Integrated mechanical earth model and quantitative risk assessment to successful drilling

Alireza Noohnejad,Kaveh Ahangari,Kamran Goshtasbi

doi:10.1007/s13202-020-01019-8

Abstract

Use of vital geomechanical parameters for determination of safe mud pressure window is generally associated with high level of uncertainty primarily because of absence of sufficient calibration data including laboratory and field test information. The traditional deterministic wellbore stability analysis methodologies usually overlooked the uncertainty of these key parameters. This paper exhibits implementing a quantitative risk assessment technique on the basis of Monte-Carlo modeling to consider uncertainty from input data so as to make it possible to survey not just the likelihood of accomplishing a desired level of wellbore stability at a particular mud weight, but also the impacts of the uncertainty in each single parameter on the wellbore stability. This methodology was implemented to a case study. The most important parameters have been recognized using a sensitivity analysis approach in which the outcome of this QRA procedure suggests the mud weight window with likelihood of well drilling success which can elude the wellbore collapse and lost circulation events. This sort of stochastic approach to deal with anticipated safe mud weight window can guarantee stable wellbore with considerable cost viability associated with drilling success. The technique built up in this paper can give the scientific foundation for assessment of wellbore stability under complicated geological circumstances. It was likewise noted that based on sensitivity analysis, uniaxial compressive strength and maximum horizontal stress are the most effective parameter in estimation of mud weight window. This accentuates the significance of trustworthy determinations of these two parameters for safe drilling of the future wells in the field.

Highlights

Proper mud weight plays a vital role in wellbore instability studies in oil and gas industry
As most of the current drilling projects including well construction and field development are challenging, safe mud weight windows have a deteriorate effect on the time schedule of the project and can drastically lessen non-productive time (NPT), issues related to instability of wellbores and unwanted costs on drilling operation (Plumb et al 2000; Elyasi et al 2013)
Ottesen et al (1999), introduced a probabilistic approach based on quantitative risk assessment (QRA) for oil and gas drilling projects which further developed by Moos et al (2003), to diagnose any uncertainty related to input data, identify wellbore collapse risk and minimize operational damages and consequent costs

Summary

Introduction

Proper mud weight plays a vital role in wellbore instability studies in oil and gas industry. QRA technique was undertaken utilizing log-derived rock elastic and strength parameters at a drilled well case to determine the disparities, errors and uncertainties associated with the obtained values, build limit state functions and response surfaces, recognize most influential parameters and their sensitivities, and evaluate how the likelihood of success can be maximized by carrying out the fundamental quantitative risk assessment technique. Compressional wave transit time (∆tP) Shear wave transit time (∆tS) Porosity Density Young’s modulus Poisson’s ratio Uniaxial compressive strength Internal friction angle Pore pressure Vertical stress Minimum Horizontal Stress Maximum Horizontal Stress These quantify the uncertainties in the input parameters required to compute the mud weight limits necessary to avoid wellbore instabilities.

Conclusions

Compliance with ethical standards