Hard Rock Horizontal Drilling—Using Mechanical Specific Energy, Downhole Vibrations Analysis, and Well Design to Optimize Performance

This paper presents a deep horizontal drilling campaign with the goal of eliminating several inefficiencies restricting the drilling performance, including downhole drilling bit or tool failures. The operator and the service company identified the inefficiencies by using engineering methods to overcome the challenges. Since 2013, the operator had been drilling horizontal wells with 600 to 1000 m of lateral targeting deep gas sandstone multilayer reservoirs with 15 to 35 kpsi unconfined compressive strength. The focus in the campaign will be from the kickoff point in the 8 3/8-in. section to the total depth (TD) of the well. Well-1 performance was greatly affected by the issues related to the wellbore instability in the build section, which dictated a change in the well program from the original fat to slim design. Later, other challenges and drilling inefficiencies resulted from this change, causing Well-6 design to be switched back to the original fat design to improve wellbore stability by having proper mud weight and other mud properties, bit and drive systems selection, as well as the drilling practices. Mechanical specific energy (MSE) is an industry recognized optimization tool to evaluate the drilling efficiency (Teale 1965) but it does not identify the sources of the inefficiencies (Chen 2019). The MSE, in addition to the downhole high-resolution drilling dynamics data, have been used to identify not only the drilling dysfunctions but also to help find the sources. This method supports the decisions for a change in the well design, bit, or the drilling practices, which in turn reduces the total number of runs and the downhole tool failures or damages. The improvements in drilling the horizontal wells since the campaign began are significant; i.e., Well-1 was drilled in approximately 165 days in 2014 while Well-6 was drilled in 49 days in 2017, which was 39 days ahead of the well plan with the majority improvements occurring in the last section. Well-6 is considered to be the most efficient Barik formation horizontal well drilled in Oman to date.