Method for Cleaning the Downhole of a Well from Cuttings While Drilling Actions Using Rotary Layers of Extended Surfaces Mechanism
Authors: Althowiqeb I. 
Published: October 2023

Hole cleaning is one of the most important subjects to consider when drilling a well. Removal of cuttings is essential to the drilling operations and the failure of transporting cuttings effectively out of the wellbore can result in multiple drilling troubles. These troubles could be excessive over-pull on trips, high rotary torque, stuck-pipe incident, hole pack-off, and slow rate of penetration. The drilling fluid considered as the primary tool that carries cuttings out from the wellbore up to surface, considering its functional ability which will be obviously depending on the cuttings size, density, shape, and annular velocity for carrying cuttings. Another important factor to highlight is drilling fluid viscosity, knowing that cuttings normally could settle down of the well if viscosity is too low. Yield Point is one of the most important properties of drilling fluid, and it's defined as the amount of resistance to initial flow, or the stress required for starting the fluid movement. This mud property used to evaluate the carrying capacity of the mud to lift cuttings out of the wellbore. YP is directly proportionally to the mud viscosity, so as the viscosity increase the YP will be increasing as well. Another important property of the drilling fluid is Gel Strength. It is the ability of drilling fluid to suspend cuttings whilst the mud in a static condition and the pumps are off. Plastic Viscosity PV known as the third important property of the drilling fluid to be considered. Basically, it is the representation of fluid viscosity cased by mechanical friction. Low values of PV indicate that mud is capable of drilling rapidly due to the low viscosity of the mud exiting through bit nozzles. On the other hand, high PV values normally caused by a viscous base fluid along with high concentration of mud solids. Therefore, to lower PV values, a reduction in solid content has to be considered which can be achieved by dilution of the mud. The effectiveness of drilling fluid in clean-out operation highly depends on their carrying capacity, which is largely a function of fluid viscosity in particular. Therefore, across the entire industry, field studies proven that mud weight have stronger effect on hole cleaning than mud rheology alone.

The primary tools for hole cleaning in the kick-off intervals are flow rate and mud rheology. This can be done practically through pumping Hi-Vis sweeps every 45 ft drilled, starting with the minimum sweep volume and observe returns at the shakers. So, based on the observation, the frequency and volume of the sweeps to be maintained for pumping may be adjusted to optimize hole condition accordingly. The Hi-Vis sweeps viscosity to be around 1.5 – 2 times the funnel viscosity of the mud in active system. If cuttings accumulate in annulus rapidly, then circulating bottom-up need to be considered at least 2 – 3 times, or as needed prior to the well condition and until having the shakers clean. Also, before penetrating formations with high potential of loss circulation, stop at +/- 50 ft above this expected zone, sweep hole with Hi-Vis pill and circulate bottoms-up to unload cuttings from annulus. After that, control ROP (rate of penetration) to prevent loading the annulus with excessive cuttings and avoid losses as well. Dropping rapid sweep sticks is also another factor to consider, dedicating 5 – 6 sticks every connection for improved hole cleaning. The number of sticks can be adjusted depending in hole condition observance. Basically, these sticks recognized as water soluble and will get dissolved and sheared viscosity sweep that will supplement hole cleaning and minimize bit balling.