It’s not only to stretch a little longer. A correct drilling strategy must maintain a proper rate of penetration while managing wear on the cutting-structure, stress on the bearings and seals, wear on the gage and other possible failure mechanisms.
Understanding Abrasive Formation Challenges
Tricone drill bit wear may be increased by hard and abrasive minerals in the formation or by repetitive impact and slide contact with the bit. Quartz-rich rocks, hard sandstones, cherts, and certain igneous or metamorphic formations may be hard to drill, although the actual wear behavior is a function of the overall formation and drilling environment.
Characteristics of Abrasive Formations
Common characteristics that can contribute to abrasive drilling conditions include:
- Hard abrasive minerals within the formation
- High rock strength or compressive strength
- Interbedded formations with significant changes in rock properties
- Fractured or broken intervals that increase impact loading
- Formation changes that alter the required drilling parameters
Quartz and other hard mineral ingredients may be responsible for abrasive wear, but there is no single mineral-content limit that delineates all abrasive production. Therefore, formation abrasiveness should be examined combined with hardness, fracture characteristics and past drilling performance.
The formation and the cutting structure may combine to cause gradual wear of teeth or implants. At the same time, the drilling fluid and rock cuttings may influence the hydraulic and exterior surfaces of the bit. It is vital to understand these diverse processes when selecting how to decrease wear.
Impact on Tricone Drill Bits
Abrasive drilling conditions can affect several parts of a tricone bit:
- Accelerated wear of milled teeth or tungsten carbide inserts
- Wear around gauge and shirttail areas
- Erosion of external bit surfaces caused by drilling-fluid flow and solids
- Increased demands on bearing and seal systems
- Potential reduction in bit life when wear or component damage becomes severe
The cutting structure isn’t the only wear point that counts. Also roller-cone bit performance is affected by the state of bearings, seals and hydraulic system. SLB covers roller-cone bit design in terms of cutting structures, cone geometry, bearings and nozzles, whereas Halliburton focuses on bearing, seal, compensation, cutting-structure and hydraulic technologies for demanding applications.
Therefore wear should be seen as a total bit-system problem rather than merely the teeth or inserts.
Advanced Tricone Bit Materials: Durability Secrets
The choice of material may affect a bit’s capacity to survive abrasive drilling conditions, but the choice of material must always be made with formation characteristics and bit design in mind.
Cutting Structure Innovations
Tricone bits commonly use either milled-tooth or tungsten carbide insert (TCI) cutting structures.
Relevant design considerations include:
- Tungsten carbide inserts selected for the required balance of wear resistance and impact resistance
- Milled-tooth designs with wear-resistant protection on the teeth
- Insert or tooth geometry matched to the expected formation
- Hardfacing used in areas where additional wear protection is required
SLB says the teeth on milled-tooth bits are made of steel with a wear-resistant carbide-composite coating, whereas TCI bits include tungsten carbide inserts that are fabricated separately and then inserted into the cone. The two cutting structures are developed for varied rock breaking needs.
This implies that increasing the hardness of the cutting element is not always the best approach. The interaction of the cutting structure with the formation should also be proper. An too aggressive or improperly matched design might increase impact or mechanical stress, rather than just enhance bit life.
Bearing and Seal Advancements
The bearing and seal system deserves particular attention when a tricone bit is expected to drill a long or demanding interval.
Important design considerations include:
- Bearing capacity under the expected downhole load
- Seal durability under the expected temperature and operating conditions
- Protection of internal bearing components from drilling-fluid and solid-particle exposure
- Lubrication and pressure-compensation requirements where applicable
The seal condition is of particular importance since seal deterioration may lead to a loss of bearing protection. SLB’s roller-cone technologies are equipped with seal systems intended to preserve bearings in extreme environments such as high WOB, RPM, mud weight and abrasive particles.
Thus, an improvement in cutting-structure wear resistance does not solve all of the bit-life constraints. The cutting structure, bearings, seals and working conditions should be considered together.
Body and Leg Protection
External surfaces can also be exposed to abrasive wear and hydraulic erosion.
Relevant protection areas may include:
- Bit legs
- Shirttails
- Gauge areas
- Other surfaces exposed to formation contact or drilling-fluid flow
Hardfacing and other wear protection measures may be applied to relevant portions of a bit. Gage protection is especially critical when the maintenance of the hole diameter is a requirement.
But the right protection is a function of the bit design and application. Operators should study real wear patterns after a bit run and not assume that all abrasive formations create the same failure scenario.
