Subsea Boosting Definition / Meaning
Subsea boosting is a production enhancement technology that uses pumps installed directly on the seafloor near the wellhead to increase the pressure of reservoir fluids (oil, gas, and water). By adding energy at the seabed, subsea boosting overcomes back pressure from long flowlines, low reservoir pressure, or high water cut, enabling greater flow rates, higher recovery, and economic development of deepwater and marginal fields.
Overview
In many offshore developments, reservoir pressure naturally declines over time. As the distance from the well to the host platform or shore increases, friction losses in the flowline become significant. Subsea boosting solves this by placing pumps at the bottom of the sea, often within a template or manifold. These pumps give the fluids a pressure boost before they travel to the surface facility. This technique is especially valuable in deepwater (over 1,000 meters) and ultra-deepwater where installing topside pumps is impractical or expensive.
How Subsea Boosting Works
A typical subsea boosting system includes one or more pumps driven by electric motors or hydraulic turbines. Power comes from the host facility via a subsea power cable. The pump impeller accelerates the flow, increasing its pressure. Control and monitoring systems adjust pump speed based on well conditions. The process can be summarized:
- Reservoir fluids enter the wellhead and flow to a subsea manifold.
- The booster pump raises the fluid pressure by 50 to 200 bar (725–2,900 psi).
- Pressurized fluid then flows through the pipeline to the host platform, FPSO, or onshore terminal.
Subsea boosting systems often include multiphase flowmeters, sand detectors, and chemical injection ports to manage flow assurance issues like hydrates and scaling.
Types of Subsea Boosting Systems
| Pump Type | Typical Application | Advantages | Limitations |
|---|---|---|---|
| Centrifugal pumps (single-phase) | Oil or water with little gas | High flow capacity, reliable, mature technology | Cannot handle high gas volumes; requires upstream gas/liquid separation |
| Multiphase pumps | Oil, gas, and water mixtures | Handles up to 90–95% gas volume fraction; no separation needed | Lower pressure boost per stage, more complex design |
| Helico-axial pumps | Multiphase flow with medium gas content | Compact, good tolerance to gas slugs | Narrower operating range than centrifugal pumps |
| Positive displacement pumps | Low flow, high pressure, viscous fluids | High differential pressure, handles viscous and emulsified fluids | Lower flow rates, pulsation, may require dampeners |
Key Benefits
- Increased Recovery — Boosting can recover 5–20% more oil compared to natural flow alone.
- Extended Field Life — Maintains production as reservoir pressure declines, delaying abandonment.
- Longer Tiebacks — Enables production from remote subsea wells 50–100 km away from host facilities.
- Reduced Back Pressure — Lowers wellhead flowing pressure, allowing more drawdown and better reservoir sweep.
- Cost Savings — Avoids the need for a dedicated platform or risers for each well.
Challenges and Considerations
- High Capital Cost — Subsea pumps, power cables, and installation are expensive; economic viability depends on field size.
- Reliability — Subsea equipment must operate for years without intervention. Redundant systems and modular designs are needed.
- Flow Assurance — Low seabed temperatures can cause hydrates, wax, or asphaltenes. Chemical injection and thermal management are critical.
- Power Supply — Long step-out distances require high-voltage power cables and efficient transmission systems.
- Intervention — Retrieving or repairing a subsea pump requires a specialized vessel and can cost millions of dollars per day.
Usage Example
In the Girassol field offshore Angola, subsea boosting pumps were installed on a large manifold to boost production from multiple wells. The system increased the total field output by approximately 30% and allowed recovery of an additional 50 million barrels of oil over the field life. This example demonstrates how subsea boosting turns a marginal deepwater project into an economically viable development.