Porosity Evolution during Chemo-Mechanical Compaction

This chapter presents the constitutive equations necessary to interpret laboratory and field data when both solid and pore volume evolve through time due to chemical and mechanical processes. The equations for the porosity evolution that are developed are generic, but the examples presented are acquired from chalk core studies. The processes at play when porosity is subject to change due to volumetric compaction and fluid-rock interactions when porous chalks are continuously flooded are presented here. As the overall solid mass is a conserved quantity, the void space is not. Constitutive equations are therefore required to estimate the time-evolution of the porosity. Laboratory triaxial tests were performed on high-porosity outcrop chalks from Obourg, Liegè, and Mons (Belgium). These tests are being compacted and continuously flooded with MgCl2 brine at elevated temperature and at high stresses. As calcite is replaced by magnesite, the overall mass and solid density change, thereby changing the volume of the solid. At the same time, the bulk volume is changing. Taking both effects into consideration, the pore volume evolution can be determined. We find that the porosity changes in nonintuitive ways as the relative importance of bulk compaction and chemical interaction may vary over time

Some effects of gas-induced fluidization in dry granular media

I denne avhandlingen har vi brukt innsikt fra sandboks modeller og teori for å forstå dannelsen av ulike geologiske fenomen og strukturer. Vi har studert hvordan, og ved hvilke fysiske parametere, væskestrøm forårsaker deformasjon i granulære medier. Vi har brukt denne kunnskapen til å estimere det kritiske trykket for dannelsen av vulkaner. Vi har studert mønsterdannelsen i den delvis fluidiserte fasen når gass injiseres i en blanding av sandpartikler av ulik størrelse. Ved konstant gasstrøm, sedimenteres den opprinnelig fluidiserte pakningen simultant med veksten av vertikale piper bestående av de store partiklene. Vi foreslår en tilbakekoblingsmekanisme som forklarer den observerte dynamikken. I denne mekanismen sedimenteres de store partiklene i de fluidiserte områdene, mens de små partiklene forblir fluidisert. Samlingen av de store partiklene endrer gass strømningen gjennom sedimentene slik at fluidiseringen og den etterfølgende sedimenteringen av store partikler lokaliseres. Vi har anvendt denne mekanismen til å forstå dannelsen av mindre vertikale pipestrukturer inne i større geologiske pipestrukturer. I tillegg har vi vist, gjennom eksperimenter, teori og numeriske beregninger, hvordan lokalisering av skjærkrefter forårsaker dannelsen av slam- og vannvulkaner i situasjoner hvor væsketrykket i sedimentene ellers ikke ville forårsake skade. Vi hevder at denne mekanismen kan være den primære faktoren for dannelsen av Lusi, gjørmevulkanen som ble ’født’ den 29. mai 2006 på øya Java i Indonesia. Gjørmevulkanen Lusi har i perioden etter sin fødsel utviklet seg til å bli en stor miljøkatastrofe hvor tre landsbyer har blitt oversvømt og 30 000 mennesker har mistet sine hjem. Det har derfor vært viktig å kaste lys på hva den underliggende årsaken til Lusi måtte være. I årene etter dannelsen av vulkanen har de underliggende årsakene og den utløsende mekanismen blitt heftig diskutert i media og i den vitenskaplige litteraturen

How stress and temperature conditions affect rock-fluid chemistry and mechanical deformation

We report the results from a series of chalk flow-through-compaction experiments performed at three effective stresses (0.5, 3.5, and 12.3MPa) and two temperatures (92 and 130◦C). The results show that both stress and temperature are important to both chemical alteration and mechanical deformation. The experiments were conducted on cores drilled from the same block of outcrop chalks from the Obourg quarry within the Saint Vast formation (Mons, Belgium). The pore pressure was kept at 0.7MPa for all experiments with a continuous flow of 0.219M MgCl2 brine at a constant flow rate; 1 original pore volume (PV) per day. The experiments have been performed in tri-axial cells with independent control of the external stress (hydraulic pressure in the confining oil), pore pressure, temperature, and the injected flow rate. Each experiment consists of two phases; a loading phase where stress-strain dependencies are investigated (approximately 2 days), and a creep phase that lasts for 150–160 days. During creep, the axial deformation was logged, and the effluent samples were collected for ion chromatography analyses. Any difference between the injected and produced water chemistry gives insight into the rock-fluid interactions that occur during flow through the core. The observed effluent concentration shows a reduction in Mg2+, while the Ca2+ concentration is increased. This, together with SEM-EDS analysis, indicates that magnesium-bearing mineral phases are precipitated leading to dissolution of calcite. This is in-line with other flow-through experiments reported earlier. The observed dissolution and precipitation are sensitive to the effective stress and test temperature. Higher stress and temperature lead to increased Mg2+ and Ca2+ concentration changes. The observed strain can be partitioned additively into a mechanical and chemical driven component.publishedVersio

