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Module 1: Build a Subsurface Model


MODULE 1: WORKFLOW


MODULE 1: RESULTS & DISCUSSION

Figure 1 shows the constructed model with acquisition geometry of one source (center) and receivers of 20m interval while Figure 2 shows the constructed model with acquisition geometry of one source (center) and receivers of 50m interval. The decrease in receiver’s interval causes more receivers to be used, hence increase in cost of acquisition. The maximum offset which is the distance between the actual shot and the farthest receiver for both acquisition is 1200m. By using these geometry, the receivers only record seismic events at the depth less than or equal to 1200m. In order to record the seismic events occurred on geological structure at the deeper depth, the maximum offset should be greater than the depth of the geological target.


Figure 1: One source (center) and receivers of 20m interval.


Figure 2: One source (center) with receivers of 50m interval.

Figure 3 shows the model with acquisition geometry of two source (50m interval) and receivers of 50m interval. This type of geometry gives the maximum offset of 1225m which will record the seismic data at the depth up to 1255m. Two number of sources will increase the signal to noise ratio of the recorded data and spatial sampling which will provide good separation between primary reflection and unwanted noise. Besides that, Figure 4 shows VSP shot with three sources (200m interval) and receivers of 30m interval. This VSP shots measures the acoustic waves between well bore and surface in high resolution and this will give the interpreter the ability to analyse wavefields in situ. This technique also provides a direct correlation between subsurface stratigraphy and seismic reflection measured at the surface.


Figure 3: Two source (50m interval) with receivers of 50m interval.


Figure 4: VSP shot with three sources (200m interval) with receivers of 30m interval.


Forward modelling process is conducted for selecting the best acquisition parameters (cable length, sources, receivers, fold, etc.) which will generate an interpretable signature on seismic data. The models, ranging from simple layers to complex geology, have been constructed to test the acquisition parameters and sampling which must be sufficient to image the reflection and enhance the signal to noise ratio. The geological objectives such as depth to targeted horizon, maximum dip and lateral as well as vertical resolution are also needs to be considered when determining the parameters during the forward modeling process. When the best parameters are achieved during the forward modelling process, it can be applied during the actual seismic acquisition to produce good seismic data.

Besides that, the reverse of forward modelling process is known as inverse modelling. Seismic inversion conducted after the survey transform the seismic reflectivity into rock impedance such as acoustic and elastic. These impedances provide a powerful tool for interpreting seismic data based on layer properties. Reservoir rock and fluids parameters determined from the inverted impedance are usually used as input to reservoir modelling and flow simulation. Furthermore, the inverted impedance also can be used for correlating with the well log data in order to validate the accuracy of the results obtained.

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