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Title: Efficient parallel simulation of CO2 geologic sequestration insaline aquifers

Abstract

An efficient parallel simulator for large-scale, long-termCO2 geologic sequestration in saline aquifers has been developed. Theparallel simulator is a three-dimensional, fully implicit model thatsolves large, sparse linear systems arising from discretization of thepartial differential equations for mass and energy balance in porous andfractured media. The simulator is based on the ECO2N module of the TOUGH2code and inherits all the process capabilities of the single-CPU TOUGH2code, including a comprehensive description of the thermodynamics andthermophysical properties of H2O-NaCl- CO2 mixtures, modeling singleand/or two-phase isothermal or non-isothermal flow processes, two-phasemixtures, fluid phases appearing or disappearing, as well as saltprecipitation or dissolution. The new parallel simulator uses MPI forparallel implementation, the METIS software package for simulation domainpartitioning, and the iterative parallel linear solver package Aztec forsolving linear equations by multiple processors. In addition, theparallel simulator has been implemented with an efficient communicationscheme. Test examples show that a linear or super-linear speedup can beobtained on Linux clusters as well as on supercomputers. Because of thesignificant improvement in both simulation time and memory requirement,the new simulator provides a powerful tool for tackling larger scale andmore complex problems than can be solved by single-CPU codes. Ahigh-resolution simulation example is presented that models buoyantconvection, induced by a smallmore » increase in brine density caused bydissolution of CO2.« less

Authors:
; ; ;
Publication Date:
Research Org.:
Ernest Orlando Lawrence Berkeley NationalLaboratory, Berkeley, CA (US)
Sponsoring Org.:
USDOE
OSTI Identifier:
925539
Report Number(s):
LBNL-63316
R&D Project: G2W026; BnR: 600301020; TRN: US0803054
DOE Contract Number:
DE-AC02-05CH11231
Resource Type:
Conference
Resource Relation:
Conference: 2007 SPE Reservoir Simulation Symposium, Houston,TX, 26-28 February 2007
Country of Publication:
United States
Language:
English
Subject:
54; AQUIFERS; BRINES; COMMUNICATIONS; CONVECTION; DISSOLUTION; ENERGY BALANCE; IMPLEMENTATION; MIXTURES; PARTIAL DIFFERENTIAL EQUATIONS; PRECIPITATION; SIMULATION; SIMULATORS; SOLAR PROTONS; SUPERCOMPUTERS; THERMODYNAMICS

Citation Formats

Zhang, Keni, Doughty, Christine, Wu, Yu-Shu, and Pruess, Karsten. Efficient parallel simulation of CO2 geologic sequestration insaline aquifers. United States: N. p., 2007. Web.
Zhang, Keni, Doughty, Christine, Wu, Yu-Shu, & Pruess, Karsten. Efficient parallel simulation of CO2 geologic sequestration insaline aquifers. United States.
Zhang, Keni, Doughty, Christine, Wu, Yu-Shu, and Pruess, Karsten. Mon . "Efficient parallel simulation of CO2 geologic sequestration insaline aquifers". United States. doi:. https://www.osti.gov/servlets/purl/925539.
@article{osti_925539,
title = {Efficient parallel simulation of CO2 geologic sequestration insaline aquifers},
author = {Zhang, Keni and Doughty, Christine and Wu, Yu-Shu and Pruess, Karsten},
abstractNote = {An efficient parallel simulator for large-scale, long-termCO2 geologic sequestration in saline aquifers has been developed. Theparallel simulator is a three-dimensional, fully implicit model thatsolves large, sparse linear systems arising from discretization of thepartial differential equations for mass and energy balance in porous andfractured media. The simulator is based on the ECO2N module of the TOUGH2code and inherits all the process capabilities of the single-CPU TOUGH2code, including a comprehensive description of the thermodynamics andthermophysical properties of H2O-NaCl- CO2 mixtures, modeling singleand/or two-phase isothermal or non-isothermal flow processes, two-phasemixtures, fluid phases appearing or disappearing, as well as saltprecipitation or dissolution. The new parallel simulator uses MPI forparallel implementation, the METIS software package for simulation domainpartitioning, and the iterative parallel linear solver package Aztec forsolving linear equations by multiple processors. In addition, theparallel simulator has been implemented with an efficient communicationscheme. Test examples show that a linear or super-linear speedup can beobtained on Linux clusters as well as on supercomputers. Because of thesignificant improvement in both simulation time and memory requirement,the new simulator provides a powerful tool for tackling larger scale andmore complex problems than can be solved by single-CPU codes. Ahigh-resolution simulation example is presented that models buoyantconvection, induced by a small increase in brine density caused bydissolution of CO2.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}

