Deliverable 1.2 Lithology Assessment & Constitutive Model

Abstract

This report focuses on assessments of lithological impact to present day in-situ stress state and integrating observations into constitutive models for application in subsequent tasks (WP1.3 and 1.4). This work is closely linked to WP3.2, and both reports seek to investigate the relative contribution of various processes (initial deposition and mineralogy, burial history including diagenesis, erosion, uplift and glacial loading) to the current in-situ stress in the North Sea basins. The content of the report includes exhumation studies using logs from DISCOS database in combination with lithology-dependent (rheological) compaction and uplift behaviour extracted from the NGI's database of soils and rocks, supplemented by rock mechanical data shared by the storage site operators. This report integrates the experimental laboratory results and empirical relationships from WP3.2 (report DV3.2), with the load history from glacial loading and burial/uplift using stress indicators from geotechnical site investigations and exhumation analysis of logs respectively. Publicly available extended leak-off tests (XLOT) and leak-off tests (LOT) complemented by additional XLOT data provided by Equinor and are used for comparison of empirical relationships defining the impact of mineralogy and burial and loading history on present day stress. We demonstrate how empirical relationships, logs and LOP data can provide useful additional insights into depth dependent and potentially lateral variations of stress within a basin, i.e. between fault blocks or CCS injection sites, and specifically in uplifted areas. Key laboratory data in report DV3.2 are brought into constitutive models to provide the link between the inferred stress history (imposed load/deformation) and the resultant stresses. A proprietary constitutive model has been applied and calibrated with laboratory datasets, which has been shown to satisfactorily capture the experimental response of various soils and soft rocks. This model calibration work is partly reported in DV1.1b, and the model is further tested and calibrated to field stress observations in this report. Workflows to assess stress from reginal trendlines in combination with a method for impact of lithology and burial history have been established and demonstrated for the SHARP CCS sites, with main focus on Aurora and Smeaheia in the Horda Platform area, and the Lisa Structure in Denmark.