Friday, July 27, 2018

SC-SSV

Ball Type Valves
The only function of a Sub‑Surface Safety Valve (SSSV) is to automatically and reliably
close in the well below the surface of the earth when there is an emergency.

It is an international requirement that offshore wells are fitted with SSSVs.

Note::
  • If the land wells in Kuwait had been fitted with SSSV, the damage to oil reservoirsand the environment in Kuwait would have been much less. All the oil fires would have gone out due to lack of fuel.

  • There were no major fires on the platforms offshore Kuwait where the SSSV  performed their function even when the wellheads were destroyed.


SSSV can be retrieved from the well using a wireline unit (wireline retrievable) or they can be part of the tubing string.

WIRELINE RETRIEVABLE TYPE SSSV


Safety Valve Landing Nipple
The SSSV are landed and locked into a special landing nipple in the tubing string. This landing nipple has two polished bores with a port between. The port is connected to the wellhead by stainless steel, small diameter tube, and then to a hydraulic control panel.
Hydraulic Control Lines

The SSSV locates into the landing nipple and the two sets of seals on the outside of the
valve seal in the two polished bores. A port in the outside of the SSSV then joins with the
port in the landing nipple.

As additional control line pressure is applied, the valve moves to the fully open position. Control line pressure is maintained at the control panel to keep the valve in the fully open position.

Hydraulic control pressure can be applied from the surface into the SSSV where it acts
against an annular‑shaped piston, then the piston moves and opens the valve.

When this control hydraulic pressure is released, a strong spring in the SSSV pushes back
the piston to close the valve. The spring force must be stronger than the weight of the
control fluid and the friction inside the SSSV. There is therefore a limit to how deep these
SSSV can be set in the wells.

OPENING PROCEDURE FOR SSSV

There is always a differential pressure across a closed SSSV. This is because of the gas
and fluid in the tubing above the valve and the increase in pressure below the valve (due to
the natural build‑up of pressure from the well).

Pressure across the valve must be equalized before the valve is opened. There are
equalizing ports in the valves to do this.

Control line pressure is applied to the valve from the surface control panel.

The well head pressure is monitored as the control line pressure is slowly increased. An
increase in wellhead pressure will show when the equalizing ports in the valve have been
exposed.

The control line pressure is kept at the level that caused the equalizing ports to open.

When the wellhead pressure is stabilised, (no more increase in pressure over a 15 minute
period), we can say that there is no pressure differential across the SSSV.

This equalizing action prevents any damage to the sealing elements of the valve.

Note::

  • Considerable damage can be done to an SSSV when it has not been equalized before applying full opening control line pressure.
  • Valve damage will not be known until the SSSV is pulled from the well or until the SSV is needed to perform its function in an emergency. IT WILL LEAK BADLY and there will be NO ISOLATION from reservoir pressure in an emergency.


Ball Type Safety Valve
Flapper Type Safety VaIve
Piston Action






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