An operator in Qatar planned to use a low-solids, non-dispersed mud system to drill a horizontal 8 1/2-in. section to 26,500 ft (8,082 m) in a limestone formation. While drilling the 8 1/2-in. section, Radiagreen EME Salt from Oleon was used to improve the lubricity of the mud system, reduce torque and drag and minimize stick and slip values.

In deviated and horizontal wells, good hole cleaning is important to avoid the formation of excessive cuttings beds. The dogleg severity must be also kept within an acceptable range to avoid excessive side friction effects so sufficient power can be transmitted to the bit. This is why adding lubricants to improve lubricity properties is generally required.

Before the lubricant was added into the active system, there were signs of high, erratic

Figure 1. Based on extrapolation of the on-bottom torque values observed before addition of Radiagreen EME Salt and the fact that the maximum allowable torque by the rig was around 32,000 ft/lb, it would have been almost impossible for this rig to reach TD. (Image courtesy of Oleon N.V.)
torque and stick and slip. Problems were persistent. The operator decided to start additions of Radiagreen EME Salt. The system was fully treated at a depth of 14,069 ft (4,291 m).

Instantly, the operator observed a drop in the on-bottom torque values, and the values were also less erratic. An increase of the average rate of penetration (ROP) was another immediate consequence of the improvement. ROP jumped from 190 ft (57.9 m)/hr up to 350 ft (106.75 m)/hr. On-bottom torque reduction after the addition of the salt was around 22%.
Based on extrapolation of the on-bottom torque values observed before the addition and the fact that the maximum allowable torque by the rig was around 32,000 ft/lb, it would have been almost impossible for this rig to reach total depth (TD). Following the actual torque and stick and slip values, the operator decided to set up a new TD for the well at approximately 28,000 ft (8,540 m).

Concerning stick and slip, at 3% Radiagreen EME Salt concentration, an average value of 10% was observed but increased to an average of 20% once the concentration in the system was fixed at 1.5% volume-to-volume (v/v).

Conclusion
After the addition of the Radiagreen EME Salt, the average friction factor dropped for the open hole from a range of 0.25 – 0.30 to 0.15 – 0.16, which represents a reduction of about 35% to 40% for off-bottom torque. The positive results applied to both torque and drag.
The lubricity of the mud was enhanced, which improved the actual drilling conditions. Observed on-bottom torque was reduced to +/- 22% and was less erratic. The same observation was made for stick and slip conditions. After the salt was added at 3% (v/v), the incidence of stick and slip dropped to an average of 10%.

The addition of the lubricity allowed faster drilling, which increased from an average of 190 ft/hr to an average of 350 ft/hr. Overall, no stick and slip situations above the 50% limit were observed after the salt was added. Alleviating stick and slip increases tool lifetime, gives better logging-while-drilling log and signal quality and better steerability, which allows the bit to remain in the reservoir sweet spot.

The salt was easily dispersed in the mud. No phasing out or greasing was observed while drilling the 81¼2-in. section. It showed tolerance to hardness, and no foaming was recorded. Most importantly, it exhibited its ability to be effective at a low concentration of around 1.5%.
All this allowed the well to be drilled deeper than was originally planned because torque in long horizontal wells is often the main limiting factor. This additive has allowed deeper wells from smaller rigs.