Numerical Approach to Evaluate Cements Sheath Barrier During Reservoir Compactation in Vertical Oil Wells

Abstract

ABSTRACT: Reservoir depletion during hydrocarbon production can lead to rock compaction. This compaction is caused by the progressive decrease in pore pressure within the porous matrix. This paper presents an axisymmetric numerical approach to evaluate the integrity of the cement and casings inside the well due to the effect of compaction. A displacement field is used as a model boundary condition and gradually applied during the production stage after the well construction. The construction of the well is considered from the geostatic equilibrium of the materials, followed by the drilling and cementing. Finally, the subsidence stage is created where the applied displacement field displaces the rock column and consequently the cement and casing. The von Mises stress curve for the casing, and the plastification index of the cement and casing were examined. It was observed that areas with the greatest von Mises stresses were proportional to areas with the greatest displacements of the rock column. A significant impact of the top of cementation (TOC) on integrity was observed. The cement acts as a transmitter of displacements to the casing, which can impact the integrity of both the cement and casing in the preceding phases before the production phase. 1. INTRODUCTION Reservoir depletion during hydrocarbon production can lead to reservoir compaction. The compactation is a densification associated with the rearrangement of the rock matrix when fluids are lost in the porous medium. Such densification affects upper layers, causing deformations that can be observed even on the seabed. These deformations can cause structural problems in oil wells, such as fractures in upper layers, loss of cement integrity, and excessive traction or compression over the casing (Figure 1). The main goal of this work is to develop a numerical axisymmetric methodology for analyzing the mechanical integrity of casing subjected to subsidence loads. For that purpose, the finite element method will be used. This method allows consideration of several simultaneous effects such, rock-cement-casing contact interactions, different materials within the model, advanced constitutive models, among others.