Incorporating electrostatic effects into the effective stress relation — Insights from chalk experiments

This is an author accepted manuscript of an article from the journal Geophysics, published by the Society of Exploration Geophysicists (SEG). Reuse is subject to SEG terms of use and conditions.Which forces are responsible for holding highly porous chalks together? We use the effective stress to quantify the electrostatic effects around particle contacts originating from the adsorption of ions onto charged mineral surfaces. The induration of chalk indicates that it is held together by contact cement,where planar crystal contacts allowthe action of short-ranged adhesive Van der Waals forces. At particle distances exceeding a few nanometers, recent studies have indicated electrostatic repulsion between water embedded adjacent particles. The magnitude of the repelling force depends, among other parameters, upon temperature and brine composition. Our premise is that by perturbing the electrostatic forces at the particle level, we can control themechanical behavior of chalk samples tested in triaxial cells.We report the results of an experimental series, investigating howthemechanical strength and stiffness varied among samples saturated with four different brines, tested at two temperatures, and tested directly or after aging for three weeks at high temperature. We associate stiffness with bulk modulus and strengthwith the stress at yield. Systematic softening and weakening is observed, especially when the pore fluid is sulfate bearing, as well as for some high-temperature experiments and for aged samples. However, softening and weakening are not totally correlated, and neither brine composition, temperature, nor aging can alone dictate the mechanical behavior of the chalk — a combination is required to predict the chalk stiffness and strength. To obtain a coherent description of our experimental results, we estimated the electrostatic stress arising from ion adsorption and found it unnecessary for these experiments to postulate significant dissolution or precipitation-related changes to the rock frame.acceptedVersio

Assessment of a mature hydrocarbon field in SE Czech Republic for a CO2 storage pilot

Preparation and execution of a CO2 storage pilot project is one of the first logical steps in the effort to kick-start CCS in the region of Central & Eastern Europe, utilizing onshore geological structures for permanent CO2 storage. The main aims of this activity are to test the suitability of local geological structures and demonstrate the feasibility and safety of the technology to local stakeholders. The Czech-Norwegian CO2-SPICER project is an example of such developments. The target structure of CO2-SPICER – Zar−3 – is a hydrocarbon field situated in an erosional relict of fractured carbonates of Jurassic age on the SE slopes of the Bohemian Massif, covered by Paleogene deposits and Carpathian flysch nappes. The first stage of site assessment has been completed, and the article provides an overview of its results. Construction of a 3D geological model of the storage complex was the first important step on the route, preparing input for subsequent reservoir simulations of the field history and planned CO2 injection. Reservoir assessment is also focusing on specific features of the fractured-vuggy reservoir and accounting for the effects associated with CO2 injection, including geochemistry and geomechanics. Geochemical studies focus on fluid-rock interactions, and geomechanical ones on formation integrity and fracture mechanics under reservoir pressure build-up and cooling of the formation by injected CO2. Risk assessment is another component of the project, aiming at identifying potential leakage pathways and assessing consequences for the area of interest. Preparatory work for the site monitoring plan includes applicability analysis of various monitoring methods, supported by execution of baseline monitoring of selected phenomena, in particular composition of soil gas, natural and induced seismicity and properties of shallow groundwater. The project also includes evaluation of advanced reservoir containment monitoring technologies including time-lapse pressure transient analysis. While the key actions are directed towards the piloting activities, the project also looks beyond to full-field implementation and potential to establish a regional CCS cluster.acceptedVersio

Evaluation of the compositional changes during flooding of reactive fluids using scanning electron microscopy, nano-secondary ion mass spectrometry, x-ray diffraction, and whole-rock geochemistry

Outcrop chalk of late Campanian age (Gulpen Formation) from Liège (Belgium) was flooded with MgCl2 in a triaxial cell for 516 days under reservoir conditions to understand how the non-equilibrium nature of the fluids altered the chalks. The study is motivated by enhanced oil recovery (EOR) processes because dissolution and precipitation change the way in which oils are trapped in chalk reservoirs. Relative to initial composition, the first centimeter of the flooded chalk sample shows an increase in MgO by approximately 100, from a weight percent of 0.33% to 33.03% and a corresponding depletion of CaO by more than 70% from 52.22 to 14.43 wt.%. Except for Sr, other major or trace elements do not show a significant change in concentration. Magnesite was identified as the major newly grown mineral phase. At the same time, porosity was reduced by approximately 20%. The amount of Cl− in the effluent brine remained unchanged, whereas Mg2+ was depleted and Ca2+ enriched. The loss of Ca2+ and gain in Mg2+ are attributed to precipitation of new minerals and leaching the tested core by approximately 20%, respectively. Dramatic mineralogical and geochemical changes are observed with scanning electron microscopy–energy-dispersive x-ray spectroscopy, nano secondary ion mass spectrometry, x-ray diffraction, and whole-rock geochemistry techniques. The understanding of how fluids interact with rocks is important to, for example, EOR, because textural changes in the pore space affect how water will imbibe and expel oil from the rock. The mechanisms of dissolution and mineralization of fine-grained chalk can be described and quantified and, when understood, offer numerous possibilities in the engineering of carbonate reservoirs.acceptedVersio

