Decision-making during drilling wells taking into account uncertainty

Abstract

The paper is devoted to the problem of decision-making in conditions of uncertainty. Earlier, the issue of making decisions on the choice of bits and regime parameters was considered by solving a two-criteria problem. In the present paper, in the continuation of this issue, the issues of drilling wells in abnormally high reservoir pressure (AHRP) and lost circulation, and decision-making under the given conditions are considered. The task of making a decision under the AHRP is to choose a mud density that, numerically in the interval between the formation pressure gradient (ηf) and the fracture pressure gradient (ηfr), would not result in a noticeable decrease in drilling speed. This problem could be solved with the help of an approach based on the theory of fuzzy sets. It is clear that in order to solve the problem posed, we need to know the values of pore (reservoir) pressure, hydraulic fracturing pressure, and also the dependence of the rate of penetration on the density of the drilling mud for the rocks of the interval under consideration. Using the technological data receiving during the drilling process, it is possible to evaluate the indicated characteristics. Taking into account the noted, an expression was obtained for estimating the necessary mud density with identification for different deposits. For the early diagnosis of lost circulation with the use of fuzzy cluster analysis, the rate of lost circulation was estimated. Classification and evaluation of risks of lost circulation was carried out