JNTU B.Tech IV OFFSHORE ENGINEERING Previous Question Paper (January/February - 2023 - R18)

A spar is a deep-draft, floating offshore structure used for oil and gas production in deep waters. It consists of a large-diameter vertical cylinder that extends deep below the water surface, supporting a deck at the top.

The concept relies on stability through a low center of gravity. By placing the center of gravity below the center of buoyancy, the structure achieves inherent stability, which is further enhanced by its deep draft that minimizes heave, pitch, and roll motions caused by wave action.

Exploratory drilling structures are mobile units designed to drill initial wells to determine the presence and commercial viability of hydrocarbon reservoirs. The primary types include:

• Jack-up Rigs: These consist of a buoyant hull with movable legs that can be lowered to the seabed. They are suitable for shallow water depths, typically up to 100-120 meters, where the legs provide a stable, fixed platform during drilling.
• Semi-Submersible Rigs: These are floating structures with columns connected to large submerged pontoons. By ballasting the pontoons, the unit is lowered to a depth that minimizes wave motion, making them ideal for deeper waters and harsh environmental conditions. They are held in position by mooring systems or dynamic positioning.
• Drillships: These are self-propelled, ship-shaped vessels equipped with a drilling derrick amidships. They offer high mobility and large storage capacity for equipment and supplies, making them highly efficient for exploration in deep and ultra-deep waters far from shore.