In exploration wells, particularly in deepwater exploration wells, the information regarding formation pressure has many uncertainties because of the lack of seismic data, logging data and daily drilling report. The present casing program design methods based on the deterministic formation pressure data did not take these uncertainties into account and the results could not satisfy field engineering requirements. This paper describes a method based on probabilistic theory for determining the formation pressure profile with credibility, and a new approach for casing program design has been also introduced. As a result, the formation pressure is not a deterministic value but a range with probability information, as the same with the casing set points selection. And then we describe a quantitative risk analysis method for quantitatively analyzing the risk of the casing point selection design. The model includes four sub-models for determining the quantitative risk due to lost circulation, kicking, collapse and sticking. The results can provide valuable information for designers. In one case study, we illustrate how this approach allows us to compute formation pressure profile with credibility and casing set points for a deep well with formation uncertainties. The risk of several casing program of this well has also been discussed finally.

You can access this article if you purchase or spend a download.