Seismic reflectivity of a carbon dioxide flux

 In the context of the geological storage of carbon dioxide (CO2), thecharacterization of the injected CO2 in a reservoir is of primeimportance for volume capacity evaluation and long-term siteperformance. In this article, we aim to characterize a CO2 accumulationin a deep layered aquifer by means of its seismic reflectivity. Formodeling the vertical distribution of CO2 saturation in the reservoir,we solve the Buckley-Leverett equation with discontinuous flux function,which describes two-phase flow in porous stratified media. To solve thisequation numerically we employ a finite-difference relaxation scheme.The scheme entails an upwinding reconstruction for the spatialderivatives and an implicit-explicit Runge-Kutta scheme for timeintegrations. Once the vertical distribution of CO2 is obtained, we usea matrix propagator algorithm to compute in the frequency domain, thegeneralized reflectivity of the reservoir due to the injected gas. Thebehavior of this reflectivity controls the amplitude of seismic wavereflections and strongly conditions the detectability of the CO2 volumein the space-time domain. The numerical approach used in this article iseasy to implement and allows to quantify the reflectivity of the carbondioxide distribution in a practical way. We show that the frequencybehavior of the reservoir reflectivity may help to interpret thevertical accumulation of CO2, which can be useful as a basis fortime-lapse geophysical monitoring.Fil: Gómez, Julián Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Departamento de Geofísica Aplicada; ArgentinaFil: Ravazzoli, Claudia Leonor. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Departamento de Geofísica Aplicada; Argentin

On the use of vertically averaged models to simulate CO2 migration in a layered saline aquifer

Geologic and flow characteristics such as permeability and porosity, capillary pressure, geologic structure, and thickness all influence and affect CO2 plume distribution to varying degrees. These parameters do not necessarily act independently. Depending on the variations in these parameters one may dominate the shape and size of the plume. In this master thesis, we consider the long-term fate and migration of a large CO2 plume that takes place in a heterogeneous (two-layer) sloping saline aquifer. We consider a vertical equilibrium (VE) mathematical model to study the effect of two different permeability layers on the shape, speed and migrated distance of the CO2 plume. The layer-permeability-ratio is k2/k1, where k2 and k1 are the permeabilities in the upper and lower layer of the aquifer, respectively. We also study the effect the thickness ratio of the lower permeability(h=H/2, h=H/4, h=H/8), where H is the thickness of the aquifer. We attain these goals by comparing the simulation results of Eclipse and VE simulators, where both simulate the movement of CO2 plume in homogeneous and layered aquifers. A VE model has been built considering one-dimensional flow in the x-direction, due to the big difference in scale length between vertical and horizontal directions. We model a 2D vertical section in Eclipse simulator, taking the vertically averaged of this section ends up with a 1D results that can compared with the VE solution. Our results shows that the variations in the vertical permeability layers may have a dramatic effects on the CO2 plume shape. Relatively lower permeability layer reduces the velocity of CO2 through it, and an increase of CO2 saturation occurs below this layer. At early time, the build up in saturation increases, and the lateral growth of the CO2 immediately below this layer increases. At later time, the saturation decreases and the vertical flow of the CO2 in this layer increases. The k2/k1 ratio and thickness of the lower permeability layer determines the plume shape and distance migrated. In some of our simulations, the results show two connected/disconnected plumes.Master i Anvendt og beregningsorientert matematikkMAMN-MABMAB39

Modelling the two-phase plume dynamics of CO2 leakage into open shallow waters

A numerical model of two-phase plume developments in a small scale turbulent ocean is proposed and designed as a fundamental study to predict the near field physicochemical impacts and biological risk to the marine ecosystem from CO2 leakage from potential carbon storage locations around the North Sea. New sub-models are developed for bubble formation and drag coefficients using in-situ measurements from videos of the Quantifying and monitoring potential ecosystem Impacts of geological Carbon Storage (QICS) experiment. Existing sub-models such as Sherwood numbers and plume interactions are also compared, verified and implemented into the new model. Observational data collected from the North Sea provides the ability to develop and verify a large eddy simulation turbulence model, limited to situations where the non-slip boundary wall may be neglected. The model is then tested to assimilate the QICS experiment, before being applied to potential leakage scenarios around the North Sea with key marine impacts from pCO2 and pH changes. The most serious leak is from a well blowout, with maximum pH changes of up to -2.7 and changes greater than -0.1 affecting areas up to 0.23 km2. Other scenarios through geological structures would be challenging to detect with pH changes below -0.27

Modelling CO2 sequestration in deep saline aquifers

In spite of the large number of research works on carbon capture and sequestration (CCS), the migration and behaviour of CO2 in the subsurface (i. e. strata below the earth’s surface) still needs further understanding and investigations with the aim of encouraging the governmental policy makers to adopt CCS technology as one of the most viable means to tackle the global warming threats. In this research work, a series of numerical simulations has been carried out using STOMP-CO2 simulation code to determine the flow behaviour and ultimate fate of the injected supercritical carbon dioxide (scCO2) into saline aquifers in medium terms of storage (i. e. few thousand years). The characteristics of the employed simulator, including the mathematical algorithm, governing equations, equations of states and phase equilibria calculations are explained in details. [Continues.

