The Jean Marie Member of the Redknife Formation is a regionally widespread Upper Devonian carbonate with estimated OGIP of 35,671 106 m3. Low matrix permeability within the Jean Marie means that fracturing due to regional tectonism and compactional drape may provide the key to good well deliverability.
The Jean Marie may be a good candidate for horizontal drilling, where the goal is generally to intersect the maximum number of open natural fractures. The optimum trajectory for a horizontal well depends on the angular relationship between the paleostress field (represented by natural fractures) and the modern in situ stress field (represented by drilling- and coring-induced fractures). Natural fractures most closely aligned with present-day maximum horizontal stress are more likely to be open in the subsurface and to remain open during production.
Paleomagnetic orientation of fractures in existing cores has proven to be a reliable, accurate method for determining paleostress and in situ stress prior to drilling. Our paleomagnetic nalyses of Jean Marie cores from 4 different wells reveal that mineralized natural fractures strike 15 °clockwise f induced fractures and that induced fractures strike ENE, consistent with published wellbore breakouts from this region in other projects, tests against FMI/FMS confirm the ccuracy of our paleomagnetic technique, which works equally well on fresh cores and on cores drilled decades ago. Paleomagnetic orientation of fractures in cores stored in thearge repositories in Calgary and Fort St. John is a wisenvestment when planning optimum trajectories for horizontal nd deviated wells in fractured resevoirs.
Within the last few years, the Jean Marie has emerged as a new and exciting target for horizontal drilling. It has been estimated1 that only 33 percent of the gas resource in the Jean arie had been discovered by 1993, leaving 24,035 106 m3 (849 Bcf) OGIP undiscovered Of the estimated 282 pools yet To be discovered, about 18 are predicted to have OGIP > 283 106 m3 (10 Bcf), and some could be as high as 2,158 106 m3 (76 Bcf).
The low reservoir quality of the matrix, combined with the reduced probability of encountering vertical fractures in vertical wells, makes horizontal drilling the preferred method or both exploring and developing the Jean Marie. Of critical importance in "fracture hunting" using horizontal wells, is the orientation of the well path, Since water production is not a concern in the Jean Marie, horizontal wellbores should be oriented perpendicular to open natural fractures. Work by Geophoto Services Ltd. utilizing air photographs indicates that the lineament pattern in this region3,4 is bimodal, with major trends of about N500 °E and S50 °E[2. Published studies based n wellbore breakouts in this region3–4 indicate that maximum horizontal in situ stress (σHmax) is oriented N61 °E, although with significant variability. Since there was a lack of detailed information where a major exploration and development program was being planned in the vicinity of the Peggo field, we used existing cores to investigate the relationship between duced and natural fractures in NE British Columbia/NW Alberta (Figure 1). Orientation of the cores was accomplished using our paleomagnetic core-orientation technique5–9.
