Deliverable 4.1 Report on initial assessments of rock-failure risks for case studies

Abstract

This report provides an initial assessment of the state of stress and the estimated conditions for rock failure at the study sites being considered in the ACT SHARP Project. The multinational SHARP consortium has the overall objective to improve understanding on: “Stress history and reservoir pressure for improved quantification of CO2 storage containment risks” SHARP Storage is a research project funded under the ERA-NET ACT programme for accelerating Carbon Capture and Storage (CCS). The overall aim is to improve the accuracy of subsurface CO2 storage containment risk management through the improvement and integration of subsurface stress models, rock mechanical failure and seismicity observations. In this report we present a preliminary assessment of the state of stress at several case study sites and make initial estimates for tensile and shear failure of reservoirs and caprocks. The intention is to provide an early assessment using currently available data to support research in the SHARP project, and with a view to improving these assessments in future. We refer to this initial work as a ‘round 1’ rock failure assessment. After we have developed novel ways to assess the many aspects of stress and strain in rock systems, we expect to develop updated and improved ‘round 2’ rock failure assessments. The case studies considered in the ‘Round 1’ rock-failure risks assessment are as follows: • Norway – Horda/Smeaheia region (mainly released datasets); • UK Southern North Sea – Bunter storage play (mainly published data, White Rose dataset); • Netherlands – Aramis site, Rotliegend pre-salt (relatively mature dataset); • Denmark – Lisa Structure (few wells, more of a ‘greenfield’ site); • India Rajasthan – Bhagewala Heavy Oil Field (mature field with no CCS assessment). Before reporting the case study assessments, we present an overview of the scientific and technical challenges involved in making rock failure assessments, which can also act as a general guide for future CO2 storage studies and site assessments. The portfolio of case studies described in the report includes a range of potential storage sites with a wide variation in the degree of storage development maturity. While detailed site characterisation and rock failure studies have been conducted for the Horda/Smeaheia region and parts of the UK Southern North Sea (SNS) Bunter storage play, rock failure characterisation studies at the Aramis site and Lisa Structure are limited to regional studies. The Bhagewala Heavy Oil Field in India is the least mature of the case studies considered in the SHARP project. While the field operator has developed extensive understanding of the field throughout its productive history, detailed studies of its CO2 storage potential are not available in the public domain. As a result, no pre-existing evaluations of the in situ stress state, seismicity, rock mechanical properties or rock failure risk are currently available to the SHARP consortium. Where detailed studies are not available, publicly available sources have been used to develop an initial understanding of in situ stress and regional seismicity. One aim of the SHARP project will be to further develop on the initial understanding of rock failure risks outlined in this report.