Q: How does the Venturi Plunger work?
A: A variable orifice in the centre of the tool creates a pressure differential causing an increase in gas velocity. The flow regime caused by the increased gas velocity exits the top portion of the tool. It is the interaction of the gas exiting the tool that helps to increase lifting efficiency.
Q: Why a variable orifice?
A: The orifice serves two purposes. On weaker wells fall velocity is not as important so we focus on utilizing the Venturi effect with a smaller orifice. On stronger wells, we try to minimize off time and are willing to sacrifice some of the Venturi effect. We base orifice selection on build rates; if the well has enough energy to start in a relatively short period of time, orifice sizing then addresses how long it takes the tool to get to bottom. The key things to remember is do not put a big orifice in a weak well.
Q: Why are some tools made of titanium and others steel?
A: Material selection is based on gas composition (sweet or sour service) as well as risk assessment and improved efficiency. The use of titanium is meant to address risk and provide greater lifting efficiency. Mass should be a key consideration on high velocity thus “potentially” risky wells. Mass also needs to be a consideration on low rate marginal wells, where slug sizes are kept to a minimum. Combinations of double heat treated stainless steel/4140/L80/astralloy 5 are all available, as well as different grades of titanium to address the above.
Q: How fast does the Venturi plunger fall?
A: As with all plungers- pressure can have a larger impact on fall velocity than tool design. Orifice selection, to address build rates, also has a drastic impact on fall velocity. See attached charts.
Q: When do I drop a fishing magnet?
A: Only when you know what you are fishing for. If the magnet lands on a standing valve, and the wells flow rate is not enough to “unseat” the magnet, it may stick to the device it’s latched onto. Typically if the gas rate is very high and you can’t “flow” your item to surface, a magnet may not help you. You should always follow a magnet with acoustic equipment such as an echometer to track it.
Q: When would I drop an impression block?
A: When you are unsure of what you are fishing for. Be sure the well has enough energy to flow the impression block back to surface. Always track the impression block with acoustic equipment.