Analysis of the Drilling of Attack Angle Effect on the Stability Geomechanics of Naturally Fractured Formations Using a Finite Element Model

Arias, Henry (Ecopetrol) | Mantilla, Hernan Dario (Ecopetrol) | Mateus, Jefferson (Ecopetrol)

OnePetro 

SUMMARY: Directional drilling in fields bedding plane formations has become a challenge to the petroleum industry because of the complexity of its operations. Therefore, drilling geomechanics plays an important role in engineering planning and calculation prior to the construction of a wellbore which makes it possible to determine a possible instability of the rock formation associated to the drilling inclination of wellbore and inclination of preexisting bedding plane. This paper analyzes the effect of the attack of angle of drilling on the geomechanical wellbore stability of formations with weak bedding plane or laminations using a finite element model and the Abaqus® software considering the rock as an isotropic medium. Three analytic tests with different drilling angles were developed, allowing to establish relationship between the attack angle and wellbore stability. Variables such stress, deformation and failure in rock bedding plane during drilling were analyzed. The results show that at higher attack angles the greater the wellbore instability is associated with the presence of the weak bedding plane

1 INTRODUCTION

During the drilling of hydrocarbon wells various types of rock and lithologic formations are drilled, including among them naturally laminated ones or bedding planes formations. These formations contain natural disorders that are called weak bedding plane, which represent a major operational challenge during drilling due to the characteristics of its surfaces with little or no cohesion between them. This causes a displacement and imminent separation of the surfaces, namely, unstable conditions when being altered mechanically with the cutting bit, generating slides and cavings into the wellbore which subsequently cause operational problems during drilling such as stuck pipe or loss of circulation causing extra costs in wellbore drilling. It is of the utmost importance to analyze the intensity of the instability of the wellbore depending on the direction and angle with which the weak bedding plane are perforated.