ABSTRACT:

Petroleum engineers and geologist are highly interested in the comprehension of the mechanical loading conditions that led to the present geological structure of sedimentary basins. This knowledge allows to better evaluate the state of stress, fracturation and damage, and their evolution within oil fields and reservoirs. Numerical simulations using the finite element method have become a useful tool to rebuild the mechanical history of sedimentary basins and to describe their evolution under various loading conditions. This paper describes such a numerical tool and several field cases applications in geology and petroleum geology.

RÉSUMÉ:

L'ingenieur petrolier et le geologue sont très interesses par la comprehension du chargement mecamque qui a conduit à la structuration actuelle des bassins sedimentaires. Cette connaissance pennet une meilleure evaluation de l' etat actuel des contraintes, de la fracturation et de l'endommagement qui afIectent les champs et les reservoirs petroliers. Les simulations numeriques utilisant la methode des elements finis sont devenues un moyen efficace pour reconstituer l'histoire mecanique des bassins sedimentaires et pour decrire leur evolution sous diverses sollicitations. Cet article presente cet outil numerique ainsi que plusieurs applications concretes dans le domaine de la geologie et de la geologie petroliere.

ZUSAMMENFASSUNG:

Ingenieure auf dem Gebiet der Erdölförderung und Geologen haben besonderes Interesse an der mechnanischen Beschaffenheit von Gesteinsformationen sowohl in der Gegenwart als auch in der Vergangenheit Der Zustand der Formation in bezug auf Spannung, Verformung und Beschadigung innerhalb eines Ölfeldes ist ebenfalls zu bewerten. Die ‘Finit Element Methode’ hat ein Hilfsmittel erhalten, das es erlaubt, die geschichtlichen mechanischen Ablaufe zu rekonstnJieren und die Entwicldung unter gegebener Belastung vorauszusagen. Dieser Beitrag beschreibt ein solches numerisches Hilfsmittel und verschiedene Anwendungs-möglichkeiten auf dem Gebiet der Geologie und der Erdölfelder in Gesteinsformationen.

1
INTRODUCTION

This paper presents details of a large strain finite element formulation coupled with an automated re-meshing method allowing simulations of very large strains and/or localisation. Three application cases are proposed to illustrate its potentialities.

2
MECHANICAL MODELING OF GEOMATERIALS:FINITE ELEMENTS AND CONS111UIlVE LAWS
2.1
Large strain formulation, equilibrium

The LAGAMINE finite element code is based on an up-dated Lagrangian formulation in the current configuration, in which the velocity gradient L reads

(Equation in full paper)

3
ADAPTIVE RE-MESIllNG STRAlEGY

When simulating geological like objects, problems of large dis- placements and strain localisation (shear strain localisation and/or mode I fracture) arise quite naturally. The difficulty of addressing correctly the localisation phenomenon on a computing numerical point of view is not yet fully solved because its very fundamentals are still mater to discussion. Several methodologies have been developed, which all lead to a regularisation of the problem at the onset of bifurcation by the introduction of an internal length scale. Here, we tackle the problem on a more practical point of view. Once strain localisation is detected, we want it model that can allow for such highly non-homogeneous displacement field. The choice of an independent re-meshing method has been made as it allows the full control on the new mesh to be created.

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