Background and Links

Structural Diagenesis

A challenge for geoscientists is to understand fractures in the deep subsurface. Fluid flow in fractured rock is increasingly important in recovering water and hydrocarbon supplies and geothermal energy, in predicting flow of pollutants underground, in engineering structures, and in understanding large-scale crustal behavior. Natural fractures, a major unknown in unconventional oil and gas reservoirs, can interact with engineered hydraulic fractures in surprising ways.  Yet learning about fractures is not easy. Fractures are exceedingly hard to sample in meaningful ways, and models to date have been hard to test, partly because fractures formed by different processes can look alike—if analysts don’t know what to look for.

Meeting the challenge of accurate fracture characterization and prediction has been the mission of the Structural Diagenesis Initiative. And breakthroughs have come from looking at the old problem of fractures in new ways. Since the first scientific notice of fractures in the 1800’s, the starting point for understanding fractures has been mechanics—a reasonable perspective given everyday experience. Rigorous application of fracture mechanics continues to yield insights. But for fractures in the deep subsurface, mechanics, no matter how complete, is inadequate. In the presence of reactive fluids like hot water, ubiquitous in the subsurface, chemical reactions are essential. Sedimentary petrologists study chemical reactions that convert sediment to rock—diagenesis—but typically neglect fractures.

Scanning-electron-microscope images of structural diagenetic textures within fractures. The linear feature in the center is a cement deposit called a bridge formed during fracture opening. Such bridges, discovered in Bureau research, allow researchers to measure key aspects of fractures, such as opening rate, that were previously inaccessible. Results can test predictive models and improve subsurface fracture diagnostics.

Focusing on the geochemical reactions in fractures and surrounding rocks was a breakthrough that led to new, more effective and accurate ways of predicting and characterizing fractures—an approach called structural diagenesis[i]—a new research and training paradigm in sedimentary geochemistry and structural geology, and a new discipline.

Structural diagenesis is the study of the relationships between deformation or deformational structures and chemical changes to sediments. In high-temperature deformation research, the alliance of structural geology and petrology is essential. But no such alliance supports research and student training on the increasingly important structural and diagenetic phenomena in lower-temperature environments in sedimentary basins. Such an alliance—structural diagenesis—can help unlock knowledge about the low-temperature realm of sedimentary basins that is of great intrinsic and practical interest.

Links to Related Sites

Fracture Research & Application Consortium

Geocosm: Advanced diagenesis research

Geological Society of America Structural Diagenesis Award

GDL Foundation

[i] Laubach, S.E, P. Eichhubl, C. Hilgers, R.H. Lander, 2010, Structural diagenesis. Journal of Structural Geology, v. 32, no. 12, p. 1866-1872. doi:10.1016/j.jsg.2010.10.001