Interpretation of seismic data from hydraulic fracturing experiments at the Fenton Hill, New Mexico, hot dry rock geothermal site

Abstract

An attempt was made to synthesize the results of active seismic experiments carried out by the Los Alamos National Laboratory's Hot Dry Rock Project staff for determining the geometrical and physical properties of the fracture system produced by hydraulic fracturing in a hot, low‐permeability rock. Interpretation of data from several reflection, transmission, and attenuation experiments using seismic probes in the frequency range from a few hundred to more than 104 Hz led us to postulate the existence of a highly complex fracture system consisting of major discrete vertical cracks intersected by several inclined joints which are surrounded by a large volume of rock containing small‐scale cracks. We found an interesting coincidence between the mean square fluctuation of P arrival time arid Q−1 of coda waves. Both are increased by nearly the same amount (35∼40%) when fluid pressure in the reservoir is increased. Another coincidence is the scale length of the inhomogeneity of roughly 3 m obtained from the frequency dependence of attenuation and also from the spatial variation of P arrival time. These results suggest that the seismic attenuation in the fractured region is caused primarily by scattering.

Deep explosive volcanism on the Gakkel Ridge and seismological constraints on shallow recharge at TAG active mound

“…Studies at deep-sea hydrothermal vents and geothermal sites on land have shown that seismic activity can affect hydrothermal flow by perturbing the thermal state and/or permeability structure of the local crust [Aki et al, 1982;Bame and Fehler, 1986;Ferrazzini et al, 1990;Bianco et al, 2004;Foulger et al, 2004;Wilcock, 2004;Cuenot et al, 2006]. While these observations provide intriguing evidence for seismic perturbation of hydrothermal flow, the extent to which they may be generalized is not clear.…”

“…Flow-induced microearthquakes generated by volume change mechanisms have been observed in geothermal areas [e.g., Ross et al, 1996;Miller et al, 1998;Foulger et al, 2004] and hydraulic fracturing experiments [e.g., Aki et al, 1982;Cuenot et al, 2006;Julian et al, 2007;Šílený et al, 2009], but this is the first time that a network small enough to detect and locate them has been deployed at a deep-sea hydrothermal field.…”

Induced seismicity in geothermal reservoirs: A review of forecasting approaches

“…This effect has been known for more than 30 years, e.g. [4,5], and has been observed in areas, such as Indonesia, the Philippines, Japan, North and South America, and New Zealand. In most cases of induced seismicity, many events are generated each year, usually with magnitudes smaller than ML=3 and hence without economic consequences.…”

SeisCORK engineering design study

“…The notion of "time lapse" seismology goes back at least 20 years when Aki proposed the method for analysis of hydrofracturing in petroleum and geothermal wells [Aki, et al, 1982]. The character of the seismic reflections in subduction zones can vary with time for at least three reasons: 1) when the state of stress on a horizon of interest varies with time a) as a result of an earthquake on the fault (over seconds), b) as a result of an earthquake in the region which changes the regional stress pattern (Coulomb stresses, over days, months and years), or c) as a result of slow deformation (over tens of years); 2) when the drilling process itself changes the in situ pressure conditions on the fault by relieving whatever pressure anomaly may have originally existed (over hours to years); and 3) when the seismic acquisition system changes.…”