MRST - MATLAB Reservoir Simulation Toolbox

Interactive Tool for Exploring Storage Capacities

Introduction

exploreCapacity is a demonstration tool for rapid exploration of storage capacities of geological formations in the Norwegian North Sea. It shows how different factors such as aquifer geometry, temperature and pressure regime, rock and fluid properties may affect the final estimate, based on the methodology described in this article.

After the user has chosen a geological formation and specified the involved parameters, an estimate of total trapping capacity is provided, broken down by trapping mechanism (structural, residual or dissolution trapping).

The tool is intended to be used for demonstrational and educational purposes, as the data involved is too limited to predict actual capacity with any confidence.

 

Launching the application

First, ensure that the geological datasets have been downloaded. This can be done in a semi-automatic fashion by launching the graphical dataset download manager as follows:

mrstDatasetGUI;

Choose the CO2Atlas entry from the menu on the left and click the Download button. These public datasets are provided by the Norwegian Petroleum Directorate. (We further discuss their use with MRST-CO2lab here).

The demonstration tool itself can be launched by ensuring the co2lab module is loaded and simply typing its name:

mrstModule add co2lab % ensure that the co2lab module is loaded
exploreCapacity;      % run the application

The exploreCapacity script can take additional arguments to change various parameters that are not available through the graphical user interface. For details, refer to this section.

NB: In release MRST2015b, an error in the code prevents the tool from launching. To fix this, change line 29 to:

var.CO2 = CO2props('sharp_phase_boundary', true);

 

 

Figure 1: exploreCapacity application interface (click for larger image)

 

User interface

After launching the application, the user is presented with the interface shown in Figure 1. On the left side of the interface is a graphical window where the currently active geological formation is displayed. Below this window is a pull-down menu where the user can choose a different formation. There are 16 formations available. The default is the Utsira formation (as shown here).

A set of radio buttons at the upper right side of the interface allows the user to specify what information should be shown along with with the geological formation in the graphical display. Below this area, a set of sliders allows the user to adjust various relevant parameters.

On the bottom right side, the current trapping capacity estimate is shown. The total figure is presented first, then its breakdown into structural, residual and dissolution trapping capacity.

Graphical display

The currently active model is shown in the graphical display. Unless the 'caprock topography' option is active, it is possible to rotate and inspect the model in three dimensions by clicking and dragging. The different display options are shown in the table below using the default Utsira formation as an examples. Notice that in some of the plots, we have changed the colormap and also used a high-resolution sampling of CO2 properties to avoid visual artifacts near the transition line from supercritical to gas phase. (Click on each image to view a larger version).

Caprock depth: The model is drawn with a colorfield indicating the depth of the caprock. This is the default property shown at startup.

Formation thickness: The model is drawn with a colorfield indicating the thickness of the formation.

Caprock temperature: The model is drawn with a colorfield indicating the ambient temperature at the depth of the caprock. This depends on the temperature gradient (adjustable) and the seafloor temperature (can be specified at startup).

Caprock pressure: The model is drawn with a colorfield indicating the fluid pressure at the depth of the caprock. This depends on the hydrostatic pressure, and the specified deviation from this pressure. The hydrostatic pressure depends on the fluid density (can be specified at startup), and the specified deviation can be adjusted using the corresponding slider.

Caprock topography: The model is drawn as a topographical map, with structural traps and spill paths between traps indicated. 3D rotation is not possible when this view is selected.

Caprock CO2 density: The model is drawn with a colorfield indicating the CO2 density at caprock temperature and pressure. The density is specified by an equation of state.

Total capacity: The model is drawn with a colorfield indicating the total trapping capacity of each vertical pillar (i.e. structural, residual and dissolution trapping combined).

Structural trap capacity: The model is drawn as a wireframe with all structural traps overlaid, colored by their trapping capacity in megatons. Local CO2 density is used to compute the involved figures.

Reachable structural capacity: The model is drawn with a colorfield that indicates how much structural trapping capacity can be reached by gravity-driven migration from a given location. In other words, each cell is drawn with a color representing the combined capacity of all structural traps ultimately reachable from injection at this location.

Sliders

The following parameters can be adjusted using the sliders:

  • Temperature gradient

    Specify how quickly temperature rises with physical depth, in degrees (centigrade) per kilometer of depth. This variable affects trapping capacity through its impact on CO2 density.

  • Pressure deviation from hydrostatic

    A value of zero means that fluid pressure is considered hydrostatic. A negative value specifies underpressure and a positive value overpressure. This variable affects trapping capacity through the impact of pressure on CO2 density.

  • Residual CO2 saturation

    This variable specifies the average residual CO2 value in the aquifer, expressed as fraction of pore space. This is a property of the rock, and refers to the amount of CO2 that is left behind as the mobile gas plume migrates. This variable affects trapping capacity through its effect on the residual trapping value.

  • Residual brine saturation

    This variable specifies the average residual water value in the aquifer, expressed as fraction of pore space. This is a property of the rock, and refers to the amount of brine that cannot be displaced by invading CO2. This variable affects trapping capacity as it puts a limit on how much of the pore space of structural traps can be effectively used for storing CO2.

  • Max dissolution

    This variable specifies how many volume units of CO2 can be dissolved per volume unit of brine. The volume of CO2 is specified at reference conditions, which by default corresponds to a CO2 density of 760 kg/m3. This variable affects dissolution trapping capacity.

   

Figure 2: Slider panel

 

Adjustable parameters at startup 

To keep the user interface simple, many adjustable parameters can only be specified at the command line when the program is launched. Additional parameters are specified on the form:

exploreCapacity('param1', value1, 'param2', value2, .., 'paramN', valueN)

where 'param1', 'param2' etc. are the names of the parameters to be specified, and value1, value2, etc. are the corresponding values.

Possible parameters that can be specified at the command line are:

  • grid_coarsening - the extent of downsampling of the grid. A value of 1 means that no downsampling is used, higher values yield progressively coarser grids. Default value is 2.
  • default_formation - name of the formation to load at startup. Default is 'Utsirafm'. (Other possible names can be found in the application's drop-down menu where the active formation is selected).
  • window_size - Size of the application window, in pixels. Default is [1024 768].
  • seafloor_depth - Depth of the sea floor, in meters. Default is 100 m.
  • seafloor_temp - Temperature at sea floor, in °C. Default is 7°.
  • temp_gradient - Temperature gradient, in °C/km depth. Default is 35.6°C/km.
  • water density - Density of brine, in kg/m3. Default is 1000.
  • press_deviation - Pressure deviation from hydrostatic in aquifer, in percent. Default is 0.
  • res_sat_co2 - Residual saturation of CO2, as fracture of pore space. Default value is 0.21.
  • res_sat_wat - Residual saturation of brine, as fracture of pore space. Default value is 0.11.
  • dis_max - Maximum dissolvable CO2 in terms of volume of CO2 at reference conditions per volume of brine. Default is 0.07 which, using a reference density of 760 kg/m3, corresponds to a dissolution of 53 kg of CO2 per cubic meter of brine.

Literature

Published January 7, 2016