/CASE STUDY
Servitec Foraco: The path to optimized diamond drilling
by Rafael Echebarrena, Technical Support Manager Brazil Operations at Servitec Foraco
Servitec Foraco were awarded a diamond drilling project located North of Brazil. The project involved an Atlas Copco CS14 drill rig. The task Search for operational excellence in a new diamond drilling project (H-size/N-size) with the objective of reaching all goals with safety, high productivity and sample quality, and low maintenance.
The solution Monitor, measure and adjust all operational parameters, such as drilling fluid, rotation, pump pressure, diamond bits, etc.
The results At the beginning of the project in March 2021 the average productivity was 13 m (≈ 43 ft) per shift and a daily average of 52 m (≈ 171 ft) per rig. With the monitoring and adjustment of operational parameters, in the following month (May 2021) the average productivity increased to 19.56 m (≈ 64 ft) per shift and with a daily average of 78.24 m (≈ 257 ft) per rig. In June 2021, we reached an average productivity of 24.15 m (≈ 79 ft) per shift and daily average of 96.60 m (≈ 317 ft) per rig. Thus, from March until June 2021 we obtained approximately 85% increase in productivity. The service life of the H-size diamond bits increased from 40 m (≈ 131 ft) to 90 m (≈ 295 ft), while the N-size diamond bits from 95 m (≈ 312 ft) to 180 m (≈ 591 ft). The result obtained was an increase of 125% in the yield of H-size diamond bits and 89% for N-size diameter.
The details We were awarded a new diamond drilling project by one of the largest mining companies in the world, located in the state of Pará (PA), Brazil. From the first meter drilled, we were monitoring the operational parameters 26
with the help of a fluid specialist, sent by our Brazilian partner - BUN Mud Solution (BMS). The specialist carried out a daily monitoring of the activities and subsequently developed the most suitable fluid for the perforated lithology. In this specific fluid, we maintained a Marsh viscosity between 45 and 50 seconds with the use of PHPA (Extravis VH) and corrected the pH of the water with the barrel, going from 6 to 9. Lubricating oil (soluble oil) was also used in this formulation, controlling the torque and favoring the preservation and the increase of the diamond bit life. After this initial stage of drilling fluid preparation, we began monitoring and adjusting the fluid’s pumping pressure rate. At the beginning, we recorded a pressure/flow rate of 63 L (≈ 17 gal) per minute, which is adequate for a pressure/flow rate of 40 L (≈ 11 gal) per minute, as high pressures in the fluid’s pumping rate can slow the penetration rate (advance) and increase the torque, which can cause a collapse of the walls of the well (in friable materials) and a series of problems. With operational parameters adjustment during drilling, we reduced torque, increased penetration rate and controlled fluid velocity during return into the annular space. Afterwards, we adjusted the rotation speeds and pressures to suit the perforated lithology. We knew we couldn’t estimate the constant (default) rotation/pressure due to variations that occured in lithology. For this reason, we advised our drillers to always be alert to the probe panel (manometers). And if they were to notice an increase in pressure/torque, they had to make the necessary corrections immediately. During drilling, it was essential to keep torque down, as we knew the direct relation of this parameter to tool weight and hole depth. As we went deeper into the hole, and placed more shanks, there was an increase in the to-
tal weight of the tool, and consequent gradual increase in the torque. Through torque we can know if at current depth, there is a hole cleaning problem due to excessive amount of cuttings and other issues that can cause premature wear of the diamond bit matrix. At the beginning of this new project, the BMS fluid specialist evaluated the situation and helped us realize that due to the large number of cuttings, we had to fully dispose of the drilling mud to achieve a decrease in torque. Following this, on every 150 m (≈ 500 ft) on average, the mud pits were emptied and new mud was prepared, avoiding the accumulation of solids and the problems generated by that. As for the fluid cost for X meters, we calculated the volume of the hole, depending on the diameter, and eliminated a possible waste of additives. The basic relationship was that for each meter drilled in N-size, we had 4.49 L (≈ 1 gal). In a 300 m (≈ 984 ft) hole we would have 1347 L (≈ 356 gal) of fluid inside the well. In H-size we had 7.23 L (≈ 2 gal) per meter and 2169 L (≈ 573 gal) at 300 m (≈ 984 ft). Thus, we kept a maximum volume Coring Magazine #17
