Cutting properties as shape, size, and density of cuttings affect hole cleaning because these properties have an effect on required lifting force to transfer them to surface. Personnel must be very careful when drilling into new formation because change in cutting properties may affect hole cleaning even though you use previous drilling parameters that you never have problem before.
Size of cutting is normally irregular shape and its size can vary from very fine sand to big pieces of rock. If you read in several text books, cutting size is assumed to be spherical shape because it is very easy to understand and predict behavior. Generally speaking, the smaller size of cuttings, the slower they will fall down due to slip velocity. Moreover, shape of cutting is typically irregular due to several reasons as bit type, hydraulic of drilling mud, ROP, etc. The more spherical shape cutting in the hole, the faster it will fall down. Additionally, bit types and cutting patterns have influence on cutting size and shape. For example, a roller cone bit gouges formation and produce rough and bit cutting size. On the other hand, a diamond bit grinds formation and produces fine cutting. Therefore, personnel must contemplate bit selection and realize its effect on how effective to clean the well.
Most of the time, people don’t pay much attention to cutting density because they assume that rock is already ground down and the effect of porosity in the rock is negligible. It is not 100% true especially when cutting size drilled is quite big. If you have big cutting, you should consider cutting density into hole cleaning because the higher cutting density, the harder to remove it from the wellbore.
source : http://www.drilling-mud.org/cutting-properties-affect-hole-cleaning/
Size of cutting is normally irregular shape and its size can vary from very fine sand to big pieces of rock. If you read in several text books, cutting size is assumed to be spherical shape because it is very easy to understand and predict behavior. Generally speaking, the smaller size of cuttings, the slower they will fall down due to slip velocity. Moreover, shape of cutting is typically irregular due to several reasons as bit type, hydraulic of drilling mud, ROP, etc. The more spherical shape cutting in the hole, the faster it will fall down. Additionally, bit types and cutting patterns have influence on cutting size and shape. For example, a roller cone bit gouges formation and produce rough and bit cutting size. On the other hand, a diamond bit grinds formation and produces fine cutting. Therefore, personnel must contemplate bit selection and realize its effect on how effective to clean the well.
Most of the time, people don’t pay much attention to cutting density because they assume that rock is already ground down and the effect of porosity in the rock is negligible. It is not 100% true especially when cutting size drilled is quite big. If you have big cutting, you should consider cutting density into hole cleaning because the higher cutting density, the harder to remove it from the wellbore.
source : http://www.drilling-mud.org/cutting-properties-affect-hole-cleaning/
