A simulated two-cone roller cone bit performance.(Image courtesy of Smith International)

The development of a comprehensive FEA system to accurately model the total drilling system grew from the need for a faster, more reliable design method to improve bit performance. The key to successful drilling ultimately is the design, construction, and selection of drill bits that are dynamically stable for the specific formation’s well profile, bottomhole assembly (BHA), and drilling system parameters. To solve the challenge, Smith Bits developed the Integrated Dynamic Engineering Analysis System (IDEAS). IDEAS is a comprehensive tool that accurately predicts a drill bit’s performance and behavior and how it behaves as an integral part of the total drilling system.

The powerful design and application process, 15 years in the making, is based on laboratory-derived drilling mechanics and physical input data using unique and proprietary equipment that accurately characterizes the cutting structure’s interactive mechanics during fundamental crushing and shearing across a broad range of different rock samples.

Interface laboratory analysis

Under controlled pressures, a comprehensive series of indentation and scrape tests are conducted to replicate the dynamics between a roller cone or PDC bit’s cutting structure and a specific rock sample. The laboratory data quantifies actual cutter forces and cuttings generated in scientific terms of magnitude and orientation as a function of the rock failure mechanism and rock removal rates. These data are then used for the design analysis in lithologies comparable to the specific field application, rather than estimated rock/cutter behaviors generated by other design tools. In some cases, actual core samples from offset wells near the application have been used.

Because the laboratory is able to precisely replicate the cutting action for both roller cone bits, which crush the rock under high loads, and PDC type cutters, which shear the rock, the simulation model can incorporate either roller cone or PDC bits.

Simulation process

The actual rock/cutter mechanics data is imported into the virtual drilling environment along with information about the specific drill bit to be evaluated, including precise cutter location, material properties, and dimensions; the bottomhole component dimensional data and the physical characteristics of each BHA element; the geometry of the proposed well bore; and the planned operating parameters. The model allows examination of bit performance in a confined mode for initial design development and also delivers an accurate projection of a bit’s performance considering the BHA and well characteristics (geometry, parameters, and lithology variations) in a fully dynamic simulation mode where the influences on the bit are basically identical to those encountered in a real-world drilling environment.

The resulting simulation outputs enable designers to match the bit’s projected performance to the desired drilling objectives, including increased rate of penetration (ROP), more footage drilled, and/or specific directional characteristics, while ensuring that the highest degree of dynamic stability is engineered into each specific design.

Bit designers use IDEAS as an interactive tool to test and understand how iterative changes to the bit’s cutting structure and other key features affect overall performance in the specific application. The modeling programs show detailed results of how subtle changes in a cutter’s position and orientation can have significant effects on drilling performance and dynamic stability of the bit and BHA. This allows the engineer to quickly arrive at an optimum design and then use the modeling process to certify the performance capabilities of each bit through a dynamic simulation and modeling methodology. Since the introduction of this new design method, bits developed and performance-certified using the simulation software have consistently outperformed previous designs when measured against the key design objectives.

Whether the goal was increased ROP, more total footage, or specific directional behavior for all types of rotary steerable tools, the certified bits have met the challenge and delivered successful results. Operators have gained significant economic benefits associated with the increased total footage and faster ROP derived from the improved dynamic stability and have been able to achieve the objects without the often slow and costly conventional methods.

Comprehensive FEA dynamic modeling allows bit technology to go from concept to field-proven performance much faster than for products developed using traditional design regimens. Because of the simulation model’s proven accuracy at predicting real-world behavior, initial testing of the new design is done in a virtual environment instead of the time-consuming multiple field-trial iterations associated with traditional bit design. This also allows design engineers to experiment and test “out of the box” ideas that would not be feasible in an operator’s well drilled for production where risks must be minimized. As a result, the operator quickly realizes the cost savings/accomplished objectives generated by the bit’s enhanced performance without incurring the time, expense, and risk of having to act as a “testing service”
for the bit manufacturer.

Directional design considerations

The historical approach to designing and applying PDC bits for directional applications has been to incorporate a set of predetermined features into a design that were believed to enhance bit stability and then promote these enhancements as essential for improving performance and achieving directional requirements. Some of these features actually created a basic bit imbalance force and slowed ROP by limiting the depth of cut of certain PDC shearing elements in an attempt to reduce vibration and improve steerability. This type design philosophy created a perception that each style of rotary steerable system or steerable motor BHA required its own precise design with highly specialized directional features incorporated into each bit. The use of comprehensive FEA dynamic modeling technology has demonstrated that this paradigm is not valid and has shown that it is indeed possible to design a bit that is dynamically stable for various types of push-the-bit and point-the-bit rotary steerable systems across a range of applications.

Utilizing the dynamic modeling system’s comprehensive analytical capabilities and field-tested accuracy has enabled the service company to take an innovative approach to designing PDC bits for directional applications. Instead of offering a “directional PDC product line” with specialized features to compensate for basic design limitations, the manufacturer uses the process to evaluate individual directional applications and recommend the appropriate certified directional design for the specific situation. These certified designs are developed and performance-confirmed using the same highly sophisticated simulation process to accurately model the total directional drilling system, including all BHA components. Because of the model’s dynamic nature and the holistic approach, the tests certify where each design is dynamically stable and directionally responsive. The result is a simpler bit selection decision process and greater latitude in designing and modifying the BHA for optimum
performance.

