Drilling Magazine Media Intelligence, Contextual Wisdom
In order to produce a full suite of roller cone and PDC drill bits, it is essential to combine the most advanced knowledge and understanding of bit design with the latest manufacturing technology. Steerability and stability are two major characteristics of a qualified drill bit. A comprehensive design approach achieves the “sweet spot” of performance through capturing drilling requirements, identifying the whole formations to be drilled, and modelling aspects such as cutter interaction and the ability to simulate the bit performance. The latest high-tech bits deliver Improved Directional Control with a faster ROP, excelling Torque management and higher Stability and Whirl/Vibration Resistance. To maximize drilling efficiency, both the bit and drilling systems have to be considered. Engineers in research and development department use the data of field run data and laboratory tests to create a guideline matrix in order to design the most effective bit for the drilling system.
This matrix considers the system type, point the bit, push the bit or hybrid as well as the power generated and drilling characteristics delivered by the tool. Voyager bits are custom designed to the operator’s specific directional profile. To do this, engineers consider the operator’s parameters for dogleg severity, borehole quality and rate of penetration (ROP). The bit’s ability to achieve a given wellbore objective relies upon two clues for design factors: stability and directional behavior – (Steerability) When designing bits for directional drilling systems, gages are specifically considered by engineers. It is imperative to design a correct gage in order to complement individual drilling system.
Gauge History
Although the mechanical behaviour of directional systems is well modelled, the directional behaviour of the bit itself coupled to the RSS has been the subject of many controversies in the drilling and scientific communities. Indeed, the deviation mechanism is different according to the RSS configuration (pushthe-bit or point-the-bit). For a push-the-bit system, the side force generally controls the deviation. However, for a point-the-bit system, it’s generally the bit tilt that controls the deviation. As a consequence, in both cases the bit is submitted to the different side forces and tilts.
A project supported by of one of the industry’s leading customers and industry leading BHA providers has been conducted to be tested in the laboratory to study the directional behaviour of drilling PDC bits submitted to various side forces and tilt angles.
Gauge Test Conclusions
Three 8 1/2-inch diameter drill bits with three various cutting profiles were designed and manufactured. These cutting structures were tested with a great number of possible configurations: More than 100 gauge configuration tests were carried out in the laboratory and the final results were fully evaluated.
In parallel, the test results were combined with ARMINES/Geosciences BHA analysis software to evaluate and quantify the findings. The final results were consistent with the results of drilling test bench.
ARMINES/Geosciences BHA analysis software is one of the most advanced software of its kind in the market to predict drilling trajectories. Indeed, this software uses a coupling between a bit model and a 3D mechanical BHA model. Although the bit and the formation effects have been ignored in the past, it is well recognized today that a correct trajectory prediction requires a coupling among the rock, the bit and the BHA.
The final stage of the project was the implementation of these results into the VAREL proprietary SPOT-DN™ drill bit design platform and now forms an integral part of the design process of the directional drill bit.
Proprietary Design Tools
PDC bit performance in directional application usually presents performance challenges in terms of efficiency versus drives and well profiles.
After years of extensive development of cutting structures which ‘’drilled on paper’’ combine with the laboratory test of the full scale bit, a process combining cutting structure, rock type and application objectives has been developed. This process which models/ simulates bit behavior during drilling process is based on ‘’bridgeable’’ software and has been packaged in the Voyager directional Product line and a guideline matrix to help design the most effective bit for the drilling system.
The Process includes a work flow analysis using various analytical tools like:
Geosciences: Determine formation type, mineralogy and Rock UCS Geoscience provides powerful tools for reconstituting lithology’s, rock fractions, abrasiveness and mechanical constraints (Unconfined Compressive Strength) from E-logs and drilling logs. The information helps determine the emphasis placed on bit hydraulic, cutting structure type (hardness, cutter type/size), and body material.
Spot.Net: Cutting structure Layout and bit signature in a given environment
Spot is a complete solution for bit design and optimization. As a support tool decision, Spot evaluates the bit performance from a user defined selection of cutters, bit features and structure design. The generated bit model then computes ROP capacities, steerability, walking tendency and bit life in different formations and rock hardness regarding to the log data information provided by Geoscience. The bit behavior is simulated in real drilling conditions including mud, borehole and operating parameters.
Directional Bit Behaviour and Steerability
In deviated wells, the capacity to realize the well plan strongly depends on the BHA and drill bit directional behaviours. Spot provides a complete directional model taking into account the BHA (rotary, RSS or motor) and the drill bit. Bit designers can evaluate the steerability of the system along the entire section or for a specified depth interval. Graphical plots, dashboard result visualization or ASCII text files offer many possibilities to analyse and report bit performance. Spot is also the entry point for generating bit signature files exploited by DIG-IT for advanced vibration and contact simulations. Once a design is validated, Spot creates a bit parameter file that will be directly imported in a CAD software when starting the bit manufacturing process.
Conclusion
While only representing a small portion of the drilling budget, drill bit designs have been proven to have a large impact on drilling economics. Also we believe that close communication between client and bit manufacturer is paramount in order to improve performances, and together with all above engineering matching the Drill bit design to any drive system is achieved each and every time.
Author: Amin Azhar