure Fixed Gravity based Structure Compliant towers 2. Floating Structures that float near the surface: Tension leg platforms SPAR Ship shaped vessel (FPSO)
- 8. JACKETED PLATFORM 8 Space framed structure with tubular members supported on piled foundations. Used for moderate water depths up to 400 M. Jackets provides protective layer around the pipes. Typical offshore structure will have a deck structure containing a Main Deck, a Cellar Deck, and a Helideck.
- 9. JACKETED PLATFORM 9 Underwater, the piles are contained inside the legs of a “jacket” structure which serves as bracing for the piles against lateral loads. Natural period (usually 2.5 second) is kept below wave period (14 to 20 seconds) to avoid amplification of wave loads. 95% of offshore platforms around the world are Jacket supported.
- 10. CLASSIFICATION OF JACK-UPS 10 Can be classified into two basic categories: 1.Independent leg jack-ups 2.Mat supported jack-ups
- 11. MAT SUPPORTED & INDEPENDENT LEG JACK- UPS 11
- 12. PROPERTIES OF JACK-UP RIGS 12 Jack-ups can be either self-propelled, propulsion assisted, or non-propelled. The majority of jack-up rigs are non-propelled. The self propelled unit although very flexible, requires a specially trained crew of seamen as well as drilling team. Jack-ups have been built with as 14 legs and as few as 3 legs. As the water depth increases and the environmental criteria becomes more severe, we find that to use more than 4 legs is not only expensive but impractical.
- 13. SELECTION OF TYPE OF JACK-UP RIG When evaluating which type of jack-up to use, it is necessary to consider the following: 1. Water depth and environmental criteria 2. Type and density of sea bed 3. Drilling depth requirement 4. Necessity to move during hurricane season 5. Capability to operate with minimum support 13
- 14. INDEPENDENT LEGS (SELF ELEVATING) JACK-UPS: PROPERTIES 14 Consists of a triangular, sometimes rectangular, shaped box section barge fitted with three (sometimes four) moveable legs which enable the vessel to stand on the sea bed. Can work in water depths of upto approx. 120 meters (400ft) Transported in long sea passages using submersible heavy lift ships.
- 15. COMPLIANT TOWER Narrow, flexible framed structures supported by piled foundations. Has no oil storage capacity. Production is through tensioned rigid risers and export by flexible or catenary steel pipe. Used for moderate water depths up to 600 M. 15
- 16. CONCRETE GRAVITY STRUCTURES 16 madeFixed-bottom structures from concrete. Used for moderate water depths up to 300 M. Part construction is made in a dry dock adjacent to the sea. The structure is built from bottom up, like onshore structure. At a certain point , dock is flooded and the partially built structure floats. It is towed to deeper sheltered water where remaining construction is completed. After towing to field, base is filled with water to sink it on the seabed. Advantage- Less maintenance.
- 17. SUBMERSIBLE RIGS (DRILLING BARGES) 17 Submersibles are used mostly for inland, shallow water drilling up to 50 ft water depth. This typically takes place in lakes, swamps, rivers, and canals. Drilling barges are large, floating platforms, which must be towed by tugboat from location to location.