Assessments of unconventional plays typically rely on single property to property relationships to define drivers for economic success. These may include fracture corridors, organic-rich facies, and high thickness-permeability products. Unfortunately this concept has been rather elusive. To a large extent, the industry uses conventional reservoir thinking to explain unconventional field observations. This results in great confusion and the generation of local experience that cannot be transferred elsewhere. A new mental picture of tight shale plays is proposed which recognizes the role of geology to generate substantial variability in material properties across seemingly similar depositional units. Understanding that subtle changes in rock composition and texture associated to geologic processes (deposition, tectonics, and diagenesis) are responsible for substantial changes in reservoir quality and completion quality properties, and understanding that log responses are also affected by rock composition and texture allow defining a new pattern for relating geology, material properties, and logs, quantitatively.
A regional evaluation of reservoir quality, completion quality, and production potential was developed for the Haynesville shale over an area of 7,185 square miles. The study was supplemented with comprehensive core studies including measurements of petrologic, geochemical, petrophysical, and mechanical properties across all facies. Rock classes with unique properties of reservoir quality and completion quality were identified based on high-resolution logs, and related to the geologic model built from core observations. The distribution of the rock classes was then tracked throughout the basin. This approach allowed mapping the reservoir potential in a very effective manner.
Integrating geology with material properties on a rock class by rock class basis provides remarkable knowledge needed for the field development. While core extractions and seismic surveys are often conducted in isolated areas, this method also provides background information for selecting the most strategic locations for supplemental cores and seismic data. This methodology can optimize the early exploration phase of unconventional plays.