Experimental investigations in CO2 sequestration and shale caprock integrity

More than sixty percent (60%) of conventional hydrocarbon reservoirs which are potential CO2 repositories are sealed by tight shale caprock. The geochemical reactivity of shale caprock during CO2 diffusive transport needs to be included in the reservoir characterization of potential CO2 sequestration sites as slow reactive transport processes can either strengthen or degrade seal integrity over the long term. Several simulation results had predicted that influx-induced mineral dissolution/precipitation reactions within shale caprocks can continuously reduce micro-fracture networks, while pressure and effective-stress transformation first rapidly increase then progressively constrict them. This experimental work applied specific analytical techniques in investigating changes in surface/near-surface properties of crushed shale rocks after exposure (by flooding) to CO2-brine for a time frame ranging between 30 days to 92 days at elevated pressure and fractional flow rate. Initial capillary entry parameters for the shale were estimated from digitally acquired pressure data evolution. Flooding of the shale samples with CO2-brine was followed by geochemical characterization of the effluent fluid and bulk shale rock through ICP-OES, XRD, EDS and pH measurements. Nano-scale measurement of changes in internal specific surface area, pore volume and linear/cumulative pore size distribution (using the BET Technique) showed that changes in the shale caprock due to geochemical interaction with aqueous CO2 can affect petrophysical properties. The intrinsically low permeability in shale may be altered by changes in surface properties as the effective permeability of any porous medium is largely a function of its global pore geometry. Diffusive transport of CO2 as well as carbon accounting could be significantly affected over the long term. The estimation of dimensionless quantities such as Peclet (Pe) and Peclet-Damkohler (PeDa) Numbers that are associated with geochemical reactivity of rocks and acidic fluid transport through porous media gave insight into the impact of diffusion and reaction rate on shale caprock in CO2 sequestration

Diagenesis and Formation Stress in Fracture Conductivity of Shaly Rocks; Experimental-Modelling Approach in CO2-Rock Interactions

In large scale subsurface injection of carbon dioxide (CO2) as obtainable in carbon sequestration programs and in environmentally friendly hydraulic fracturing processes (using supercritical CO2), long term rock-fluid interaction can affect reservoir and seal rocks properties which are essential in monitoring the progress of these operations. The mineralogical components of sedimentary rocks are geochemically active particularly under enormous earth stresses, which generate high pressure and temperature conditions in the subsurface. While geomechanical properties such as rock stiffness, Poisson’s ratio and fracture geometry largely govern fluid flow characteristics in deep fractured formations, the effect of mineralization can lead to flow impedance in the presence of favorable geochemical and thermodynamic conditions. Simulation results suggested that influx-induced mineral dissolution/precipitation reactions within clay-based sedimentary rocks can continuously close micro-fracture networks, though injection pressure and effective-stress transformation first rapidly expand the fractures. This experimental modelling research investigated the impact of in-situ geochemical precipitation at 50°C and 1,000 psi on conductivity of fractures under geomechanical stress conditions. Geochemical analysis were performed on different samples of shale rocks, effluent fluid and recovered precipitates both before and after CO2-brine flooding of crushed shale rocks at high temperature and pressure conditions. Bulk rock geomechanical hardness was determined using micro-indentation. Differential pressure drop data across fractured composite core were also measured with respect to time over a five a day period. This was used in estimating the conductivity of the fractured core. Three experimental runs per sample type were carried out in order to check the validity of observed changes. The results showed that most significant diagenetic changes in shale rocks after flooding with CO2-brine reflect in the effluent fluid with calcium based minerals dissolving and precipitating under experimental conditions. Major and trace elements in the effluent fluid (using ICP-OES analysis) indicated that multiple geochemical reactions are occurring with almost all of the constituent minerals participating. The geochemical composition of precipitates recovered after the experiments showed diagenetic carbonates and opal (quartz) as the main constituents. The bulk rock showed little changes in composition except for sharper peaks on XRD analysis, suggesting that a significant portion of amorphous content of the rocks have been removed via dissolution by the slightly acid CO2-brine fluid that was injected. However total carbon (TOC) analysis showed a slight increase in carbon content of the bulk rock. Micro-indention results suggested a slight reduction in the hardness of the shale rocks and this reduction appear dependent on quartz content. The differential pressure drop, its 1st derivative and estimated fracture conductivity suggests that reactive transport of dissolved minerals can possibly occlude fracture flow path at varying degree depending on equivalent aperture width, thereby improving caprock integrity with respect to leakage risks under CO2 sequestration conditions. An exponential-natural logarithm fit of the fracture conductivity can be obtained and applied in discrete fracture network modelling. The fit yielded lower and upper boundary limits for fracture conductivity closure. Higher temperature and pressure conditions of experimental investigations may be needed to determine the upper limit of shale rock seal integrity tolerance, under conditions that are similar to sequestration of CO2 into deep and hot sedimentary rocks

