The Horn River shale gas play has been estimated at 500 TCF. Multiple large slickwater fracture stimulations are applied to horizontal wells to initiate gas production. A typical Nexen Dilly Creek shale gas well pad has 16 to 20 horizontal wells drilled parallel to the principal insitu stress. The horizontal legs are spaced approximately 300 m apart. A typical well receives 16 to 25 fracture stimulations spaced at 100 m intervals along the horizontal lateral. A slant drilled observation well (Dilly Creek c-F1-J) was drilled and completed and between two stimulated wells. The drilling of the well was concluded in early November, 2013. A string of 2-3/8″ tubing was installed and the well was suspended until July 2014 when wells on the pad were fracture stimulated. During the suspension period a gas head from the formation developed. First indication of a well problem occurred during attempts to land data recorders in the tubing in June 2014, seven months after the well was suspended. Tubing joints were recovered, the deposits were analyzed and a casing inspection log was conducted. Lab tests were then conducted on several recovered tubing joints. Drilling, completions and suspension procedures were reviewed and analyzed. It was concluded that the untreated oxygen in the suspension fluid in combination with the 10% CO2 formation gas caused the severe tubing corrosion.

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This paper presents well construction details and pressure responses for a slant well in a dry gas shale resource in northern British Columbia, Canada. We will present the drilling and completions plan for a Multi-Stage Hydraulic Fracturing (MSHF) campaign on a ten well half pad including consequences of an aggressive fluid environment. Horn River shale gas development involves Multi-well MSHF horizontal wells from a single surface pad location. The wells are treated sequentially from toe to heel of the horizontal section, alternating between wells. Strategic placement of an Open Hole (OH) slant well equipped with slotted liner, tubing, and pressure data recorders will be presented. Pressure responses during the MSHF campaign will be presented and reviewed against calibrated closure pressure data from Diagnostic Fracture Injection Test (DFIT) data and end of job instantaneous shut-in pressures (ISIP).The initial concept of drilling an OH well placed between MSHF wells was to evaluate the fracture system between stimulated wells and to test whether an unstimulated open hole well placed between stimulated wells can economically produce gas. Other objectives were to provide an Oil Based drilling Mud (OBM) free wellbore that would enable water-based imaging logs. Water-based logs have enhanced ability to identify and map natural fractures. Initial logs would evaluate the natural fractures and subsequent post-completion logs would evaluate the hydraulic fracture transiting the shale resource rock to the OH well. Knowledge of how pre-existing natural fracture networks react to the hydraulic fracture process along with pressure response data recorded from all wells on the pad would be used to provide geoscientists and engineers the means to optimize stimulation programs for horizontal wells and wellbore placement within the various resource reservoirs in the Horn River Basin. This paper will discuss the compromises that were made to the initial conceptual model that maximized learnings from the slant OH wellbore, and how the well was unexpectedly lost. Pressure interference data for future hydraulic fracturing models will be provided along with methods to describe how hydraulic fractures from nearby wells transect a well and interact with various reservoirs exposed within the OH segment of a slant wellbore.

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The submitted manuscript has been authored by a contractor of the U.S. Government under contract No. W-31-109-ENG-38. Accordingly, the U.S. Government retains a nonexclusive. royalty-free license to publish or reproduce the published form of this contribution, or allow others to do so, for U.S. Government purposes.