Volume Attributes

VOLUME ATTRIBUTES

1. Local Structural Dip :

A) Event local structural dip

Inline TWT 1979:

From the above, we can see the anticline structure that probably indicating trap of gas accumulation. The left window is without smoothing while the other one with smoothing. The local structural dip is compute using event method. The event method computes the downslope azimuth of the estimated event.

Without smoothing;

The upper part of the data is yellow with slightly red colour show that it is almost horizontal flat surface. The area below the anticline structure ,is high dipping area showed by the blue and cyan colour. We can observe the contrast between low and high dipping area, bounded by the anticline structure , which can be conclude as trap formation.

With smoothing;

We can analyst the data a lot more clearer compare the data before smoothing is applied. The left top and the right top of the data has almost horizontal or flat dipping indicate by the yellow with slightly red in colour but the middle top of the data slightly over the anticline structure is moderate dipping area represent by the green colour. The trace of cyan colour below the anticline is greatly decrease as compared to the non- smoothing data indicate that the area has very high dipping. As we can see, there is no sign of leaking of gas as there is no escape point which can be determine by the dipping contrast.

Xline TWT 1615:

Faults are indicated by the red line. Without smoothing, we can hardly detect faults possibly because of the presence of noises. However, smoothing reduce some unnecessary noise and thus, more faults are found after the structural smoothing. But, the continuity of fault, both in with and without smoothing, are hardly detectable. Meaning that, the end of the fault is not clearly visible . Apart from that, the continuity of the horizon is interrupted by fault.

B) Gradient local structural dip:

Inline TWT 1979

From the above, we can observe the elongated shape on the data marked by the anticline structure. The red section represented the lowest dipping area while the blue section represented the highest dipping area. On the left windows, the anticline structure are characterize by high contrast dipping represented by the red and blue section in the middle that may indicate the presence of hydrocarbon potential. We can observed the the yellow and red section dominate the area at the left, right and the top of the anticline structure that formed like a barrier. So we can conclude that the hydrocarbon were trapped below the anticline structure . After the data undergone the smoothing process, the potential hydrocarbon formation can be seen more clearly. However, the distribution of the colour section are differrent from the non-smoothing area.

Xline TWT 1615:

From the above, we can clearly see fault’s structure. The left window is without smoothing while the right window is with smoothing. The local structural dip is compute using gradient method. The gradient method is the instantaneous azimuth of the sample neighbourhood.

Without smoothing:

The low dipping area is represented by red and yellow section with the colour bar range from 0 to 30. High dipping area is represented cyan and blue section with colour range 50 to 90. The green section indicate the moderate dipping area with colour range 30 to 40 We can observe the faults that is mark by black line. There is no sign that indicate the accumulation of oil and gas.

With smoothing:

When we apply smoothing on the seismic data, we can see a huge difference based on the colour of dipping area. The data is dominated by red and yellow colour represent the low dipping area. The lowest dipping can be observe at the middle and upper part of the data. The faults is easier to observe in the data with smoothing.

C) Principal component local structural dip:

Inline TWT 1979

From above, the interpretation window is showing anticline that 3D window shows the various colours that indicate different value of dip. The red to yellow that colour bar range of 0-30 indicate small dip while green to blue that colour bar range of 45-90 indicate greater angle of dipping. Thus, the yellow with slightly red at the middle have the low level dipping. There is some blue colour at the middle that we assuming can enhance interpretation of seismic geomorphology. It has a good ability for detecting features from dip of reflections such as channel edges. These are using position of 1979 with increment of 10 that indicate the parameters to make it more clears.

Xline TWT 1615

Seismic processors commonly used the principal-component filter or also known as the Karhunen-Loeve filter in seismic processing, to estimate linear noise and multiples and subsequently to subtract them from the data.

Faults are indicated by the red line. The faults shown here are nearly similar to what is observe in principle-component filtering without smoothing. Smoothing is applied just to reduce a little bit of noise. The reason why there is not much difference when smoothing is applied probably because the function of principle-component itself to estimate linear noise and multiples and subsequently to subtract them from the data. The low dipping area is represented by the yellow and red sections and the color bar range of 0-25. The blue section and the colour bar ranging from 30-60 represent the high dipping area.