A laboratory scale approach to wettability restoration in chalk core samples

Wettability in chalk has been studied comprehensively to understand fluid flow mechanisms impacting coreflooding experiments. Wettability becomes paramount in understanding the parameters influencing chalk-fluid interactions. The main objective of this work is to evaluate as to which degree the wettability in chalk core samples can be controlled in the laboratory. Kansas chalk samples saturated with brine (1.1 M/64284 ppm NaCl) and an oil mixture (60% - 40% by volume of Heidrun oil and heptane) were aged at a constant temperature of 90oC with aging time as the laboratory control variable. A multimodal method incorporating contact angle measurements, wettability index via USBM test, and SEM-MLA analysis was applied in evaluating wettability. A systematic approach was applied with the three different methods to quantify the degree of uncertainty linked to a) wettability estimation and b) the aging procedure to control wettability alteration of Kansas chalk. With a comprehensive suite of samples, we were successfully able to alter the wettability of chalk cores

A techno-economic Analysis Tool for Regional CO2 Capture, Transport, Use and Storage Scenarios

Carbon capture from industrial, high concentration CO2 sources, combined with CO2 transport, utilization and storage (CCUS) is a way to reduce greenhouse gas emissions. CCUS will play an important role in our transition into, and, also beyond the green shift, as CCUS both significantly reduces emissions from industrial processes and offsets emissions from hard-to-remove sectors – leading to the global net-zero society. We study here how the deployment of CCUS networks and commonly shared infrastructure could be evaluated using a dedicated techno-economic analysis tool presented here. A scenario-approach was taken in the development of CCUS network to decarbonize industrialized regions. In this context, a scenario is defined as a planned deployment of capture, transport, utilization and storage units – each at a given location and at given time between now and 2050. The Excel-based tool presented in this paper, allows for both the design and technical-economic analysis at regional scale. It allowed to define scenarios in a time-dependent spatial network connecting capture points to CO2utilization factories and storage locations via transport by pipelines, or via trains, trucks, or vessels/barges. To set up different scenarios, and to ensure both their internal consistency and comparability with each other, a dedicated tool was developed in the STRATEGY CCUS project funded though EU Horizon 2020 program (grant agreement No 837754). The tool use common input variables shared between different modules of the tool and scenarios which enables comparison between decarbonization of different regions. The tool aims to provide more realistic, and comparable estimates for future energy and material use, emissions avoided and negative emissions, revenues created by downstream industries, broken down in discounted and un-discounted costs per ton of CO2 avoided. The tool allows for future cost reductions due to technology maturation, economy of scale and learning, as well as inflation and energy price outlooks. This paper describes in more detail the structure of the tool, how it was used, and the lessons learned from its development. Basically, the tool underwent two development stages: The first when the internal logic was developed and the tool itself was put together, and secondly, when eight regional European teams used the tool, its quality and internal consistency significantly improved. Feedback and constructive criticism by users were paramount in the development of the tool

Residual Corticosteroid Production in Autoimmune Addison Disease

Context - Contrary to current dogma, growing evidence suggests that some patients with autoimmune Addison disease (AAD) produce corticosteroids even years after diagnosis. Objective - To determine frequencies and clinical features of residual corticosteroid production in patients with AAD. Design - Two-staged, cross-sectional clinical study in 17 centers (Norway, Sweden, and Germany). Residual glucocorticoid (GC) production was defined as quantifiable serum cortisol and 11-deoxycortisol and residual mineralocorticoid (MC) production as quantifiable serum aldosterone and corticosterone after > 18 hours of medication fasting. Corticosteroids were analyzed by liquid chromatography–tandem mass spectrometry. Clinical variables included frequency of adrenal crises and quality of life. Peak cortisol response was evaluated by a standard 250 µg cosyntropin test. Results - Fifty-eight (30.2%) of 192 patients had residual GC production, more common in men (n = 33; P P P P P P P  Conclusion - In established AAD, one-third of the patients still produce GCs even decades after diagnosis. Residual production is more common in men and in patients with shorter disease duration but is not associated with adrenal crises or quality of life