Capillary Heterogeneity in Sandstone Rocks During CO2/Water Core-flooding Experiments

AbstractWe have successfully applied a novel experimental technique to measure drainage capillary pressure curves in reservoir rocks with representative reservoir fluids at high temperatures and pressures. The method consists of carrying out 100% CO2 flooding experiments at increasingly higher flow rates on a core that is initially saturated with water and requires that the wetting-phase pressure is continuous across the outlet face of the sample. Experiments have been carried out on a Berea Sandstone core at 25 and 50°C and at 9MPa pore pressure, while keeping the confining pressure at 12MPa. Measurements are in good agreement with data from mercury intrusion porosimetry. The technique possesses a great potential of applicability due to the following reasons: (a) it can be applied in conjunction with steady-state relative permeability measurements, as it shares a very similar experimental configuration; (b) it is faster than traditional (porous-plate) techniques used for measuring capillary pressure on rock cores with reservoir fluids; (c) by comparison with results from mercury porosimetry, it allows for the estimation of the interfacial and wetting properties of the CO2/water system, the latter being unknown for most rocks; (d) by combination with X-ray CT scanning, the method allows for the observation of capillary pressure–saturation relationships on mm-scale subsets of the rock core. The latter are of high relevance as they directly and non- destructively measure capillary pressure curve heterogeneity in sandstone rocks

Assessing the Potential of Mineral Carbonation with Industrial Alkalinity Sources in the U.S

AbstractThe availability of industrial alkalinity sources is investigated to determine their potential for the mineral carbonation of CO2 from point-source emissions in the United States. The available aggregate markets are investigated as potential sinks for the mineralized CO2 products. Additionally, a life-cycle assessment of aqueous mineral carbonation suggests that a variety of alkalinity sources and process configurations are capable of net CO2 reductions. The CO2 storage potential of mineral carbonation was estimated using the life-cycle assessment results and alkalinity source availability

Impact of Reservoir Conditions on CO2-brine Relative Permeability in Sandstones

AbstractWe demonstrate experimentally, that the spatial distribution of fluids in the pore space is the primary control on CO2 relative permeability, and that the importance of spatial heterogeneity in rock properties such as capillarity, porosity and permeability on fluid distributions is controlled by viscous forces. The importance of viscous forces during drainage core floods is evaluated using fluid viscosity as the varying parameter in CO2-brine core floods, and flow rate in N2-water core floods. A transition from a heterogeneous to a homogeneous displacement is observed with increasing viscous force applied to the core. During capillary dominated core flooding the relative permeability is sensitive to flow rate and viscosity. Homogeneous displacements have an invariant relative permeability and as such are a measure of the true relative permeability of the rock

A Study of Residual Carbon Dioxide Trapping in Sandstone

AbstractThe storage of carbon dioxide (CO2) in deep brine-filled geologic strata is largely seen as one of the most important tools for CO2 emissions mitigation on industrial scales. Residual trapping is a major factor in determining the ultimate extent of CO 2 migration within the reservoir. At the same time there are few studies that have observed the trapping characteristics for CO2-brine systems in permeable rocks, including the impact of reservoir conditions, and this remains a major uncertainty for geologic CO 2 storage. In this experimental study, we take advantage of flow conditions that enhance the capillary end effect so that a large saturation gradient across the core is created during drainage with CO2. We observe residual trapping of CO2 in sandstone rocks across the wide range of conditions representative of subsurface reservoirs suitable for CO2 storage. The observations are made using a reservoir condition core-flooding laboratory that includes high precision pumps, accurate temperature control, the ability to recirculate fluids for weeks at a time and a rotating X-ray CT scanner. Application of residual trapping curves in reservoir scale simulation has also been discussed

Characterising Drainage Multiphase Flow in Heterogeneous Sandstones

In this work, we analyse the characterisation of drainage multiphase flow properties on heterogeneous rock cores using a rich experimental dataset and mm-m scale numerical simulations. Along with routine multiphase flow properties, 3D sub-metre scale capillary pressure heterogeneity is characterised by combining experimental observations and numerical calibration, resulting in a 3D numerical model of the rock core. The uniqueness and predictive capability of the numerical models are demonstrated by accurately predicting the experimentally measured relative permeability of N2-DI water and CO2-brine systems in two distinct sandstone rock cores across multiple fractional flow regimes and total flow rates. The numerical models are used to derive equivalent relative permeabilities, which are upscaled functions incorporating the effects of sub-metre scale capillary pressure. The functions are obtained across capillary numbers which span four orders of magnitude, representative of the range of flow regimes that occur in subsurface CO2 injection. Removal of experimental boundary artefacts allows the derivation of equivalent functions which are characteristic of the continuous subsurface. We also demonstrate how heterogeneities can be re-orientated and re-structured efficiently to obtain large amounts of information about expected flow regimes through different small-scale rock structures. This analysis shows how combined experimental and numerical characterisation of rock samples can be used to derive equivalent flow properties from heterogeneous rocks

Calibration of astigmatic particle tracking velocimetry based on generalized Gaussian feature extraction

Flow and transport in porous media are driven by pore scale processes. Particle tracking in transparent porous media allows for the observation of these processes at the time scale of ms. We demonstrate an application of defocusing particle tracking using brightfield illumination and a CMOS camera sensor. The resulting images have relatively high noise levels. To address this challenge, we propose a new calibration for locating particles in the out-of-plane direction. The methodology relies on extracting features of particle images by fitting generalized Gaussian distributions to particle images. The resulting fitting parameters are then linked to the out-of-plane coordinates of particles using flexible machine learning tools. A workflow is presented which shows how to generate a training dataset of fitting parameters paired to known out-of-plane locations. Several regression models are tested on the resulting training dataset, of which a boosted regression tree ensemble produced the lowest cross-validation error. The efficiacy of the proposed methodology is then examined in a laminar channel flow in a large measurement volume of 2048, 1152 and 3000 μm in length, width and depth respectively. The size of the test domain reflects the representative elementary volume of many fluid flow phenomena in porous media. Such large measurement depths require the collection of images at different focal levels. We acquired images at 21 focal levels 150 μm apart from each other. The error in predicting the out-of-plane location in a single slice of 240 μm thickness was found to be 7 μm, while in-plane locations were determined with sub-pixel resolution (below 0.8 μm). The mean relative error in the velocity measurement was obtained by comparing the experimental results to an analytic model of the flow. The estimated displacement errors in the axial direction of the flow were 0.21 pixel and 0.22 pixel at flows rates of 1.0 mL/h and 2.5 mL/h, respectively. These results demonstrate that it is possible to conduct three-dimensional particle tracking in a representative elementary volume based on a simple apparatus comprising a microscope with standard brightfield illumination and a camera with CMOS sensor