HR: 1340h
AN: S23B-0314    [Abstracts]
TI: "Interactive Seismics", Aki & Richards, Chapter 16
AU: * Leary, P C
EM: pcleary\_mog@compuserve.com
AF: Geospace Engineering Resources International, 7007 Pinemont, Houston, 77040 United States
AU: Walter, L
EM: lwalter@geo-eng-res.com
AF: Geospace Engineering Resources International, 7007 Pinemont, Houston, 77040 United States
AU: Crampin, S
EM: scrampin@glg.ed.ac.uk
AF: University of Edinburgh, Grant Institute West Mains Road, Edinburgh, EH9 3JW United Kingdom
AB: The defining physical character of cold brittle crustal rock hosting geofluid reservoirs and earthquake instabilities is '1/f-noise' spatially-correlated fluctuations in fracture-density. Evidence for 1/f-noise fracture-density fluctuations is manifest in power-law-scaling well-log spectra from $<$1/km to $>$1/cm, spatial correlation of well-core porosity and log(permeability), and the Gutenberg-Richter relation. Unlike spatially-uncorrelated randomness, power-law-scaling spatially-correlated randomness provides no reliable spatio-predictive relation between a sample and the whole. In particular, no point-measurement sequence in a crustal reservoir -- static well-log, temporal pressure-log or strain-log, or earthquake locations - accurately samples a reservoir state. Rather, useful knowledge of a reservoir state requires broadband observation of the whole reservoir as it is perturbed. Such observations could be called 'interactive seismics'. 'Interactive seismics' reservoir monitoring is becoming routine in the oil and gas industry, as embedded sensors record time-lapse source signals to determine where water replaces produced oil and gas. Interactive seismics is feasible with CO2 injection, and may become feasible for active fault zones. Interactive seismics benefits from stable downhole sources and sensors. Imperatives for better hydrocarbon reservoir observation are providing compact, robust, stable seismic sources and vector-sensors, and the means to deploy them downhole. Extensive crosswell seismic data, including monitored travel-times in a tectonically active crust, establish useful performance levels for downhole seismic sourcing at wavelengths 5-50m: crosswell transmission scale $\sim$1km, single-well back-scattering scale $\sim$200m, source wavelet stability \delta S/S $\sim$ 0.03%, and travel-time resolution \delta\tau/\tau $\sim$ 0.03%. Using the attested downhole source parameters, we simulate interactive seismic observation of a 1/f-noise fracture volume undergoing strain increments due to local seismic slip. The simulations use in situ velocity/strain data to estimate how downhole sourcing in the geometry of the prospective SAFOD multi-lateral completion can 1) scan 1/f-noise fracture volumes to locate high-strain response zones that potentially indicate where subsequent slip events will occur, and 2) detect strain-weakening along source-sensor ray-paths that possibly predict incipient slip events. Such development of crustal reservoir seismic observation may in time prompt an Aki & Richards Chapter 16 called, perhaps, 'Interactive Seismics'.
DE: 7209 Earthquake dynamics and mechanics
SC: Seismology [S]
MN: 2004 AGU Fall Meeting