Schlumberger

Case Study: First Successful Application of HPWBM Seals Problematic Shales

Challenge: The operator in this area utilizes a standard KCl/Glycol/sulfonated asphalt system to drill these regular hole sections. In wellbores with angles from 30°-45° the success rate is approximately 60% with no NPT experienced. There are three formations drilled during this section that are causes for concern. The Fiqa is a soft marl of calcareous shale and argillaceous limestone. The Laffan and Nahr Umr are brown grey shales indurated with streaks of limestone. They can be very problematic and unstable when mechanically disturbed. Problems experienced include sloughing shale, packing off, extreme overpull, and hard back reaming, and some instances of bit/stabilizer accretion. The operator was looking for a water base fluid with better performance because Non-Aqueous Fluids are not an option.

Solution: M-I SWACO proposed the ULTRADRIL high-performance water-based mud system with the new POROSEAL sealant additive. In preliminary core sample testing, with different base fluids, it was observed that the rock has many natural fractures that interact with the fluid to destabilize the shale. This problem was addressed with the application of POROSEAL. Lab data showed ULTRADRIL fluid to provide better inhibition than the conventional system with regards to shale recovery, bulk hardness, accretion, and linear swelling. The inhibition performance of ULTRADRIL fluid coupled with the sealing characteristics of POROSEAL provided a fluid solution to drill the problem formations more effectively.

Result:

  • The section was drilled to total depth and no pumping out or back reaming was required
  • No fill or obstructions when tripping indicated good hole cleaning and wellbore stability
  • Finer than normal mesh shale shaker screens were run allowing solids to be more effectively removed at the flowline immediately, thereby reducing dilution
  • Hole cleaning was very good during the section, as predicted by M-I SWACO VIRTUAL HYDRAULICS software
  • Inhibition performance was verified with the integrity of the cuttings observed at the shaker
  • Mud properties were more stable than the conventional system simplifying on-site engineering
  • Total fluid consumption and discharge to the environment was reduced by 1,000 barrels (159 m3)

Well Information
Location Offshore Abu Dhabi, United Arab Emirates
Well type Directional at 34°
Bit size 12 ¼”
Interval length Total of 3,855 ft (1,175 m) drilled from 5,586 ft to 9,441 ft (1,703 to 2,878 m)

The Details

PlannedMinimumMaximum
Density SG
lb/gal
1.20 – 1.41
10.0 – 11.75
1.2
10.0
1.41
11.75
Plastic Viscosity cP ALAP 21 43
Yield Point lb/100ft2 15 – 30 16 40
6 rpm 12 - 18 4 10
API Fluid Loss cc/30 min <3.0 1.5 3.2
pH 9.0 – 9.5 8.5 10.3
MBT ppb
kg/m3
<10
<28

0
7.5
21.4
Drilled Solids % <7.0 0 2.7
ULTRAHIB % v/v 2 – 3 2.65 3.42
ULTRACAP PLUS ppb
kg/m3
2.5
7.1
2.3
6.6
2.6
7.4
ULTRAFREE % v/v 2 – 3 2.5 3.5

Download: First Successful Application of HPWBM Seals Problematic Shales (0.56 MB PDF)

Related services and products

 
 
Contact Us

Learn More

POROSEALShale Recovery
PrevNextZoom1 of 2