Unconventional Exploration: Will Your Next “Sweet Spot” Have Once Been a “Hot Spot”?

Abstract

One of the persistent problems encountered during exploration for unconventional plays is the inability to identify the “sweet spots” prior to leasing and drilling. Typically, seismic is used for high grading, but it is expensive, ground access can be limited resulting in partial coverage and, as with many technologies, the interpretations can be ambiguous. However, there are less expensive alternatives such as remote sensing, integrated organic/inorganic petrography, gravity, magnetic, and various types of thermal maturity data that can be used to initially identify areas with higher production potential. After this 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. In separate studies, experts have recently independently converged on the concept of using a combination of less expensive screening technologies to identify areas of localized high heat flow where recurrent movement of basement faults in areas already known to contain rich source rocks results in the maturation and trapping of hydrocarbons by hydrothermal fluids. Their publications indicate that at both a mega-scale as well as a micro-scale, an internally consistent genetic model can be developed that shows, in multiple diverse locations, “sweet spots” for oil accumulations in unconventional plays are often related to local “hot spots”. In turn, igneous intrusions into sedimentary successions, which are far more common than is generally realized, often drive the hydrothermal activity that is responsible for these “hot spots”. Recurrent movement on faults and lineaments that extend to the basement can provide conduits for hydrothermal fluids into the sedimentary section. At such “hot spots”, the hydrothermal fluids and associated volatiles can have a significant impact on hydrocarbon generation and migration as well as on host rock permeability, porosity, fracturability, and overpressuring. In this presentation, examples given from the Eagle Ford at First Shot Field in Texas and the Parshall and Stanley fields in the Williston Basin illustrate that better production is related to areas of localized convective heat flow. Convective heat flow via hydrothermal fluids is much more efficient than the transfer of heat by conductive heat flow. Evidence for hydrothermal activity in both areas is provided by relatively inexpensive screening techniques. Such examples demonstrate the commercial benefit of exploiting low cost alternative methods to effectively and efficiently identify “sweet spots” for unconventional plays. A different tool box adapted to unconventional resource exploration can improve project economics.

AAPG Datapages/Search and Discovery Article #90193 © 2014 Rocky Mountain Section AAPG Annual Meeting, Denver, Colorado, July 20-22, 2014