Optimize hole cleaning strategy, minimize risk

During a three-well ERD operation in Southeast Asia, an operator wanted to measure and optimize its hole cleaning strategy to mitigate risk when drilling 12 1/4-in × 13 1/2-in sections. The primary challenge was to deliver a long horizontal section at 70° with average departure greater than 5,000 ft [1,524 m] while minimizing the number of bit runs, avoiding overloading the annulus with cuttings, and maintaining wellbore stability.

ERD has proven to be an efficient solution in reservoirs with restricted production, reducing wellsite footprint and minimizing environmental effects while dramatically improving reservoir drainage at reduced cost. However, using this method to drill horizontal wells requires advanced technology that can accurately describe downhole conditions to identify the causes of harmful vibrations, BHA damage, poor performance, and inadequate hole cleaning.

Use CLEAR service to maintain wellbore stability

The CLEAR hole cleaning and wellbore risk reduction service was used by the operator to monitor cuttings removal from the hole and to analyze the efficiency of the hole cleaning strategy. The weight of cuttings reaching the surface is continuously measured and analyzed as they come off the shale shakers. By comparing measured and theoretical volumes, the service provides early detection of inadequate hole cleaning and of excess returns caused by wellbore instability (caving) or formation damage.

Information provided by the CLEAR service showed that the drilling fluid rheology was ineffective and, because of insufficient hole cleaning, the well was degrading further. Acting on this information, the drilling team adjusted the approach by raising the low-end fluid rheology, improving hole cleaning and avoiding the need for unplanned circulation.

Improved drilling performance, saved time and expenditures

Using the CLEAR service, the hole cleaning and pill strategy was successfully optimized. The frequency of the pills used was decreased without detrimental effect on the hole cleaning, improving the net ROP and decreasing hidden time spent on mud treatment.

Through correlation and systematic benchmarking on the impact of cutting lifting of the pills, the size, frequency, and type of pills used were revised according to the data to optimize efficiency and control time dedicated for a secondary hole cleaning. These results decreased the invisible lost time. High-viscosity pills were maintained for the larger-OD slant hole, and tandem pills were assessed and measured as having optimal performance in smaller ODs.

The solution led to an overall improvement in drilling performance. The average time spent per stand for circulating and pumping pills decreased by 11 minutes compared with previous wellbores. Due to a more systematic approach, the operator saved 16 hours of rig time and USD 194,000 in direct costs.