Carbon Capture and Storage ebook ebook overview 1

Carbon Capture and Storage e-book

e-book overview 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. Climate change and energy consumption CCS as an option for CO 2 emission reduction Geologic storage and trapping mechanisms Storage potentials and capacity estimates Site selection + Characterisation CO 2 -EOR Storage risks Monitoring Numerical modeling of CO 2 storage Regulatory and social aspects of CCS technology

lecture 5 Site selection and Characterisation by Niels E. Poulsen Geological Survey of Denmark and Greenland

lecture overview § § § § § introduction country screening and basin-scale assessment prospective storage site screening detailed site characterisation examples from project exercise summary glossary references

introduction A set of basic selection criteria, based on geological parameters and important ranking criteria is described in this e-lecture. For a site being suitable for CO 2 (carbon dioxide) storage some basic, geologically related criteria has to be fulfilled. These are: 1. sufficient depth of reservoir to ensure that CO 2 is present in a supercritical dense phase but not so deep that permeability and porosity are too small 2. integrity of seal to hinder CO 2 escape 3. sufficient CO 2 storage capacity to hold the CO 2 expected to be released from the CO 2 emission source 4. effective petrophysical reservoir properties to ensure CO 2 injectivity to be economically viable and that sufficient CO 2 can be obtained from the source site.

introduction (cont. ) Fulfillment of these basic criteria depends on the values of several geological and physical parameters. In the search for suitable sites for CO 2 storage, it is therefore important to estimate if the basic criteria listed before and their associated geological and physical parameters are fulfilled. The first step in a site selection process is to screen sedimentary basins for CO 2 storage potential. The goal with the screening process is to identify predictable, laterally continuous, suitable permeable reservoir rocks overlain by potentially good quality caprocks at a suitable depth based on existing data. The screening provides an overview of those sites which are best described and best fulfil the storage criteria using the existing data. The screening therefore narrows the search at an early stage so that costly and timeconsuming supplementary investigations, such as collecting and interpreting seismic data, is confined to potentially prospective areas only. Structures, which do not satisfy one or more of the criteria in the screening process, should be excluded. However, those structures may form additional storage sites, but detailed site-specific studies are needed in order to prove their ability to store CO 2.

introduction (cont. ) If several, equally suitable CO 2 sites are pointed out in the screening process, other non-geological criteria as economic, logistical, and conflict of interest considerations may be used to select those sites that shall be investigated in more details. For example the proximity to the source site may be valued high based on economic considerations (short pipeline route). A potentially CO 2 storage site may also be excluded if there are conflicts of interest. For example, deep aquifers with high porosity for CO 2 storage would also be potentially suitable for geothermal energy production or they may form strategic reserves for the storage of natural gas. Once the best suited site(s) is(are) chosen based on existing data, it should be decided which supplementary geological information need to be collected to ensure that a site is suitable for CO 2 storage. Guidelines for detailed site characterisation procedures are given in Chadwick et al. , 2008.

country screening + basin-scale assessment Defined criteria for reservoir and barrier rocks are reservoir rocks depth (top of reservoir formation): > 800 m net thickness of reservoir rocks within reservoir formation: > 10 m porosity of reservoir rocks: > 10 % permeability of reservoir rocks: >10 m. D (millidarcy, see p. 18) barrier rocks (seal) adequate lithology (e. g. clay stones, salt (halite)) depth (base of barrier formation): > 800 m thickness of adequate barrier rocks: > 20 m. Parameters are derived from the “Storage Catalogue of Germany” (based on EU project “CO 2 STORE”).

country screening + basin-scale assessment (cont. ) basic steps for site selection: site characterisation basin assessment country/region screening

country screening + basin-scale assessment (cont. ) As first steps in country screening and basin-scale assessment, it is important to identify and map potential storage sites (storage structures, e. g. anticlines) and their seal (also referred to as caprock or roof) to be able to select storage sites for CO 2 effectively. If several, equally suitable CO 2 storage sites are pointed out in the screening process other non-geological criteria as economic, logistical, and conflict of interest considerations may be used to rank sites for to be investigated in more details, i. e. § identified and mapped potential storage sites (storage structures, e. g. anticlines) § understanding trapping mechanisms for CO 2 storage § rough estimation of the CO 2 storage capacity for the structures after [CO 2 CRC, 2008]; [Chadwick et al. 2008].

effective basic site selection criteria The basic site criteria, depth of reservoir, petrophysic reservoir properties, integrity of seal, and storage capacity, are described in the following together with their associated geological and physical parameters. For a site being suitable for CO 2 storage, some basic, geological related criteria have to be fulfilled. These are: 1. sufficient depth of reservoir to ensure that CO 2 reach its supercritical dense phase but not so deep that permeability and porosity are too low. 2. integrity of seal to hinder CO 2 escape 3. sufficient CO 2 storage capacity to hold the CO 2 expected to be released from the source 4. be economically viable and that sufficient CO 2 can be obtained from the source.

depth of reservoir The density of CO 2 -rich gases increases with depth as a result of increasing temperature and pressure. Under normal reservoir conditions, there is a steep increase in density with an associated decrease in the volume of CO 2 at depths between 600 m to 800 m (see figure to the right). This is dependent on the geothermal conditions and pressure of the formation in Density of CO at hydrostatic pressure and 2 question. At depths of more than 800 m typical geothermal gradients. (pressure about 8 MPa), the CO 2 will be in its dense (liquid or supercritical) phase, whereas at depths less than this, it will be in its gas phase and therefore not dense enough for storage to be economically viable. Due to this, storage is recommended in formations at depths of 800 m or deeper.

