Multi-network Microseismic Monitoring of Fracturing Jobs – Neuquen TGR Application

Robein, E.; Cerda, F.; Drapeau, Didier; Maurel, L.; Gaucher, Emmanuel; Auger, E.

doi:10.3997/2214-4609.201400495

Cited by 8 publications

(3 citation statements)

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“…Strike-slip source mechanisms were found for example by Rutledge and Phillips (2003) in Cotton Valley and Droujinine, Oates and Ita (2011) in shale formations. Dip-slip events were observed for example by Robein et al (2009. While this (and no other finite) choice of source mechanisms does not cover the entire spectrum of observed mechanisms of microseismic events, based on our experience we believe this choice is covering the most important types of induced microseismic events as it represents vertical fractures.…”

Section: Forward Modelling Of a Source Mechanismmentioning

confidence: 99%

Stability of source mechanisms inverted from P‐wave amplitude microseismic monitoring data acquired at the surface

Staněk

Eisner

Moser³

2014

Geophysical Prospecting

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We study the stability of source mechanisms inverted from data acquired at surface and near‐surface monitoring arrays. The study is focused on P‐wave data acquired on vertical components, as this is the most common type of acquisition. We apply ray modelling on three models: a fully homogeneous isotropic model, a laterally homogeneous isotropic model and a laterally homogeneous anisotropic model to simulate three commonly used models in inversion. We use geometries of real arrays, one consisting in surface receivers and one consisting in ‘buried’ geophones at the near‐surface. Stability was tested for two of the frequently observed source mechanisms: strike‐slip and dip‐slip and was evaluated by comparing the parameters of correct and inverted mechanisms. We assume these double‐couple source mechanisms and use quantitatively the inversion allowing non‐double‐couple components to measure stability of the inversion. To test the robustness we inverted synthetic amplitudes computed for a laterally homogeneous isotropic model and contaminated with noise using a fully homogeneous model in the inversion. Analogously amplitudes computed in a laterally homogeneous anisotropic model were inverted in all three models. We show that a star‐like surface acquisition array provides very stable inversion up to a very high level of noise in data. Furthermore, we reveal that strike‐slip inversion is more stable than dip‐slip inversion for the receiver geometries considered here. We show that noise and an incorrect velocity model may result in narrow bands of source mechanisms in Hudson's plots.

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Section: Forward Modelling Of a Source Mechanismmentioning

confidence: 99%

Stability of source mechanisms inverted from P‐wave amplitude microseismic monitoring data acquired at the surface

Staněk

Eisner

Moser³

2014

Geophysical Prospecting

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“…This is costly as (in most cases) a borehole cannot be under production while borehole sensors are recording. An emerging alternative technique is the use of surface sensors deployed in large arrays to monitor microseismicity (e.g., Duncan 2005; Robein et al 2009). As the signals recorded at the surface are typically below the signal‐to‐noise ratio for individual traces, migration style approaches can be used to image events in the reservoir.…”

Section: Introductionmentioning

confidence: 99%

Testing the ability of surface arrays to monitor microseismic activity

Chambers

Kendall

Brandsberg‐Dahl

et al. 2010

Geophysical Prospecting

131

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A B S T R A C TRecently there has been much interest in the use of data from surface arrays in conjunction with migration-based processing methods for passive seismic monitoring. In this study we use an example of this kind of data recorded whilst 18 perforation shots, with a variety of positions and propellant amounts, were detonated in the subsurface. As the perforation shots provide signals with known source positions and origin times, the analysis of these data is an invaluable opportunity to test the accuracy and ability of surface arrays to detect and locate seismic sources in the subsurface. In all but one case the signals from the perforation shots are not visible in the raw or preprocessed data. However, clear source images are produced for 12 of the perforation shots showing that arrays of surface sensors are capable of imaging microseismic events, even when the signals are not visible in individual traces. We find that point source locations are within typically 45 m (laterally) of the true shot location, however the depths are less well constrained (∼150 m). We test the sensitivity of our imaging method to the signal-to-noise ratio in the data using signals embedded in realistic noise. We find that the position of the imaged shot location is quite insensitive to the level of added noise, the primary effect of increased noise being to defocus the source image. Given the migration approach, the array geometry and the nature of coherent noise during the experiment, signals embedded in noise with ratios ≥0.1 can be used to successfully image events. Furthermore, comparison of results from data and synthetic signals embedded in noise shows that, in this case, prestack corrections of traveltimes to account for near-surface structure will not enhance event detectability. Although, the perforation shots have a largely isotropic radiation pattern the results presented here show the potential for the use of surface sensors in microseismic monitoring as a viable alternative to classical downhole methods. *

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“…This greater flexibility has led to the deployment of large aperture arrays that provide greater fold and increased range of azimuths to the area of interest which aids moment tensor estimation (e.g., Duncan, 2005;Robein et al, 2009;. However, microseismic signals recorded at the surface are typically at or below the signal-to-noise ratio (e.g., Chambers et al, 2010) due to high noise levels and the relatively large distances between source and receiver.…”

Section: Introductionmentioning

confidence: 99%

Surface microseismic imaging in the presence of high-velocity lithologic layers

et al. 2015

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Surface microseismic monitoring above regions containing high velocity units will be influenced by a reduction in the effective array aperture and contain significant seismic coda due to an increase in reflected and converted wave energy which can influence the capability of surface arrays to image microseismic events. We examine the imaging difficulties due to reduction of effective array aperture and increased coda within microseismic data caused by the presence of a fast anhydrite layer. We generate and use finite-difference, full waveform microseismic synthetics derived from one-dimensional sonic log data taken from an unconventional shale reservoir in complex anhydrite geology. Two imaging techniques are used to locate the synthetic microseismic events. A simplistic and easily reproducible Standard Diffraction Imaging (SDI) procedure and a more sophisticated technique, MomentTensor Microseismic Imaging TM (MTMI TM ). We confirm that the presence of high velocity layers, such as anhydrite, reduces the overall aperture of a surface array, which results in poor resolution of imaged events and reduction in accuracy of event locations. More im-1 portantly, we demonstrate that coda in the microseismic data can isolate itself from the direct arrival, stack into the final imaging result and be misinterpreted as separate events located directly below the true source location, which is unavoidable given the ambiguity between event location and time. Comparison of the two imaging procedures show that even though the more sophisticated MTMI was able to better cope with the effects caused by high velocity layers, it still demonstrated a significant reduction in resolution of imaged events, a reduction in accuracy and evidence of multiple and converted energy still present in the final imaging result. All images produced using the same procedure as that for Figure 3. 2 LIST OF FIGURES

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Multi-network Microseismic Monitoring of Fracturing Jobs – Neuquen TGR Application

Cited by 8 publications

References 0 publications

Stability of source mechanisms inverted from P‐wave amplitude microseismic monitoring data acquired at the surface

Stability of source mechanisms inverted from P‐wave amplitude microseismic monitoring data acquired at the surface

Testing the ability of surface arrays to monitor microseismic activity

Surface microseismic imaging in the presence of high-velocity lithologic layers

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