Safety in production processes
RWE Dea implements a range of safety measures not only during the drilling operations, but also for the subsequent production phase. The cased borehole is specially prepared in the lead-up to the well coming on stream. The focus here is on managing pressures as well as the delivery medium safely. All the components are designed to cope with the prevailing pressures and are tested under realistic conditions:
- Sealing element
- Subsurface safety valve
- Wellhead assembly
- Monitoring and control systems
Once a borehole has been completed and cleaned, the installation of the production line begins. Individual tubes about 9.5 metres in length are screwed together to form a long pipe run. A sealing element, the so-called packer, is attached to the bottom end of the production line. Once in position, the packer is operated by means of hydraulics: extremely durable rubber cuffs and wedges extend from the packer and form a gas-proof seal against the inner wall of the casings. A protective fluid is then introduced into the annular space created between the production line and the casing.
Subsurface safety valve
In wells where gas or oil flows naturally due to the internal formation pressure, a subsurface safety valve is installed at a depth of around 90 metres. This is a self-closing design which is kept open during normal operation by means of hydraulic pressure. Once the hydraulic pressure is removed, the valve shuts off the flow automatically. The valve release is hard-wired into the safety shutdown facility and so ensures that the well is automatically shut down and secured in the event of an emergency. These quick-closing valves can also be operated manually from the continuously attended control room.
All the casings as well as the production lines are trapped and sealed by means of a flange. This flange is topped by the so-called wellhead assembly (also known as Christmas tree), a device that fulfils the same function during production as the blow-out preventer did during drilling. It is fitted with a number of slide valves that serve different purposes. Should the wellhead assembly or any of the connected piping be damaged, a contact pressure gauge or a pressure drop in the control lines will cause the well to be shut off and secured automatically.
Monitoring and control systems
Sophisticated monitoring and control systems provide multiple levels of safeguards for all production facilities. Submersible centrifugal pumps are used to extract oil in situations where the oil not longer flows naturally. In the event of deviations in production parameters, the pumps switch off automatically.