Summary Ultralarge-diameter polycrystalline-diamond-compact (PDC)-bit drilling is a fast-growing cost-effective solution in high-tier deepwater drilling operations in the US Gulf of Mexico (GOM) where salt is encountered in the shallow part of the wellbore. Conventional design called for roller-cone (RC) (IADC Code 111-115) drill bits on positive-displacement motors (PDMs) in these ultralarge-diameter intervals. Cost savings on drilling fluid alone, in the form of rate-of-penetration (ROP) gains through the salt interval, has the industry trending to drill these riserless sections with the use of PDC drill bits on rotary-steerable-system (RSS) drilling assemblies. New robust high-torque-capacity topdrives, stronger drillpipe (DP) connections, larger-diameter RSS tools, and improved mud programs have all largely contributed to this step change in drilling performance. In addition, evolved bit and bottomhole-assembly (BHA) design, efficient operating parameters, improved hydraulics, and vibration-prediction modeling have all aided in the success of these runs. Although this emerging new trend reduces drilling times and associated cost, experience has shown there are multiple challenges that must be overcome to complete a successful run in a single trip. These challenges vary from well to well and include, but are not limited to, BHA steerability, rig-equipment limitations, efficient operating parameters, identification of both sediment and salt formations, hole cleaning and hydraulics, salt creep, drilling-fluid displacement, DP torque limitations, stabilization placement, lateral/ torsional BHA vibrations, and others. This paper will concentrate on the multiple aspects of ultralarge-diameter riserless PDC-bit drilling applications and the considerations that have been used to optimize them. Prior SPE papers and data from previous deepwater GOM case histories were heavily researched and scrutinized to support the conclusions provided within the body of this paper. Together with industry experience available, these findings have resulted in a set of defined recommendations, providing operators with a guide to justify a lower-cost-per-foot approach through the potential reduction of drilling time in these challenging applications.

The increasing complexity of deepwater Bottom Hole Assemblies (BHAs) requires a complete systematic approach to each phase of the drilling process: pre-job planning, execution and evaluation. This approach was successfully applied to a recent multi-well project in the Gulf of Mexico, whose vertical 12¼ in x 13½ in sections were historically plagued by shocks and vibrations while drilling. The root cause of inefficient drilling performance could not be accurately determined based on drilling data, but severe vibrations resulted in multiple downhole tool and BHA component failures. With the implementation of a complete, holistic approach to the drilling system, the drilling proceeded with no downhole tool failures and a significant reduction in drilling time and costs. The key to these successes were the multistage preparation process that was utilized, which included: A detailed analysis of all the offset data available for the same field and for fields with similar lithologies and formation properties. A rock strength analysis based on Logging While Drilling (LWD) data and Compressive Confined Strength (CCS) measurements. A bit and reamer matching process taking into account CCS, lithology, directional profile and cutters layout while matching the performance criteria for both drill bit and underreamer. Advanced tools and technology, including critical speed analysis and asymmetric vibration tool placement, were applied and supported by high-frequency downhole dynamics memory data with corresponding post-run drilling performance and vibration analysis. Some of the major contributors to the successful application were the designed-for-purpose engineered BHA and optimized operational environment. This approach can be applied to borehole enlargement wells, as well as vertical, directional and horizontal wells. The analyses of the measurements gathered during all phases of the project, including a description of the obtained results, are discussed in detail. The results highlight a consistent improvement in drilling performance for the 12¼ in x 13½ in well section, where vibrations were the main limiting factor. Efficient drilling performance is achieved by implementing this complete approach to the deepwater drilling system and these engineering solutions for vibration mitigation, increasing ROP and improving BHA integrity and wellbore quality.

The advent of wired drill pipe has the ability to allow a variety of measurements to be distributed throughout the whole drilling assembly. One such measurement is acceleration to better determine the impact of how vibration events are distributed through from the bottom hole assembly to the upper drillstring or vice versa. In turn we can now investigate the potential use of distributed dynamics by utilizing a set of designed for purpose independent Downhole Dynamic Data Recorders (DDDR), for real-time decision making. A test project was executed to acquire vibration data along the drill string on a horizontal well in Oklahoma's Woodford Shale. This project allowed the evaluation of data acquired from the bit and the bottom hole assembly (BHA), in the horizontal section, as well as the sensors located in the upper assembly showing the dynamics throughout the vertical section, curve, and landing point of the horizontal. This paper focuses on the analysis of the measurements gathered during the project and it will provide detailed descriptions of the obtained results. Several concepts as well as common known misconceptions related to drilling dynamics will be discussed, among them the decoupling effect of the mud motor to drilling vibrations, the value of downhole torque, weight and bending moment for the understanding of distributed dynamics along the drill string. The importance of the vibration sensors' placement and data recording frequency in order to diagnose and mitigate drilling dysfunctions will also be discussed.

