Engineering considerations of electromagnetic logging while drilling

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Being able to record some parameters during the drilling of oil wells is very useful because it provides us with a lot of data mostly geological that can be correlated with data from other neighboring wells and thus be able to make good decisions during the drilling of the well.

There are tools that measure the resistivity of the electric current in the subsurface formations, which use electromagnetic waves (EWR) and that among all logging tools is the standard of the logs that are made in the well during drilling (LWD).

Resistivity measurement systems

The objective of being able to measure the resistivity in the subsurface geological formations while drilling is to obtain a true resistivity value of the formation, so it is essential to measure the resistivity by electromagnetic logging while drilling.

The advantage of applying this type of electromagnetic logging is that not only can we obtain information of the real resistivity values, but we can also quantify the depth of the damage caused by the invasion of the drilling fluid filtrate, since the geological formation as we are drilling is exposed to a favorable pressure of the drilling fluid causing much of that fluid to invade the pore space of the formation, so it is useful to know the damage of such invasion, and for this we can count as a tool to record it with the electromagnetic log during drilling.

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In the previous image we can see how the left side log called Gamma Ray (GR) is not conclusive to determine the depth of the drilling fluid seepage damage to the formation, while on the right side we can see how at 2800 feet deep the resistivity begins to increase and then begins to decrease at 3030 feet deep, which makes us conclude that there is a formation interval that goes from 2800 feet to 3030 feet where the invasion of the drilling fluid seepage into the formation occurred.

Although the resistivity values help us to know where there is an interval where oil or natural gas may exist, it is also known that where the resistivity values are altered is because it is probably a zone where damage occurs and a possible invasion of the drilling fluid filtrate into the formation.

Conclusion

Logs whose measurements are taken during drilling are very important in exploratory wells and serve to contrast other geological data from neighboring wells, which is why electromagnetic logs allow us to measure the resistivity to know the producing interval, but also to assess the depth of damage in the invasion of drilling fluid filtrate into the formation, which can be estimated to know the possible work to be done in the future in these wells to improve their future production.

References

Logging while drilling (LWD)

Types of logs

PEH:Drilling-Data_Acquisition