Rock mechanical testing of core from the Eos Northern Lights CCS confirmation well and implications for the Geomechanics of North Sea CO2 storage

Abstract

This study presents and analyses the results of rock mechanical testing of sandstone and shale samples from the CO₂ storage confirmation well 31/5–7 (Eos) in EL 001 in the North Sea. Although detailed experimental laboratory programs are performed for many hydrocarbon development projects in the North Sea, only a limited number of site-specific experimentally-derived mechanical data are available in the literature. The tested samples included sandstone from the Cook (2680.25–2680.5 m) and Johansen (2761.00–2761.25 m and 2725–2725.25 m) formations, and shale from the Intra-Drake Formation (2592.00–2595.18 m). For each of the sandstones, Brazilian tests, three drained isotropically-consolidated (CID) triaxial tests, one hydrostatic test, and one anisotropically-consolidated uniaxial strain test (CAUST) were performed. For the shale, the testing comprised four permeability tests conducted on both vertical and horizontal plugs, five undrained isotropically-consolidated triaxial tests (CIU; three on vertical plugs and two on horizontal plugs), seven Brazilian tests (on four horizontal and three vertical plugs), and a uniaxial strain test (CAUST). The tests were designed to characterize the mechanical behaviour of the reservoir and cap rocks within stress and strain regimes relevant to CO₂ injection scenarios. Measurements of the elastic and poroelastic properties, strength, failure criteria, and permeability are provided, including an assessment of the mechanical and hydraulic anisotropy in the case of the shale samples. The data, accessible through CO2Datashare (Northern Lights JV, 2023), significantly enhance the understanding of North Sea lithologies and supply critical parameters for accurately modeling the geomechanical response of the reservoir and overburden in response to CO₂ injection.