Finite Element Analysis of Compaction and Subsidence — Experience Gained from Several Chalk Fields

Abstract

For North Sea chalk fields, finite element models are used to evaluate the reservoir compaction and the associated seafloor subsidence. The present paper addresses aspects of the calibration of the stress strain laws to be used for the chalk and the overburden. Results of laboratory tests do not reflect the large scale deformation behaviour. The calibration is therefore mainly based on the back analysis of measured formation movements. Another topic is the coupling with reservoir simulation models, which provide the reservoir pressure. This coupling should be improved, if a local compaction cannot be derived from a simultaneous change in reservoir pressure at that location. RESUME: La methode des elements finis est utilisee pour evaluer la compaction et la subsidence du fond de la mer dans Ie cas de champs petroliers de mer du Nord. Aspects de la calibration de modeles de comportement utilises dans l'etude numerique de reservoir en craie et des couches de toit sont detaillees. Les resultats de mesures au laboratoire ne pas represent les deformations a grande echelle. Le calibration est donc essentiellement fondee sur Ie calcul a posteriori des deplacements mesures. Le couplage de calculs de geotechnique et de calcul de modeles de reservoir doit etre evalue avec des methodes ameliorees puisque la compaction en un point n'est pas fonction uniquement de la pression des pores en ce point. ZUSAMMENFASSUNG: Finite-Element-Modelle dienen der Berechnung der Kompaktion von Kreidereservoirs in der Nordsee und der daraus resultierenden Setzungen des Meeresbodens. Der Beitrag Q.ehandelt Aspekte der Kalibrierung der Spannungsdehnungsbeziehungen fUr Kreide und die Uberdeckung. Ergebnisse von Laborversuchen geben nicht das groBraumige Verformungsverhalten wieder. Die Kalibrierung erfolgt daher durch die RUckrechnung von Verformungsmessungen. Ferner wird die Kopplung mit Reservoirsimulationsmodellen diskutiert, die verbessert werden sollte, falls eine ortliche Volumenanderung nicht aus Druckanderungen zu gleicher Zeit und an gleicher Stelle resultiert.

Compaction of North-Sea Chalk by Pore-Failure and Pressure Solution in a Producing Reservoir

“…The overburden is mainly composed of clays and shales with thin interlayered limestone or silty layers [11,14]. The permeability is extremely low (10 −18 -10 −21 m 2 , 10 −3 -10 −6 mD) [16].…”

“…With the introduction of water injection scheme the attention shifted toward the effect of water and how it decreases the material strength of chalk. This phenomenon is often referred as "water weakening" of chalk and several models were created to explain it (e.g., [14,15]). A more detailed review of the previous models can be seen in Data Sheet 1 in Supplementary Material.…”

Mapping Reservoir Volume Changes During Cyclic Steam Stimulation Using Tiltmeter-Based Surface-Deformation Measurements

“…Numerical modeling for reservoir compaction and surface subsidence usually involves the finite element method (FEM). Researchers use either the FEM or nonlinear FEM (Plischke 1994;Abdulraheem et al 1993;Chin et al 1993;Bruno and Bovberg 1992;Hamilton et al 1992; Lewis and Sukirman 1993). The analytical/semianalytical method refers to the use of the basic solution because of the center of dilation source (Mindlin and Cheng 1950) or numerical integration of the Green's function because of the center of dilation source over certain reservoir shapes in a poroelastic medium (Geertsma 1966(Geertsma , 1973Segall 1985).…”

Water‐flooding and consolidation of reservoir chalk – effect on porosity and Biot's coefficient

“…This indicates that apparent anisotropy in otherwise massive chalk can be caused by exhumation and formation of horizontal micro‐cracks. During production of hydrocarbons by draw down, the pore pressure decreases, and for North Sea chalk fields the reservoir may be assumed to consolidate in a close to uniaxial strain geometry (Kågeson‐Loe et al., 1993; Plischke, 1994; Kristiansen, 1998).…”