Over the last decade or so, unconventional shale resources have been playing an increasingly important role in hydrocarbon production due to advanced drilling, fracturing and completion technologies enabling the recovery of previously uneconomic reserves, and multi-stage fracturing technology has been widely used to exploit them in the North American oil & gas industry. During that time the completion process has been evolving, starting with the Plug and Perf method and then with multiple ball seat size actuated sliding sleeves gaining attention. However both methods have their drawbacks, the former requiring multiple re-entries and mill out operations, the latter having a limited number of fracturing stages due to the graduated seat sizes needed and the probability of the need for milling out the seats upon completion to remove flow restrictions (Wozniak 2010).
As a result of these drawbacks, the industry has been driven to the development of some high-performance multi-stage fracturing completion systems which are emerging in the marketplace as alternatives to both plug and perf and traditional ball-activated frac sleeves. Three such unlimited multi-stage fracturing systems, which have been developed in recent years, can be cemented in place if desired and have a full-bore internal diameter (ID) or as close as possible to the host tubular string after fracturing and do not need milling-out operations, reducing overall completion time and improving fracturing and production efficiency. These include:
Coiled Tubing (CT)-Operated sleeve – this incorporates a Bottom-Hole Assembly (BHA) which is used to isolate the target zone and shift the sleeve open with fracturing being performed down the CT/Casing annulus on an nearly unlimited number of sleeves.
An evolutionary ball-activated frac system – this uses a single size ball and ball seat for each zone, which allows an essentially unlimited number of frac stages.
Radio-Frequency-Identification (RFID) frac sleeves – by simply dropping RFID tags in the completion string, the RFID frac sleeve system can be run with an unlimited number of frac stages.
This paper will review developments in multi-stage fracturing completions, describe in detail their unique features and capabilities which are not available in earlier systems and present simulations of frac efficiency with quantitative comparisons. The analysis will indicate that these three new frac sleeves technologies can be used to optimize hydraulic fracturing operations in both horsepower and stimulated reservoir volume while dramatically reducing overall completion costs.