seismic interpretation project

8/17/2019 Seismic Interpretation Project

1/10


2/10

The coursework consists of the seismic interpretation of acquired Troll field seismic

lines, both in paper and through the Petrel Software. The interpretation aimed to identify the

main faults and the BCU (Base Cretaceous Unconformity) horizon.

The Troll field lies in the northern part of the North Sea, near Bergen, and contains

about 40% of total gas reserves on the Norwegian continental shelf, Troll is also one of the

largest oil fields in Norway. In 2002, the oil production was more than 400,000 barrels per

day. The enormous gas reservoirs lying 1,400 meters below sea level are expected to

produce for at least another 70 years. The reservoir is located in three eastward-tilted fault

blocks 1500 m subsea and consists of cyclic shallow-marine sandstones formations overlain

by Upper Jurassic to Paleocene clays (rocks formed around 150 to 60 million years ago).

Located in the eastern margin of the Viking Graben, water depths range from 300 – 355 m

[3].

The Petrel software is a Schlumberger owned E&P software platform that providesan integrated solution from exploration to production. By bringing the whole workflow into

a single application, risk and uncertainty can be assessed more carefully. According to the

manual, the system allows the user [1]:

Seismic visualization and interpretation in 2D and 3D windows.

Perform well correlation.

Build reservoir models suitable for simulation.

Gridding of 2D structural surfaces and the generated 3D fault model.

3D visualization of geophysical, geological, petrophysical and production data.

3D property modeling based on well logs and trend data.

Facies and Fracture Modeling.

Volume calculations, data analysis and plotting.

Among others.

Figure 1 is a screenshot of the Petrel interface, with the location of its main features.

Figure 1 – Petrel Interface [2]

http://en.wikipedia.org/wiki/Fault_blockhttp://en.wikipedia.org/wiki/Fault_blockhttp://en.wikipedia.org/wiki/Sandstonehttp://en.wikipedia.org/wiki/Formation_%28stratigraphy%29http://en.wikipedia.org/wiki/Paleocenehttp://en.wikipedia.org/wiki/Clayhttp://en.wikipedia.org/wiki/Grabenhttp://en.wikipedia.org/wiki/Grabenhttp://en.wikipedia.org/wiki/Clayhttp://en.wikipedia.org/wiki/Paleocenehttp://en.wikipedia.org/wiki/Formation_%28stratigraphy%29http://en.wikipedia.org/wiki/Sandstonehttp://en.wikipedia.org/wiki/Fault_blockhttp://en.wikipedia.org/wiki/Fault_block


3/10

Firstly, there was the familiarization with the software 3D window, by discovering

and testing shortcuts (‘H’, ‘P’ and ‘V’ buttons, mouse buttons and movements, zoom in/out,

etc.), always respecting the arrow pointing north, on its green side to locate the correct side

and direction of the seismic data. Then, it was created an interpretation folder, which was

used to carry out the 2D interpretation of the faults, with the ‘create fault interpretation’

function; and the contour of the BCU, with the ‘create seismic horizon’ function. The

contour was made using primarily the seeded 2D auto tracking, followed by guided auto

tracking and manual tracking. Gaps were encountered where the BCU intercepted faults.

The result is showed in Figure 2.

Figure 2 – BCU and main faults tracked in “2D” (Red=Elevated, Blue=More Profound)

The next step was the creation of the contoured surface map based on the BCU

horizon made, with the later addition of the 2D faults. The results are present in Figure 3. It

can be noted the effect of the faults in the second map.

Figure 3 – Contoured Surface Map (Red=Elevated, Blue=More Profound)


4/10

The scanned 2D hand-made map of the troll field, as showed in Figure 4, was

imported to the project, and its coordinates corrected to coincide with the map coordinates.

Figure 5 shows this map overlapped over the project. As the hand-made map was not

finished (it was just marked the faults observed in the seismic trace), it can just be observed

the faults coinciding whit the software interpretation.

Figure 4 – Scanned Map

Figure 5 – Scanned Map over the surface

To begin with the 3D interpretation, it was to reconnect missing files of the survey 1

to generate the 3D map, resulting in X, Y and Z planes that can be slided up/down (Z) and

right/left (X,Y). The X and Y planes represent the structural and stratigraphic variations, the

Z-plane, the variation in the reflectivity of the waves (generated in the surface, to provide

the seismic response after correction, noise reduction, processing). After that, it was

obtained the variance (measure for trace to trace variability calculated for a sliding window

along each seismic trace, enhancing faults, in red), through Volume attributes process.Figure 6 shows these planes.


5/10

Figure 6 – Variance planes, Reflectivity and structural variation planes

The next step was to develop the reinterpretation of the key faults (right, middle and

center faults) in the 3D volume. Then, generate the BCU “surface”, by first, making the 2D

contour, from east to west, then using the 3D auto tracking feature (Points will be tracked

outwards from the seedpoints in all directions, with good quality reflectors). To enhance

there is yet the 3D track in the horizon settings. The result is in Figures 7&8

Figure 7 – 3D Faults


6/10

Figure 8 – 3D BCU

It can be observed that the faults follow the variance details in Figure 7 and in Figure

8, the surface follows the stratigraphy of the region and respects the faults which cut the

BCU. Lowering the quality of the 3D track feature, the 3D BCU surface covers more of the

volume, as show in Figure 9.

Figure 9 – 3D BCU with the 3D track feature

Figure 10 shows the Dip/azimuth surface created through surface attributes and the

thickness map comparing the BCU without and with faults. The first show the difference

between the faults and the stratigraphy, and in the second, the effects of the faults in with the

areas around can be seen with clarity.


7/10

Figure 10 – Dip/azimuth surface and Thickness map


8/10

The impact of faulting in the reservoir deliverability of the field:

The fault can fulfill a lot of function in a petroleum geological system. Faults can be:

Migration paths for the oil/gas to migrate from the source rock to the reservoir

Traps for the oil not to exudate to the surface Links to connected/adjacent reservoirs

Increase the porosity/permeability of reservoirs due to stress

These factors help the deliverability of the field.

An exploration well can be placed in several locations, based on the correct

interpretation of the subsurface, and identifying the main conditions that define a good

petroleum reservoir. The best condition to identify a big reservoir is the difference between

the BCU and the top reservoir horizon, adjacent to a fault, near a flat spot (horizontal

reflector, resulted from the increase of seismic impedance), denoting a large gas column

overlying a liquid-filled porous rock (greater thickness of reservoir). Figure 11 and 12 shows

a location that has these characteristics.

Figure 11 – Locations of a possible well


9/10

Figure 12 – Location of a possible well in the base map


10/10

REFERENCES

[1] Schlumberger (2014). Petrel E&P Software Platform. Available at:

http://www.software.slb.com/products/platform/Pages/petrel.aspx (Accessed: 8th December

2014).

[2] Petrofaq (2014). Petrel . Available at: http://petrofaq.org/wiki/Category:Petrel (Accessed:

8th November 2014).

[3] Statoil (2014). The Troll Area. Available at: http://www.statoil.com/

en/ouroperations/explorationprod/ncs/troll/pages/default.aspx (Accessed: 8th November

2014).

[4] Huuse, Mads (2014). Class Notes.

seismic interpretation project

Documents