Field Scale Geomechanical Modelling Using a New Automated Workflow
Authors: Monaco Silvia S. , Capasso Gaia , Mantica Stefano , Datye Deepak , Vitali Roberto 
Published: March 2015

Abstract
In the past, a workflow was internally developed in eni for the field scale study of geomechanical effects induced by reservoir depletion. This workflow, however, included non-automated procedures as well as simplifications related to the geometry description, such as smearing of faults and a simplified treatment of layer pinch-outs.
Recently, in the framework of cooperation between eni and Simulia, new features were implemented in the finite element simulator Abaqus. A fully automated workflow, completely manageable in Abaqus/CAE, is now available that significantly changes the approach and the capabilities of geomechanical reservoir modelling.
Moreover, new iterative linear solvers were implemented in the code, allowing for increasingly larger models to be run on parallel machines, with grid resolution approaching that of reservoir static and dynamic simulation studies.
In the present paper, the new workflow is described with reference to a field scale geomechanical study.
The finite element grid is automatically built starting from the flow dynamic corner point model with the possibility of interactively adjusting elements and nodes, performing up- and down-scaling and detecting faults.
The geostatic equilibration is automatically performed and the material properties and load history are applied within Abaqus/CAE to run the simulation.
As shown in the example application, the capabilities developed in Abaqus/CAE are a significant innovation for reservoir geomechanical simulations: they allow overcoming the limitations of the previous workflow and simultaneously providing significant automation.

1.0 Introduction
The study of field scale geomechanical processes in a hydrocarbon field mainly concerns the compaction of producing soil layers and the associated subsidence. These phenomena have a great impact on the field productive behavior in terms of variation of the reservoir properties, reduction of well rates, casing collapse and well failure and an impact on the environment in terms of land subsidence due to on shore withdrawal and land subsidence near the coast line. The evaluation of reservoir compaction and surface subsidence induced by hydrocarbon production then represents a big issue to oil companies and geomechanical analysis play a key role for monitoring and controlling the exploitation of the field.
Geomechanical studies are mainly performed by eni through the finite element code Abaqus provided by Dassault Systèmes Simulia. Input data of these simulations directly come from the dynamic model built with Eclipse (Schlumberger, 2011) which is the flow simulator currently used. A workflow was developed internally by eni and described in (Capasso and Mantica, 2006) in order to study the geomechanical effects due to field scale reservoir depletion through Abaqus. The automation of this procedure and some improvements which allow for a more precise evaluation of stress and strain at reservoir scale is presented in this paper with reference to a test case. A reservoir modeler plug-in, which covers all the steps of this standard workflow for subsidence studies, has been implemented. Each task of the workflow is listed in a Guided User Interface (GUI): a few steps are performed outside of the plug-in, but their statuses are documented within the plug-in and they are properly executed in Abaqus/CAE. All information entered by the user is stored on the custom data base on a model-by-model basis and is persistent across sessions. This allows for providing significant automation and makes it easier to the user to complete all the steps for the creation of a geomechanical model.