Changes in the physical properties of a reservoir during hydraulic fracturing of the hydrocarbon bearing layer are performed to increase the productivity of oil-and-gas wells. These changes in physical properties were studied using analyses of seismic recordings of perforation shots carried out on two monitored wells within the Fort Worth Basin, North Texas (USA). Seismic recordings obtained from monitor wells distributed at a distance not exceeding 1000m from the source were chosen for analysis. The process of hydraulic fracturing included multiple stages; perforation shots were set off before the start of the process as well as between stages. The signals were recorded using a system of 12 three-component seismic receivers, installed vertically in the monitor well.
The analysis of waveforms and spectral characteristics of P-waves has shown that the character of the recorded signal and the P-wave spectrum are being repeated with high precision (correlation coefficient >0.95) for shots that are close in time (interval between shots < 10mins) and in space (distance between blasts < 15m). Lower correlation coefficients (<0.3) and spectral differences were observed for signals diffusing from the same point (distance between shot locations - 12m), but separated in time by hydraulic fracturing. These results confirm that the process of hydraulic fracturing leads to substantial changes in the physical properties of the reservoir that can be shown experimentally and analyzed theoretically.
Various natural and artificial processes that occur in the Earth's crust - natural earthquakes, hydrothermal activity, the development of geothermal reservoirs, the injection of waste water into reservoirs, and the processes of hydraulic fracturing during the completion of oil-and-gas reservoirs - significantly influence the physical properties of geological media. However, until recently, a priori defined seismic models built on initial data and not corrected for errors associated with underlying processes have been used in seismological research. The use of this approach with time leads to interpretation of results that no longer adequately reflect the reality of the medium. Theoretical investigations of complex media indicate that changes in the stress state and fluid saturation of the medium lead to substantial changes in its physical properties (Nur, 1971; Rathore et al., 1994; Cesnokov et.all, 2009; Zatsepin and Crampin, 1997).
URTeC 1619217
