Simulation of Wellbore Stability during Underbalanced Drilling Operation

Reda Abdel Azim

doi:10.1155/2017/2412397

Abstract

The wellbore stability analysis during underbalance drilling operation leads to avoiding risky problems. These problems include (1) rock failure due to stresses changes (concentration) as a result of losing the original support of removed rocks and (2) wellbore collapse due to lack of support of hydrostatic fluid column. Therefore, this paper presents an approach to simulate the wellbore stability by incorporating finite element modelling and thermoporoelastic environment to predict the instability conditions. Analytical solutions for stress distribution for isotropic and anisotropic rocks are presented to validate the presented model. Moreover, distribution of time dependent shear stresses around the wellbore is presented to be compared with rock shear strength to select appropriate weight of mud for safe underbalance drilling.

Highlights

Very recent studies highlighted that the wellbore instability problems cost the oil and gas industry above 500$–1000$ million each year [1]
Factors that lead to formation instability are coming from the temperature effect which is thermal diffusivity and the differences in temperature between the drilling mud and formation temperature
Breakout shear failure occurred during underbalance drilling operation; it is very important to predict the failure at the wellbore wall using failure criteria

Summary

Introduction

Very recent studies highlighted that the wellbore instability problems cost the oil and gas industry above 500$–1000$ million each year [1]. Factors that lead to formation instability are coming from the temperature effect (thermal) which is thermal diffusivity and the differences in temperature between the drilling mud and formation temperature This can be described by the fact that if the drilling mud is too cold, this leads to decreasing the hoop stress. Numerous scientists presented powerful models to simulate the effect of poroelastic, thermal, and chemical effects by varying values of formation pore pressure, rock failure situation, and critical mud weight [3, 6]. These models mentioned that controlling the component of the water present in the drilling fluid results in controlling the wellbore stability. This paper presents a realistic model to evaluate wellbore stability and predict the optimum ECD window to prevent wellbore instability problems

Derivation of Governing Equation for Thermoporoelastic Model

Validation of Poroelastic Numerical Model

Failure Criteria

Case Study

Results and Discussion

Conclusion