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The new geophysics

Shear-wave splitting provides a window into the crack-critical rock mass

University of Edinburgh, Scotland, U.K.

Corresponding author: scrampin@ed.ac.uk; http://www.smsites.org/; http://www.glg.ed.ac.uk/scrampin/opinion/

Editor's note: This paper is an updated version of an article in Significant Developments in Seismic Exploration in the Last Decade and Future Developments, a special issue of the CSEG Recorder in 2001. The reader is referred to that article for a detailed reference list. Many of the referenced papers can be found at http://www.glg.ed.ac.uk/scrampin/opinion/.

The first 20% of the full text of this article appears below.

In this article, I suggest a new style of geophysics as a critical system, which has profound implications for almost all aspects of prefracturing deformation in the crust, particularly reservoir characterization, time-lapse seismics, and hydrocarbon recovery. One of the most important features of the new geophysics for the oil industry is that the high-resolution details of fluid-saturated reservoirs and rocks vary with time and place. Current techniques using conventional technology and conventional geophysics may well be near their limit in resolution. Further enhancements will monitor the new geophysics where sensitivity to seemingly negligible disturbances is expected, and has now been observed.

The overall evidence for the new geophysics is overwhelming, but to explicitly demonstrate these results directly is difficult because of the essential inaccessibility of rock at depth. Thus to provide definitive proof is difficult because we need to look at details that are troublesome and expensive to obtain with conventional instrumentation and conventional techniques. Consequently progress has been slow. There are many effects. Those proven to date include: (1) oil production that has been shown by Heffer et al. to be linked across substantial distances in mature reservoirs; (2) Angerer et al. have shown that the effects of fluid-injection may be calculated almost from first principles (in effect predicted, with hindsight); and (3) in the first direct observations, seismic velocities, shear-wave splitting, well pressures, and GPS measurements have now been shown by my group to vary with low-level seismicity at 70 km (and by implication, volcanic activity at 240 km). This new geophysics means that one can no longer expect to understand and interpret the detailed behavior of rocks by looking at a limited local picture (whatever the virtual reality!). We extract oil from an integrated crack-critical rock mass. Future advances depend on new technology and a new understanding . . . [Full Text of this Article]