The field of geofluids addresses questions of how crustal fluids and fluid–rock interactions influence a wide variety of geologic processes. Geologic fluids or geofluids, which can occur at depths of up to 100 km, are not easily accessed. Frequently, evidence of geofluid–rock interactions has had to be inferred in a forensic analysis of altered rocks at or near the Earth's surface. A geofluid is not a liquid that one would ever want to drink. They are hot (100 to 1200 °C), saline and often contain large quantities of dissolved magmatic gases, such as CO2. In some instances, water is not even the solvent!
Geofluids research began in the 1950s with the seminal work of Hubbert and Rubey (1959) on the lubricating effects of fluids on the mechanics of thrust faulting. These authors resolved a longstanding dilemma that frictional forces acting along thrust faults were too great to permit the displacement of long, relatively thick thrust sheets in mountainous terrains. This work later provided the theoretical basis for understanding the role of excess pore pressures on induced seismicity associated with hazardous waste injection. During the 1960s to 1990s the field of geofluids gained breadth with the recognition that fluid circulation played an important role in the genesis of ore deposits and hydrocarbon accumulations, metamorphism and the cooling of magma bodies. Geofluids was finally recognized as a discipline in the 1990s with the publication of books by Bredehoeft et al. (1990) and Ingebritsen and Sanford (1998). Since then, hundreds of M.Sc. theses and Ph.D. dissertations have been published on this topic.
The new book, Frontiers in Geofluids by Bruce Yardley et al., presents the state-of-the-science in this field. This book is a compilation of a set of invited papers, originally published electronically, as a special double volume of the journal Geofluids to celebrate its 10th anniversary. Manning, Yardley and Garven have chosen a top-notch set of authors, and this is reflected in the quality of their book. Frontiers in Geofluids is divided into four parts. The first set of articles focus on new developments in the characterization of aqueous fluid properties, as well as mineral solubility and fluid composition at elevated temperatures and pressures using experimental and theoretical approaches. The second section of the book focuses on the role of geofluids in petroleum basins. These articles cover a broad range of topics including the role of fault permeability architecture in petroleum migration and entrapment, the evolution of basinal brines, and oil-charge analysis using petroleum containing fluid inclusions. A third set of papers focuses on thermal and geochemical conditions of geofluids within sub-seafloor environments including mid-ocean ridge systems and subduction zones. Two papers from this section assess how sub-seafloor permeability conditions affect temperature and salinity patterns. A final set of papers focuses on geofluids within the continental crust. Some of the many topics covered in this section include new measurements and hypotheses regarding crustal permeability, the response of crustal fluids to seismic events, geofluids in retrograde metamorphism and metallogenesis, the use of fracture sets and orientations to deduce fluid pressure, and stress regimes.
Why purchase a book on such a seemingly esoteric topic? The era of cheap, easy-to-find oil is over. The petroleum industry is increasingly exploring for oil in ultra-deep environments. During the last decade, climate change scientists have expended considerable resources to assess the feasibility of injecting vast quantities (30 Gt) of supercritical CO2 into deep saline reservoirs annually. Concurrently, the geothermal industry has been focused on developing engineered geothermal systems by hydrofracturing crystalline rocks at depths of 4–6 km. The findings presented in Frontiers in Geofluids have important implications for all of these initiatives.