Abstract

Numerical simulation of CO2 storage in basalts and related reactive lithologies requires modeling complex, coupled hydrologic and chemical processes, including multi-phase flow and transport, partitioning of CO2 into the aqueous phase, and chemical interactions with aqueous fluids and rock minerals. We conducted reactive transport simulations of the Wallula pilot-scale CO2 injection into the flow tops of the Grande Ronde Basalt using our Pacific Northwest National Laboratory STOMP-CO2 simulator with the ECKEChem reactive module. Our mineralization simulation of the ∼1,000 tons of injected CO2 into the interflow zones was based on the hydrologic transport model we previously developed. For this work, the simulations considered geochemical reactions involving the basalt components, precipitates, formation brine, and injected CO2. In our benchmark case, carbonate minerals precipitated, resulting in ∼20% of the CO2 being mineralized in 10 years. Increasing the reaction rate of a single primary mineral phase (clinopyroxene) by an order of magnitude resulted in a carbon mineralization reaction extent of ∼90% over the same time interval. Based on these initial sensitivity analysis results, it is clear that a thorough understanding of primary mineral dissolution rates is required for accurately predicting long-term fate and transport of injected CO2 into basalt formations. Our reactive transport numerical simulations will be key components of commercial-scale CO2 storage operation permitting, de-risking, and optimization in mafic and ultramafic reservoirs.

Introduction

In 2009, the Wallula Basalt Pilot project was initiated with the drilling of a CO2 injection well to a depth of 1,253 m below ground level (bgl) at the Boise White Paper Mill property at Wallula, Washington. The well intersected three deep layered basalt flowtops starting at 830 m (Figure 1) that received ∼1,000 tons of CO2 in August of 2013 over three weeks. After 24-month, sidewall cores were extracted from the injection zone as part of an extensive post-injection characterization champaign. Laboratory analysis performed on the retrieved core identified anthropogenic carbonate mineral assemblages (e.g. ankerite, aragonite, and siderite) that were isotopically, texturally, and chemically linked to the injected CO2 (Depp et al., 2022; McGrail et al., 2017a; McGrail et al., 2017b; Polites et al., 2022). Recently, our detailed analysis of pre-injection and post-injection hydrologic testing in the context of a robust hydrogeologic Wallula model indicated that ∼60% of the injected CO2 mineralized in only two years (White et al., 2020). The objective of this present study is to numerically simulate the CO2 transport and reactivity at Wallula and determine how predicted carbon mineralization rate determinations compare with our recent carbon mineralization quantification (White et al., 2020), laboratory results, and field data.

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