THE VOLUME CONCEPT OF 3D DATA
Voxel
An acronym for volume pixel element
A cube representing a seismic sample
If the software open the seismic data an 8-bit voxel volume
The original attribute values of each sample are assigned a new voxel value
The original attribute values of each sample are no longer available
How data is coverted to an 8-bit voxel volume?
All data loaded into an 8-bit voxel volume by dividing the original attribute data by 256 and assigning the grouped data to a single value (Voxel value). The data is not clipped.
With 3D Data, the interpreter is working directly with a volume.
The subsurface seismic wavefield is closely sampled in every direction.
Volume of Data = number of lines x number of crosslines x number of time samples x number of data types
To view; approaches with horizontal sections, time slice, incline, cross line, arbitary line, fault surface, geobody
Properties of 3D Seismic Dataset
Basic of 3D
Line (Inline) : The vertical section in the direction of boat movement or cable lay-out.
Crossline : The vertical section perpendicular to this direction.
Timeslice : The horizontal slice; also known as horizontal section, or depth section/section.
Adds-On of 3D
Diagonal Line : Extracted to tie to locations of interest (wells)
Arbitary Line : Vertical sections formed from diagonal lines
Horizontal Slice : A slice along or parallel to a structurally interpreted horizon, and hence along one bedding plane.
Fault slice : Generated parallel to a fault face.
Horizon & Attributes Display
3D Volume Visualization
A method of seismic interpretation in which the seismic reflectivity of the subsurface is directly evaluated in 3D space by applying various levels of transparency to the data.
Voxel Values Application
Unsigned 8-bit : 0-255 (Maximum Dynamic range)
Signed 16-bit : -32768 to +32767 (Maximum Dynamic range)
Signed 32-bit : -2147483648 to 2147483647 (Maximum Dynamic range)
Dynamic Range on Interactive Interpretation
Low amplitude : Associated with noise
Moderate amplitude : Rock formations
High amplitude : Usually hydrocarbon (DHI)
If the data is 32-bit, we load into 8-bit computer, scaling of the 32-bit amplitude must be done during data loading.
Often severely limit the dynamic range (some high amplitude, might be destroyed and not available for interpretation)
Why colour is important in 3D Volume Visualization
To distinguish features with clarity
To enhance the contrast between 2 features
To identify which is the high polarity or low polarity
Give effects to the eyes of the interpreters
Colour generally maintain the opaqueness throughout the interpretation.
A single base colour (Red) can be expressed in 256 variations, due to 8-bit opacity editor
Each opacity level, produced different variations of red colour (easy for us to identify which one is the high amplitude, hence higher reflection, for marking the horizons