Based on our interpretation using surface attributes and volume attributes, abundant channels have been found in this project. Those channels represent the depositional environment in this area which located in transitional zone most probably in delta or swampy area. Bishop (2002) mentioned that reservoir rock for Oligocene and lower Miocene of Malay basin were include coarse to medium grained fluvial and alluvial fan sandstones. Thus, this proved that depositional environment of this data is in transitional zone. Depositional environment will influenced the hydrocarbon quality and also be the dominant factor in determining the types of organic matter found in a rock.
After we interpret using realized dip deviation and realized event local structural dip in volume attributes, few channel can clearly be seen in the seismic data as shown below. In realized event local structural dip attribute in timeslice at TWT -120.00, small channels can be seen at the upper part and lower part of timeslice. Meanwhile, a big branching channel can be seen at the lower part of timeslice.
Fig. 1 Event local structural dip at TWT -120
In realized dip deviation attribute in timeslice at TWT -124, small meandering channel can be seen at the upper part of the timeslice meanwhile branching channel can be seen at the lower part of the timeslice. At TWT -404, big meandering channel with the width 578 meter at the upper part of the timeslice. Thus, these attributes can enhance the outline of channel geometry and channel edge in the seismic geomorphology interpretation.
Fig. 2. Dip deviation at TWT -124
Fig. 3. Dip deviation at TWT -404
From our observation throughout doing this project, we have found a huge gas chimney that most probably the kerogen type-III which are the main hydrocarbon source in this Malay basin. Kerogen type-III was derived mostly from higher plants and composed of vitrinite, a maceral formed from land plant wood. Thus, the channels that we have found in our seismic interpretation are the proof that the hydrocarbon source in Malay basin was derived from transitional zone. Besides, as we all know coals formed by the remains of plants in paralic swamps and abandoned river channels and was classified in kerogen type-III.
Petroconsultant (as cited in Bishop, 2002) mentioned that discoveries in this area are dominantly gas with some oil in Oligocene to Early Miocene deltaic sandstones in anticlinal traps. Anticline trap is a fold structure with an arch of non-porous rock overlying porous , providing a trap of gas in this Malay basin. Anticlinal trap can be classified in structural trap which was formed due to tectonic movement. After we have applied the seismic attribute in given seismic data, we have found anticlinal trap in inline at TWT 1979.This anticline occured parallel to the faulted half grabens and involve sediments deposited in the thickest portion of the half graben (Bishop, 2002).
Bishop (2002) explained that the combined effects of northward and westward convergence of the India, Australia and Pacific plates caused reversed the motion of the fault zone to right-lateral wrenching along the Axial Malay fault. The resulting of these convergence boundary formed inverted the previous half-graben basins and inversion increases from mildly inverted structures in the north to completely inverted half grabens in the southern part of the basin formed anticline folds which plays the role as hydrocarbon trap. Below is the video we have taken showing the anticline which trap the gas and parallel to the graben.
DIRECT HYDROCARBON INDICATOR INTERPRETATION
Fault is crucial as a trap for hydrocarbon migration. In this seismic data, we found a lot of fault system at the depth about 200 m to 1600 m. Graben fault formation formed parallel to the gas chimney. To determine and estimate the hydrocarbon potential, we applied some attributes to the raw seismic data. At first we determined the DHI potential by reducing amplitude’s opacity of the seismic data set. By doing this, we managed to estimate DHI at some point. Then, when we compared the sweetness and RMS attributes of the realized one (z-line), there is a similarity of the DHI result and information which the enhanced part of the sweetness (dark blue) is intersect with the highest RMS amplitude (yellow). We emphasized on the second horizon for DHI. Then, we used acoustic impedance of volume attribute to emphasize high amplitude which is important in detecting DHI. We combined the attributes with the fault we have made, then it was confirmed that the hydrocarbon is mostly trapped at the fault system.
So lastly we estimate the area and thickness of the hydrocarbon spot. Hydrocarbon spot is about 1223.9 m from surface. We take the width and length of the maximum hydrocarbon spot, 4749.78 m and 6045.94 m respectively. Then we take the thickness from the starting point of hydrocarbon to the end point of hydrocarbon with about 159.697 m. The area estimated is about 29.28 km2 and volume estimated about 5.8km3.