microseismic general Flashcards
For both surface arrays and shallow shallow
buried grids, the ____ accuracy is very low.
Compared to a surface array, the receiver density reduces significantly in the shallow buried grids in which _________(3C) receivers are deployed in 20–180 m deep boreholes
Before starting a pre-survey design study, it is important to know the availability and accuracy of these modeling tools. Also, understanding the limitations of these tools is important which requires asking key questions including:
An ____ model, which is typically
built from the sonic and density logs, is calibrated using both the available P and S-wave arrival times and the back-azimuth estimates from the P-wave signals on the available perforation shots or string shots.
The hypocenter location for each event is then estimated by
using the available arrival times and polarization angles (back-azimuths). In the case of multi-well monitoring data, hypocenter locations can be estimated reliably using the _____ arrival times only.
Fracking related microseismic events often have negative _____ magnitudes
Typically, we apply a _____ filter to the microseismic data to remove any unwanted noise and focus only on the frequencies of interest.
For downholemicroseismic data, we begin with the instrument response correction and the conversion of amplitude units to ground displacement or ground velocity. The 3C waveform data is then _____ corrected to remove any DC bias
Fracking related microseismic events often have _____ moment magnitudes
The ______ (Q) in the medium affects the traveltime, frequencies and the amplitudes of recorded waveforms. Prior knowledge of Q values from seismic data is, therefore, important for assessing the event detectability.
The loss of energy is _____ proportional to Q for each wavelength of travel through the medium.
how is the youngs modulus and poissons ratio related to the total seismic moment released during hydraulic fracturing (Mtotal)
The processing of surface and shallow buried grid is often done on the vertical component recordings that contains the ___-wave information However, Artman et al. (2012) argued that the survey design and processing scheme should adequately handle ____-waves, which dominate the energy radiated from the source. By using both ___ and ___-waves, we can improve the depth accuracy of microseismic events from the surface and near-surface microseismic data
A receiver array that is _______ to the treatment zone records
events with overlapping P and S-wave arrivals, which are difficult to process, and cause additional complexities to accurate estimation of their hypocenter locations
Depending on the orientation of the symmetry axis, a TI medium
can be called _________ (TTI; dipping
layers or set of fractures).
surface and near-surface arrays have lower _____
sensitivity mainly because of the large source-receiver distance
Using the ___-wave arrivals on the calibration
shot (e.g. perforation shot, string shot or a ball drop event), we compute the receiver orientations.
The _____ from the analogue settings can be used to estimate the number of detectable events (NEV ) above a given magnitude threshold (MC), often called the magnitude of completeness.
Typically, we use _____ to represent this energy loss with respect to time or distance.
Event ______ can also be affected by many other
factors including the background noise level, the source-receiver distance, and the anelastic attenuation (quality factor; Q) of the medium.
Event detectability for a given receiver array can be affected by the ____variations in waveform amplitudes related to
the source radiation patterns
The main advantage of downhole microseismic monitoring is the proximity of the receivers to the treatment zone, thus leading to high ______ for events that are up to 1 km away from the monitoring or observation well
To improve on a simple magnitude-distance plot showing minimum detection limits for different background, a more complete relationship can be used:
The total seismic moment released during hydraulic fracturing (MTotal ) can also be estimated using the equation:
Because of the geometrical ___ and _____, amplitudes of the waveforms from a microseismic event decrease with increasing observational distance.
In addition to the traveltime inversion, other approaches such as the ____ and the _______ can be used for estimating hypocenter locations.
A pre-survey design study requires _____ and/or _____modeling tools for calculating amplitudes and traveltimes of P and S-waves generated by several microseismic sources, that are recorded at a certain distance with a specific receiver array configuration.
The hypocenter location for each event is then estimated by
using the available ___ times and ____ angles (back-azimuths). In the case of multi-well monitoring data, hypocenter locations can be estimated reliably using the P and S-wave arrival times only.
The most probable maximum magnitude
can also be written in terms of seismic index (E)
and total injected volume (VINJ) as:
From the existing projects in analogue settings, a relationship between the occurrence of microseismicity and the injection rate and duration (total volume) can be established. In addition, the following information can be used to understand the
expected microseismicity:
The probability of occurrence of an
event with a magnitude greater than a certain magnitude ~M in terms of the total injected volume (VINJ ) and seismogenic index can be calculated as:
In surface microseismic monitoring
_____ or more stations (typically _____ component geophones) are deployed in either a star, grid or in a patch configuration
The b-values from the analogue settings can be used to estimate the number of ________ (NEV ) above a given magnitude threshold (MC), often called the magnitude of completeness.
