Fundamentals of Subsea Drilling Operations (g: Floating Rigs 2 - Drill Ships)

Overview of Drill Ships vs. Semi-Submersibles

Cost Comparison

• The cost of operating a drill ship is approximately $1 million per day, while some semi-submersibles can be contracted for as low as $250,000 per day.

Introduction to Drill Ships

• UGI introduces the topic of drill ships and outlines the discussion points: merits and demerits, deck plans, rig movement modes, station keeping, examples of drill ships, and classification ratings.

Characteristics of Drill Ships

Stability Issues

• Drill ships are less stable than semi-submersibles due to their design; they experience significant movements from waves (roll, sway, surge). This instability poses challenges in rough weather conditions.

Advantages of Drill Ships

• A key advantage is the large deck space available on drill ships which allows for efficient operation far from shore by reducing logistics costs associated with supply vessels.

• They can store a substantial amount of supplies necessary for operations in remote locations without frequent resupply trips.

Concerns Regarding Drill Ship Operations

Maintenance and Crew Requirements

• Due to their vessel nature, drill ships require more maintenance and an experienced crew to manage operational challenges effectively. Environmental forces can significantly impact performance in adverse weather conditions.

Decision-Making Factors

• When deciding between a drill ship and a semi-submersible, factors such as environmental conditions (rough vs calm waters), logistics costs, and operational needs must be considered through a detailed cost-benefit analysis.

Operational Insights

Recommendations Based on Environment

• In very rough environments, it is advisable to use semi-submersibles; conversely, in calmer waters far from shore where logistical efficiency is paramount, contracting a drill ship is recommended.

Structural Overview of Drill Ships

Deck Layout

• The layout includes essential components like the moon pool location for drilling operations and various tanks designed for stability by managing fluid density within the ship's structure.

Station Keeping Mechanism

• The station keeping system utilizes dynamic positioning similar to that used in semi-submersibles; it involves constant communication with control systems to maintain position against current forces during operations.

Dynamic Positioning of Vessels

Overview of Vessel Positioning Systems

• Current forces, including wind and wave impacts, are continuously monitored. If a vessel deviates from its designated position, this information is relayed to the control system.

• The control system communicates with the thruster power system to correct the vessel's position. It activates the thrusters to nudge the rig back on location.

• This process is cyclical; once adjustments are made, feedback is sent back to the position and heading reference system confirming that the vessel has returned to its intended location.

Visual Representation of Drill Ships

• A visual representation of drill ships is provided, highlighting specific vessels such as "Discover Spirit" and "GSF RF Bar," illustrating their operational context in deep water environments.

• The speaker encourages engagement by asking listeners to share, like, and comment on the topic discussed.