|The Brief - Technical Article|
| A new lubricant has
been tested successfully in Trinidad and Egypt ! Finding a lubricant for water-based muds
that works under a variety of conditions is difficult. Conventional, or
"chemical," lubricants generally act by forming a film on the steel and rock
surfaces. However, they will also adsorb on solids in the mud, and they must compete with
other surface-active components of the mud for the steel and rock surfaces. Furthermore,
at high shear rate the emulsified lubricant tends to become so stabilized that adsorption
is prevented, and often the film that is formed is too weak and/ or thin to provide much
lubrication. All of these factors may cause the performance of a chemical lubricant to
A different class of lubricants, called "physical" or "mechanical" lubricants because they tend to act as ball bearings rather than by forming a film, have significant promise as replacements for conventional lubricants, particularly in extended reach wells and in muds that contain polymers and other surface active components, e.g. lignosulfonates.
In January of this year, Amoco EPTH Drilling, Tulsa Drilling Technology conducted several torque reduction tests in horizontal well at Catoosa using PAC mud and three lubricant candidates. Thuslick, a powdered plumbago graphite coated with silicon based PDMS was added at the recommended concentration of 4 lb/bbl and outperformed the other two additives. Compared to the base mud, Thuslick reduced the surface torque by 10 to 20 % over the torque range of 1,000 to 3,200 ft-lb.
Before testing THUSLICK in the field, however, another concern needed to be addressed: if THUSLICK were to be used in horizontal wellbores, would it cause formation damage? Particle size analysis indicated that THUSLICK has a similar size distribution as conventional barite. Laboratory tests indicated, however, that although THUSLICK can travel into the pore network of a sandstone in a manner similar to barite, it is also easily produced back, with the result that no incremental damage is expected directly from the addition of THUSLICK to a mud.
On the basis of these results, Thuslick has been recommended for use in extended reach wells. Amoco Trinidad Oil Company tried Thuslick on the Samaan C 5 XX horizontal well. A fresh-water PAC Mud counting substantial level of lost-circulation material (RESINEX, GRAN-SEAL, E-SEAL and KWIK-SEAL fine) was used to drill an 8 1/2" hole from the kick-off point at 6,1000 ft MD, building angle to 90 degrees at the rate of 8 degrees/100 ft from 7,600 ft to 8,900 ft. However, at 8,372 ft MD, the torque increased to about 680 amps, causing sliding problems. Treatment of the active mud system with 4 lb/bbl Thuslick reduced the torque to 450 amps. At 8,800 ft MD the angle reached 89 degrees, and lateral drilling was begun. The angle, however, continued to increase, reaching 90 to 93.7 degrees at 9,393 ft MD. The decision was made to reduce angle and increase TVD, but this proved difficult due to erratic torque, which exceeded 600 amps. Increasing the concentration of Thuslick to 5 lb/bbl solved the problem, and the torque backed down to 500 amps.
Slug treatments of Thuslick were also found to be helpful at other times. For example, while slicking rotary drilling to 8,820 ft., erratic torque (450 to 650 amps) was brought under control (at 450 amps) to permit sliding. While back reaming out of a tight hole at 8,447 ft, slug treating with Thuslick brought the torque down from 650 amps to 550 amps. Beyond 9,500 ft MD, erratic torque of 600 to 800 amps was observed and reduced to 530 amps with a high-concentration Thuslick pill.
The success experienced with Thuslick in Trinidad was repeated, though not as emphatically, in the Nile Delta on the Jj69-2 Hapy No.4. An appraisal well, Hapy No. 4 was planed as a highly deviated well drilled from a diverless template set over the discovery well Hapy No1. The well plan had a kick off point just bellow the 30" drive pipe at 574 ft (175mt) building at 4° /100 ft using a 17 ½ " bit and 9 5/8" AKO steerable assembly, to a terminal angle of 57.5°. The inherent problem with this design was the high torque and drag associated with the normal forces acting at the kick off point as the well got deeper and the drill string tension increased. The intermediate hole section had been finished by setting the 9 5/8" casing at the top of the reservoir and a PAC/glycol mud was being used to the 8 ½ section through the pay zone.
A slick BHA was tripped in the hole and the top of the cement was tagged at 8,563 ft (2,610 m) MD, and drilling of the shoe track was attempted. However, the drill string could not be rotated without axial motion, and circulating/conditioning the mud did not improve the friction factor. A decision was made to change out the BHA in order to reduce normal forces in the build section. The string was pulled out of the hole and run back in with the new steerable BHA with HWDP used for bit weight, which brought about a immediate reduction of about 250 amps (6,250 ft-lbs. total @ 25 ft-lbs/amp), or 25% in rotational torque with the pumps on Drilling of the cement, float collar and the shoe track ensued. However, in the shoe track the measured torque was still high: 600 to 700 amps. So, during the last 16 ft (5m) of the shoe track the mud was displaced with mud containing 4 lb./bbl Thuslick, whereupon the surface torque was dropped by an additional 50-100 amps (11%), and P/U and S/O drag was also reduced 10-20 klbs (10%). The effect was continued, as the well was drilled (currently conventional coring section of the Payzone
The apparent success of Thuslick in the two wells suggests that use of this mud additive should be considered in other extended reach or directional wells where drilling operations may be compromised by high or erratic torque. In contrast to the conventional lubricants, the performance of inert physical lubricants like Thuslick is expected to be relatively independent of the mud system.
IMPORTANT NOTE: This article is taken from THE BRIEF
( A Joint Industry Publication of Drilling Technology,
AMOCO EPTG, CHEVRON and CONOCO )
Publisher and Editor Mr. Michel Murphy, Murphy Publishing, Inc.
PHONE 281 398 0224