With unconventional exploration expanding into basins with little seismic data and few wellbores, some lower cost technologies should be exploited up front to select areas of greater economic potential. Typically, 3D seismic is used for high grading, but it is expensive, ground access can be limited resulting in partial coverage, and, as with many technologies, interpretations can be ambiguous. However, there are less expensive alternatives such as remote sensing, gravity and magnetics, geochemistry, and petrography that can be used to initially identify areas with higher potential. After the initial screening evaluation, the high graded areas can subsequently be appraised using more expensive techniques. Using less expensive screening alternatives up front can improve results and project economics.
As an example, in some unconventional plays, such as the Parshall Field in the Williston Basin, better production is related to areas of localized convective, high heat flow that is associated with recurrent movement of basement faults. Convective heat flow via hydrothermal fluids is much more efficient than the transfer of heat by conductive heat flow. In the greater Williston Basin, gravity and aeromagnetic data along with remote sensing data have been used in regional structural evaluation and statistical fracture analysis to identify different types of basement. Faults and lineaments that have been mapped in the area of the Parshall and Stanley fields may have served as conduits for acidic brines and hydrothermal fluids in the Parshall Field. Previously, Parshall Field was thought to be in an area that was thermally immature, but geochemical data indicate the Bakken at Parshall Field is actually at peak oil generation with significant amounts of oil having been generated in situ as a result of convective hydrothermal heat flow.
The screening data support the hypothesis that recurrent movement on faults and lineaments provided conduits for hydrothermal fluids and igneous volatiles. This is interpreted to have had an important impact on in situ hydrocarbon generation, and petrography further suggests that precipitation of minerals from these hydrothermal fluids has affected porosity, permeability, rock fracturability and overpressuring. Parshall Field has produced more than 65 million barrels of oil and 30 billion cubic feet of natural gas.