Large areas of the North Sea contain Cretaceous sediments, which form a massive hard layer of chalk that historically has presented a major drilling risk and expense to operators in the area. To mitigate such problems, a Norwegian operator gathered an integrated team to thoroughly analyze drilling records and lessons learned from previous offset wells and to re-engineer the drilling process. The positive results of this effort are described in the paper.
In 2011, an operator initiated preparations for drilling a series of deep, high-pressure/high-temperature exploration wells in the Norwegian part of the central North Sea. Given the depth of the exploration objectives, the first three wells in the program had to penetrate a massive body of hard Cretaceous chalk belonging to the Shetland geological group. Acknowledging the challenge and the fact that a discovery would lead to the drilling of successive wells though the same troublesome interval, an integrated team representing both the operator and technologists from the key suppliers was assembled. Individuals from this same group are the authors of this paper. The team’s task was to produce and execute a strategy that made it possible to drill the entire 12¼-in.-hole section, including the hard chalk, in one bit run.
In order to accomplish the goal of completing the entire section in one bit run, a basic strategy was formulated by the team leader: Drill with a high point load, and preserve a defined bottomhole cutting pattern. The strategy was built on the hypothesis that the drill-bit cutters are not the primary source of stick/slip vibrations in hard chalk....
Faster Rate of Penetration in Hard Chalk: Proving a New Hypothesis for Drilling Dynamics
01 February 2016