B.M. Krooss

The effects of fluid flow through porous media on the distribution of organic compounds in a synthetic crude oil

Abstract In a controlled laboratory simulation of petroleum migration, a 17-component mixture containing hydrocarbons and heterocyclic compounds was flowed through restricted mineral phases using a modified liquid chromatographic (LC) apparatus. The solid phases, tested in wet and dry conditions, consisted of quartz, quartz/montmorillonite and a reservoir rock sample containing quartz and clay minerals. The redistribution of hydrocarbon and other compounds along the migration paths was determined for replicate LC simulation runs of each solid phase and quantified using gas chromatographic (GC) analysis against an external standard. Liquid/solid chromatographic interactions enrich the earliest eluting fractions in saturated compounds and in lower molecular-weight compounds and, conversely, increase the concentrations of more polar compounds in the fractions which remain on the solid phases. The changes in compound composition are reproducible and verifiable outside the margin of error, despite the low levels of solid phase activity and short migration distances (15 cm) employed in this study. The results indicate specific parameters which may identify migration phenomena in the subsurface, e.g. trends in the quinoline concentration of a crude oil and trends in the ratio of a crude oils concentration of n -C 16 /dibenzothiophene or n -C 16 /2-methylphenanthrene.

CO2 migration processes in argillaceous rocks: pressure-driven volume flow and diffusion

The capillary sealing efficiency of fine-grained sedimentary rocks has been investigated by gas (CO2, N2) breakthroughexperiments and CO2 diffusion experiments. Experiments were performed on initially fully water-saturated samples. Absolute (single phase) permeability coefficients (kabs), determined by steady-state flow tests, ranged between 6 × 10−22 and 5.5 × 10−19 m2. Maximum effective permeabilities to the gas phase (keff), measured after gas breakthrough, ranged from 1 × 10−23 up to 1.1 × 10−18 m2. Capillary displacement pressures (Pd) ranged from 0.06 to 6.7 MPa. However, for individual claystone samples, gas breakthrough with subsequent pressure-driven volume flow (Darcy flow) was not observed even at much higher differential pressures (15 MPa). In these instances, molecular diffusion is the dominating transport process. It was shown that for nominal permeability coefficients below 10−24 m2, a distinction between pressure-driven volume flow and diffusion processes is no longer possible. Repeated diffusion experiments with CO2 on the same sample plug yielded varying effective diffusion coefficients ranging from 10−9 to 10−11 m2/s. This variability is taken as an indication of complex mineral matrix interactions affecting the molecular transport properties.

3D-modelling of thermal history and simulation of methane and nitrogen migration along the Northeast German seismic DEKORP profile 9601

Abstract The Northeast German Basin (NEGB) is generally regarded as a long-lived intracontinental sedimentary basin. Deeply buried Carboniferous rocks are the main source rocks for hydrocarbon gases and nitrogen in the basin. For the northern part of the NEGB the thermal and burial history was reconstructed and simulated. Open system non-isothermal pyrolysis was used to determine the generation potential of methane and nitrogen and the corresponding kinetic parameters. These experimental data are used in a kinetic model to estimate timing and efficiency of gas generation in the NEGB and to assess, in a subsequent step, the gas migration pathways. Pyrolysis experiments of overmature Carboniferous samples and their corresponding kerogen concentrates indicate that a considerable amount of nitrogen comes from the inorganic matrix, probably ammonium illite. The simulation results reveal that the main methane generation took place during the rapid subsidence of Upper Rotliegend to Middle Triassic sediments. A residual gas potential exists only in the northern parts of the basin.

