Chinmoy Pathak Choudhury_LTV Internship report

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  1. 1. ANALYSIS OF A TYPICAL OFFSHORE BRIDGE CONNECTING ADJACENT OFFSHORE PLATFORMS SUMMER INTERNSHIP AT L&T VALDEL ENGINEERING LIMITED SUBMITTED BY CHINMOY PATHAK CHOUDHURY 27th JUNE, 2012 26th JULY, 2012 DEPARTMENT OF CIVIL ENGINEERING ASSAM ENGINEERING COLLEGE, JALUKBARI GUWAHATI 781013
  2. 2. Table of Contents 1. INTRODUCTION 1 2. EXPLORATION, DRILLING AND EXTRACTION 2 3. OFFSHORE DEVELOPMENT 5 4. TYPES OF OFFSHORE STRUCTURES 7 5. PRELIMINARY REQUIREMENTS FOR DESIGNING 11 6. TYPES OF LOAD ON PLATFORM 12 7. INSTALLATION OF FEXED STEEL STRUCTURES 13 8. TYPES OF ANALYSIS 15 9. LOADOUT ANALYSIS 17 10. LIFT ANALYSIS 19 11. TRANSPORTATION ANALYSIS 22 12. DESIGN CONSIDERATIONS 26 13. APPENDIX A - PLATFORM POSITIONING AND BRIDGE SPECIFICATIONS 27 14. APPENDIX B - CODES, STANDARDS AND REFERENCE DOCUMENTS 34 15. APPENDIX C - DESIGN CALCULATIONS AND COMPUTER MODEL FOR IMPLACE AND LIFT ANALYSIS 36 16. APPENDIX D - BASIC LOADING AND LOAD CASE SUMMARY 45
  3. 3. P a g e | 1 Chinmoy Pathak Choudhury Assam Engineering College, Jalukbari Guwahati - 781013 1. INTRODUCTION Oil a d gas a e o side ed to e a o g the o ld s ost i po ta t esou es. The oil a d gas industry plays a crucial role in driving the global economy. Oil is not only an essential raw material to over 2,000 end products but also useful for transportation, heating, electricity and lubrication. It supplies a out 5 % of the o ld s total e e g e ui e e ts. Deep ate oil ese es a e e pe ted to play an important role in the future of the world oil and gas energy. So, intensive activities for exploration and exploitation of the oceans, especially the growing demands for hydrocarbons led to the development of wide range of offshore structure during the last decades. Throughout the world, estimated proved reserves of petroleum have been reported to be about 1.29 trillion barrels of oil and about 6,110 trillion cubic feet of natural gas. More than 90 percent of reserves were based on land or near shore. About 90 countries produce oil, although a few major producers account for the bulk of world output. Oil reserves are heavily concentrated in the Middle East while gas reserves in the Russian Federation. The variety of Offshore structure concerning the function, size, geometrical configuration and material selection as well as the variability of the environment factors complicate the development of a unique design procedure. Therefore, a separate investigation of the interaction between the actual structure and the environment is necessary. On the other hand, Offshore structures must have an acceptable margin of safety during all phases of their life i.e. construction, transportation, installation, operation, and retrieval. The most adverse conditions during the entire life of the structure have to be taken into consideration in its design process.
  4. 4. P a g e | 2 Chinmoy Pathak Choudhury Assam Engineering College, Jalukbari Guwahati - 781013 2. EXPLORATION, DRILLING AND EXTRACTION The petroleum industry comprises of upstream and downstream sectors. The Upstream sector involves exploration, development and production of oil and gas; Downstream sector covers transport, refining petrochemicals, distribution and retail. Oil and gas consists of the processes and methods involved in locating and discovering potential sites for oil and gas drilling and extraction. This is the first stage of oil and gas production. Production Platforms may have separate drilling platforms nearby while large production platforms may have their own production drilling equipment. The different forms of drill rigs are as follows 2.1. Jack-up Drill Rig A Jack-up drill rig or a self elevating unit is a type of mobile platform that consists of a buoyant hull fitted with a number of movable legs capable of raising its hull over the surface of sea. These platforms are designed to move, under its own power or using tugboats, from place to place and then anchor themselves by deploying the legs that are driven into the sea bed using motors. Then the derrick slides outward into position and the drilling operation begins. There are two ways to mount the drilling equipment on the hull which can be further categorized as Cantilevered Type - This is the most popular design of jack-up platform. The drilling derrick is mounted on two arms, or cantilevers, that extend away from the platform and over the sea surface. This design provides the derrick with a large range of motion and therefore can operate in a considerable area at some instance of leg positioning. Fig 1. A Model of Cantilevered type Jack-up Drill Rig Slot-Type - In a slot-type jack-up, the platform has a slot through the floor of the hull. A drilling derrick is positioned over it during operations. When the platform moves to another location, the derrick is lifted above it before the transportation operation is started.
