The current frac'ing industry paradigm is to isolate stimulation intervals. Cased cemented horizontal well stimulations follow a rigidly prescribed format. The casing is perforated, a hydraulic fracture treatment is pumped, and isolation is set ‘above’ the previously stimulated interval before the casing is perforated for the next interval. These steps are repeated as necessary to stimulate the entire lateral section. Isolation is held as a fundamental requirement of completions under the belief that a lack of isolation between intervals will result in the loss of stimulation fluid through previously perforated intervals.
This paper illustrates a brief history of field tests which resulted in a paradigm shift towards non-isolated intervals. Events are discussed which led to the discovery that slick water fracs can be executed in the Horn River Basin with no isolation between frac stages (Nexen Energy ULC patent pending plugless frac'ing process). Multi-stage plugless horizontal completions are examined on a number of horizontal well pads. Experimental results cover 80+ plugless intervals on multiple pad developments over a period ranging from 2008 to 2014. Included is an example of a complete 25 interval horizontal wellbore with no isolation between any frac stages. The benefits of the plugless stimulation method are many fold, including reduced operational risk during pumpdown operations; no plugs to get stuck or set in the wrong place; no plugs to drill out and no plug debris on flowback, eliminating costly and time consuming operations; making longer horizontal sections possible as length is not limited by the capability to drill out plugs; and faster cycle times.
Well information and surveillance data will be described for the plugless fracs deployed to date. The data illustrates successful application of the technology in Nexen's Horn River shale development. Surveillance and production data is considered in order to present possible explanations on the mechanics behind the success of this technique.