This paper outlines the second generation test Nexen Energy ULC has conducted in the Horn River shales involving the use of cased uncemented multi-fractured horizontal well (MFHW) technology. Horn River shale gas development involves drilling and hydraulically fracturing multiple horizontal wells from a single surface pad location. The wells are hydraulically fractured in a sequential manner from the toe to the heel of the horizontal section, alternating from well to well. Frac treatment and microseismic event (MSE) data show that hydraulic fracture stimulation results in a very complex stimulated reservoir volume. At a development pad level, there is also a very high degree of complexity created within the stimulated reservoir volume (SRV). Surveillance data including MSE as well as proppant and fluid tracers show that hydraulic fractures reactivate the natural fracture system and can extend beyond inter-well distances. Production analysis however indicates that the effective drainage volume post stimulation is much smaller than what is observed with MSE. Field results have also shown that multiple cluster perforations per frac stage improve the reservoir contact and complexity of the (SRV) over single perforation cluster intervals.
The objective of the uncemented MFHW was to achieve improved productivity when compared to the standard cased cemented horizontal well design. The hypothesis was that uncemented wellbores would have improved connection to the reservoir and pre-existing natural fracture system in the shales. In addition, the uncemented well would benefit from increased reservoir contact and connection to fractures created by offset wells on the pad. The first experimental well was drilled on Nexen's 18-well pad, completed in 2012. A swellable packer system was conveyed as part of the casing string to isolate each hydraulic fracture stage. This paper will discuss details behind the second generation test on a 10-well pad involving the use of mechanical packers in 2013. Surveillance data including microseismic, chemical fluid tracers and gamma emitting tracers was collected. Results and comparisons to the first generation swell packer test will be discussed along with recommendations for further evaluation of the technology. The work presented will make technical contributions in the areas of shale gas wellbore design, hydraulic fracture stimulation, reservoir surveillance technologies and shale gas recovery.