  5. 5. P a g e | 3 Chinmoy Pathak Choudhury Assam Engineering College, Jalukbari Guwahati - 781013 2.2. Semi-submersible Drill Rig These are rigs having legs of sufficient buoyancy to the structure to float but of weight sufficient to keep the structure upright. It can be moved from place to place and can be ballasted up and down by altering the amount of flooding in buoyancy tanks. They are generally anchored by cable anchors during drilling operations. Semi-submersible drill rigs are the most stable of any floating rig and chosen mainly for harsh conditions because of their ability to withstand rough waters. Based on the way the rig is submerged in the water, there are two main types of semi-submersibles. Bottle-type It consist of bottle-shaped hulls below the drilling deck that can be submerged by filling the hulls with water. Column-stabilized Here, two horizontal hulls are connected via cylindrical or rectangular columns to the drilling deck above the water. Smaller diagonal columns are used to support the structure. Fig 2. Semi-submersible Drill Rig Fig 3. A 3D model of Semi-submersible Drill Rig
  6. 6. P a g e | 4 Chinmoy Pathak Choudhury Assam Engineering College, Jalukbari Guwahati - 781013 2.3. Drillships It is a marine vessel that has been fitted with drilling apparatus. It is most often used for exploratory offshore drilling of new oil or gas wells in deep water but can also be used for scientific drilling. It can conduct drilling operations upto 2500 m deep. Drillships have extensive mooring or positioning equipment, as well as a helipad to receive supplies and transport staff. Drillships are differentiated from other offshore drilling units by their easy mobility. However, they are susceptible to being agitated by waves, wind and currents. Fig 4. A Typical Drillship Fig 5. A 3D Model of Drillship
  7. 7. P a g e | 5 Chinmoy Pathak Choudhury Assam Engineering College, Jalukbari Guwahati - 781013 3. OFFSHORE DEVELOPMENT In Offshore development, different types of structures are used depending on the size and water depth. Typical Offshore platforms consist of a substructure called Jackets supporting processing facilities referred to as Topsides. Such Offshore platforms are installed offshore in water depths ranging from 8 m to 600 m. Offshore platforms can be classified as below based on their purpose: 1. Wellhead Platforms - It is an offshore structure which is an assembly of fittings, valves and controls providing facilities for the extraction of crude oil, gas and water composite from the sea which is then transported by risers (pipelines) to the process platform. It stands either on a tripod (3 legged) or a 4 legged jacket arrangements. The wellhead operation can be conducted either on the process platform or underwater which feeds into the Process plants from where the crude oil and gas composites are sent into separators. 2. Process platforms - It is a processing plant which generally stands on a 6 legged or 8 legged jacket arrangements located on the sea which partially processes the crude oil and gas before exporting the hydrocarbon onshore by means of pipelines or are stored so that it can be loaded on tankers for transportation to onshore production facilities. Generally, there are 3 levels of a Central Processing Plant viz. Cellar, Mezzanine and Main Deck. 3. Living Quarters Platforms It is built to house personnel working on those Offshore platforms. A typical Offshore complex consists of Process platforms and several Wellheads underwater connected to the process platforms by risers or pipelines. Fig 6. A Typical Process Complex
  8. 8. P a g e | 6 Chinmoy Pathak Choudhury Assam Engineering College, Jalukbari Guwahati - 781013 Offshore structures can be classified into 3 broad categories based on their foundation concepts as 3.1. Bottom Fixed Structures Jacket Compliant Tower Gravity based Structures 3.2. Floating Type Structures Tension Leg Platforms Floating Production, Storage and Off-loading (FPSO) Floating Production Systems (FPS), etc. 3.3. Subsea Systems Each type of platforms carries some advantages and disadvantages. However, the foundation concept selection depends upon various factors such as depth of installment, purpose of installment, Topside information, Intensity of Environmental Loads, etc.
  9. 9. P a g e | 7 Chinmoy Pathak Choudhury Assam Engineering College, Jalukbari Guwahati - 781013 4. TYPES OF OFFSHORE STRUCTURES 4.1. Bottom Fixed Structures Fixed Platform (FP) is a platform extending above the water surface and supported at the sea bed by means of piles, spread footings, etc. It consists of a jacket (a tall vertical section made of tubular steel members) with a deck placed on top, providing space for crew quarters, a drilling rig and production facilities. The fixed platform is economically feasible for installation in water depths upto 500 m deep. Compliant Tower (CT) consists of a narrow, flexible tower and a piled foundation that can support a deck for drilling and production operat