Conference:
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  • In this study, we address a series of fundamental questions regarding the processes and effectiveness of geologic CO{sub 2} sequestration in saline aquifers. We begin with the broadest: what is the ultimate fate of CO{sub 2} injected into these environments? Once injected, it is immediately subject to two sets of competing processes: migration processes and sequestration processes. In terms of migration, the CO{sub 2} moves by volumetric displacement of formation waters, with which it is largely immiscible; by gravity segregation, which causes the immiscible CO{sub 2} plume to rise owing to its relatively low density; and by viscous fingering, owingmore » to its relatively low viscosity. In terms of sequestration, some fraction of the rising plume will dissolve into formation waters (solubility trapping); some fraction may react with formation minerals to precipitate carbonates (mineral trapping); and the remaining portion eventually reaches the cap rock, where it migrates up-dip, potentially accumulating in local topographic highs (structural trapping). Although this concept of competing migration/sequestration processes is intuitively obvious, identifying those sub-processes that dominate the competition is by no means straightforward. Hence, at present there are large uncertainties associated with the ultimate fate of injected CO{sub 2} (Figure 1). Principal among these: can a typical shale cap rock provide a secure seal? Because gravity segregation will always keep the immiscible CO{sub 2} plume moving towards the surface, caprock integrity is the single most important variable influencing isolation security. An extremely thick shale cap rock exists at Sleipner (several 100 m); here, however, we examine the performance of a 25-m-thick cap, which is more representative of the general case. Although the cap rock represents the final barrier to vertical CO{sub 2} migration, what is the effect of intra-aquifer permeability structure? Because this structure directs the path of all CO{sub 2} migration processes within the target formation, it will effectively determine the spatial extent of plume-aquifer interaction, and thereby exert a controlling influence on all sequestration processes. Here, we consider three common settings: a homogeneous saline aquifer, one with inter-bedded laterally continuous shales (continuum representation of microfractured shales), and one with inter-bedded laterally discontinuous shales (discrete representation of lateral facies changes). For each configuration, we examine the unique character of immiscible CO{sub 2} migration paths, describe the dependent location, timing, and extent of associated solubility and mineral trapping, and detail the relative partitioning of injected CO{sub 2} among the immiscible plume, formation waters, and carbonate precipitates. While intra-aquifer permeability structure establishes the spatial framework of plume-aquifer interaction, the effectiveness of solubility and mineral trapping within this setting is largely determined by compositional characteristics of the aquifer and (if present) its inter-bedded shales. Here, we focus on Sleipner, where the saline aquifer consists of unconsolidated impure quartz sand saturated with a seawater-like aqueous phase, and there is strong evidence of thin interbedded shales. Based on our modeling results for this environment, we infer the effect of varying fluid composition from dilute to saline to brine, and the effect of varying sand and shale mineralogy within relevant limits. In addition, we describe those compositional characteristics required to maximize solubility and mineral trapping for a given permeability configuration. We also address the fundamental yet infrequently posed question: what happens when CO{sub 2} injection is terminated? Hydrologic and geochemical evolution may be very different during the relatively brief ''prograde'' (active-injection) and subsequent long-term ''retrograde'' (postinjection) regimes of geologic sequestration. Most importantly, are prograde trapping mechanisms enhanced or reversed during the retrograde phase (which spans geologic time scales)? We will demonstrate that there are indeed significant differences between prograde and retrograde sequestration.« less
  • Geologic sequestration represents a promising strategy for isolating CO{sub 2} waste streams from the atmosphere. Successful implementation of this approach hinges on our ability to predict the relative effectiveness of subsurface CO{sub 2} migration and sequestration as a function of key target-formation and cap-rock properties, which will enable us to identify optimal sites and evaluate their long-term isolation performance. Quantifying this functional relationship requires a modeling capability that explicitly couples multiphase flow and kinetically controlled geochemical processes. We have developed a unique computational package that meets these criteria, and used it to model CO{sub 2} injection at Statoil's North-Sea Sleipnermore » facility, the world's first saline-aquifer storage site. The package integrates a state-of-the-art reactive transport simulator (NUFT) with supporting geochemical software and databases (SUPCRT92). In our Sleipner study, we have quantified--for the first time--the influence of intra-aquifer shales and aquifer/cap-rock composition on migration/sequestration balance, sequestration partitioning among hydrodynamic, solubility, and mineral trapping mechanisms, and the isolation performance of shale cap rocks. Here, we review the fundamental elements of geologic CO{sub 2} sequestration in saline aquifers as revealed from model XSH of our Sleipner study; this model, unlike CSH and DSH, does not address the complicating (yet advantageous) presence of intra-aquifer shales.« less