The current hydraulic fracturing industry paradigm is to isolate stimulation intervals. 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. 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. In this paper, performance of plugless hydraulic fracturing process for horizontal stages and wellbores eliminating need for mechanical bridge plug diversion is estimated. The plugless process has been applied in horizontal wells that target one of three shale gas resource formations. Laterals in Nexen's Dilly Creek field currently target: Muskwa, Otter Park and Evie geological horizons. Recent applications of a plugless toe approach provides a solution for completing hydraulic fracturing stages beyond the reach of conventional coil tubing equipment. Elimination of drillable bridge plugs at these measured depths without compromising completion quality is key for enabling longer lateral lengths with significant cost saving during a low commodity price environment. Full plugless wellbores reduce cost even further and eliminates significant risk associated with mechanical isolation plug installation and removal. The scope of the work presented in this paper takes into account field production and completion data, original analysis of surveillance data, completion technology solution & advancement and computational work.
Surveillance methods interpretation, pressure and rate transient analysis, advanced transient analysis such as deconvolution technique, Diagnostic Fracture Injection Test (DFIT) analysis and numerical simulation have been conducted to understand the plugless effect in unconventional shale gas reservoirs. The possible applications of the information provided in this paper are the determination of expected ultimate recovery, production performance and completion efficiency on a per stage basis.
Evidence of the plugless effect thru surveillance response shows new deformation opposite new perforations and little deformation opposite previous fractured stage perforations. This paper will look at pore pressure, fracture conductivity and fracture dimensions as the main dials to obtain performance in hydraulic fracture stages in reservoir models. We stated specific conclusions of this case study and how these conclusions differ from previous work on the same subject.
The significance of the subject matter is related with 3 major technical contributions in the area of design, completions and reservoir engineering in unconventional shale gas reservoirs. The additions to the technical knowledge base of the petroleum industry are numerous and insightful.