Perspective: To put this quote from Price’s 1999 paper Origins and characteristics of the basin-centered continuous unconventional oil-resource base of the Bakken Source System, Williston Basin, 1999/2000 in perspective, here is a chart containing Price’s low reserve estimate with the proven and potential reserves of the major petroleum producing countries of the world.
Stratigraphic Column: The Bakken Formation has gross thicknesses in the neighborhood of 150 ft and is a “shale sandwich.” Two world-class high TOC marine shales sandwich a brittle dolomitic siltstone with very little native porosity and permiabilities on the order of 0.04 millidarcies.
Parshall Field – Conventional Processing: The Bakken Test line was shot and processed to maximize the seismic thin-bed resolution. This is a segment of the line in Parshall Field that was “dumbed-down” in the processing for comparison. By any standard, this would be considered at or near the top of the quality scale for seismic imaging in this area. However, these data were recorded and processed at 1ms sample rate and the p-wave section above contains additional stratigraphic information that, when properly handled, can point to prospective drill locations.
Parshall Field – VHF Processing: This is the same segment as shown previously, but processed to exploit the high-resolution capacity of the 1ms broad-band data. Vector High Fidelity has successfully separated several thin-bed reflectors and imaged a very subtle fault near the top of the gentle structure. The red trough just under the Bakken top, correlates nicely with the Middle Bakken.
Sanish Field – Conventional Processing: Much farther west on the Vector Bakken Test line, in the Sanish Field, the seismic character is significantly different at the Bakken Level. The Sanish Facies is much sandier.
Sanish Field – VHF Processing: But even here, Vector High Fidelity processing does an excellent job of reducing seismic noise and improving thin bed resolution.
3C Geophones: The 3-component geophones used by Tesla-Conquest to record the Vector Bakken 2D/3C Test Line were made by Sensor and are true geophones. Each unit contains three orthogonal elements permanently mounted in a solid aluminum case – about 2-1/4 inches in diameter and 6.5 inches long. Each phone was buried in a pre-drilled pilot hole.
3C Field Layout: This schematic illustrated how it is critical that each receiver have a common compass orientation in the field. Of course, this is a simple matter but no less important for a 2D line where one of the principal axes is along the line azimuth. It becomes more complex when recording a 3D/3C survey.
3C Processing Layout: I the processing, it is necessary to mathematically orient the geophones into source-centric axes. The radial shear orientation will face away from the shot whereas the transverse, or cross-line polarization will be perpendicular to this azimuth. Notice that the polarization of the geophones on either side of the source are reversed from each other. This has to be accounted for in the processing as well.
P-wave Dry Hole: This is the p-wave version of the seismic profile at the Behm Energy dry hole.
S-radial Dry Hole: This is the radial shear-wave version of the same segment at the dry hole. Note that the Bakken reflection is continuous in the absence of fractures. Note also that there appears to be some evidence of vertical (tectonic) fractures both east and west of the dry hole. This suggests that the tectonic fractures, by themselves, are insufficient to predict hydrocarbons if the well is outside of the thermal-maturity limit for oil expulsion.
P-wave Parshall Field: Parshall Field looks very similar to the dry hole with the p-wave seismic. There is a slightly higher noise level as you progress to the west across the basin. But essentially, there is nothing that would tell an explorationist to drill here and to avoid the Behm location.
S-radial Parshall Field: The radial-shear version of this line segment tells a dramatically different story. Notice that the presence of hydraulic fractures is having a profound effect on the polarized wave field. The pseudo time structure visible on this image is a manifestation of the distortion of the wave front due to fractures and fluids rather than a true mappable time structure. Also notice that the continuous deeper reflection at about 3.400 sec. attests to the fact that the wave field distortion is a localized phenomena. Compare with the deep reflector at the Behm Energy dry hole.
Bakken Edge: The Behm Energy dry hole could have been avoided if the test data generated by Vector had been available. The identification of the limits of the Middle Bakken reservoir in North Dakota and Canada is possible with high-resolution, multi-component surface seismic methods, and at significantly less money that even a single dry hole. To this end, Vector is currently conducting a seismic reconnaissance survey to tag the so-called Bakken Edge and to further identify sweet spots where natural fractures will greatly enhance the economic success of a horizontal well.