Field test results of Radiagreen EME Salt

A horizontal well drilled by an operator in Qatar, using LSND mud system for the horizontal 8 1/2” section planed till 26,500 ft in a limestone formation (Figure 1).

Figure 1: Well Profile

• To improve the lubricity of the mud system while drilling the 8 1/2” section; it was decided to use the Radiagreen EME Salt to reduce as much as possible the Torque and Drag as well as maintaining Stick and Slip values to a minimum.
• 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 acceptable range to avoid any excessive side friction effects in order to be able to transmit the power to the bit. This is why good lubricity properties by adding the lubricants is required (Figure 2).

Figure 2: Dogleg severity and inclination

• Prior to adding the Radiagreen EME Salt into the active system there were signs of high erratic torque and Stick and Slip (=~150% or 300 rpm)
• At 13,815 ft, it was decided to POOH and and make up a new BHA. The new BHA was similar with the exception of the addition of a roller reamer. After RIH and resume drilling, problems were persistant and still unable to build angle
• It was decided to start additions of Radiagreen EME Salt at a initial concentration of
3% (v/v). The addition was done with a concentrated premix (44 bbls of Radiagreen dispersed into 115 bbls of fresh mud). The premix was bled into the active system over one
circulation. The system was fully treated at a depth of 14,069 ft. Noted that all subsequent Radiagreen additions into the system were performed using the same method. (i.e via a premix)
• Instantly, it was observed a drop in the On-Bottom Torque values and also they were less erratic compared to was they used to be (Figure 3)

Figure 3: On-Bottom Torque and Stick & Slip readings

• The torque peak values observed before the addition of Radiagreen EME Salt had also disappeared. Another immediate consequence of the improvement observed was the increase of the average ROP which jumped from 190 ft/hr up to 350 ft/hr on average.
• Radiagreen EME concentration was kept at 3% (v/v) till 16,800 ft; after the concentration in the system depleted consequence of dilution and lack of Radiagreen on board. At 19,110 ft, the concentration had dropped to 1.3% in the active.
• A new BHA was run, with the only change being a 2-cone bit. Stick and slip was observed for the first 60 ft (Figure 4). This was due the drop in concentration to 1.2% and as soon as mud containing 1.5% passed the bit an immediate improvement was recorded.

Figure 4: On-Bottom Torque Average & Maximum values and Stick & Slip

• Noted that On-Bottom Torque reduction was around 22% compared as before the addition of the Radiagreen (Figure 4). 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 Kft.lbs,it would have been almost impossible for this rig to reach TD. It was however, decided, following the actual Torque and stick & slip values, to set up a new TD for the well at approximately 28,000 ft.
• About Stick & Slip, it has to be said that at 3% Radiagreen EME Salt concentration, an average value of 10% was observed but increased to an average of 20% once the Radiagreen concentration in the system was fixed at 1.5% (v/v) (Figure 5).
• The On-Bottom Torque followed the new trend resulting from the addition of the Radiagreen in the system (Figures 4). Nevertheless around 23,000 ft till TD, the WOB applied while drilling increased from and average of 8-13 Klbs since beginning of the 8 1/2“ section up to 20-25 Klbs. Ditto for ROP which increased with peaks up to 500 ft/hr. This explained why after 23,000 ft and till TD, erratic Torque readings were observed, and sometimes were above the generated trend line. However it was possible to reach the new TD set up at 28,000 ft.

Figure 5: Stick & Slip values in %

As Torque and Drag for deviated wells is too complicated to establish on a simple comparison based on torque readings, Wellplan for Windows software was used to input all relevant drilling data and particularly its torque and drag analysis helped, to generate a set of friction coefficients. (Figure 6).
This graph shows undoubtedly the effect of the lubricant to reduce the Torque when it was added into the active mud system. In this graph the actual recorded Bottom Torque values from the driller were plotted against the theoretical set of friction coefficients.

It should be noted that in this graph, the friction coefficients represent the average value for both Cased and Open Hole; meaning that at this stage, no discrimination was made between the Cased and Open Hole frictions factors.

For Torque, the average friction coefficients went from 0.25-0.30 down to 0.15-0.16 which represents a reduction of about 35 to 40% for Off-Bottom Torque.

This resulted in a better power transmission to the bit as less power was lost by friction in the cased and open hole. For Drag values, same comments and results before and after addition of Radiagreen EME Salt apply.

Figure 6: Generated Torque Chart 8 ½” section

Figure 7: Generated Drag Chart; 8 ½” section

• No particular adverse effect has been observed between the Radiagreen EME Salt and the LSND mud system.
• No greasing out or phasing out or foaming were observed along the well. It has showed its tolerance to hardness and effectiveness at low concentration.
• Radiagreen was easily dispersed in the mud; all additions were done via premix which were later bled into the active. No ill effects were observed.

Conclusions

• After the addition of the RADIAGREEN EME Salt, the average friction factor dropped for the Open Hole from 0.25-0.30 down to 0.15-0.16 which represents a reduction of about 35 to 40% for Off-Bottom Torque as compared before the use of Radiagreen.
This was observed for both Torque and Drag;

• The lubricity of the mud was enhanced which improved the actual drilling conditions; observed for the On-Bottom Torque reduced to +/- 22% and was less erratic.
Same observation was made for the Stick and Slip conditions; after addition of the Radiagreen EME Salt at 3% (v/v), it dropped to an average of 10%.
When Radiagreen EME concentration was set at 1.5%, the Stick & Slip average values
were increased to an 20% which is still far below the limit of 50%.

• The addition of the lubricity allowed faster drilling from an average of 190 ft/hr up to an average of 350 ft/hr.
Overall no Stick & Slip situations above the 50% limit were observed after the addition of the Radiagreen. This increases the tool lifetime and less or no failures were observed. Also this gives better LWD log and signal quality.
A better ‘steerability’ which allows the bit to remain in the reservoir “sweet spot”.

• The Radiagreen was easily dispersed in the LSND mud; no phasing out or greasing was observed while drilling the 8 ½” section.
It showed its tolerance to hardness and no foaming was recorded.
Most importantly it exhibited its ability to be effective at low concentration of around
1.5%.

• All this allowed this well to be drill deeper well than it was originally planed as torque in long horizontal wells is often the main limiting factor.
This allows deeper wells from smaller rigs.