Gas Transfer Through Clay Barriers

Gas transport through clay-rocks can occur by different processes that can be basically subdivided into pressure-driven flow of a bulk gas phase and transport of dissolved gas either by molecular diffusion or advective water flow (Figure 1, Marschall et al., 2005). The relative importance of these transport mechanisms depends on the boundary conditions and the scale of the system. Pressure-driven volume flow (“Darcy flow”) of gas is the most efficient transport mechanism. It requires, however, pressure gradients that are sufficiently large to overcome capillary forces in the typically water-saturated rocks (purely gas-saturated argillaceous rocks are not considered in the present context). These pressure gradients may form as a consequence of the gravity field (buoyancy, compaction) or by gas generation processes (thermogenic, microbial, radiolytic). Dissolved gas may be transported by water flow along a hydraulic gradient. This process is not affected by capillary forces but constrained by the solubility of the gas. It has much lower transport efficiency than bulk gas phase flow. Molecular diffusion of dissolved gas, finally, is occurring essentially without constraints, ubiquitously and perpetually. Effective diffusion distances are, however, proportional to the square root of time, which limits the relevance of this transport process to the range of tens to hundreds of metres on a geological time scale (millions of years). 2 Process understanding and the quantification of the controlling parameters, like diffusion coefficients, capillary gas breakthrough pressures and effective gas permeability coefficients, is of great importance for up-scaling purposes in different research disciplines and applications. During the past decades, gas migration through fully water-saturated geological clay-rich barriers has been investigated extensively (Thomas et al., 1968, Pusch and Forsberg, 1983; Horseman et al., 1999; Galle, 2000; Hildenbrand et al., 2002; Marschall et al., 2005; Davy et al., 2009; Harrington et al., 2009, 2012a, 2014). All of these studies aimed at the analysis of experimental data determined for different materials (rocks of different lithotype, composition, compaction state) and pressure/temperature conditions. The clay-rocks investigated in these studies, ranged from unconsolidated to indurated clays and shales, all characterised by small pores (2-100 nm) and very low hydraulic conductivity (K < 10-12 m·s-1) or permeability coefficients (k < 10-19 m²). Studies concerning radioactive waste disposal include investigations of both the natural host rock formation and synthetic/engineered backfill material at a depth of a few hundred meters (IAEA, 2003, 2009). Within a geological disposal facility, hydrogen is generated by anaerobic corrosion of metals and through radiolysis of water (Rodwell et al., 1999; Yu and Weetjens, 2009). Additionally, methane and carbon dioxide are generated by microbial degradation of organic wastes (Rodwell et al., 1999; Ortiz et al., 2002; Johnson, 2006; Yu and Weetjens, 2009). The focus of carbon capture and storage (CCS) studies is on the analysis of the long-term sealing efficiency of lithologies above depleted reservoirs or saline aquifers, typically at larger depths (hundreds to thousands of meters). During the last decade, several studies were published on the sealing integrity of clay-rocks to carbon dioxide (Hildenbrand et al., 2004; Li et al., 2005; Hangx et al., 2009; Harrington et al., 2009; Skurtveit et al., 2012; Amann-Hildenbrand et al., 2013). In the context of petroleum system analysis, a significant volume of research has been undertaken regarding gas/oil expulsion mechanisms from sources rocks during burial history (Tissot & Pellet, 1971; Appold & Nunn, 2002), secondary migration (Luo et al., 2008) and the capillary sealing capacity of caprocks overlying natural gas accumulations (Berg, 1975; Schowalter, 1979; Krooss, 1992; Schlomer and Kross, 2004; Li et al., 2005; Berne et al., 2010). Recently, more attention has been paid to investigations of the transport efficiency of shales in the context of oil/gas shale production (Bustin et al., 2008; Eseme et al., 2012; Amann-Hildenbrand et al., 2012; Ghanizadeh et al., 2013, 2014). Analysis of the migration mechanisms within partly unlithified strata becomes important when explaining the 3 origin of overpressure zones, sub-seafloor gas domes and gas seepages (Hovland & Judd, 1988; Boudreau, 2012). The conduction of experiments and data evaluation/interpretation requires a profound process understanding and a high level of experience. The acquisition and preparation of adequate samples for laboratory experiments usually constitutes a major challenge and may have serious impact on the representativeness of the experimental results. Information on the success/failure rate of the sample preparation procedure should therefore be provided. Sample specimens “surviving” this procedure are subjected to various experimental protocols to derive information on their gas transport properties. The present overview first presents the theoretical background of gas diffusion and advective flow, each followed by a literature review (sections 2 and 3). Different experimental methods are described in sections 4.1 and 4.2. Details are provided on selected experiments performed at the Belgian Nuclear Research Centre (SCK-CEN, Belgium), Ecole Centrale de Lille (France), British Geological Survey (UK), and at RWTH-Aachen University (Germany) (section 4.3). Experimental data are discussed with respect to different petrophysical parameters outlined above: i) gas diffusion, ii) evolution of gas breakthrough, iii) dilation-controlled flow, and iv) effective gas permeability after breakthrough. These experiments were conducted under different pressure and temperature conditions, depending on sample type, burial depth and research focus (e.g. radioactive waste disposal, natural gas exploration, or carbon dioxide storage). The interpretation of the experimental results can be difficult and sometimes a clear discrimination between different mechanisms (and the controlling parameters) is not possible. This holds, for instance, for gas breakthrough experiments where the observed transport can be interpreted as intermittent, continuous, capillary- or dilation-controlled flow. Also, low gas flow rates through samples on the length-scale of centimetres can be equally explained by effective two-phase flow or diffusion of dissolved gas.

Correction to: A reference high-pressure CO2 adsorption isotherm for ammonium ZSM-5 zeolite: results of an interlaboratory study

The original version of this article was published open access. Unfortunately, due to a technical issue, the copyright holder name in the online version (HTML and XML) is incorrectly published as “Springer Science+Business Media, LLC, part of Springer Nature 2018”. Instead, it should be “The Author(s) 2018”.

The Dependency of Diffusion Coefficients and Geometric Factor on the Size of the Diffusing Molecule: Observations for Different Clay-Based Materials

In order to investigate in more detail the relation between the size of diffusing molecules and their diffusion coefficients (and geometric factors), diffusion experiments with gases of different size and tritiated water (HTO) have been performed on different clayey samples (Boom Clay, Eigenbilzen Sands, Opalinus Clay, Callovo-Oxfordian Clay, and bentonite with different dry densities). We observed that, for unreactive gases in clayey materials, the effective diffusion coefficient varies with the size of the diffusing molecule and this variation can be described by an exponential or a power law function. The variation of the geometric factor can also be described by an exponential function. The observed experimental relations can be used to estimate diffusion coefficients; by measuring experimentally in clay the effective diffusion coefficient of two unreactive dissolved gases with a different size, the diffusion coefficients of other dissolved gases (with a size in between the two measured gases) can be estimated by using the fitted exponential relationship.

Gas breakthrough and flow tests on opalinus clay - Ambiguities in the interpretation of experimental data

We present and discuss the results of a comparative study of two laboratory procedures for the determination of the capillary gas breakthrough pressures of low-permeable lithotypes with intrinsic permeability coefficients below 10-20 m². Well-characterized and mineralogical homogeneous core section of the Opalinus Clay (Mont Terri) were used in this study. The experimental conditions corresponded to a depth of approximately 1500 m depth, representative of a typical CO2 storage scenario (30 MPa confining pressure, 45°C).