Coupled Modeling of Sedimentary Basin and Geomechanics: A Modified Drucker–Prager Cap Model to Describe Rock Compaction in Tectonic Context

Abstract

The aim of basin modeling is to characterise fluids and rocks in a basin considering its history and data partly describing its present state. In usual basin simulators, only a simplified description of geomechanics based on the hypothesis of oedometric strain is used. In order to both enhance the modelling of basin history and to characterise actual in situ stresses, the effect of stress redistribution, horizontal stresses and strain variations during basin history should be considered. To address this point, a coupled basingeomechanics framework based on a new constitutive law is proposed in this paper using the prototype simulator A 2. This framework has been built to provide relevant results for various kinds of basin cases including tectonic loading. A finite strain poro-mechanical approach is considered along with an modified Drucker-Prager Cap model to describe rock compaction under natural sedimentation, erosion and tectonics. The constitutive model can be seen as a tensorial extension of the compaction models of Athy or Schneider as it allows to recover the same behaviour in oedometric context. Simple test cases are modelled considering typical sand or shale properties, emphasing the effect of tectonic loading on present day pore pressures and in situ stresses. It appears that even relatively moderate tectonic loading (5% of horizontal strain) can lead to overpressures of several hundreds of bars and to a complete change in in situ stress regime for deeply buried layers (above a depth of 2000 meters).

Formulation of reference solutions for compaction process in sedimentary basins

“…By substituting the previous equation into Equation 13 and then integrating it with the initial condition H(0) = 0, we obtain the gravitational compaction law in the elastic phase:…”

“…To overcome this limitation inherent to the analyses based on phenomenological porosity-stress laws, several contributions have focused in the last decades on the formulation of constitutive models that rely upon a more comprehensive description of the mechanics involved in basin deformation. [7][8][9][10][11][12][13][14][15][16] Developed in the context of tensorial formalism, these models have been applied in basin simulations under different geological scenarios, demonstrating the importance of addressing deformation in sedimentary basins within a three-dimensional (3D) framework. As regards the chemical fluid-rock interactions and their implications on the sedimentary material behavior, several approaches have been devoted to describe the complex aspects of dissolution and precipitation of minerals in siliciclastic and carbonate rocks.…”

“…However, such models are not devised for relevant assessment of the horizontal stresses induced by compaction phenomena, nor for capturing the impact of lateral deformations induced by tectonics, which may strongly affect the poro‐mechanical state of the basin, eventually resulting in seal rock fracturing and fault reactivation. To overcome this limitation inherent to the analyses based on phenomenological porosity–stress laws, several contributions have focused in the last decades on the formulation of constitutive models that rely upon a more comprehensive description of the mechanics involved in basin deformation 7–16 . Developed in the context of tensorial formalism, these models have been applied in basin simulations under different geological scenarios, demonstrating the importance of addressing deformation in sedimentary basins within a three‐dimensional (3D) framework.…”

An Assessment of Stress States in Passive Margin Sediments: Iterative Hydro-Mechanical Simulations on Basin Models and Implications for Rock Failure Predictions

“…The coupling is implemented in a prototype software named A 2 [71]. Following an iterative procedure, the two codes exchange inputs and outputs at each simulation step, until providing a consistent set of porosity, permeability, fluid pressure, and stress tensor in each cell of the basin model.…”

“…The same grid is used by the two codes and the convergence criterion is based on a comparison between the porosity values they compute. A full description can be read in [71] and [75].…”