Optimizing Drilling Parameters for Extended Bit Life
Bit material and design is just half of the wear equation. WOB, rotational speed, hydraulics and drilling-fluid conditions also impact the loading of the cutting structure and other bit components.
Weight on Bit (WOB) Management
The WOB should be chosen as a function of the bit design, the formation and the entire drilling system.
Some helpful techniques are:
- If possible, start in the manufacturer’s suggested operating range
- Increase WOB in a regulated way and watch the drilling reaction
- Don’t give up too much WOB only to get more ROP
- Watch ROP, torque, vibration and other available drilling statistics for change
Further mechanical loads might raise stress on the cutting structure and other bit components. In contrast, the absence of WOB may not let the bit to act effectively against the formation.
The aim thus is to seek an operating window that achieves efficient rock breakage without introducing additional mechanical loading.
Rotary Speed Considerations
Rotary speed should also be considered in relation to formation characteristics and bit design.
Rather than assuming that lower RPM always produces less wear, operators should evaluate:
- Bit design and cutting structure
- Formation hardness and abrasiveness
- WOB
- ROP
- Torque and vibration behavior
- Bearing and seal operating conditions
Cone and bearing rotation for roller-cone bits are related to bit rotation and drilling circumstances. Monitoring of drilling parameters during drill-bit operation and assessment, as per IADC drilling instructions.
The practical objective is to get a WOB and RPM combination that produces effective rock failure without incurring extra wear or compromising drilling dynamics.
Hydraulics Optimization
Hydraulics can influence both drilling performance and bit wear.
Key considerations include:
- Adequate bottomhole cleaning
- Appropriate nozzle selection and placement
- Efficient transport of cuttings away from the bit
- Avoiding unnecessary erosion caused by unsuitable flow conditions
- Maintaining drilling-fluid properties required by the drilling program
Fluid jets assist to lift the cuttings from the bottom of the hole and clean the cutting structure. SLB says nozzle number, positioning, direction and location might impact bit cleaning, cuttings removal and penetration effectiveness.
Cleanliness is especially crucial when drilling abrasive formations, since recirculated cuttings may interfere with effective rock breaking and create extra wear.
Drilling Fluid Selection and Management
Drilling fluid management should support both hole cleaning and the overall drilling system.
Important considerations include:
- Maintaining properties appropriate for the formation and well conditions
- Controlling drilled solids where the drilling-fluid system requires it
- Supporting effective cuttings transport
- Managing fluid-related erosion and other hydraulic effects
- Using suitable lubricating practices when required by the drilling program
Drilling fluid should never be thought of as a panacea for bit wear. It functions to cooperate with the hydraulic design of the bit and the overall drilling program.
Good solids management, for example, may assist to regulate the concentration of drilled solids being circulated through the system, while appropriate fluid characteristics can aid with cuttings transport and hole cleaning. The exact fluid program will be decided depending on well conditions and drilling-fluid needs.
Conclusion
Simply using a tougher cutting material is not enough to reduce wear on tricone drill bits in abrasive formations. Formation features, cutting-structure design, bearing and seal protection, drilling parameters, hydraulics and drilling-fluid management all impact bit performance.
A realistic strategy is to start with a formation assessment. Operators may then compare the bit configuration and cutting structure to the predicted rock qualities, choose appropriate WOB and RPM settings and optimize hydraulics for efficient bottomhole cleaning.
Evaluation after the run is just as crucial. You can often tell if the major problem was cutting-structure wear, gage or leg wear, erosion, bearing or seal degradation, or some other drilling problem by looking at the bit’s dull state and wear patterns. The IADC’s ongoing development of bit dull grading and drilling forensics is an example of the industry’s focus on usage of wear information to assist root-cause research and optimize future drilling operations.
As such, the best wear reduction method is an iterative process; analyze the formation, pick the proper bit design, regulate operating parameters, monitor drilling performance, and utilize the pulled bit state to optimize the next bit selection.
Call to Action
If you are selecting a Tricone drill bits solution for an abrasive formation, the drilling conditions should be considered before choosing a bit configuration.
When discussing an application with Welong, useful information can include:
- Hole size
- Formation type and known abrasiveness
- Drilling interval
- WOB and RPM
- Hydraulic or drilling-fluid conditions
- Previous bit performance or dull-condition information, if available
Providing this information can make the technical discussion more specific and help connect the bit selection with the actual drilling environment.
Contact Welong at oiltools15@welongpost.com to discuss your Tricone drill bits requirements and provide the available drilling information for your application.
