seismic das Flashcards
Seismic signals are ____-frequency (usually <____Hz) displacement waves travelling through a geological
structure
Seismic signals are low-frequency (usually <100 Hz) ______waves travelling through a geological
structure
what is PRM
In marine seismic exploration, the sensors are towed behind a seismic acquisition vessel in arrays known as ____that reach some 10 km in length.
In marine seismic exploration, the sensors are towed behind a seismic acquisition vessel in arrays known as streamers that reach some 10 km in length. The sensors have traditionally been ______, but recent developments [5] have added multi-axis _____that allow far better reconstruction of the
waves arriving at the receiver arrays and, thus, better processing of the seismic image
The sources for marine seismic exploration are generally compressed-air impulsive sources (known
as ____) and are limited in their power by a number of considerations, including damage to cetaceans.
Another category of marine seismic acquisition involves ocean bottom sensors, either permanently installed in ___or in the form of retrievable ___or ____
In land seismic applications, the sensors are generally _____ that sense particle velocity, although ___are sometimes used.
The seismic source on land is sometimes ____ (____or ____) for localised surveys, but usually ____,
____ are used for large-area surveys.
Naturally, considerable thought has been given to using distributed optical fibre sensor (DOFS) in seismic acquisition. In this application, only the ______ measurement techniques have so far been proven to be suitable:
In this application, only the differential phase measurement techniques have so far been proven to be suitable: the intensity measurement of the backscatter signals is not sufficiently ______
to meet the requirements of seismic acquisition, where the signal sent to the signal processing must have a known transfer function in relation to incoming seismic waves
DVS, particularly ______ DVS (dΦ-DVS), is rapidly developing into an accepted alternative to conventional, electrical sensors in borehole seismic acquisition
Borehole seismic measurements, also known as _______, consist of inserting one or more vibration sensors into a borehole and using sources external to the borehole to generate a seismic signal that is detected by the borehole
sensors.
There are several motivations for conducting VSP measurements. First and foremost is the calibration of the _____model
The surface seismic survey provides a ___- or ____-dimensional
map of the sub-surface using reflections from layers of contrasting acoustic impedance
The surface seismic survey provides a two- or three-dimensional
map of the sub-surface using reflections from layers of contrasting _______
The surface seismic survey provides a two- or three-dimensional
map of the sub-surface using reflections from layers of contrasting acoustic impedance. However, this
information is mapped in the ___ domain, i.e. as a delay from the source energy being coupled to the
ground to a reflection being detected.
The surface seismic survey provides a two- or three-dimensional
map of the sub-surface using reflections from layers of contrasting acoustic impedance. However, this information is mapped in the time domain, i.e. as a delay from the source energy being coupled to the ground to a reflection being detected. In order to relate the time information to real, physical depth it is necessary to know the _____of the waves in each of the layers
In order to relate the time information from microseismic to real, physical depth it is necessary to know the velocity of the waves in each of the layers. The seismic picture can then be
____from time to depth.
A specific motivation for using optical DVS techniques in borehole seismic applications is the elimination
of downhole _______
