Numerical Analysis on the 3D Mechanical Behavior of Completion Tubing under Subsidence Loading
Authors: Shen Xinpu , Pounds Rob 
Published: March 2015

Abstract
For openhole completions in a weak sand formation, the failure of completion tubing frequently occurs under the loading from formation subsidence resulting from production. This paper investigates the integrity of completion tubing in this environment using the 3D finite element method (FEM). An elastoplastic analysis was performed on four sets of completion tubing using 3D FEM. A porous elastoplastic model was used to model the mechanical behavior of a weak sand formation. The interaction between the completion tubing and the sand formation was modeled with frictional contact constraints. The inclination angles of the completion tubing are set at 15°, 35°, 50°, and 75°. With a given geostress field and pressure depletion from production, the numerical results obtained with the 3D FEM model include subsidence of the sand formation, distribution of the equivalent plastic strain, and von Mises equivalent stress within the completion tubing and its deformed mesh. The principal conclusions include:major loading factors affecting tubing failure are the axial pulling force and the bending moment or normal pressure applied on the external surface of the formation subsidence;including an extendable tubing section can release the axial tensile stress caused by production-induced formation subsidence, and thus keep the tubing intact;various scenarios have been checked for a safe pore pressure depletion value with a variation of tubing parameters values.
This work presents a best practice for estimating the completion tubing integrity under subsidence loading by using a 3D FEM tool.

Introduction
For openhole completions in a weak sand formation, the failure of completion tubing frequently occurs under the loading from formation subsidence arising from production. In the past decades, a few researchers investigated this topic.
Green (1991) discussed the subsidence that occurred in a Gulf Coast field and introduced his subsidence measurement technique; this technique uses existing downhole wireline tools configured to provide high-resolution results. Salamy et al. (1999) investigated the monitoring of wellbore stability caused by production and compaction. Earles et al. (2011) introduced a new generation compaction monitoring device, a fiber optic support device called 'real time monitoring compaction system'. Dudley et al. (2009) introduced their works on subsidence prediction by using an integrated method that combines geomechanical core testing, field monitoring, and 3D numerical modeling. Hoang et al. (2010) reported their work on pore pressure depletion-related reservoir compaction and its effect on the design of multilateral horizontal wells. Furui et al. (2010) reported their work on the stability of openhole, cemented liner and uncemented liner completions in a highly compacted chalk formation. Various scenarios of liner collapse were investigated numerically. Shen (2010) reported his work on numerical modeling and analysis to subsidence prediction and casing integrity induced by pore pressure depletion. Hilbert et al. (2011) introduced their works on geomechanical modeling and analysis used to assess the risk of compaction-induced deformation and the potential failure of horizontal gravel pack completion in a field that is located in deep water but at a shallow depth below the seafloor.
This work presents the results of the numerical stress analysis for tubing and the formations in which the tubing lies. The completion tubings of four wells are involved in this work: A15, A35, A50, and A75. The number in the well name indicates the inclination angle of that well. For example, well A15 has inclination angle of 15°.
This study investigates the integrity of completion tubing under loads from the formation caused by production and subsidence. The complete study includes data derivation from results of 1D analysis with Drillworks® Finite Element Method (FEM) modeling and analysis. Numerical calculations were performed with Abaqus 3D Finite Element software on the mechanical behavior of completion tubing under subsidence loading.