Fluid-Assisted Compaction and Deformation of Reservoir Lithologies: Final Report
OAK (B204) The compaction and diagenesis of sandstones that form reservoirs to hydrocarbons depend on mechanical compaction processes, fluid flow at local and regional scales and chemical processes of dissolution, precipitation and diffusional solution transport. While the mechanical processes that govern grain-scale compaction of sedimentary rocks in the absence of reactive fluids are well documented, those that control time-dependent compaction and solution transfer in the presence of fluids are not. Our research has established the critical hydrostatic and triaxial loading conditions required for mechanical cracking of quartz aggregates under diagenetic conditions and rates of creep under sub-critical stress conditions. Our results include effects of grain size, presence of an aqueous fluid, and fluid flow rate. We have developed models that predict fluid chemistry on the basis of stress-induced solution transport and crack damage at grain contacts. Mechanisms of deformation at the experimental conditions have been identified unambiguously by monitoring acoustic emissions and by quantitative study of microstructures at grain contacts. Our research has led to a significant reassessment of conditions that favor subcritical cracking and strain-induced dissolution versus those that favor stress-induced solution transfer creep. Microstructural observations of our samples and acoustic emissions monitored during experiments show that fluid-assisted cracking is the predominant mechanism of deformation at stresses well below critical conditions (Pe * 0.35 Pe* where Pe* is the critical hydrostatic state for grain crushing and pore collapse). These results have implications for the range of natural conditions that favor fluid-assisted cracking, particularly as effective stresses required for this process will be even lower in the Earth as characteristic loading times are increased. They also have implications for non-equilibrium silica concentrations of percolating pore fluids, as elevated silica concentrations due to deformation are governed by increased surface areas following brittle failure rather than by stress heterogeneities and local interfacial values of pore fluid pressure, Pf. This research has led to a thorough PhD Dissertation and to an outstanding MS Thesis. We report our findings in 7 papers, 3 of which are in print, and 4 manuscripts that have been submitted to journals for publication. In addition, we have submitted 2 more manuscripts based on earlier DOE-BES support.
- Research Organization:
- Texas A&M Research Foundation
- Sponsoring Organization:
- USDOE Office of Science (SC)
- DOE Contract Number:
- FG03-98ER14887
- OSTI ID:
- 811914
- Report Number(s):
- DOE/ER14887-4; TRN: US200706%%632
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
03 NATURAL GAS
36 MATERIALS SCIENCE
58 GEOSCIENCES
ACOUSTICS
CHEMISTRY
CREEP
CRUSHING
DEFORMATION
DIAGENESIS
DISSOLUTION
FLUID FLOW
GRAIN SIZE
HYDROCARBONS
HYDROSTATICS
MONITORING
PRECIPITATION
QUARTZ
SANDSTONES
SEDIMENTARY ROCKS
SILICA
STRESSES
SURFACE AREA
TRANSPORT
diagenesis of reservoirs rock-fluid interactions mechanical compaction compaction creep solution transfer subcritical cracking