Stress and pore pressure histories in complex tectonic settings predicted with coupled geomechanical-fluid flow models

Abstract

. (2016) 'Stress and pore pressure histories in complex tectonic settings predicted with coupled geomechanical-uid ow models.', Marine and petroleum geology., 76 . pp. 464-477. Further information on publisher's website: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. AbstractMost of the methods currently used for pore pressure prediction in sedimentary basins assume one-dimensional compaction based on relationships between vertical effective stress and porosity. These methods may be inaccurate in complex tectonic regimes where stress tensors are variable. Modelling approaches for compaction adopted within the geotechnical field account for both the full three-dimensional stress tensor and the stress history. In this paper a coupled geomechanical-fluid flow model is used, along with an advanced version of the Cam-Clay constitutive model, to investigate stress, pore pressure and porosity in a Gulf of Mexico style mini-basin bounded by salt subjected to lateral deformation. The modelled structure consists of two depocentres separated by a salt diapir. 20% of horizontal shortening synchronous to basin sedimentation is im-posed. An additional model accounting solely for the overpressure generated due to 1D disequilibrium compaction is also defined. The predicted deformation regime in the two depocentres of the mini-basin is one of tectonic lateral compression, in which the horizontal effective stress is higher than the vertical effective stress. In contrast, sediments above the central salt diapir show lateral extension and tectonic vertical compaction due to the rise of the diapir. Compared to the 1D model, the horizontal shortening in the mini-basin increases the predicted present-day overpressure by 50%, from 20 MPa to 30 MPa. The porosities predicted by the mini-basin models are used to perform 1D, porosity-based pore pressure predictions. The 1D method underestimated overpressure by up to 6 MPa at 3400 m depth (26% of the total overpressure) in the well located at the basin depocentre and up to 3 MPa at 1900 m depth (34% of the total overpressure) in the well located above the salt diapir. The results show how 2D/3D methods are required to accurately predict overpressure in regions in which tectonic stresses are important.

Assessing the implications of tectonic compaction on pore pressure using a coupled geomechanical approach

“…Then the error is computed as the difference between the overpressure predicted by the numerical models and that obtained by means of the EDM. It should be highlighted that in the present work the sedimentation and tectonic events are sequential rather than synchronous as in Obradors-Prats et al (2016).…”

Enhanced velocity based pore pressure prediction using lithofacies clustering: A case study from a reservoir with complex lithology in Dezful Embayment, SW Iran

“…Lithology, porosity, and fluid content variations have a significant effect on the accuracy and precision of pore pressure estimation based on P-wave velocity (Obradors-Prats et al, 2016;Wang and Wang, 2015;Oloruntobi et al, 2018). This can be explained by the strong dependence of P-wave velocity with lithological and geomechanical parameters.…”

“…However, generating a comprehensive velocity model compound of various type of data is not straightforward. For instance, One should keep in mind that above methods heavily depend on the relationship between porosity and pore pressure (Mannon and Young, 2017;Wang and Wang, 2015;Zhao et al, 2014) which may not be a valid assumption in case of complex lithology (Obradors-Prats et al, 2016). Also, the presence of secondary phases (e.g., methane, brine) introduce a major uncertainty and may lead to false interpretation of the velocity data and inaccurate pore pressure estimation (Nour and AlBinHassan, 2013).…”

Deformation, stress, and pore pressure in an evolving suprasalt basin

“…This implies that the stress ratio of deviatoric stress and mean effective stress ( q / p ′ ) is constant throughout the area where pore pressure is predicted. However, it is clear from our preceding analysis that the stress ratio is not constant (Figure ), and some recent studies emphasize the effect of stress ratio ( q / p ′ ) on compaction and pore pressure in the regions near salt bodies or where stresses are perturbed [e.g., Nikolinakou et al , ; Obradors‐Prats et al , ]. Here we apply three different methods to predict overpressure.…”

“…However, it cannot include the effect of change in stress ratio ( q / p ′ ). Some recent studies explain the importance of both mean effective stress and deviatoric stress on compaction and pore pressure [e.g., Hauser et al , ; Nikolinakou et al , ; Obradors‐Prats et al , , ] and emphasize the effect of stress ratio ( q / p ′ ) on compaction and pore pressure in the regions near‐salt bodies or where stresses are perturbed [e.g., Nikolinakou et al , ; Obradors‐Prats et al , ]. To address this, we apply the MCC model approach, to predict pore pressure.…”