Passive seismic tomography using induced seismicity at a petroleum field in Oman

Zhang, Haijiang; Sarkar, Sudipta; Toksöz, M. Nafi; Küleli, H. Sadi

doi:10.1190/1.3603687

Cited by 9 publications

(20 citation statements)

References 10 publications

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“…The expression ΔC ij is the perturbation on the density normalized elastic moduli; ΔL is the perturbation on the layer thickness; ΔX is the perturbation on the hypocenter and origin time of events; ΔT is the traveltime residual; and Δφ is the back azimuth residual. Following the strategy by Zhang and Thurber (2006) and Zhang et al (2009), we use larger w t and w φ in the beginning, and we gradually decrease these weights with iteration. This dynamic weighting approach first determines the absolute event locations and the velocity model, as the layered velocity structure is only sensitive to the absolute information , then improves the event relative locations by gradually emphasizing the relative information.…”

Section: Inversion Methodsmentioning

confidence: 99%

“…We first used the best vendor's layered isotropic velocity models, one for each well, to locate 100 selected events with a global search method (e.g., Zhang et al, 2009) for hypocenters and origin times that minimizes the traveltimes and the back azimuth information. The determined values from the global search are then used as the initial guess for further study.…”

Section: Inverted Microseismic Event Locations and Anisotropic Paramementioning

confidence: 99%

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Microseismic joint location and anisotropic velocity inversion for hydraulic fracturing in a tight Bakken reservoir

Morton

et al. 2014

GEOPHYSICS

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To improve the accuracy of microseismic event locations, we developed a new inversion method with double-difference constraints for determining the hypocenters and the anisotropic velocity model for unconventional reservoirs. We applied this method to a microseismic data set monitoring a Middle Bakken completion in the Beaver Lodge area of North Dakota. Geophone arrays in four observation wells improved the ray coverage for the velocity inversion. Using an accurate anisotropic velocity model is important to correctly assess the height growth of the hydraulically induced fractures in the Middle Bakken. Our results showed that (1) moderate-to-strong anisotropy exists in all studied sedimentary layers, especially in the Upper and Lower Bakken shale formations, where the Thomsen parameters (ϵ and γ) can be greater than 0.4, (2) all the events selected for high signal-to-noise ratio and used for the joint velocity inversion are located in the Bakken and overlying Lodgepole formations, i.e., no events are detected in the Three Forks formation below the Bakken, and (3) more than half of the strong events are in two clusters at approximately 100 and 150 m above the Middle Bakken. Reoccurrence of strong, closely clustered events suggested activation of natural fractures or faults in the Lodgepole formation. The sensitivity analysis for the inversion results showed that the relative uncertainty in parameter δ is larger than other anisotropy parameters. The microseismic event locations and the anisotropic velocity model are validated by comparing synthetic and observed seismic waveforms and by S-wave splitting.

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Section: Inversion Methodsmentioning

confidence: 99%

Section: Inverted Microseismic Event Locations and Anisotropic Paramementioning

confidence: 99%

Microseismic joint location and anisotropic velocity inversion for hydraulic fracturing in a tight Bakken reservoir

Morton

et al. 2014

GEOPHYSICS

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“…For real application we use data from a five-station network monitoring induced seismicity at a petroleum field (Sarkar 2008;Zhang et al 2009). The method is tested with data from a synthetic seismic event and then applied to real events selected from an oil and gas field.…”

Section: Introductionmentioning

confidence: 99%

Focal mechanism determination using high-frequency waveform matching and its application to small magnitude induced earthquakes

Li¹,

Zhang²,

Küleli³

et al. 2011

Geophysical Journal International

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S U M M A R YWe present a new method using high-frequency full waveform information to determine the focal mechanisms of small, local earthquakes monitored by a sparse surface network. During the waveform inversion, we maximize both the phase and amplitude matching between the observed and modelled waveforms. In addition, we use the polarities of the first P-wave arrivals and the average S/P amplitude ratios to better constrain the matching. An objective function is constructed to include all four criteria. An optimized grid search method is used to search over all possible ranges of source parameters (strike, dip and rake). To speed up the algorithm, a library of Green's functions is pre-calculated for each of the moment tensor components and possible earthquake locations. Optimizations in filtering and cross correlation are performed to further speed the grid search algorithm. The new method is tested on a five-station surface network used for monitoring induced seismicity at a petroleum field. The synthetic test showed that our method is robust and efficient to determine the focal mechanism when using only the vertical component of seismograms in the frequency range of 3-9 Hz. The application to dozens of induced seismic events showed satisfactory waveform matching between modelled and observed seismograms. The majority of the events have a strike direction parallel with the major NE-SW faults in the region. The normal faulting mechanism is dominant, which suggests the vertical stress is larger than the horizontal stress.

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“…The distribution of induced events in the field recorded by the surface network is shown in Figure 1 (Sarkar, 2008;Sarkar et al, 2008;Zhang et al, 2009). All the events have a residual traveltime of less than 30 ms, indicating they are well located.…”

Section: Induced Microearthquake Datasetmentioning

confidence: 99%

“…The northeast-southwest major network of faults and fractures partially connects all parts of the fields together (Figures 1, 2). The main oil production is from the Lower Cretaceous Shuaiba chalk overlain unconformably by Nahr Umr shale, while gas is produced from the shallower Natih Formation overlain by the Fiqa shale Formation (Sarkar, 2008;Zhang et al, 2009). …”

Section: Induced Microearthquake Datasetmentioning

confidence: 99%

Focal mechanism determination of induced microearthquakes in an oil field using full waveforms from shallow and deep seismic networks

Küleli

Zhang

et al. 2011

GEOPHYSICS

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A new, high frequency, full waveform matching method is used to study the focal mechanisms of small, local earthquakes induced in an oil field, which are monitored by a sparse near-surface network and a deep borehole network. The determined source properties are helpful for understanding the local stress regime in this field. During the waveform inversion, we maximize both the phase and amplitude matching between the observed and modeled waveforms. We also use the polarities of the first P-wave arrivals and the average S/P amplitude ratios to better constrain the matching. An objective function is constructed to include all four criteria. For different hypocenters and source types, comprehensive synthetic tests show that our method is robust to determine the focal mechanisms under the current array geometries, even when there is considerable velocity inaccuracy. The application to several tens of induced microseismic events showed satisfactory waveform matching between modeled and observed seismograms. The majority of the events have a strike direction parallel with the major NE-SW faults in the region, and some events trend parallel with the NW-SE conjugate faults. The results are consistent with the in-situ well breakout measurements and the current knowledge on the stress direction of this region. The source mechanisms of the studied events together with the hypocenter distribution indicate that the microearthquakes are caused by the reactivation of preexisting faults. We observed that the faulting mechanism varies with depth, from strike-slip dominance at shallower depth to normal faulting dominance at greater depth.

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Passive seismic tomography using induced seismicity at a petroleum field in Oman

Cited by 9 publications

References 10 publications

Microseismic joint location and anisotropic velocity inversion for hydraulic fracturing in a tight Bakken reservoir

Microseismic joint location and anisotropic velocity inversion for hydraulic fracturing in a tight Bakken reservoir

Focal mechanism determination using high-frequency waveform matching and its application to small magnitude induced earthquakes

Focal mechanism determination of induced microearthquakes in an oil field using full waveforms from shallow and deep seismic networks

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