Material properties of an isotropic medium can be described by a stiffness matrix comprising just two independent components, which are known as the ___ coefficients (λ and μ)
The transverse isotropy (TI) with a single axis of rotation symmetry is a common type of anisotropy in ______ rock, which is often used to explain a parallel set of fractures or thin
bedding of layers.
A receiver array can be deployed in any of the horizontal
wells adjacent to the treatment well sharing the same pad, but a supporting _____ array deployment is required in a nearby well to yield accurate hypocenter
locations.
what is the equation for MMAX
For downholemicroseismic data, we begin with the instrument response correction and the conversion of ____ units to ground displacement or ground velocity.
In seismology, a microseismic event is defined as an earthquake that has a magnitude smaller than ____ and is not felt at the surface by the public
The b-values from the analogue settings can be used to estimate the number of detectable events (NEV ) above a given magnitude threshold (MC), often called the ______.
Ideally, receivers should be placed as
close as possible to the ______ zone for efficient recording of the microseismicity
For a given Q-value (energy loss), we can express the amplitude attenuation with respect to time as
what is orthorhombic
These fracking related microseismic events often have negative moment magnitudes and their waveforms are characterized as ____-period and ______ (10– 1000 Hz) signals
For a VTI medium (vertical transverse isotropic, shale reservoirs, vertical axis of symmetry), the stiffness matrix comprising five independent components is given by:
For the sources at similar depth in a homogeneous velocity model, the angular aperture of the receiver array _____ and therefore, the uncertainty in hypocenter location increases with
observational distance.
The typical outputs from microseismic data processing include hypocenter locations, event magnitudes and source mechanisms (seismic moment tensors) that are useful for inferring the length, height, width, orientation, and complexity of the fracture<br></br>network. We can also determine the ____ orientation and ______ mechanism.
Q-value of P-wave (QP) is typically
_____ than the Q-value of S-wave QS
the minimum detection limit _________ with the observational distance.
Depending on the orientation of the symmetry axis, a TI medium
can be called ______ (VTI; shale reservoirs),
Using the P-wave arrivals on the calibration
shot (e.g. perforation shot, string shot or a ball drop event), we compute the receiver orientations. The microseismic data are then rotated into geographic coordinate system (east, north, vertical). We also pick the ____-wave arrivals on the
calibration shot.
Depending on the orientation of the symmetry axis, a TI medium
can be called ________ (HTI; vertical fractures)
We can integrate the fracture and stress related information obtained from microseismic data with other available geological (\_\_\_, \_\_\_\_ and \_\_\_\_), geophysical (\_\_\_\_ and \_\_\_\_), and engineering (\_\_\_\_, \_\_\_\_\_, \_\_\_\_\_) to understand the reservoir geomechanics and to improve the well placement in the future
The recorded microseismic data from any of the afore-mentioned receiver configurations are processed to obtain the ____ locations and the ____-related information.
For elastic media, the linearized equations of motion can be written as
Additional processing efforts are
often required to detect and locate microseismic events on relatively low ___ surface
and near-surface microseismic data sets.
S-wave propagation results in _______intrinsic attenuation as more frictional heating is caused by the shear motion between particles
For an array with fixed number of receivers, the ______ aperture decreases with observational distance from the treatment well
As the observational distance _____, the number of small
magnitude events decreases and only a few large magnitude events are detected at far offsets.
This detection bias is commonly seen in single well monitoring of long horizontal treatment wells and can be reduced by using multiple monitoring wells
In a constant Q-value region in the subsurface, the higher frequencies complete more wavelengths for the same distance as compared to the lower frequencies and are, therefore, attenuated at a _____ rate.
Unlike the downhole microseismic monitoring, both the surface arrays and shallow buried grids provide good ___ coverage
what is monoclinic
A microseismic monitoring project is typically initiated to achieve one or more of the following objectives
The b value is the slope of the histogram for events ______ than the magnitude of completeness. The magnitude of completeness, Mc—the smallest magnitude at which all events of that size are detectable—is calculated using maximum curvature method
For a fixed source-receiver distance and background noise level, a large magnitude event is _____likely to bedetected successfully as compared to a smaller magnitude event.