The modeling program can also be used effectively as an expert bit selection tool because it can accurately predict how several different bit designs will perform in specific formation types, with a specific rotary steerable system, under various operating parameters, and with a specific BHA configuration. It gives the operator/service company’s engineering team the opportunity to virtually drill the same interval multiple times with different bits and then choose the most appropriate tool for the application.

Comprehensive analysis reports

When it is used for bit selection purposes, the dynamic modeling program generates an applications-focused output of the design simulation system. Using the operator-supplied BHA configuration, anticipated lithology, hole size and geometry, operating parameters, and other pertinent application information, the analysis engineer inputs the complete data set into the simulation model, then evaluates the individual bit design’s performance. Typically, several bit designs will be evaluated, and the optimum performance choice will be selected. An output is then presented to the operator including:
• A summary of the applications details, the bit performance, objectives, bit layout, graphical representation of the well profile, and the specific BHA which will be used;
• Output from the dynamic simulation for each bit, which includes the bit bottomhole profile, the bit center trajectory, torque, lateral forces, and lateral accelerations; and
• Optimized bit RPM and ROP projections.

The comprehensive FEA dynamic analysis modeling program has helped introduce a more quantitative, accurate, and objective approach to the bit design and selection processes.

Optimizing BHA i-DRILL is the service company’s extension of the IDEAS modeling process into high-end drilling consulting for finding solutions to costly, complex drilling problems. i-DRILL is a highly accurate predictive modeling system that can analyze complex drilling operations and develop optimized solutions to reduce risks and lower drilling costs. The advanced dynamic drilling simulation service uses FEA and highly detailed drill string visualization. Unlike a static analysis, which can only provide a small slice of data for a fixed point in time, the system’s dynamic drilling simulations create a virtual world that brings the modeled well to life, enabling engineers to visualize the downhole environment prior to drilling.

i-DRILL is one of the industry’s most powerful pre-well planning analysis resources and is capable of optimizing the total drilling process, including bit selection, operating parameters, BHA design, and placement of each individual BHA component. This approach allows the service provider to accurately identify the root causes of inefficient and damaging drilling behavior and then allows engineers to objectively and precisely evaluate multiple approaches for correcting the problems.

Using the modeling system, the costly trial-and-error methodology to achieve improvements in the BHA configuration and performance has been practically eliminated. The modeling technology allows the operator to rapidly increase knowledge and to consider more creative, less conventional approaches to efficiently achieving wellbore construction without the potential economic risks.

The system can process a multitude of simulations that represent any combination of drill bit options, drilling assembly components, drill string designs, and component placement. The high degree of accuracy provided allows the engineering team to quantitatively evaluate various scenarios and then choose the optimum solution with confidence that the predicted performance will be achieved in the actual drilling operation.

Capabilities

i-DRILL can help accurately identify the operational technical limits without risking lost rig time. It also eliminates inefficiencies resulting from operating too far below the technical limits and unnecessary trips to change out the BHA when operators are attempting to identify the optimum drilling system configuration to solve a particular drilling challenge.

Modeling process

Offset well data is used to calibrated the simulation software for each individual application. The data can include:
• Details regarding the physical characteristics of the entire drill string, the BHA, and the drill bit;
• Directional surveys and caliper logs to characterize the hole geometry;
• Surface and downhole operating parameters such as weight on bit, torque and RPM; and
• Mud log and wireline log data to characterize the formations being drilled.

This information is used to build a computer model of the offset drilling assembly, the formations, and the wellbore. The program is run to simulate the operation of the drilling assembly as a function of time. Because the software allows analysis of the specific target lithology and the behavior of each BHA component, suspect behavior is identified, quantified, and illustrated using the system’s advanced graphics capabilities. The simulation video clips accurately show what would actually be occurring down hole. The process identifies damaging and efficiency-reducing dysfunctions such as high rotary steerable system contact forces, bit whirl, and excessive bending moments.

Once the underlying causes of undesirable drilling characteristics are identified, the engineer can reconfigure the modeled drilling assembly and use the simulation analysis to correct the issues. Corrective actions can include switching out the drill bit, changing to roller reamers instead of stabilizers, moving the relative position of individual BHA components, changing operating parameters, or a combination of changes until significant performance improvements can be confirmed.

Finally, a comprehensive report documenting the findings and analysis process is presented to the operator. It contains the results of each simulation and identifies all of the potential changes that could be made to the drilling assembly and the effect that each would have on performance. The operator can then select the best option to meet drilling objectives, minimize problems, and improve performance.

Results

Smith International has published numerous technical papers and case studies that document the success of using a sophisticated dynamic modeling and simulation process to help achieve operators’ objectives of drilling a high-quality wellbore while avoiding problems, improving drilling efficiency, and reducing the cost of drilling. Operators now have an improved tool for putting together more accurate drilling plans, for reducing uncertainty and risk, and for ultimately moving more quickly down the learning curve for drilling optimization.