During the field-development life of a mature extended-reach drill (ERD) project, a wide range of drilling tools and practices were introduced to continuously improve drilling performance and well delivery times. One of the main challenges encountered in the ERD wells was in the 12?-in. curve section, and drilling through interbedded hard layers with severe downhole stick/slip and downhole vibrations. Historically, both motor and motorized rotary steerable system (MRSS) bottomhole assemblies (BHAs) were used to drill this section. However, the motor BHA’s lower rate of penetration (ROP) and weight transfer problem cause it to be an economically inefficient strategy in contrast with the MRSS BHA, successfully drilled through all of the challenges with higher ROP and a relatively lower overall cost. Driven by cost reduction necessity, an intensive engineering effort was implemented by the operator and service provider drilling engineering teams to change the motor BHA into a cost- effective drilling strategy for the challenging 12?-in section. Analyzing the design and performance of all previous motor BHAs led to identifying the main challenges. Detailed modeling was then performed, involving well trajectory design, BHA design optimization, hydraulics modeling, and torque and drag modeling. The modeling included static simulation as well as drillstring vibrations using finite element analysis (FEA) dynamic simulation. This extended engineering analysis improved the bit and BHA selection capability. Several drill bits and BHA options were modeled and simulated under different drilling conditions to determine the most stable configuration. Simultaneously through the dynamics simulation, a stable drilling parameters plan was generated to improve the drilling performance. The modeling results indicated that the lighter BHA configuration minimized BHA - formation contact area, allowing for smoother and efficient weight transfer downhole. A reduction in BHA vibration produced a step improvement in ROP and drilling performance. The engineering modeling results were implemented by replacing the previously used motor BHA drill collars with heavy-weight drillpipe and smaller size jars. This hardware change resulted in an unprecedented cost reduction, a 52% improvement over the previous motor BHA in delivering the challenging section, achieving multiple additional records, and 56% ROP improvement over the field. This paper will present the design process and the detailed results for each run. Recommendations will be provided on how this process can be applied to increase ROP performance and reduce the cost per foot for such drilling applications.
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