Coiled tubing (CT) is a unit equipped with a flexible continuous tubing. Coil tubing is a promising and developing area in the oil and gas industry and is widely used in technological, as well as workover operations carried out in gas, oil and gas condensate wells. Coiled tubing is successfully used in highly corrosive and high temperatures environments. Coiled tubing replaces traditional sectional drill pipes. Due to its flexibility, coil tubing is able to work in lateral and horizontal bores, providing mechanical and hydraulic connection between the milling tool (drill bit) working at the bottom and surface drill equipment. Technologies using coiled tubing make it possible to involve most of hard-to-recover reserves (HTRR) of hydrocarbons in Russia into development.
It provides for installation of isolating plugs on CT and perforation per one RIH (mainly for high-flow multi-stage fracturing). To form a connection with the reservoir and to isolate previous processing intervals within the only RIH, a cumulative perforator with a composite explosive packer plug is used, which can withstand a pressure drop of at least 700 atm. To activate the packer plug and cumulative perforator, a cable through the CT is used, which transmits various electrical pulses to disconnect the packer plug and cumulative perforator. Both packer plug installation and perforation are performed per one RIH/POOH.
This technology allows to:
• choose promising formation zones for perforation according to data (WL);
• perform frac in an equal-bore casing;
• reduction in the number of RIH (setting plug and perforating within one run);
• minimum time to drill composite plugs and displacing balls.
CTAF (Coil Tubing Annular Fracturing) Technology
Provides pumping frac treatment through a CT annulus. When using this technology, a special bottom hole assembly (BHA), mounted on CT, is applied, which allows multiple resetting during an operation.
The technology has two options:
1. With reusable movable sleeves. Sleeves are set down during the well construction.
2. Without sleeves - in a cemented liner/monobore casing. As a method of secondary opening, hydraulic jet perforation (Sand jetting) is used.
Before fracturing, BHA on CT is activated and the sleeve is opened, or the Sand jetting is performed. Being in the well during frac, it is possible to monitor bottomhole pressure, which allows effectively adjusting parameters of frac pumping. In case of any complications / “sand-offs”, it is possible to wash out the well bore without additional RIH.
Advantages of CTAF Technology:
• Controlling bottomhole pressure during the frac treatment;
• In the case of “sand-off”, quick cleaning wellbore out of proppant;
• Opportunity to increase stages.