The decrease in amplitude due to the geometrical spreading is the result of the _______of total energy and the increasing ______ of the expanding wavefront.
We can also write stress in terms of the displacement components using the material’s constitutive equation (Hooke’s law) in matrix form
The b-values from the analogue settings can be used to estimate the number of detectable events (NEV ) above a given _____ (MC), often called the magnitude of completeness.
An ________, typically, comprises a high number of small magnitude events occurring near a receiver array
Although the event depths are more accurately
estimated with downhole microseismic data, the error in horizontal (XY) location of a microseismic event increases away from the monitoring well because of the significant
errors in the estimated ______. Moreover, the downhole arrays have small ______ and, therefore, provide poor subsurface coverage.
We can also write stress in terms of the displacement components using the material’s constitutive equation (Hooke’s law):
what is a MDP plot
The ________ (MDP) is a useful tool for assessing the minimum detection limit as a function of distance and understanding the detection bias of a receiver array.
what are “string shots”
Typically, a string shot refers to the explosion of 6–24 m long primer cord, which is wrapped on a
steel bar and lowered into the wellbore
Surface and near-surface arrays S/N of the recorded waveforms is very low due to ________
In a typical processing workflow, the ___ units of surface or near-surface microseismic data are converted to ground displacement or ground velocity. Also, the data are corrected for ____ bias and are_____ filtered. To further improve the
S/N, additional filtering techniques can be applied
An initial velocity model, which is typically
built from the ____ and ____ logs, is calibrated using both the available P and S-wave arrival times and the back-azimuth estimates from the P-wave signals on the available perforation shots or string shots.
the following relationship can be used to
model theminimum detection limit for different detection thresholds and background noise level
what is the equation for NEV
The typical outputs from microseismic data processing include ______, _______ and _______ (seismic moment tensors) that are useful for inferring the length, height, width, orientation, and complexity of the fracture network.
An initial velocity model, which is typically
built from the sonic and density logs, is calibrated using both the available ______ and the _______ from the P-wave signals on the available perforation shots or string shots.
The optimum receiver geometry minimizes the survey costs, records high-quality microseismic data, and provides good angular aperture for the accurate estimation of
_______ locations and source parameters
The waveform modeling tools can also be used in the event detectability modeling. For this purpose, the following information gathered from previously available projects in the same field, area or in analogue settings can be useful:
The Q values can be estimated from surface seismic, VSP and ______ data using numerous approaches
including the spectral-ratio method
shales have _____ values of Q as compared to
sandstones
Surface and near-surface arrays can reliably detect all events with MW larger than ___ to ___ assuming favorable noise conditions.
Well logs and seismic velocities are used to build an initial ________ model
Waveform modeling workflow is comprised of the following steps:
For an isotropic medium, we can write the constitutive equation in terms of Lamé coefficients and the displacement components as:
Using both surface arrays and shallow buried grids, long multi-lateral well developments can be consistently imaged without being affected by the _____ bias
The ___ and _______ can be used to test the capability of different source-receiver geometries for robust calibration of the velocity model and the estimation of hypocenter locations
and source parameters
A pre-survey design study requires ray tracing and/or waveform modeling tools for calculating amplitudes and traveltimes of P and S-waves generated by several microseismic sources, that are recorded at a certain distance with a specific receiver array configuration. These modeled _____ and _____are then used for assessing the event detectability and understanding the expected challenges in the processing of the recorded microseismic data.
We also pick the S-wave arrivals on the calibration shot. Often, we rotate the waveforms into ____ centered coordinate system (__, ___, ___) to improve the arrival picking
The superposition of VTI and HTI symmetries results in
an orthorhombic system, which is fully described by ___ independent components in the stiffness matrix
During presurvey model designing, the resolution resulting from a data processing algorithm is considered good when
the diagonal elements of the resolution matrix ______to unity or the trace of the resolution matrix equals the number of model parameters
We can also evaluate the _____ accuracy of microseismicity recorded at a specific receiver array using the condition number analysis of the Fréchet-derivative
matrix
