Geologic Commonalities (and differences) among Resource Shale Plays
Most of the gas- and oil-producing resource shales have a number of fundamental properties in common: they all (1) have some porosity and permeability for storage and transport of hydrocarbons, (2) are composed of common minerals that partially govern geomechanical properties, (3) contain organic matter as a hydrocarbon source rock, (4) have geomechanical properties that affect drilling and fracturing, (6) are stratified,which also affects geomechanical properties, and (6) exhibit a generally common sequence stratigraphic stacking pattern. However, there are differences in these properties among the various shales, as follows: (1) There are several different pore types, and their abundance differs among the shales; (2) common minerals as quartz, calcite, clays, and dolomite vary in abundance among the shales; (3) TOC varies in abundance, distribution, and maturity among the shales; (4) geomechanical properties are a function of mineralogy, porosity and TOC content, and thus vary with these properties of the shales; (5) thickness, amount, composition and orientation of laminae and strata differ among the shales, which also affects geomechanical properties; (6) orders of cyclicity are recorded in stratigraphic stacking patterns at a number of scales, thus affecting the stacking of brittle and ductile strata, often into 'brittle-ductile couplets'. These properties are all interrelated, and often predictable when viewed within a sequence stratigraphic framework. This can lead to improved stratigraphically-targeted drilling of horizontal wells and identification of stratigraphic sweet spots. To optimize this improvement, one should seek to document the detailed differences in addition to the commonalities of the shales. In the case of the resource shales "the devil is in the details".
AAPG Search and Discovery Article #90176©AAPG Mid-Continent Meeting, Wichita, Kansas, October 12-15, 2013