Abstract
Abstract
Gas production can be enhanced by the unloading of liquid accumulated in the wellbore. Conventionally, it is addressed by dropping soap sticks into a gas well. The foamability of soap sticks tends to decrease in the presence of condensate. Alternativity, well can be kicked-off by using N2 lifting but it is an expensive method that involves coil tubing operation. In this paper, an innovative and simple method of unloading a condensate-bearing gas well using dry ice is described.
Gas wells accumulated with liquid or condensate can be unloaded by displacing it with CO2 gas. It also helps to reduce hydrostatic pressure during kick-off well. Dry ice pellets can be inserted inside the wellbore, which can be settled down by gravity and CO2 gas formation inside the wellbore due to dry ice sublimation. The dry ice sublimation rate can be restricted by encapsulating it with self-degradable polymers that can be hydrolyzed inside the wellbore. Cylindrical dry ice pellets from the food industry having a half-inch diameter and a couple of inches long were used in this work.
Dry ice is the solid form of CO2 having an expansion ratio of 1 to 554 for solid to gas at sublimation point −78.5 °C and atmospheric pressure. The density of dry ice is 1.562 gm/cm3. A series of lab experiments were conducted to show CO2 gas generation from dry ice in the water. After inserting a dry ice pellet into the water column, it settled down at the bottom and started releasing CO2 gas with a sudden expansion in volume. CO2 foam was also generated by inserting dry ice pallets with foaming agents inside the water column. The release of CO2 gas in the wellbore and foam generation can assist in decreasing hydrostatic pressure and lifting liquid inside the wellbore. At the well site, a simple modification is required to insert dry ice into the wellbore. The cylindrical chamber needs to be installed above the master value of the Christmas tree. This is described in the paper with the procedure to follow during the operation. A mathematical tool has been developed to estimate the amount of dry ice pallets required for a given well geometry. For 4.5 inch, 1000 ft long production tubing, 1000 kg dry ice can release 51.7 bbl of CO2 gas, which can generate a 495 psi increase in pressure.
Well intervention operations are complex and expensive processes. It is preferred to use simpler, quicker, safer, and more cost-effective methodologies. The use of dry ice to unload gas well is simple, cheaper and an innovative solution. The release of CO2 gas from dry ice can offer additional benefits such as better and faster cleanup and the removal of condensate blockage in the near-wellbore area.