Verdon J.P.,University of Bristol |
Wuestefeld A.,ESG Solutions
74th European Association of Geoscientists and Engineers Conference and Exhibition 2012 Incorporating SPE EUROPEC 2012: Responsibly Securing Natural Resources | Year: 2012
The effect of fractures on seismic waves is controlled by the normal and tangential compliances of the fractures (BN and BT). Rock physics models and laboratory experiments have indicated that BN/BT will be influenced by (1) the bulk modulus of the fluid filling the fracture, (2) the degree of connectivity between the fracture and equant pore space, and (3) the internal architecture of the fracture, such as the roughness of fracture faces, or the presence of detrital or diagenetic infilling material. Therefore, measurements of BN/BT will provide useful information during hydraulic fracture stimulation. We develop a method to invert S-wave splitting (SWS) data, measured on microseismic events recorded on downhole geophone arrays, for the ratio of normal to tangential compliance (BN/BT) of sets of aligned fractures. We demonstrate this method by inverting for BN/BT using SWS measurements made during hydraulic fracture stimulation of the Cotton Valley tight gas reservoir, Texas. When the full SWS dataset is inverted, we find that BN/BT=0.74±0.04. Windowing the data by time, we have been able to observe temporal variations, finding that BN/BT varies as the stimulation progresses, and most notably when proppant is injected.
Dorion J.-F.,Niobec Inc. |
Hosseini Z.,ESG Solutions
47th US Rock Mechanics / Geomechanics Symposium 2013 | Year: 2013
The Niobec underground niobium mine is located twenty-five kilometres northwest of Ville de Saguenay (Chicoutimi), within the limits of the municipality of Saint-Honoré, Québec. The mine is North America's only source of pyrochlore, the primary niobium ore. All of Niobec ore is extracted by bulk open stope mining with no fill. A mining throughput rate of 10Mtpy is expected with the future block caving method. The life-span of the mine is estimated at about 40 years with the known mineral resource. Some seismic events have occurred in the last number of years. Most of these events occurred in pillars between open stopes or directly in open stopes. Damage from these events has included small rock projections, raveling and fractures. As Niobec has no seismic detection system in place, the epicenter location of each event has been difficult to determine. The design of a seismic system was undertaken in the summer of 2012. Niobec will be able to monitor seismic activity for the current open stope mining operator as well as for the future block caving method by strategically placing the equipment in existing openings above any planned undercuts for the progression of the caves. Copyright 2013 ARMA, American Rock Mechanics Association.
Leslie I.,ESG Solutions
Mining Magazine | Year: 2013
As the depths of open-pit operations continue to increase, stresses within and beneath pit walls can cause considerable instability on slope surfaces. Monitoring systems represent an essential tool to mitigate economic and safety risk associated with slope failure. Despite the fact that seismic monitoring of underground mines is well established, the application of this technology to monitor open-pit mines is relatively recent. The knowledge of seismicity behind pit walls offers engineers an excellent opportunity to evaluate rock-mass behaviour, track fracture propagation and potentially predict slope stability issues before they manifest on the surface. Natural expansion of microseismic systems can be used to aid the transition from large open-pit operations to underground mass mining, during which considerable seismicity is expected.
Jechumtalova Z.,Academy of Sciences of the Czech Republic |
Sileny J.,Academy of Sciences of the Czech Republic |
Trifu C.-I.,ESG Solutions
Geophysical Journal International | Year: 2014
The resolution of event mechanism is investigated in terms of the unconstrained moment tensor (MT) source model and the shear-tensile crack (STC) source model representing a slip along the fault with an off-plane component. Data are simulated as recorded by the actual seismic array installed at Ocnele Mari (Romania), where sensors are placed in shallow boreholes. Noise is included as superimposed on synthetic data, and the analysis explores how the results are influenced (i) by data recorded by the complete seismic array compared to that provided by the subarray of surface sensors, (ii) by using three-or one-component sensors and (iii) by inverting P-and S-wave amplitudes versus P-wave amplitudes only. The orientation of the pure shear fracture component is resolved almost always well. On the other hand, the noise increase distorts the non-double-couple components (non-DC) of the MT unless a highquality data set is available. The STC source model yields considerably less spurious non-shear fracture components. Incorporating recordings at deeper sensors in addition to those obtained from the surface ones allows for the processing of noisier data. Performance of the network equipped with three-component sensors is only slightly better than that with uniaxial sensors. Inverting both P-and S-wave amplitudes compared to the inversion of P-wave amplitudes only markedly improves the resolution of the orientation of the source mechanism. Comparison of the inversion results for the two alternative source models permits the assessment of the reliability of non-shear components retrieved. As example, the approach is investigated on three microseismic events occurred at Ocnele Mari, where both large and small non-DC components were found. The analysis confirms a tensile fracturing for two of these events, and a shear slip for the third. © The Authors 2014. Published by Oxford University Press on behalf of The Royal Astronomical Society.
Jhamandas S.,ESG Solutions
Hart's E and P | Year: 2011
ESG Solutions, one of the world's only designers of microseismic-specific instrumentation, has successfully transformed a short-term fracture mapping technique into a powerful, cost-effective reservoir monitoring technology. Steam chamber growth can be mapped, and adjustments can be made to steaming programs to target any identified regions of bypassed oil. The frequency characteristics of a well casing shear can be characterized, enabling operators to react immediately to potentially hazardous events. Advanced geophysical analysis such as seismic moment tensor inversion (SMTI) can characterize micro-seismic events by their specific failure type, allowing engineers and geophysicists to learn exactly how the reservoir rock is breaking. The microseismic analysis can be used to validate the engineering process and calibrate geomechanical models that can be used to forecast reservoir response to subsequent stimulation programs.