Mechanical testing and sealing capacity of the Upper Jurassic Draupne Formation, North Sea

Abstract

Nine meters of shale core have been cut from the upper part of the Upper Jurassic Draupne Formation within the Ling Depression in the central part of the North Sea. The main objective was to provide high quality core for rock mechanical and geophysical studies related to seal integrity evaluation for future CO₂ storage sites in the North Sea. In this work the first results from the core opening, initial logging, material characterization and mechanical testing for parts of the core are presented. Our results indicate very low permeable shale with small pore throats ensuring a high capillary sealing for the intact shale, whereas the observed shear fracture is more uncertain with respect to both formation and sealing capacity. Mechanical testing show bedding related anisotropy in the shale with the weakest plane along the bedding, as confirmed by the bedding parallel Mode I unloading fractures observed along the core. Evaluation of high-quality core samples from the Draupne Formation are considered an important input to further geomechanical modelling of caprock integrity, and will presumably provide a significant contribution for further seal evaluation and development of CO₂ storage potential in the North Sea.

1. INTRODUCTION

Nine meters of shale core have been cut from the upper part of the Upper Jurassic Draupne Formation within the Ling Depression in the central part of the North Sea. The main objective was to provide high quality core for rock mechanical and geophysical studies related to seal integrity evaluation for future CO₂ storage sites in the North Sea. In this work the first results from the core opening, initial logging, material characterization and mechanical testing for parts of the core are presented. Our results indicate very low permeable shale with small pore throats ensuring a high capillary sealing for the intact shale, whereas the observed shear fracture is more uncertain with respect to both formation and sealing capacity. Mechanical testing show bedding related anisotropy in the shale with the weakest plane along the bedding, as confirmed by the bedding parallel Mode I unloading fractures observed along the core. Evaluation of high-quality core samples from the Draupne Formation are considered an important input to further geomechanical modelling of caprock integrity, and will presumably provide a significant contribution for further seal evaluation and development of CO₂ storage potential in the North Sea.