The Oil Drum

7 comments on Logging a well, does not mean a two by four between the eyes

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Twilight on November 20, 2005 - 11:01pm

Thanks for the explanation, I had no idea how they estimated what was down there. How many wells are logged in an area once it is suspected that oil is there? Do they try to find the edges of the formation this way? I would think it might be quite expensive to go about punching a large number of holes for logging in order to find the extend of the field, but on the other hand this would be valuable information.

Also, how accurate is this method? Things like porosity can be measured directly, but some of it is relying on secondary and tertiary effects.

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Heading Out on November 21, 2005 - 12:13am

Virtually all wells are logged, but this is after they have been drilled in the hope of finding oil or gas, and there is some evidence that oil or gas exists. And I have to confess that I simplified this quite a lot, since there are a wide variety of instruments that are now used that can tell with a fair degree of accuracy, what is down there. However it gets a bit more difficult as we move away from the well, and that may be the subject of a later post.

Generally you have an idea of the geological shape that you are drilling into before you put the well in, but you don't completely know where the oil level is, and some of the papers from Aramco suggest this is still the case, until you physically go down there and look - with an instrument. This gets even more important when you are trying to steer a bit to hit the rock with the oil in it rather than the water.