Casing Sleeves with Thru-Coiled Tubing Frac
Half-Straddle option for low-rate fracs
In formations with thin reservoirs and water-bearing zones nearby, it is usually best to complete with a large number of stages and smaller fracs to avoid the water. These smaller frac volumes—typically 10 bpm or less— can be pumped through the coiled tubing rather than down the coiled tubing/casing annulus. The Multistage Unlimited Half-Straddle option is ideal for these completions, and it reduces water requirements by as much as 50%. It’s called the Half-Straddle, because it resembles a coiled-tubing straddle with only a lower seal; the upper seal is achieved by closing the annulus at the surface during the frac.
Whenever the Half-Straddle option can be used, it provides a number of important advantages:
- Reduces water and chemicals usage by up to 50%
- The low frac rates and frac volumes make it easy to control frac dimension
- No need for a high-pressure wellhead stack, since the coiled tubing contains all the frac forces
The only equipment difference between the Half-Straddle and the Multistage Unlimited annular frac system is the addition of a frac-port sub between the sand-jet perforating sub and the resettable bridge plug. When it is opened, the frac-port sub allows the frac to flow down the coiled tubing and out the sliding sleeve frac ports.
The Half-Straddle option operates just like the annular-frac system. After the isolation bridge plug is set and the sleeve is shifted open, the frac is pumped down the coiled tubing. When the frac is away, a pull on the coiled tubing closes the frac valve and unsets the frac plug, and the assembly is moved to the next stage.
Adding stages on the fly
The Half-Straddle option also allows stages to be added in blank casing using sand-jet perforating, without tripping out of the hole.