Introduction of the Concept of Probabilistic Risk Assessment for Evaluating the Borehole Stability in Horizontal Directional Drilling

Annular pressure analysis that determines the likelihood of hydraulic fracture occurrence is critically important for evaluating the feasibility of horizontal directional drilling (HDD). The traditional method of annular pressure analysis in HDD makes insightful comparisons between minimum required annular pressure, Pmin, and maximum allowable annular pressure, Pmax, along the bore path. However, such a method seems deterministic rather than considering the potential variability in estimates of annular pressure (both Pmin and Pmax) due to the uncertainties within the parameters and models used. This paper proposes a concept of probabilistic risk assessment that allows incorporating such uncertainties in the annular pressure analysis in HDD. For a better understanding, the newly proposed concept of probabilistic annular pressure analysis in HDD is discussed in relation to the probabilistic method used in other geotechnical engineering applications. Lastly, information required for developing risk criteria for evaluating the risk of hydraulic fracture in HDD is presented.