Bit cleanability – What is the significance of the Junk Slot Area?

What is the junk slot area (JSA)?

Harrie Oort, co-owner and director of Aurora

The junk slot area is a measure of the total cross-sectional area from each junk slot if the drill bit were viewed face-on, expressed in square inches.

It is a specialised area designed to clear away debris, also known as “cuttings”, from the bit face while drilling. In video one, Co-owner, Harrie Oort is showing the location of these slots on the outer edge of the bit. They consist of flutes or grooves that aid in removing the cuttings.

Why is JSA important in drilling operations?

The junk slot area is a crucial component to remove cuttings during drilling. Cuttings can cause blockages, reducing drilling efficiency and increasing wear on the bit. Efficient removal maintains a clear path, reducing resistance, less opportunity to trigger vibration and results in smoother drilling with less wear or breakage at the bit face.

Are there factors that impact the design and size of the junk slot area?

The size and shape of the junk slot area can vary depending on the type of drilling operation, drilling fluid type being employed and the lithology being drilled. In general, the softer the formation and higher the penetration rate in a drilling operation, the larger the junk slot area will need to be to pass the volume of cuttings to the annulus.

Furthermore, in high angle holes, optimising the JSA can help to prevent swabbing when tripping in and out of the hole past cuttings beds.

Another key consideration in designing the junk slot profile is to ensure that it provides enough space for the drilling fluid to flow freely while also preventing the cuttings from clogging the bit.

Why is the face volume ratio important?

Harrie Oort, co-owner and director of Aurora

As Harrie explains in video two, at Aurora, we prefer to focus on the face volume ratio of a product. As the JSA only considers a cross sectional area at the entry point to the bits gauge, the face volume considers the volume in between the blades from the centre of the bit and across it’s entire profile. This measurement considers better the capacity of the bit to effectively clear cuttings from it’s face and into the borehole annulus, resulting in increased drilling system efficiency.

Don’t hesitate to contact our team of experts at Aurora with any questions on drill bit designs or want to discuss how we can help you maximise your drilling efficiency.