Print this pageEvaluating Thermogenic Tight Gas Shales, the Unconventional Frontier with Proven Success
From an analytical view, tight gas shales
can be separated into 3 broad classes; Biogenic (immature clay), Biogenic
(mature clay), and Thermogenic. Thermogenic
tight gas shales can be subdivided into 4 main types
based on similar lithofacies, common clay and kerogen types. One of the most widely recognized and
successful types of thermogenic tight gas shales could be identified as Thermogenic
Classic (examples include the Barnett,
Dominant lithofacies common to this type of shale include; Calcareous Mudstones, Silica rich Mudstones, and “Low Resistivity” Claystones. Other lithofacies are present and can be important “economically” or “mechanically” when present but are not considered common, by the author, across the different basins in which this type of shale is producing. Clays are generally mixed layer smectite-illites with other clays fading in and out. Kerogen types are dominantly mixed percentages of Kerogen Type II and III.
This type of consistency would suggest that these shales could be targeted similarly. However, field experience and laboratory measurements suggest that they require varying completion strategies as dictated by kerogen maturity, changes in diagenic alterations, subtle changes in clay and kerogen type, and even more often by changes in stress regimes and seal arrangements. Unlocking the productivity of these complex reservoirs requires a detailed level of evaluation not common to the industry.