Award Abstract # 0635876
Collaborative Research: Using Pore Fluid Pressure Gradients to Test the Relative Importance of Hydrologic Versus Mechanical Heterogeneity in Fracture Formation

NSF Org: EAR
Division Of Earth Sciences
Recipient: UNIVERSITY OF MASSACHUSETTS
Initial Amendment Date: January 22, 2007
Latest Amendment Date: January 22, 2007
Award Number: 0635876
Award Instrument: Standard Grant
Program Manager: David Fountain
EAR
 Division Of Earth Sciences
GEO
 Directorate for Geosciences
Start Date: August 1, 2007
End Date: July 31, 2011 (Estimated)
Total Intended Award Amount: $140,780.00
Total Awarded Amount to Date: $140,780.00
Funds Obligated to Date: FY 2007 = $140,780.00
History of Investigator:
  • David Boutt (Principal Investigator)
    dboutt@geo.umass.edu
Recipient Sponsored Research Office: University of Massachusetts Amherst
101 COMMONWEALTH AVE
AMHERST
MA  US  01003-9252
(413)545-0698
Sponsor Congressional District: 02
Primary Place of Performance: University of Massachusetts Amherst
101 COMMONWEALTH AVE
AMHERST
MA  US  01003-9252
Primary Place of Performance
Congressional District:
02
Unique Entity Identifier (UEI): VGJHK59NMPK9
Parent UEI: VGJHK59NMPK9
NSF Program(s): Tectonics
Primary Program Source: app-0107 
Program Reference Code(s): 0000, OTHR
Program Element Code(s): 157200
Award Agency Code: 4900
Fund Agency Code: 4900
Assistance Listing Number(s): 47.050

ABSTRACT

Extension fractures are common elements of a wide range of geologic settings. They are generally inferred to form in response to high pore fluid pressure and to nucleate on mechanical heterogeneities. Such fractures are of particular societal interest where they provide pathways for fluid flow or contaminant transport in reservoirs or aquifers, yet we still lack the capability to predict where they are likely to form, and in what density. This project examines the hypothesis that spatial variations in hydrologic properties are as important as spatial variations in mechanical properties in controlling where and when fractures form. Thus, a rock's mechanical behavior is a function not only of its heterogeneous mechanical properties, but also its heterogeneous ability to transmit and maintain elevated pore fluid pressures. The relative importance of hydrologic and mechanical heterogeneities in controlling the formation of extension fractures in sandstone, a common natural rock reservoir/aquifer is being investigated in this project. To accomplish this goal, laboratory experiments in that initiate hydraulic fractures while producing a pore fluid pressure gradient within a test sample are being carried out. A drop in both stress and fluid pressure at the boundary creates transient conditions conducive to the generation of extension fractures in finely laminated, well cemented, fine-grained, low diffusivity sandstone samples. By integrating pore fluid pressure gradient experiments with extensive bulk and grain-scale characterization of mechanical and hydrologic heterogeneity, fracture formation can be related to the petrophysical characteristics of a rock - an important step toward predictability. Pre-test analyses include the measurement of hydraulic diffusivity, tracer break-through curves (a proxy for degree of homogeneity), and poroelastic properties in different orientations relative to bedding, the most common physical heterogeneity in sedimentary rocks. Measurement of these bulk responses is complemented by detailed, grain-scale study of both the rock's solid framework and the pore network, and mm-cm scale variations in permeability.

Fractures provide important pathways for fluids (such as water or oil) to move underground. Current understanding of how fractures form and grow under geologic conditions is extremely limited. This study attempts to better understand the role of subsurface fluids on the genesis of fractures in rock by studying their growth in a newly developed laboratory-based testing method. Through the combination of detailed analyses of the rock prior to and post fracturing the important variables that that control the timing, location, and intensity of fracturing can be evaluated. Incorporation of this information into models of the subsurface will allow scientists and engineers to more effectively produce or store fluids in the sub-surface of the Earth.

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