Integrating Hole Cleaning Solution
in the Drill String to Lower Drilling Costs
Relatively speaking, drill pipe is a small capital expenditure compared to the cost of Non Productive Time (NPT) associated with its use. Studies have estimated the global industry losses related to stuck pipe and lost circulationto be in the order of 2 billion US dollars per year. This corresponds to more than twice the total amount spent to buy drill pipe in the first place and represents about 20% of the total NPT losses associated with drilling operations affected by hole cleaning or the lack thereof.
Increasingly complex and extended reach drilling (ERD) wells are constantly redefining drill pipe performance limits. For Vallourec this means that focusing on well safety and hole cleaning efficiency capabilities of the drill string is key to providing the best product performance.
A holistic engineered approach to a universal problem
While hole cleaning is generally considered to be well understood, many drillers still have difficulty properly managing the entire process. Yet managing this process with measurements of key performance indicators (KPI) is essential when drilling deviated and horizontal wells. Experience reveals that less-than optimal hole cleaning can lead to hole problems with poor hole quality, especially when the hole is downgraded, and sometimes to the loss of the drill string or even the well. Large holes drilled in highly deviated wells at high ROPs are usually inefficient to clean. Whereas smaller shallow ERD holes and long lateral section have annular pressure challenges requiring different pipe solutions. Those challenges are best met through a holistic engineered approach to planning.
Safer and faster drilling
Hydromechanical cleaning devices are part of that holistic approach for safer and faster drilling. Use of fit-for-purpose technology can improve drilling efficiencies and reduce NPT. When properly used in the drill string these devices have proven to have better hole cleaning characteristics than standard drill pipe in all geometries and hole sizes.
Hole Cleaning is time consuming and can have a significant impact on drilling performance, especially offshore where rig costs are high. Land operators, on the other hand, are more inclined to accept using rig time to address these issues which increase drilling costs and risk. The paradox and misconception with maintaining residual cuttings at acceptable levels is that the build-up goes unnoticed until symptoms from the well signal a growing problem. If left unattended, the problem becomes more obvious when indicators such a reduced ROP (rate of penetration), need for higher WOB (weight on bit), erratic drilling torque, increasing ECD (equivalent circulating density) , string whirl, tight hole or ultimately stuck pipe can develop into a high risk situation or lead to the loss of the well. Remedies, which can also be interpreted as red flags, include additional wiper trips, reaming, sweeps and long circulating times, all of which end up consuming additional rig time.
Total system approach
In many respects, the first approach to hole cleaning can look simple when only considering cutting transportation by rotation of the drill string and cutting displacement using drilling fluid circulation. Mud rheology is also deemed to play a major role but is only one part of the total system approach which requires all aspects of cutting behavior to be addressed in concert. Analyzing cutting sizes re-drilled by rotation of the drill string and cutting volumes measured over the shakers is a first step towards setting hole cleaning KPI’s. Keeping the well clean does not mean removing 100% of the cuttings from the well but is generally understood as removing sufficient cuttings to allow for trouble-free operations and usually dictates the amount of rig time spent on hole cleaning and, time not drilling. Performance analysis of the drill string including evaluation of flat time, ECD and Torque & Drag are commonly used for setting targets and for planning. The execution at the well site usually requires the drilling team to manage preestablished rig practices and well-site procedures to achieve real-time performance through well bore monitoring . Pick up Weight (PUW), for example, is one of the tripping indicators measured while running pipe in and out of the hole and reciprocating the drill string. Measurements of Pressure while Drilling (PWD) are routinely applied tor monitoring cutting bed height equilibrium close to the bit and considered as an indicator of “out of control” hole cleaning. These practices are designed to mitigate drilling risks through planning and execution of a hole cleaning system approach. To this end, an in-depth performance analysis review of the drilling process with emphasis on maximizing drilling time drives the entire process. When economically justifiable, mechanical hole cleaning devices should be considered to increase hole cleaning efficiencies and drilling performance. These devices are too often overlooked and misunderstood.
The Hydroclean® Solution
Vallourec offers a patented solution to hole cleaning challenges with its Hydroclean® product line.
Hydroclean® comes in range 2 and 3 and is integrally machined over the full length. A portion of the tool joint bearing section is machined to a larger OD with a profile to reduce friction. The dual OD configuration provides several advantages:
• Offset bladed sections from the borehole wall
• Improved mud flow pattern around the pipe OD
• Less friction than a standard tool joint
• Increased wellbore stand-off
• Reduced total circulating time
• Fewer wiper trips
• Less or no back-reaming
• Elimination of sweeps
• Better and faster hole cleaning
• Lower annular pressure
• Trouble-free BHA trips
• Smooth casing runs
• Bigger cuttings
• More time spent drilling
• Faster ROP
• Extended service life of the drill string
Though the Hydroclean® tool is used globally, few effective field studies have been conducted showing how drilling performance can be improved with an all-inclusive system approach and measurable KPIs. The blueprint for success with Hydroclean® includes rig practices and procedures with a hole cleaning management system approach. A flow chart process that includes planning, execution and, a post job review analysis with lessons learned. These quantifiable lessons learned can be transformed into objectives with recommendations for continuous improvement. There is, for example, a minimum quantity of Hydroclean® tools required to be spaced in the drill string and a minimum RPM to achieve effective removal of cutting beds. The RPM can be further increased to the threshold where “viscous coupling” between the pipe and the drilling fluid is achieved. A common mistake is to use fewer tools than required in order to reduce costs, thus defeating the purpose of the entire exercise. As a rule of thumb, it is generally recommended to place one Hydroclean® joint every two or three stands of drill pipe with the first Hydroclean® placed just above the Bottom Hole Assembly (BHA). Depending on the well profile and drilling parameters, the Heavy Weight Drill Pipe of the lower section of BHA is fully substituted by Hydroclean® Heavy Weight (HHW). An alter-native option to this placement rule is to place one HHW in every stand of standard HWDP.
Hydroclean® was used Ьу TNK-Uvat in Russia to address drilling difficulties encountered in the Ust-Tegusskoye field. Wells planed for drilling were characterized by complex trajectories with long extensions and difficulties in hole cleaning. The accumulation of cuttings was accompanied bу а loss of circulation, stuck pipe, hydraulic fracturing of formation. Boreholes drilled were often constructed with poor quality and with considerable carvings and washouts. A field trial with Hydroclean® was planned on three directional wells with different trajectories and designs. Wells were drilled with a total measured depth of 4.5 km and with a lateral displacement of up to 3 km.
Evaluation of efficiency was based on monitoring key performance indicators (KPI) which were compared with offset wells drilled in the field and 3 wells with Hydroclean® drill string assemblies.
While drilling the intermediate hole sections an increase of cutting of 1.5 – 2 times in volume was measured at surface by comparison with offset wells. No slurry was observed in the section of the BHA configured with stabilizers and virtually no residue cuttings were encountered during tripping.
As a result, the number of wiper trips were reduced from 3 to 1 allowing for an increase in the average ROP.
The need for clean packs sweeps was also eliminated. Additional costs saving on chemicals were incurred due to the larger cutting sizes recovered at surface. Wash outs and caving were dramatically reduced leading to smoother casing runs and better cement jobs. The rig time saving per well ranged from 6 to 9% or 2 to 3 days with the potential to further reduce the number of days per well.
Time and cost savings were
achieved with the use of
Hydroclean® in all 3 wells.
Several drilling problems
were also solved or improved:
• Control of hole cleaning issues
• Increased average ROP
• Fewer wiper trips
• Reduction of non-productive time
• Lower surface drilling torque
• Reduction in chemical costs.