Number of drill cuttings per length of hole drilled

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The only way to drill a well is through a technique in which the drill bit rotates, and as it rotates it removes pieces of rock in the subsoil, these pieces of formation rock are called cuttings, the important thing in this case and what I want to explain in this post is that you can calculate the amount of cuttings for each foot that we drill.

The estimation of the amount of cuttings per foot that we drill will increase as the diameter of the hole is larger, which means that in the first holes, i.e. in the conductor hole and the shallow hole is where we are going to generate a high volume of cuttings.

Being able to calculate the amount of cuttings that we are going to obtain in a drilling is very important, since all those cuttings we are going to have on the surface, so it is necessary to move them to a final disposal to a place where it can be treated to eliminate contamination, with this we can plan in terms of logistics, i.e. how many trucks we are going to need to move those cuttings.

With the calculation of the volume of solids in the drill cuttings we can estimate the volume of cuttings in each phase of drilling an oil well, the important thing here is to be aware that the volume of cuttings is not equal to the volume of the hole, since the volume of cuttings is greater than the volume of the hole for the simple reason that the cuttings once generated are exposed to the wettability of the drilling fluid, in addition to this we must also take into account the expansion factor of the rock, which is why the volume of cuttings is a separate calculation from the one made when calculating the volume of the hole.

There are English system units to calculate the volume that are used in the oil industry and are very common, such as cubic feet, barrels and gallons, however here in my country Venezuela the volume capacity of the trucks that transport cuttings is in cubic meters, which is why the equation to calculate the volume of drill cuttings that I am going to show you is to calculate the volume of cuttings in cubic meters:

Example of drill cuttings solids volume calculation

Suppose a 26-inch diameter well is being drilled to the depth of 560 ft, the porosity of the rock being 25%. What volume of drill cuttings solid is generated in that section of the well?

We can analyze that for a well whose diameter is 26 inches and with a rock whose porosity is 25%, in 560n feet drilled will generate 43.85 cubic meters of cuttings or drill cuttings.

If the porosity of the rock is higher, the volume of cuttings will be lower, if the diameter of the hole is smaller then the volume of cuttings will be lower, and the deeper the length of the drilled hole then the higher the volume of cuttings, all these variables are important in your analysis when estimating the volume of drilling cuttings.

References

Formulas and Calculations for Drilling, Production and Workover / Lapeyrouse, 2002.

Drilling Fluids Engineering Manual, M-I SWACO, Version 2.0, 2001.

Applied Drilling Engineering / SPE Textbook Series, Volume 2, 1986.