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Geology/Mapping using Wireline log


Dear Sir,

I am working on 13 well.

Geology of area is Intracratonic and Fluvial Lacustrine deposition.

I have completed interpretation of sandstone and Siltstone using wireline log, and also created NS and EW cross section. Same for fluvial facies which are fluvial channel, floodplain and crevasse splay. As I am working on three formation, I also created Isopach map for each formation.

I wanted to create map, can you please guide me which map is good to present depositional environment and palaeography of each formation. I wanted to create a detail model and map for this area.

Dear Muhammad,

Thanks for sending me your question.

You have not mentioned how big the area your 13 wells covers. Some suggestions for your project;

First you have to divide each formation on different sub units on the basis of  logs correlation(use GR as a key log) and define them in terms of depositional environment. Sequence Stratigraphic interpretation scheme would be useful if you can do it. Prepare  more than two cross section.

Check the type of GR response and try to establish fining and coarsening upward cycles on each of your well. Finning upward cycles(channel point bar in Alluvial or fluvial setting) coarsening upward cycles (prograding coastal plains or prograding Delta margin. Once you are able to distribute these sub-units on a map  and connect each point where appropriate then this will give you an clear  template to distinguish from one depositional environment to another.

Use the GR logs for lithological interpretation which you have already did and color those units giving certain percentage of lithology (for example; yellow for  sandstone greater than 60% or green where shale or silt is greater than 60%). Now you can fill the color in the template map which will reflect the lithological variation of subunit on the basis each well control point.

Similarly,you can do on each unit and their sub units and prepare maps. Use color pencils if you do not want on any mapping software. Prepare Gross thickness map of each unit and combined units.

Prepare sand to shale, or sand to siltstone ratio maps. (Sand -shale ration is more appropriate then Sand to siltstone map).

Once you will come up with several type of maps then you may easily define the paleo-depth and paleo- relief profile--keeping in mind that thicker sands are closer to its clastic source and its content starts to cut down as farther away it travels from the source and so the thickness of each unit.

Crevasse splays interpretation you can do in abnormally thicker sand units than other wells.
I understand that data of only 13 wells are far too low to construct a paleo-geography map but you still can try.

If the area where your wells are located once was a flat plain with or without significant gradient or slope then lithological variation may be minimum but it depends how distantly apart each well is and how big your study area is.

You must have to establish the direction of source and direction of flow of the fluvial channels and the direction at which delta formed before the delta loaded with sediments prograding towards shelf and then to the basin.

Hopefully, this answer will be helpful.

Please let me know if I can be of further help


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Syed Tariq Hasany


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