Ultra-large diameter Polycrystalline Diamond Compact (PDC) bit drilling is a fast growing cost-effective solution in high-tier deepwater drilling operations in the U.S. Gulf of Mexico (GOM) where salt is encountered in the shallow part of the wellbore. Conventional design called for roller cone (RC) (IADC Code 111-115) drill bits on positive displacement motors (PDM) in these ultra-large diameter intervals. Cost savings on drilling fluid alone, in the form of Rate of Penetration (ROP) gains through the salt interval, has the industry trending to drill these riserless sections with the use of PDC drill bits on Rotary Steerable System (RSS) drilling assemblies. New robust high torque capacity top drives, stronger drillpipe connections, larger diameter RSS tools and improved mud programs have all largely contributed to this step change in drilling performance. Additionally, evolved bit and BHA design, efficient operating parameters, improved hydraulics and vibration prediction modeling have all aided in the success of these runs. Although this emerging new trend reduces drilling times and associated cost, experience has shown there are multiple challenges that must be overcome to complete a successful run in a single trip. These challenges vary from well to well and include, but are not limited to: BHA steerability, rig equipment limitations, efficient operating parameters, identification of both sediment and salt formations, hole cleaning and hydraulics, salt creep, drilling fluid displacement, drillpipe torque limitations, stabilization placement, lateral/ torsional BHA vibrations, and others. This paper will concentrate on the multiple aspects of ultra-large diameter riserless PDC bit drilling applications and the considerations that have been used to optimize them. Prior SPE papers and data from previous deepwater GOM case histories were heavily researched and scrutinized to support the conclusions provided within the body of this paper. Together with industry experience available, these findings have resulted in a set of defined recommendations, providing operators with a guide to justify a lower cost per foot approach through the potential reduction of drilling time in these challenging applications.

Pre-job engineering tasks conducted during the drilling design phase have often been an overlooked aspect regarding time and cost savings. This is a critical phase that directly impacts efficiencies and effectiveness while drilling. This paper highlights the multiple benefits of an engineering solution that automates and triggers advanced engineering computations simultaneously. The objective is to realize time savings and accuracy gains necessary for quick evaluation and resolution of the decision-making processes, while eliminating unintentional oversight on engineering requirements. The approach focuses on a fully customizable application that automates sequences of models/ actions; interpretation and validation of results, based on pre-determined criteria; and reporting functionality. This automated solution uses established workflows and conditions, and user defined calculations to conduct typical pre-drill engineering tasks. To demonstrate the tool's capabilities, two wells were reviewed by multiple engineers of varying experience levels. Each performed the pre-drill engineering tasks assigned based on proposed requirements. The outcome reviews the time taken to deliver validated engineering solutions; accuracy of result validation and ability to track compliance to standards. Results from the evaluation of these three Key Performance Indicators (KPI's) are presented and thoroughly described. The validation conducted revealed significant time efficiency gains when executing pre-engineering tasks and automatically validating each simulation (71% overall time-reduction). The accuracy of results was always guaranteed when using the automated method, with a 100% accuracy for both wells analyzed, compared to an average of 92% from the focus group. This improvement is key to ensure the delivery of flawless well designs, consistently and reliably. Additionally, the described potential for ensured compliance based on standardized rules specific to each organization, allows for repeatability and accountability, enhanced through the use of auditable trails. Automation of processes, workflows and equipment is driving the innovative and creative direction for the industry, but it should also steer toward an increase in reliability, performance and minimization of risk in every step of the well delivery process. This fully customizable engineering tool proved to be a highly efficient approach that allows users to eliminate manual, time consuming tasks while removing the potential for accidental oversight in identifying future issues before drilling begins.