Fundamentals of Subsea Drilling Operations (h: Other Rig Types)

Overview of Rig Types in Field Development

Introduction to Rig Types

• The discussion focuses on various types of rigs used for field development beyond the commonly known swamp rigs, jackups, semi-submersibles, and drill ships.

• The speaker encourages viewers to subscribe before delving into the details of different rig types.

Fixed Jacketed Structure

• The fixed jacketed structure is introduced as a comprehensive facility that includes drilling derricks, cranes, helidecks, and living quarters.

• This structure is designed based on thorough evaluations to ensure cost-effectiveness for field development.

• Major disadvantages include high capital expenditure (capex), which increases with depth due to steel corrosion and maintenance needs.

• Demobilization costs can be significant, sometimes exceeding mobilization costs by 1.5 to 2 times.

Tender Assisted Drilling Rig

• The tender assisted drilling rig is smaller than the fixed jacketed structure and primarily supports drilling operations from a floating tender.

• It operates effectively only in calm waters; rough conditions hinder its functionality.

• Most equipment required for drilling is located on the tender while minimal operations occur directly on the jacket.

• Similar to fixed jackets, this setup incurs high capex and ongoing maintenance costs throughout field development.

Tension Leg Platforms

• Tension leg platforms consist of facilities supported by tensioned legs connected to wells below.

• High operational costs are associated with these platforms due to potential fatigue issues with tensioned legs and limited storage capacity.

Gravity Structures vs. Guy Towers

• Gravity structures have concrete bases buried at the bottom supporting their topside facilities; they differ from guy towers that use piles supported by guy wires for stability.

• Both structures feature similar topside facilities but differ significantly in their foundational support systems.

Summary of Rig Types

• A summary comparison highlights key similarities and differences among various rig types discussed throughout the session.

Overview of Offshore Drilling Rigs

Advantages and Disadvantages of Different Rig Types

• Jack-Up Rigs:

• Mobile and stable when elevated, especially with spud cans and truss structures.

• Low cost and efficient for shallow water operations.

• Limitations of Jack-Up Rigs:

• Instability in shallow waters with significant movement; restricted to areas where the legs can sit on the bottom.

• Difficulty relocating if shallow gas is detected, as they cannot be easily moved like semi-submersibles.

• Semi-Submersible Rigs:

• Operate at greater depths (up to about 10 knots), providing stability in rough environments.

• Medium to large deck area but face high initial and operating costs, along with limited dry docking options.

• Challenges with Semi-Submersibles:

• Complicated mooring systems and handling BOPs (Blowout Preventers) in rough seas.

• Increased operational difficulties as water depth increases, particularly during bad weather.

Drill Ships: Capabilities and Challenges

• Advantages of Drill Ships:

• Designed for deep-water operations; ample deck space allows for extended supply storage away from shore.

• Disadvantages of Drill Ships:

• Require highly skilled personnel due to instability in rough seas caused by low freeboard.

• Complex mooring systems pose challenges during operation.

Tension Leg Platforms: Features and Drawbacks

• Benefits of Tension Leg Platforms:

• Highly mobile, reusable, and have low maintenance costs compared to other rigs.

• Drawbacks of Tension Leg Platforms:

• High initial investment costs alongside substantial subsidy expenses.

• Potential issues related to fatigue in tension legs over time.

Thank you for following this module on the fundamentals of subsiding operations!