A tender assisted drilling rig, commonly referred to as a TAD rig, is a specialized offshore drilling system used extensively in oil and gas exploration and production. This article breaks down the key features, applications, and types of TAD rigs, offering a clear understanding of their role in the industry.
What is a Tender Assisted Drilling Rig?
A tender assisted drilling rig is one of offshore drilling rigs, essentially a two-part system comprising a tender vessel and a self-contained drilling package. Here’s a closer look at each component:
1. Tender Vessel:
- Storage: The tender vessel is equipped with storage facilities for essential drilling equipment, fluids, pipes, and other necessary items.
- Living Quarters: It houses the crew, typically ranging from 120 to 200 people, providing living quarters and amenities.
- Power Generation: The vessel is equipped with power generation facilities to support its operations.
- Cranes: There are cranes on board for lifting and handling heavy equipment, making logistics easier.
- Helideck: The vessel includes a helideck for helicopter access, ensuring efficient transportation of personnel and supplies.
2. Self-Contained Drilling Package:
- This component includes the actual drilling equipment. It is designed to be self-erecting and operates independently, ensuring flexibility and efficiency during drilling operations.
Applications of Tender Assisted Drilling Rigs
TAD rigs are known for their versatility and cost-effectiveness, making them suitable for various offshore drilling scenarios. Here are some key applications:
1. Versatility in Water Depth:
- TAD rigs can operate in both shallow (as low as 30 feet) and deep water (up to 6,000 feet). This flexibility is a significant advantage over other rigs that are restricted to specific water depths.
2. Development Drilling:
- These rigs are often used for drilling multiple wells on existing platforms, especially in cases where the platform itself is not equipped for drilling operations.
3. Workover and Plug and Abandonment (P&A):
- TAD rigs are ideal for maintenance and well closure operations on existing wells. This includes tasks such as repairing and re-entering wells to enhance production.
4. Cost-Effectiveness for Marginal Fields:
- For smaller oil and gas reserves, a dedicated platform may not be economically viable. TAD rigs offer a cost-effective alternative due to:
- Lower Construction Costs: The tender vessel is less expensive to construct compared to a full drilling platform.
- Flexibility: The drilling package can be moved to different platforms after completing operations at one location.
- Large Deck Space: The tender vessel’s ample deck space can reduce logistical costs for the operator, making the overall operation more efficient.
Types of Tender Assisted Drilling Rigs
There are two main types of TAD rigs, each designed for specific environmental conditions and operational needs:
1. Tender Rigs:
- These rigs are typically used in shallower waters. They usually feature a flat-bottomed barge design, making them suitable for calm, shallow marine environments.
Tender Drilling Rig – EDrill2 rig; Source: Edrill
2. Semi-Tender Rigs:
- Designed for deeper water and harsher environments, semi-tender rigs often use semi-submersible tender vessels. This design provides better stability in rough sea conditions, ensuring safe and efficient operations.
Semi Tender – Rig West Vencedor rig; Source: Seadrill
Advantages of Tender Assisted Drilling Rigs
Tender assisted drilling (TAD) rigs offer a range of benefits that make them a valuable asset in the offshore oil and gas industry. Here’s a detailed look at their key advantages:
Versatility : Multiple Applications:
- Development Drilling: TAD rigs are ideal for drilling multiple wells on existing platforms. This is particularly useful when the platform itself is not equipped for drilling.
- Workover and Plug and Abandonment (P&A): They are suitable for maintenance operations and well closure activities on existing wells, ensuring continued productivity and safe decommissioning.
Cost-Effectiveness
1. Lower Construction Costs:
- Economical Build: The construction cost of tender vessels is generally lower than that of full drilling platforms. This cost savings can make a significant difference, especially in marginal fields where budget constraints are a concern.
2. Flexibility and Reusability:
- Optimized Resource Utilization: The self-contained drilling package of a TAD rig can be moved to different platforms after completing operations at one location. This reusability optimizes resource utilization and reduces the need for multiple dedicated rigs.
3. Reduced Logistical Costs:
- Efficient Storage: The large deck space on the tender vessel allows for efficient storage of equipment, drilling fluids, pipes, and other essentials. This can reduce the need for frequent supply boat traffic, leading to lower logistical costs and improved operational efficiency.
Disadvantages of Tender Assisted Drilling Rigs
Require the platform to put the rig package.
- TAD requires to put the rig package on the platform. The weight of the rig must be carefully considered when installed on the platform since the platform must be strong enough to support all required load while drilling. Additionally, TAD cannot work on open water like jack up rigs therefore, it cannot be used for drilling exploration and appraisal wells.
Weather Dependence
- Stable Connection Challenges: TAD rigs rely on a stable connection between the tender vessel and the platform. Rough seas and strong currents can disrupt this connection, leading to operational challenges.
- Operational Pauses: During adverse weather conditions, operations may need to be paused to ensure safety. This can lead to delays and increased costs, impacting the overall project timeline.
Complex Positioning
- Precise Positioning Required: TAD rigs need to be precisely positioned and anchored near the platform. This positioning process can be complex and time-consuming, requiring careful planning and execution.
- Anchoring Challenges: Ensuring stable anchoring in varying seabed conditions adds another layer of complexity to the operation, potentially affecting the efficiency and stability of the drilling process.
Safety Considerations
- Risky Transfers: The transfer of personnel and equipment between the tender vessel and the platform is inherently risky, especially in rough sea conditions. Ensuring the safety of the crew and equipment during these transfers requires meticulous planning and strict safety protocols.
- Operational Hazards: The potential for accidents and injuries increases in challenging weather conditions, making safety a critical concern in TAD rig operations.