Experimental investigations of caprock integrity in CO\u3csub\u3e2\u3c/sub\u3e sequestration

The geochemical reactivity of shale caprock during post-injection CO diffusive transfer should be included in the reservoir characterization of CO sequestration sites as slow reactive transport processes can either improve or degrade seal integrity over the long term. Simulation results reported by various researchers suggested that influx-induced mineral dissolution/precipitation reactions within shale caprocks can continuously close micro-fracture networks, while pressure and effective-stress transformation first rapidly expand then progressively constrict them. This experimental work applied specific analytical techniques in investigating changes in mineralogical and microstructural properties of crushed shale rocks after exposure (by flooding) to CO -brine for a time frame ranging between 30 days to 92 days at elevated pressure and fractional flow rate. The initial mineralogical composition in the samples showed bulk clay, quartz and feldspar as the major components of the formation. Initial capillary entry parameters for the shale were estimated from digitally acquired injection pressure profile. Flooding of the shale samples with CO -brine was followed by geochemical characterization of the effluent fluid and bulk shale rock through pH and XRD measurements. Nano-scale measurement of changes in internal specific surface area and cumulative pore size distribution (using the BET Technique) revealed that changes in the shale caprock due to geochemical interaction with aqueous CO can affect petrophysical properties. The naturally low permeability in shale may be altered by changes in specific surface area as the effective permeability of any porous medium is largely a function of its total pore geometry/volume, and particularly the pore throat-diameter. The geochemical reactivity of shale caprocks through acidic fluid transport in interconnected pore networks gave insight into the impact of diffusion and reaction rate on shale caprock integrity in CO sequestration. 2 2 2 2 2

Fracture Conductivity Modelling in Experimental Shale Rock Interactions with Aqueous CO\u3csub\u3e2\u3c/sub\u3e

In large scale subsurface injection of carbondioxide (CO ) as obtainable in carbon sequestration programs and in environmentally friendly hydraulic fracturing processes (using supercritical CO ), long term rock-fluid interaction can affect reservoir and seal rocks properties which are essential in monitoring the progress of these operations. The mineralogical components of sedimentary rocks are geochemically active particularly under enormous earth stresses, which generate high pressure and temperature conditions in the subsurface. While geomechanical properties such as rock stiffness, Poisson\u27s ratio and fracture geometry largely govern fluid flow characteristics in deep micro-fractured formations. Simulation results suggested that influx-induced mineral dissolution/precipitation reactions within clay-based sedimentary rocks can continuously close micro-fracture networks, though injection pressure and effective-stress transformation first rapidly expand the fractures. This experimental modelling research investigated the impact of in-situ geochemical precipitation on conductivity of fractures under geomechanical stress conditions. Bulk rock geomechanical hardness was determined using Vickers\u27 micro-indentation. Differential pressure drop data across fractured composite core were also measured with respect to time over a five day period. This was used in estimating the conductivity of the artificially fractured cores with 25 μm-bore microtubings embedded. Three experimental runs per sample types were carried out in order to check the repeatability of observed changes. The results showed that most significant diagenetic changes in shale rocks after flooding with CO -brine, reflect in the effluent fluid with predominantly calcium based minerals dissolving and precipitating under experimental conditions. Micro-indentation results suggested slight reduction in the hardness of the shale rocks and this reduction appears dependent on diagenetic quartz content. Estimated fracture conductivity indicated that reactive transport of dissolved minerals can occlude micro-fracture flow paths, thereby improving caprock seal integrity with respect to leakage risk under CO sequestration conditions. 2 2 2

Diagenetic influence on fracture conductivity in tight shale and CO\u3csub\u3e2\u3c/sub\u3e sequestration