Geomechanical Stability Analysis for Co2 Sequestration in Carbonate Formation

Geomechanical analysis is one of the fundamental pillars to build up the confidence of geological sequestration of CO2. Large scale CO2 sequestration in deep carbonate formation is a complicated geological process, which will non-reversibly transform the presumed equivalent and stable status of a sedimentary basin that formed over millions of years: chemically, hydraulically, geothermally, and geomechanically. In this dissertation, thermoporoelasticity guides the theoretical establishment of a conservative baseline for the geomechanical stability analysis of CO2 sequestration. Extensive laboratory tests, including CO2 flooding tests, permeability tests, uniaxial and triaxial tests, Brazilian tensile strength tests, poroelasticity tests, point load tests, and fracture toughness tests, etc, were conducted on Indiana limestone and Pierre shale to investigate the effects of CO2 sequestration on storage rock and caprock. Numerical simulations using finite difference method of FLAC3D were also conducted to understand the mechanism of strain localization due to pore pressure fluctuation. Based on these laboratory and numerical tests, it is concluded that two mechanisms are competing for rock failures in deep carbonate formations during CO2 sequestration. One is the faulting induced by pore-pressure buildup, and another is the compaction failure because of rock quality deterioration due to exposure to CO2 enriched solution. Fracture toughness measurements on limestone and shale suggest that the fracture toughness of target formation may not be necessarily lower than that of cap rock formation; then the fractures developed in target formation may be easily extended to the cap rock formation, ruining the sealing mechanism. As such, preventing extensive fracturing, and monitoring the seismicity in target formation are essential. Finally, the potential problems of CO2 sequestration in the Williston Basin were investigated. The in-situ stress regime of the Williston Basin was estimated as a mixture of normal and strike-slip faulting regimes, in favor of a vertical or sub-vertical fracture development pattern, which is negative to the CO2 sequestration. However, as the basin is not very close to an incipient failure, compaction failures are expected to be more pronounced, and naturally occurred geological phenomena, stylolites, will help to understand the CO2 sequestration in deep carbonate formation in the long run

Seismic reflectivity of a carbon dioxide flux

In the context of the geological storage of carbon dioxide (CO2), thecharacterization of the injected CO2 in a reservoir is of primeimportance for volume capacity evaluation and long-term siteperformance. In this article, we aim to characterize a CO2 accumulationin a deep layered aquifer by means of its seismic reflectivity. Formodeling the vertical distribution of CO2 saturation in the reservoir,we solve the Buckley-Leverett equation with discontinuous flux function,which describes two-phase flow in porous stratified media. To solve thisequation numerically we employ a finite-difference relaxation scheme.The scheme entails an upwinding reconstruction for the spatialderivatives and an implicit-explicit Runge-Kutta scheme for timeintegrations. Once the vertical distribution of CO2 is obtained, we usea matrix propagator algorithm to compute in the frequency domain, thegeneralized reflectivity of the reservoir due to the injected gas. Thebehavior of this reflectivity controls the amplitude of seismic wavereflections and strongly conditions the detectability of the CO2 volumein the space-time domain. The numerical approach used in this article iseasy to implement and allows to quantify the reflectivity of the carbondioxide distribution in a practical way. We show that the frequencybehavior of the reservoir reflectivity may help to interpret thevertical accumulation of CO2, which can be useful as a basis fortime-lapse geophysical monitoring.Facultad de Ciencias Astronómicas y Geofísica

Buoyancy-driven flow in a confined aquifer with a vertical gradient of permeability

We examine the injection of fluid of one viscosity and density into a horizontal permeable aquifer initially saturated with a second fluid of different viscosity and density. The novel feature of the analysis is that we allow the permeability to vary vertically across the aquifer. This leads to recognition that the interface may evolve as either a rarefaction wave that spreads at a rate proportional to$t$, a shock-like front of fixed length or a mixture of shock-like regions and rarefaction-wave-type regions. The classical solutions in which there is no viscosity ratio between the fluids and in which the formation has constant permeability lead to an interface that spreads laterally at a rate proportional to$t^{1/2}$. However, these solutions are unstable to cross-layer variations in the permeability owing to the vertical shear which develops in the flow, causing the structure of the interface to evolve to the rarefaction wave or shock-like structure. In the case that the viscosities of the two fluids are different, it is possible that the solution involves a mixture of shock-like and rarefaction-type structures as a function of the distance above the lower boundary. Using the theory of characteristics, we develop a regime diagram to delineate the different situations. We consider the implications of such heterogeneity for the prediction of front locations during$\text{CO}_{2}$sequestration. If we neglect the permeability fluctuations, the model always predicts rarefaction-type solutions, while even modest changes in the permeability across a layer can introduce shocks. This difference may be very significant since it leads to the$\text{CO}_{2}$plume occupying a greater fraction of the pore space between the injector and the leading edge of the$\text{CO}_{2}$front in a layer of the same mean permeability. This has important implications for estimates of the fraction of the pore space that the$\text{CO}_{2}$may access.</jats:p