Paradigm for Determining the Optimal Ultradeep and Super-thick Saline Aquifer for High-TDS Mine Water Geological Storage

Abstract

Saline aquifers are the most popular waste and CO₂ injection and storage reservoirs worldwide. This project proposes that several optimal injection positions should be investigated as hydraulic pressure-focused positions, in order to relieve the high demands of pump performance. The comprehensive indices (F_i) representing the injectivity of different burial depths were obtained by using information entropy, based on the mercury injection experimental data of 13 rock samples. The results demonstrated that the burial depths of No. 4, No. 1 and No. 2 in the Liujiagou Formation were the most suitable positions for hydraulic focused injection, which means the upper 30 m thickness could be regarded as the hydraulic focused range in the saline aquifer with an average thickness of 400 m. In addition, some laboratory experiments and in situ tests were carried out for the purpose of certifying and analyzing results, including SEM, XRD, brittleness index and logging. The results suggested that the rock samples at the No. 4, No. 1 and No. 2 burial depth ranges have loose microstructure, weak cementation, as well as dual pores and fractures. The lithology is mainly quartz and feldspar, but the clay mineral content is high (10%–25%), which is positive for dissolution. The lithology is suitable for hydraulic fracturing to form extended cracks and micro-fissures during high-TDS (total dissolved solids) mine water injection, because of the high brittleness index. Finally, a theoretical and technical framework for high-TDS mine water injection was established, based on operating pilot engineering. Some theoretical defects and drawbacks learned from the field practices were summarized and solutions proposed. The research in this study could provide guidance and a paradigm for the inexpensive treatment of high-TDS mine water by injection and storage.