Most sedimentary rock formations (tight or highly porous) have geochemical characteristics that can lead to significant reactive ion exchange processes in aqueous media in the presence of carbondioxide. While geomechanical properties such as rock stiffness, poisson\u27s ratio and fracture geometry largely govern fluid flow characteristics in deep fractured formations, the effect of mineralization can lead to flow impedance in the presence of favorable geochemical and thermodynamic conditions. Shale caprock which seals more than two-thirds of oil and gas reservoirs have natural fractures that are unevenly distributed in the geosystem. Experimental works which employed the use of analytical techniques such ICP-OES, XRD, SEM/EDS and BET techniques in investigating diagenetic and micro-structural property of crushed shale caprock/CO -brine system concluded that net precipitation reaction processes can affect the distribution of petrophysical nanopores in the seal rock. XRD analyses indicated the presence of quartz, feldspar and bulk clays (muscovite, chlorite, kaolinite with the quantitative mineralogy estimates varing significantly with respect to quartz-bulk clay ratio in the six samples that were analyzed. Quartz and feldspar are reactive at low pH with the tendency to impact seal integrity. The presence of quartz in shale gives a reasonably high mechanical strength whereas clays make shale easily deformable with a potential to creep. The results showed that geochemical precipitates can be formed such that fluid flow through open micro and macro fractures may be constrained. Peclet-Damköhler reactive flow dimensionless number confirmed diffusion as the governing transport mechanism in aqueous CO -caprock interaction. Simulation results reported by various researchers suggested that influx-induced mineral dissolution/precipitation reactions within shale caprocks can continuously close micro-fracture networks, while pressure and effective-stress transformation first rapidly expand then progressively constrict them. The presence of traces of carbonate streaks which are soluble in low acidic pH environment is undesirable in caprocks. This experimental research investigated the impact of in-situ geochemical precipitation on conductivity of open micro-fractures under geomechanical stress conditions. Fracture conductivity in core samples of shale caprock with known mineralogical composition from different formations where CO injection is on-going are quantitatively evaluated under axial and radial stress using pulse-decay liquid permeametry/core flooding systems. This system incorporates high temperature and pressure conditions. The shale caprock cores were obtained during the drilling of vertical and short-radii injection wells in Alabama and South Louisiana as part of reservoir characterization for CO sequestration/enhanced oil recovery projects. Nano-indentation of multiple representative samples was applied to determine geomechanical properties evolution which can be correlated with the geochemistry of the shale caprock. This information will be useful as input data for simulation of subsurface CO plume in contact with overlaying shale caprock. Modeling of the diffusion controlled fluid flow and induced fracture diagenetic alterations in the shale caprocks are performed using CMG-GEM numerical simulators with imposed axial and radial geomechanical stress. The possibility of rock-fluid geochemical interactions constricting natural fracture conductivity in long term subsurface CO sequestration can lead to significant improvement in shale caprock seal integrity and mitigate injection induced perturbation. 2 2 2 2 2

Geo-spatial distribution of serologically detected bovine Foot and Mouth Disease (FMD) serotype outbreaks in Ilesha Baruba, Kwara State-Nigeria

ABSTRACT The study was aimed at assessing the prevalence and distribution of bovine Foot and Mouth Disease (FMD) serotypes in Ilesha Baruba, Kwara stateNigeria. To identify the source of epidemics, geospatial analysis was done on the FMD outbreak locations (n=15) using Global Positioning Service (GPS) device (Etrex R ). Randomly sampled bovine sera (n=64) from herd representatives were subjected to FMD 3ABC enzyme-linked immunosorbent assay (FMD 3ABC ELISA) and solid-phase competitive ELISA (SP-cELISA), for the screening and serotyping of FMD virus, respectively. Through ELISA, the FMD serotypes detected in this study were-serotype O (83%; n=53/64), serotype A (7.8%; n=5/64), serotype vaccine O (1.6%; n=1/64)), and serotype vaccine SAT2 (1.6%; n=1/64). Multiple serotypes were observed in two different combinations; these were O and A (4.7%; n=3/64), and O and SAT2 (1.6%; n=1/64). FMD multiple serotype infections were associated with absence of cross-immunity between serotypes and cross reactivity enhanced by clustered herds, highland study area topography, road and river interconnectivity, possible human settlements, activities and traffic. This study provides baseline information on geo-spatial distribution, and identification of prevalent FMD serotypes in Ilesha Baruba, Kwara state-Nigeria

