Successful Mitigation of Excessive Backreaming in Troublesome Vertical Applications in the Sultanate of Oman

Abstract

Drilling through some of the reactive shale formations in the western gas fields in the Sultanate of Oman has proven challenging and often troublesome. Frequently, time spent on backreaming would exceed the time required to drill the related hole sections. In addition, the carbonate Natih sequence has also proven problematic. High levels of vibrations are often encountered. Such drilling dysfunctions are known to be destructive to both bit and bottom hole assembly (BHA). Different mud systems, drive systems and reamer types were used in separate attempts to alleviate the faced dysfunctions to little avail. This paper illustrates a trial campaign introducing an alternative design stabilizer (ADS) and reamer (ADR) to the drilling BHA with the aim of addressing and resolving the aforementioned limiters. Based on a set of agreed-on key performance indicators (KPIs), and following a methodical approach, a 4-well trial was conducted in order to introduce a unique stabilizer-reamer design while simultaneously scrutinizing and optimizing the BHA configuration accordingly. Two of the candidate wells targeted the 17-1/2" section while the other 2 wells targeted the 12-1/4" sections. The main goals were to reduce the time spent on backreaming by 50% and minimize the experienced levels of vibrations in order to extend bit runs and reliability of the different BHA components. For further comparisons, the same approach was tested on a rotary BHA as well as a steerable motor BHA in the larger hole sections. Both 17-1/2" sections were each drilled in a single run similar to the second 12-1/4" section. The first 12-1/4" also proved smooth and required 2 runs due to bit hours, still noting a record section distance run for a single bit. All BHAs were optimized around the placement of the new design stab and reamer design combination. The optimized BHA configuration enabled pulling out of hole (POOH) on elevators for all 4 sections almost fully eliminating the hard backreaming experienced in past wells. In addition, it was also noted that in all cases the levels of vibrations were significantly reduced compared to what is typically experienced and recorded in the offset wells. This enabled a record setting bit run for that particular section and field. The authors detail the historical challenges encountered drilling such wells then present the applied benchmarking exercise and the adopted systematic approach to tackle those challenges. Following, the unique design characteristics of the deployed technology are highlighted and how this is applied in each of the runs in view of optimizing casing point to casing point section delivery times. Finally, the achieved results and gains are underlined together with a roadmap forward.