Page 136 - Well Control for Completions and Interventions

128 Well Control for Completions and Interventions

Figure 3.33 Injection valve. (Image courtesy of Halliburton).

3.19.3 Equalizing or nonequalizing valve?
Early equalizing valves were less reliable than their nonequalizing equiva-
lent. In recent years, the reliability of equalizing valves has improved to
the point where there is little to choose between them. Most, although
not all, equalizing valves are equipped with a simple check seat recessed
into the flapper, when control line pressure is applied to the valve the
flow tube moves down until it contacts the flapper. If there is differential
pressure across the valve it cannot open. However, the bottom of the
flow tube pushes the equalizing port open. This allows pressure to equal-
ize across the valve. Once pressure across the flapper is equalized, contin-
ued application of hydraulic pressure moves the flow tube down, fully
opening the valve. Older types of equalizing valves had more compli-
cated, hence less reliable, equalizing systems.

3.19.4 Tubing retrievable or wireline retrievable valves?
Surface controlled safety valves can either be run as an integral part of the
completion tubing (tubing retrievable), or run through the tubing and set
in a ported safety valve landing nipple (wireline retrievable).