Diagenetic Influence of Aqueous CO2 on Fracture Conductivity of Shaly Rocks

Most sedimentary rock formations (tight or highly porous) have geochemical characteristics that can lead to significant reactive ion exchange processes in aqueous media in the presence of carbondioxide. While geomechanical properties such as rock stiffness, Poisson\u27s ratio and fracture geometry largely govern fluid flow characteristics in deep fractured formations, the effect of mineralization can lead to flow impedance in the presence of favorable geochemical and thermodynamic conditions. Shale caprock which seals more than 60% of oil and gas reservoirs have natural fractures that are unevenly distributed in the geosystem. Experimental works which employed the use of analytical techniques such ICP-OES, XRD, and SEM/ EDS techniques in investigating diagenetic and micro-structural property of crushed shale caprock/CO - brine system concluded that net precipitation reaction processes can affect the distribution of petrophysi- cal nanopores in the seal rock. The results showed that geochemical precipitates can be formed such that fluid flow through open micro and macro fractures may be constrained. Simulation results reported by various researchers suggested that influx-induced mineral dissolution/precipitation reactions within shale caprocks can continuously close micro-fracture networks, while pressure and effective-stress transformation first rapidly expand then progressively constrict them. This experimental research investigates the impact of in-situ geochemical precipitation on conductivity of open micro-fractures under geomechanical stress conditions. Fracture conductivity in core samples of shale caprock with known mineralogical composition from different formations where CO injection is on-going are quantitatively evaluated under axial and radial stress using pressure pulse-decay liquid permeametry/core flooding systems. Modeling of the diffusion controlled fluid flow and induced fracture diagenetic alterations in the shale caprocks can be performed using CMG-GEM with artificial core imposing axial and radial geomechanical stress. The possibility of rock-fluid geochemical interactions constricting natural fracture conductivity in long term subsurface CO sequestration can lead to significant improvement in shale caprock seal integrity and mitigate injection induced geomechanical perturbation. 2 2

Geochemical Markers in Shale-CO\u3csub\u3e2\u3c/sub\u3e Experiment at Core Scale

Most sedimentary rock formations (tight or highly porous) have geochemical characteristics that can lead to significant reactive ion exchange processes in aqueous media in the presence of carbon dioxide. The injection of carbon dioxide (CO ) in large scale as obtainable in carbon sequestration programs and in environmentally friendly hydraulic fracturing processes (using supercritical CO ), long term rock-fluid interaction can affect reservoir and seal rocks properties. The mineralogical components of sedimentary rocks are geochemically active particularly under enormous earth stresses, which generate high pressure and temperature conditions in the subsurface. It has been postulated that the effect of mineralization can lead to flow impedance in the presence of favourable geochemical and thermodynamic conditions. Simulation results suggested that influx-induced mineral dissolution/precipitation reactions within clay-based sedimentary rocks can continuously close micro-fracture networks, though injection pressure rapidly expand the fractures. This experimental modelling research investigated the impact of in-situ geochemical precipitation on conductivity of fractures. Geochemical analysis were performed on four different samples of shale rocks, effluent fluids and recovered precipitates both before and after CO -brine flooding of crushed shale rocks at moderately high temperature and pressure conditions. Three experimental runs per sample types were carried out in order to check the repeatability of observed changes. The results showed that most significant diagenetic changes in shale rocks after flooding with CO -brine, reflect in the effluent fluid with predominantly calcium based minerals dissolving and precipitating under experimental conditions. Major and trace elements in the effluent fluid indicated that multiple geochemical reactions are occurring with almost all of the constituent minerals participating. The geochemical composition of precipitates recovered after the experiments showed diagenetic carbonates and opal (quartz) as the main constituents. The bulk rock showed little changes in composition except for sharper and more refined peaks on XRD analysis, suggesting that a significant portion of the amorphous content of the rocks have been removed via dissolution by the slightly acid CO -brine fluid that was injected. It can be inferred that convective reactive transport of dissolved minerals are involved in nanoscale precipitation-dissolution processes in shale under carbon sequestration conditions. 2 2 2 2