2. Coherence-Variance:

Inline TWT 1979

From above, the interpretation window shows the inline of coherence-variance that presence of fault marked by red line. The legend on the left side shows the colours that indicate the low or hig dipping level. The light blue and dark blue section and the colour bar range of 0.0-0.8 represent high dipping area. The low dipping area is represented by red to orange sections and colour bar range of 0.7-0.8 at the middle part. The fault feature is visible but the extended (continuity downward) fault that indicate the end of fault is not clearly visible. This is because the noise interference that interrupt the observation. The noise interference problem can be reduce by using structural smoothing that fault indication is highlighted by the hot variance colour and the continuity of horizon is disrupted by the presence of the fault.

Xline TWT 1615

Variance (coherence) attribute is applied to image the edge and also as the detection method.Variance (edge method) with some adjustment on inline range, crossline range, and vertical smoothing enable us to detect fault clearly. At the upper part, fault feature is seen clearly and we could see the extension of the fault. However, at the bottom part we could hardly detect the extension (continuity downward) of the fault indicating that the end of the fault is not clearly visible. This is probably because of the interruption of noise which can be reduce by smoothing. However, adjusting too much smoothing will make some important features such as fault to disappear. But, even after adjusting a little bit of vertical smoothing, we still cannot see clearly the continuity of the fault.

3. Dip deviation:

Inline TWT 1979

The figures above show the difference between the original and smoothed dip deviation. As seen from the legend on the top left, red is low angle dip while yellow is dip of angle 10°-20°. However, even after parameters were adjusted, there is still noise and no continuity. Hence, structural smoothing was used on the dip deviation in order to produce more continuous data and also to avoid mislead in interpretation. After smoothing was applied, gas seepage and anticline structure can be clearly seen.

Xline TWT 1615

In dip deviation attribute, threshold angle parameter was used to reduce the dip deviation below the threshold angle and at the same time enhance larger deviation. From the legend, we can see that the red colored one have lowest dip angle while yellow represent 10°-20° dip angle. The parameter used was 3 which means to reduce the dip deviation below 3° which usually angles around the fault were eliminated because it usually associate with the downthrown side of fault. Hence, from the figure above we can see faults were visible at the upper part because unwanted angles have been removed and deviation was enhanced.

4. Curvature:

Inline TWT 1979

Xline TWT 1615

5. Sweetness:

Inline TWT 1979

Xline TWT 1615

5. Acoustic impedance:

Inline TWT 1979

Xline TWT 1615

Mean curvature was used to interpret inline because maximum and minimum curvature does not show much distinction. Hence, mean curvature was the best method to show the structures presence in the inline. The parameter was increase from default because when default was used, fault and other structures cannot be seen, only white surface. Hence, parameter need to be increase. No fault was found here, but more to anticline structure.

Most negative curvature

Most positive curvature

Mean curvature

The diagrams above show the curvature attributes applied on the Xline surface. Three methods of curvature were used and compared. Different parameters were used and adjusted in order to get the clearer image. Maximum curvature (most positive curvature) was used to see visible fractures and fault. At first, the default parameter does not show clear trace of fault which is like the one shown in the mean curvature methods. Then, after increase the parameter, the faults can be seen. In max curvature, smaller radius means largest curvature. But the parameter of max curvature above is high, hence, the curvature is low. May be the fault and fractures are not so prominent. Same result was seen in minimum curvature (most negative curvature) even though same parameters were used. Usually minimum curvature was used to see axis along channels and valleys.

The white ellipse probably indicates gas cloud. There are flat spot feature below the anticline structure due to the accumulation of gas. The green line represent the strong amplitude reflection from the reflector which located above shallow gas accumulation.

Faults which are indicated by the blue line can be clearly detected. The structure of the fault could be listric fault. Apart from that, the lithology below the faults structure could probably be shale by looking at the low amplitude and low frequency reflector.

Smoothing has removed some unnecessary noises. Without structural smoothing, we can hardly detect some important features such as gas cloud probably because of the interruption of noise. However, after the structural smoothing, we are able to see the reflector clearly. The white ellipse shows the gas cloud as gas is acoustically flat. This probably indicate the changes in the acoustic impedance. With structural smoothing (on the right side), we can see that the reflection events underneath the gas cloud vanished. The blue arrow indicated the strong amplitude reflection from the reflector which located above shallow gas accumulation.

The above diagram shows Xline acoustic impedance without smoothing. Fault are indicated by the red line. Significant features such as fault can be detected but it is still hard to see the continuity of the fault. Meaning that, the end of the fault is not clearly visible. Apart from that, reflector cannot be seen clearly probably because of the unnecessary noises.