Abstract

A novel wave-mechanics approach is developed specifically for understanding instabilities that form large natural fluid-transmissivity networks in unconventional reservoirs located in a nominally impermeable matrix. These natural flow networks are trapped in the ductile equivalent of brittle faults characterized by the solid-mechanical Arthur-Vardoulakis angle. The main mechanism for ductile deformation and in situ fluid generation is identified to be a chemical reaction such as diagenesis. Diagenesis involves fluid-release mineral reactions of the general type ABsolidAsolid + Bfluid and switches on suddenly in the diagenetic window between 100°C and 200°C. Diagenetic reactions often relate to dewatering reactions of phyllosilicates and can involve concentrations of smectite, aqueous silica compound, illite, potassium ions, quartz, feldspar, goethite, hematite, pyrite, calcite, kaolinite, organic matter, water, and gas. In classical petroleum engineering, such interlayer water/gas release reactions are considered to cause cementation and significantly reduce porosity and permeability. However, if a tectonic load is applied, there are critical loading conditions in which the inverse dissolution reaction can form fluid-channeling instabilities. This new wave-mechanics approach might assist in the next paradigm shift for exploration, production, and flow assurance of unconventional gas and oil, underpinned by a better understanding of significant instabilities from volumetric deformation controlled by diagenetic reactions.

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