A constitutive model for mechanical and chemo‐mechanical compaction in sedimentary basins and finite element analysis

Abstract

Summary Compaction and associated fluid flow are fundamental processes in sedimentary basin deformation. Purely mechanical compaction originates mainly from pore fluid expulsion and rearrangement of solid particles during burial, while chemo‐mechanical compaction results from Intergranular Pressure‐Solution (IPS) and represents a major mechanism of deformation in sedimentary basins during diagenesis. The aim of the present contribution is to provide a comprehensive 3D framework for constitutive and numerical modeling of purely mechanical and chemo‐mechanical compaction in sedimentary basins. Extending the concepts that have been previously proposed for the modeling of purely mechanical compaction in finite poroplasticity, deformation by IPS is addressed herein by means of additional viscoplastic terms in the state equations of the porous material. The finite element model integrates the poroplastic and poroviscoplastic components of deformation at large strains. The corresponding implementation allows for numerical simulation of sediments accretion/erosion periods by progressive activation/deactivation of the gravity forces within a fictitious closed material system. Validation of the numerical approach is assessed by means of comparison with closed‐form solutions derived in the context of a simplified compaction model. The last part of the paper presents the results of numerical basin simulation performed in one dimensional setting, demonstrating the ability of the modeling to capture the main features in elastoplastic and viscoplastic compaction. Copyright © 2016 John Wiley & Sons, Ltd.

Formulation of reference solutions for compaction process in sedimentary basins

“…Comparison with FE solutions derived from a basin simulator that integrates the effects of large irreversible porosity change on the elastic properties as well as on plastic/viscoplastic hardening laws 36,51 provides ample evidence of the ability of derived semianalytical solutions to relevantly reflect most of local and overall features of the basin deformation. In particular, it has been shown that the simplifying approximations introduced in the resolution formulation affect very little the accuracy of obtained predictions.…”

“…The role of pore pressure and geothermal gradient has been assessed through numerical formulations in previous works. 9,41,44,51,52 The sedimentary basin undergoing compaction is modeled as an infinite layer, perpendicular to the e 3 direction and lying on a rigid substratum along the plane x 3 = 0. Neglecting the tectonic activity, the gravitational field g = −ge 3 stands for the only external loading in the compaction process.…”

“…An associated flow rule g vp = f vp shall be assumed in the subsequent analysis. The evolution law for p vp has been formulated 51 and stems from the heuristic idea that similarity can be preserved between the plastic and viscoplastic models:…”

“…The numerical results do not refer to a real data life basin but rather to an academic problem and are only intended to illustrate some features of basin deformation in the context of purely gravitational compaction under oedometric conditions. In the framework of such simplified scenario, the accuracy of the approach predictions is assessed through comparison with FE solutions derived from the basin simulator developed by Brüch et al 36,51 . This simulator, which implements a finite thermo-poro-mechanics modeling, is specifically devised to deal with 3D analyses of purely mechanical and chemo-mechanical compaction in sedimentary basins.…”

“…In order to formulate semianalytical solutions for the compaction process in sedimentary basins, a simplified setting relying upon the following assumptions is adopted: (a) the whole sedimentation process takes place under oedometric conditions; (b) the sediment constitutive material exhibits homogeneous and isotropic mechanical properties in its reference state, that is, at the time it is deposited at the top of the basin; (c) the hydromechanical coupling is disregarded in the subsequent analysis (i.e., the effect of pore pressure is not considered), which amounts to addressing the particular case of highly permeable sediment material (fully drained conditions); and (d) the mechanical evolution of the basin is analyzed under isothermal condition, disregarding the effect of geothermal gradient on the material properties and deformation. The role of pore pressure and geothermal gradient has been assessed through numerical formulations in previous works 9,41,44,51,52 …”