It is well known in the industry that drilling and under-reaming can be very demanding. Destructive vibration is one of the main concerns, especially when drilling through interbedded formations. In today’s Gulf of Mexico (GoM) deepwater market, in order to reach greater depths and overcome narrower operational mud window, well construction design typically accounts for multiple casing strings, thus the use of concentric under-reamers has become almost mandatory.
In the last three years, much work has been done by service companies and operators to better understand bit and reamer synchronization along with bottomhole assembly (BHA) design and modeling. These are essential aspects for successful under-reaming runs although, in some applications, severe vibration still prevails. When that happens with an under-reamer in the BHA, it is hard to identify whether the source of vibration is the bit, the under-reamer, the BHA, drilling parameters, or a combination of all. A solution for the problem is elusive since, in many cases, the source has yet to be identified.
The use of downhole drilling dynamics data along with downhole drilling parameters, measured and transmitted in real time by a specialized drilling optimization tool, in combination with the proper use of surface and downhole mechanical specific energy (MSE) data has proven to be effective for identifying under-reamer’s drilling dysfunctions, which could not be identified solely with the use of surface drilling parameters.
This paper will present GoM deepwater project case histories where the use of the downhole drilling data optimization process was used in both real-time and post-well analysis. Emphasis will be on how the data was analyzed and how the learning’s were applied to optimize the operations and improve performance.