A flare or vent disposal system collects and discharges gas from atmospheric or pressurized process components to the atmosphere to safe locations for final release during normal operations and abnormal conditions (emergency relief). In vent systems, the gas exiting the system is dispersed in the atmosphere. Gas-disposal systems for tanks operating near atmospheric pressure are often called atmospheric vents or flares, and gas-disposal systems for pressure vessels are called pressure vents or flares. A flare or vent system from a pressurized source may include a control valve, collection piping, flashback protection, and a gas outlet. A scrubbing vessel should be provided to remove liquid hydrocarbons. The actual configuration of the flare or vent system depends on the hazards assessment for the specific installation. RP 520, Part 1, Sec. 8, and RP 521, Secs. 4 and 5, cover disposal and depressuring system design.
Topside payloads range from 5 to 50,000 tons, producing oil, gas, or both. A vast array of production systems is available today (see Figure 1). The concepts range from fixed platforms to subsea compliant and floating systems. In 1859, Col. Edwin Drake drilled and completed the first known oil well near a small town in Pennsylvania, U.S.A. This well, which was drilled with cable tools, started the modern petroleum industry.
The majority of offshore fields have been developed with conventional fixed steel platforms. One common feature of fixed steel structures is that it is essentially "fixed" (i.e., it acts as a cantilever fixed at the seabed). This forces the natural period to be less than that of the damaging significant wave energy, which lies in the 8- to 20-second band. As the water depth increases, these structures begin to become more flexible, and the natural period increases and approaches that of the waves. The consequence of this is the structure becomes dynamically responsive, and fatigue becomes a paramount consideration.
As oil and gas production moves into deeper water, the cost of surface production platforms becomes prohibitively high. The industry has found that surface facilities must be kept to a minimum and shared by satellite fields to be commercial. Subsea processing is a key toward a cost-effective, "hub-and-spoke" development (Figure 1), allowing the industry to operate successfully in deeper water. Subsea processing refers to the separation of produced fluids into gas and liquid--or gas, oil, and water--for individual phase transport and disposal (in the case of water). The liquid stream can be pumped to a central facility for final processing.
There are different definitions of what is Well Integrity. The most widely accepted definition is given by NORSOK D-010: "Application of technical, operational and organizational solutions to reduce risk of uncontrolled release of formation fluids throughout the life cycle of a well." Other accepted definition is given by ISO TS 16530-2 "Containment and the prevention of the escape of fluids (i.e. Well Integrity is a multidisciplinary approach. Therefore, well integrity engineers need to interact constantly with different disciplines to assess the status of well barriers and well barrier envelopes at all times.
Figure 1.6--The Baldpate Compliant Tower is one of the tallest free-standing structures in the world – Empire State Building (right) for comparison (Web Photograph, Amerada Hess Corp., New York City). Figure 1.9a--Worldwide fleet of installed and sanctioned semisubmersible FPS (courtesy of BP). Figure 1.9c--Worldwide fleet of installed and sanctioned spars (courtesy of BP). Figure 1.10--Semisubmersible FPS planned for the Thunder Horse field (courtesy of BP). Figure 1.11--Alternative proven technology field development options (courtesy of BP). Figure 1.12--Subsea production trees used in conjunction with a fixed jacket structure (Intec Engineering, Houston).
Decommissioning involves the safe plugging of the hole in the earth's surface and disposal of the equipment used in offshore oil production. Decommissioning is a rapidly developing market sector in the petroleum business, with major potential and major risks. It is a source of major liability for counties, operators, contractors and the public and it must be understood if it is to be managed cost effectively. Offshore decommissioning involves 10 steps: project management, engineering, and planning; permitting and regulatory compliance; platform preparation; well plugging and abandonment; conductor removal; mobilization and demobilization of derrick barges; platform removal; pipeline and power cable decommissioning; materials disposal; and site clearance. Each step is discussed below.
Although variables that affect kick-killing do not necessitate a change in the basic procedural structure, they may cause unexpected behaviors that can mislead an operator into choosing the wrong procedure. The one-circulation method is used to demonstrate the effect of these variables. The influx type entering the wellbore plays a key role in casing-pressure behavior. The influx can range from heavy oil to fresh water. The most common is gas or salt water; each has a pronounced casing pressure curve and different downhole effects.
Because UBD involves working on a live well, a hazard operational ("hazop") analysis is required for the full process. To this end, a flow chart is created that shows all the elements in the UBD process. Using the diagram (Figure 1), each element can be analyzed for input and output and the diagram has also been used to good effect to ensure that all items of an UBD system are reviewed during the hazop. It also allows procedures and documentation to be reviewed for all parts of the UBD system. The drilling liquid system (1), the gas system (2), and the reservoir characteristics (3) specify the well system (4).