Patent Application
20150158059
This invention relates to a hydraulic flushing system and method of flushing a downhole control line in an underwater, e.g. subsea, hydrocarbon well facility.
Surface controlled sub-surface safety valves (SCSSVs) on production fluid wells are controlled by high pressure hydraulic fluid switched through a directional control valve (DCV). After a period of time, the hydraulic fluid can deteriorate or become contaminated resulting in possible failure of the SCSSV to operate when required. In order to prevent this problem, well operators insist that the design of the hydraulic system allows for flushing of the hydraulic fluid from the hydraulic control lines right down to the SCSSV itself However, existing methods of achieving this involve a second ‘flushing’ DCV and typically venting of the flushed hydraulic fluid to the sea. This creates two new problems: a) the hydraulic fluid can be contaminated with particles which can lodge in the flushing DCV causing it to fail to close resulting in total failure of the SCSSV control; and b) the hydraulic fluid, normally not a pollutant when vented to sea, can be contaminated with downhole fluids including hydrocarbons, which cause the hydraulic fluid to become a pollutant. The invention aims to overcome some of the above problems.
During normal operation, the SCSSV 1, is opened and closed by operating a DCV 6, whilst a ‘flushing’ DCV 7 remains closed. In order to flush a hydraulic downhole control line 8 of the SCSSV 1, the DCV 6 is closed, the DCV 7 is opened followed by the opening of DCV 6, allowing control fluid to flow through the hydraulic downhole control line 8, to the SCSSV 1, and then back up a second control line 9 (acting as a purge or flushing line), through the DCV 7, through a flow transmitter 10, if fitted (this component may be omitted in practice), a metallic check valve 11, and finally a seawater check valve 12 before being vented to sea. The orifice in a DCV such as DCV 7 in this system is typically only 3 millimetres in diameter, and is thus prone to blockage from contaminating particles.
As previously described, prior art systems such as the one shown in
According to a first aspect of the invention there is provided a hydraulic flushing system comprising: a hydraulic downhole control line that runs from a hydraulic source to a surface controlled sub-surface safety valve of an underwater hydrocarbon extraction facility, said hydraulic downhole control line having a directional control valve therein; and a purge line that runs from the hydraulic downhole control line downstream of the directional control valve to a service line, said purge line having a fluid isolation valve therein.
According to a second aspect of the invention there is provided a method of flushing a hydraulic downhole control line, said control line comprising: a hydraulic downhole control line that runs from a hydraulic source to a surface controlled sub-surface safety valve of an underwater hydrocarbon extraction facility, said hydraulic downhole control line having a directional control valve therein; and a purge line that runs from the first hydraulic downhole control line downstream of the directional control valve to a service line, said purge line having a fluid isolation valve therein, said method comprising the steps of: closing the surface controlled sub-surface safety valve; opening the fluid isolation valve; and opening the directional control valve.
The fluid isolation valve could be operated by a hydraulic line which is independent of the hydraulic downhole control line. The fluid in said hydraulic line could be of relatively lower pressure than the fluid in the hydraulic downhole control line.
The service line could be an annulus service line, which in turn could vent into a well fluid production line.
The fluid isolation valve could have an internal orifice of between 0.5 inch (1.27 centimetres) and 2 inches (5.08 centimetres) in diameter.
In an embodiment of the present invention, the flushing DCV in a typical hydraulic fluid flushing system, which is prone to particle contamination blockage, is replaced with a hydraulically operated fluid isolation valve (FIV), which has a much larger fluid flow path orifice, via which contaminated fluid is vented into a well service line, such as an annulus service line, rather than into the sea, which avoids potential sea pollution. The FIV is typically controlled by hydraulic operation.
As for
During normal operation, the SCSSV 1 is opened and closed by operating DCV 6, whilst the FIV 13 remains closed. More particularly, while the orifice in a DCV such as DCV 7 is typically only 3 millimetres in diameter, and is thus prone to blockage from contaminating particles, the FIV 13 has an internal orifice that can be between 0.5 inch (1.27 centimetres) and 2 inches (5.08 centimetres) in diameter, and thus is not prone to blockage from contaminating particles.
In order to flush the downhole control line 8, the SCSSV 1 is closed, the FIV 13 is opened and then DCV 6 is opened, allowing control fluid to flow downhole to the SCSSV 1, and then back up the purge line 9, through the FIV 13, and into the service line 14, such as an annulus service line. Once the required amount of fluid has been circulated through the loop, the FIV 13 is closed and normal operation can be resumed.
In the embodiment shown in
Purged fluid may be stored in the service line 14. On completion of the first part of the flushing activity, the FIV 13 is closed. Then pressure is applied to the service line 14 from a host facility (i.e. a surface platform, a floating production, storage and offloading (FPSO) unit, etc.) and a path opened from the service line 14 into a production line of an underwater hydrocarbon well facility, which allows the purged fluid to be pushed into the production line after which it flows back to the host facility.
The present invention may prevent the failure of the hydraulic control line flushing system from particle contamination.
The present invention may reduce the risk of pollution of the sea due to chemical contamination of flushed and vented hydraulic fluid.
This written description uses examples to disclose the present invention, including the best mode, and also to enable any person skilled in the art to practice the present invention, including making and using any computing system or systems and performing any incorporated methods. The patentable scope of the present invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1321510.8 | Dec 2013 | GB | national |
