Tower oil and gas is a term that refers to the offshore production of oil or gas using a fixed rig structure called a compliant tower (CT). A CT consists of narrow, flexible towers and a piled foundation supporting a conventional deck for drilling and production operations. CTs are designed to withstand harsh environmental conditions, such as high winds, waves, and currents, by allowing some lateral deflection of the towers.
CTs are one of the types of offshore platforms that can be used to exploit hydrocarbon resources in deep and ultra-deep waters. Other types include fixed platforms, floating production systems, tension-leg platforms, and spar platforms. The choice of the platform type depends on various factors, such as water depth, reservoir characteristics, environmental conditions, and economic feasibility.
The following table compares some of the advantages and disadvantages of CTs with other platform types:
| Platform Type | Advantages | Disadvantages |
|---|---|---|
| Fixed Platform | Simple and robust design; low maintenance cost; easy access to wells | Limited to shallow water depths (up to 500 m); high installation cost; vulnerable to storm damage |
| Floating Production System | Suitable for deep and ultra-deep water depths (up to 3000 m); flexible and adaptable to different reservoirs; easy to relocate | High capital and operating cost; complex mooring and riser system; limited storage capacity; susceptible to motion and fatigue |
| Tension-Leg Platform | Stable and rigid structure; minimal motion and wave impact; suitable for deep water depths (up to 2000 m) | High installation and maintenance cost; sensitive to tendon failures; difficult to access wells |
| Spar Platform | Stable and rigid structure; minimal motion and wave impact; suitable for deep and ultra-deep water depths (up to 3000 m) | High installation and maintenance cost; complex mooring and riser system; difficult to access wells |
| Compliant Tower | Suitable for intermediate water depths (500-1000 m); low installation and operating cost; easy access to wells | Limited to moderate environmental conditions; complex design and analysis; requires large deck area |
One of the examples of CTs is the Benguela Belize Lobito Tomboco (BBLT) platform, located in the Angolan offshore, at a water depth of 390 m. The BBLT platform has a height of 475 m and a weight of 51,000 tonnes, making it one of the tallest and heaviest structures in the world. The platform can produce up to 200,000 barrels of oil and 350 million cubic feet of gas per day.
Another example of CTs is the Baldpate platform, located in the Gulf of Mexico, at a water depth of 530 m. The Baldpate platform has a height of 554 m and a weight of 37,000 tonnes, making it the tallest freestanding structure in the world at the time of its installation in 1997. The platform can produce up to 80,000 barrels of oil and 150 million cubic feet of gas per day.
CTs are one of the innovative solutions for the offshore oil and gas industry, as they combine the benefits of fixed and floating platforms, while overcoming some of their limitations. CTs offer a cost-effective and reliable option for the exploitation of hydrocarbon resources in intermediate water depths, where conventional platforms are not feasible or economical. CTs also have the potential to be applied in deeper water depths, with further research and development.
