Camron K. Miller1, Ira D. Sasowsky2
(1) Schlumberger Oilfield Services, Sugar Land, TX
(2) University of Akron, Akron, OH
ABSTRACT: Petroleum Reservoir Potential of Stress-Release Fractures Near Paleovalleys and Residual Paleohighs
Stress-release fracturing produces an anisotropic network of fractures that parallels valley walls and increases original rock permeability by several orders of magnitude. In modern day settings this process is responsible for significant fracture porosity, as well as anisotropic karst porosity. These near-surface fracture systems are interconnected and become conduits for the movement of fluids, and the formation of shallow, stress-release aquifers. The goal of this study is to evaluate whether such high permeability zones might be preserved upon burial, and serve as hydrocarbon reservoirs.
Geological, well log, and production data were compiled to evaluate reservoir quality within the South Eubank Field, Kansas, and Killbuck Township, Ohio. Geophysical and geologic data for productive center-targeted wells were compared to those for productive marginal wells in order to evaluate the hypothesis. The major fracture indicators on well logs were caliper expansion and unexplained spiking in density correction and dual induction logs. Other indicators include rubble zones and kicks in the drilling rate.
Fractures were detected, in varying degrees, within the geophysical data for wells drilled into or adjacent to the paleovalley system in Kansas. Four of the wells contained strong indications of marginal fractures. To a lesser degree, fractures were detected for wells that were drilled into Knox remnants within Ohio. Four of these wells contained moderate indications of fractures along the margins of buried structural highs. Additional drilling targets may exist within settings containing paleovalleys and/or residual paleohighs as a result of stress-release fracturing.
AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado