The shoe-valve is fitted to the lower end of a well screen and the well screen is in turn fitted to the bottom of the production tubing. As usual the production tubing is used to lower the well screen and show valve assembly to the pay-zone during well completion.
It should be noted that the show valve is used only for wells for which no packer needs to be fitted (i.e. the production fluid needs to be pumped out). The show valve is designed to help with water washing of downhole not only before the initial well screen installation but also every time the well screen clogs up with sand. The shoe valve acts as a one-way valve (non-return valve) when water is pumped with high pressure down the production tubing from the surface, and forces the shoe-valve which is fitted at the very bottom of the production tubing string to open up to allow water to pass through it to the bottom of the well where the sand and loose drilling debris are washed up to the surface through the annulus (between the production tubing string a the production casing). The sand and debris which appear at the surface will be filtered out at the surface and then clean water is circulated back under pressure to the bottom through the production tubing. The process can continue for a number of hours until the required level of cleaning is achieved. It should be noted that as the water is sent to the bottom through the production tubing, not only it flows out of the shoe-valve but under pressure it will also try to go through the well screen (which is fitted just above the shoe-valve) from the inside of the well screen to its outside surface and thus in this process the water will push out the sand which were clogging up the well screen and washes it up to the surface through the annulus. This process will therefore allow the unclogging of the well screen in situ without having to raise it to the surface for unclogging and cleaning by raising the whole of the production tubing string. Being able to clean the clogged up well screen in situ at the bottom of the well therefore save a great deal of costs and time.
Clearly as the shoe-valve acts only as a one-way valve it will not allow any dirty production fluids to flow from the bottom of the well into the shoe-valve, well screen and production tubing assembly (string) and thus the only way the produced fluid can get into the production tubing is through the well screen where any sand content will be filtered/screened out. Depending on the sand conditions if a lot of sand is screened out and left outside of the well screen as the production continues, the screen sand can clog up the well screen again at which time production should be stopped and the washing cycle of the well screen as explained above will be conducted again.
This shoe-valve is designed to be mounted on the lower end of the well screen fitted to production tubing diameters (OD) of 73mm and 89mm (OD of tubing couplings) which is the most common tubing size used.
|Production casing diameter, mm||140, 146, 168|
|Production tubing diameter OD, mm||73, 89|
|Differential pressure, MPa||10|