Improvements to polycrystalline diamond compact drillbit technology have been one of the major factors in driving improved drilling efficiencies throughout the world. Advancements in design capabilities, performance simulation and analysis tools, and material technologies have made year-on-year efficiency gains to the expected outcome of many drilling operations around the world. Operators that can achieve the efficiency gains the fastest have a significant advantage in the market. The drilling performance can be modeled before the run, observed during the job and evaluated at the end of the job. This makes it a perfect candidate for rapid improvements, where the results are tangible and can be dramatic in improving the overall field economics.

The underlying challenge becomes how to improve the effectiveness of each iteration and accelerate each cycle of learning so that successive wells drilled in a field compound with each other.

When thinking about the desired attributes of a drillbit, it can be helpful to distill the attributes into four performance categories: ROP, durability, reliability and steerability. Increasing ROP means less time is spent for the rig and associated drilling-related services. Durability determines how long the drillbit and bottomhole assembly (BHA) can stay in the hole. Reliability speaks to not only the tools themselves but also the consistency to achieve the desired results. The final criteria is steerability, which has become critical in today’s directional and horizontal wells to ensure the trajectory is placed in the target zone with both speed and creation of a quality wellbore.

Case study

The wells for consideration in this study were located in the Denver-Julesburg (D-J) Basin in Colorado. Drilling time had to be dramatically reduced to make the field and wells economical in this section. The challenge encompasses the entire well, with a goal of drilling the 8½-in. vertical, curve and lateral sections in less than 30 hours of drilling time.

The vertical section of these wells is about 1,067 m (3,500 ft). The curve section, which operators typically try to land in the Niobrara or Codell formation, builds at about 10 degrees/30.5 m (100 ft) to 12 degrees/30.5 m for about 274 m (900 ft) in total length. The final lateral sections can vary from a short 1.2 km (1 mile) to more than 2.4 km (2-plus miles) in length. The ideal solution for these wells would be to make a good clean hole extremely fast in a single BHA and drillbit trip.

Although the specifics change, this scenario repeats itself daily across the globe, with a constant focus on iterated improvements over time. Whatever the well profile and whatever the drilling challenge was yesterday, how can improvements be made for the next well? Speed and efficacy of new design iterations are integral to this question. The basic premise sounds intuitive— the more familiar an engineer and designer are with an application, the better each successive solution generation will be at improving the desired attributes. The best solutions come when the highly technical designer also has a thorough understanding of the drilling application and customer objectives, designs the solution, evaluates the performance and then also is able to execute the next iterative improvement. When the same personnel handle all aspects of the process, each iteration through the cycle can be faster and more effective because the challenges and lessons learned are not lost in translation outside of the core team.

In the D-J Basin challenge the local engineering team, which had extensive experience in the field and with drillbit design, collaborated with the drilling engineer and directional company personnel to clearly understand the objectives and systems used to drill the wells. When coupled with extensive bit record information for designs run in the local area, the design attributes needed to achieve the objectives could be established. The design needed to be very fast in the vertical section; have directional control that allowed good toolface control and steerabilty in the curve section; and have enough durability to complete the vertical, curve and entire lateral section in a single run of the BHA.

Based on these challenges it was clear that a new bit design was needed that would encompass all four drillbit attributes to help improve the overall drilling economics of the well. The solution was a steel-bodied five-bladed bit design. The steel body design with short overall length and maximum junk slot volume was ideal for cleaning in high-ROP applications. A combination of 167-mm and 19-mm cutters was laid out in a way to provide the needed toolface control in the curve while also providing high ROP capability for the vertical and lateral section. Diamond volume and an optimized profile were used to give the bit the durability needed to complete the sometimes 4,267-m (14,000-ft) sections in a single run.

The resulting bit designed through this iterative process was able to achieve record-setting runs, completing the entire vertical, curve and lateral section in a single run. The design and lessons learned were shared throughout the area quickly, setting a new standard in the region in both ROP and durability. This new design will be the basis for the next iterative cycle to continue to improve the resulting drilling efficiencies.

Accelerating the learning curve

The complexity and heterogeneity of drilling challenges necessitates the ability to constantly match the design to the application challenges. The feedback time frame for drillbit design provides the perfect oilfield experimental bed to understand how best to iterate solutions, test the solution and identify the next application. There are several key steps that can be followed to help minimize the time between learning opportunities.

Application intelligence involves understanding the specific challenges and setting the targeted efficiency and desired performance improvements. Information on offset data, mineralogy, directional objectives, drilling objectives and the drilling fluids program are evaluated in this phase. Locally optimized solutions are designed with best-in-class simulation software by local experts. Local knowledge is leveraged to help maximize performance and efficiency of the solution. Superior execution involves setting drilling parameters and custom manufacturing if necessary to deliver to the rig site with great speed. Performance monitoring and data collection are also an important part of this phase.

Performance analysis provides evaluation of the predicted performance vs. the actual run. Case histories are prepared, field analytics are performed and lessons learned are captured to feed the continuous improvement cycle.

In opportunity identification, a collaborative team consisting of the operator, drilling company and drillbit company shares analysis and performance information. Future target criteria and needs are discussed and challenges identified to help continually optimize the efficiency and the performance for the next optimization cycle.

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