depth of reservoir (cont. ) Impurities in the CO 2 -rich gases have a negative depth dependent effect on the compression rate of the gas and it may therefore be necessary to include this aspect when a minimum depth of the reservoir is considered. However, with increasing depth the permeability and porosity of the sandstone reservoir normally decrease due to diagenetic alterations. This has a negative effect on the CO 2 storage capacity of the reservoir and the ability to inject CO 2 into the reservoir as described below in section on petrophysic reservoir properties. For this reason, it is recommended as a rule of thumb that the storage depth is not greater than 2500 m unless well data is available to validate acceptable porosity and permeability values at greater depth [Chadwick et al. , 2008]. This means that at depth greater than 2500 m the reservoir rock is usually compacted and permeability and porosity are too low.

effect of impurities 0 0 100 200 300 1000 depth [m] The effect of impurities (2. 75 % O 2 and other components) on CO 2 density varies with depth; after [Chadwick et al. , 2008]. Impurities within a CO 2 stream result in a decrease in density at a given depth. density [kg/m 3] 2000 3000 4000 pure CO 2 97 % CO 2 400 500 600 700

phase behaviour of CO 2 In thermodynamics, a critical point is defined as the end point of a phase equilibrium curve. The most prominent example is the liquid-vapour critical point, the end point of the pressure-temperature curve that designates conditions under which a liquid and its vapour can coexist.

what is supercritical CO 2 like? Gas or liquid? Answer: § gas-like in relation to viscosity § liquid-like in relation to density Space required? Answer: § the storage space required for supercritical CO 2 is several times smaller than for the gaseous phase.

petrophysical reservoir properties A reservoir must have some basal petrophysic properties to be suitable for CO 2 storage. The basic parameters are the permeability and the porosity. High permeability values ensure that it is easy to inject CO 2 into the reservoir and high porosity values ensure that there are pore space available for the CO 2 storage. (Text obtained from a website by the Global CCS Institute. ) The parameters are permeability and porosity, which are explained in more details below.

permeability Permeability is a measure of the ability of a material to transmit fluids. In the case of CO 2 storage the material typically is a rock of sedimentary origin. The permeability is of great importance in determining the flow characteristics of the injected carbon dioxide in the reservoir. Permeability is commonly symbolized as κ, or k. The unit used for describing permeability should be the millidarcy (m. D). Permeability needs to be measured, either directly (using Darcy's law) or through estimation using empirically derived formulas. As a general rule of thumb the formation permeability must exceed 200 m. D for a specific reservoir to provide sufficient injectivity (van der Meer, L. G. H. 1993). However, values greater than 300 m. D are preferred. (Text above obtained from a website by the Global CCS Institute. ) Rock permeability is usually expressed in millidarcy (md) because rocks hosting hydrocarbon or water accumulations typically exhibit permeability ranging from 5 to 500 m. D. Permeability in fluid mechanics and the earth sciences is a measure of the ability of a porous material (often, a rock or an unconsolidated material) to allow fluids to pass through it. A Darcy (darcy unit), or millidarcy (md or m. D), is a unit of permeability, named after Henry Darcy.

examples of permeabilities CO 2 Injection at Sleipner, Norway, North Sea 27 % to 42 % porosity and 1 D to 8 D (1000 m. D to 8000 m. D) permeability [Chadwick et al. , 2004] CO 2 Injection at Snøhvit, Norway, Barents Sea 14 % to 18 % porosity and permeability 20 m. D to > 500 m. D [Eiken et al. , 2011] Ketzin CO 2 Storage Project, North Germany porosity 5 % to > 35%, permeability 0. 02 m. D to > 5000 m. D [Norden et al. , 2010] Hontomín site, North Central Spain porosity 7 % to 21 %, permeability 60 m. D to 490 m. D [Iglauer et al. , 2014] In-Salah Gas Project, Central Algeria porosity 13 % to 17 %, permeability 13 m. D [Ringrose et al. , 2009; Rutqvist et al. , 2010]. Sleipner, deep saline aquifer, 1 Mt CO 2/a stored since 1996. In-Salah, gas reservoir, between 2004 and 2017 over 3. 8 Mt of CO 2 has been stored.

examples of permeabilities (cont. ) Gassum Formation, Denmark depth 1800 m porosity 25 % permeability 200 m. D to 2000 m. D Gassum Formation, Denmark depth 3000 m porosity 16 %, permeability 10 m. D As a rule of thumb, permeability should exceed 200 m. D.

porosity Porosity is a measure of the relative volume of void space in a rock to the total rock volume. The void may contain, for example, air, water or hydrocarbons. Porosity is measured as a fraction, between 0 and 1, or as a percent between 0 % to 100 %. Effective porosity (also called open porosity) refers to the fraction of the total volume in which fluid flow is effectively taking place. These pores are in the juvenile state water bearing and in the case of petroleum findings additionally filled with natural oil and/or gas. A high effective porosity promotes the amount of CO 2 to be stored. The volume of a reservoir’s pore space that can be filled by CO 2 either in free or dissolved form is called the storage efficiency. In the case of natural gas storage in aquifers, a bulk gas saturation of more than 50 vol. -% may be reached. For trap structures the ability to displace pore fluids from within the trap to surrounding reservoir rocks will govern the value of the storage efficiency (see figures next pages). As a general rule of thumb, porosities should be larger than 20 % [Chadwick et al. 2008].

Newton’s cradle Newton’s third law states that all forces between two objects exist in equal magnitude and opposite direction. The link to CCS is the following: When you inject CO 2 in one end of the reservoir the pressure (not the CO 2 molecules) is distributed towards other parts of the reservoir. (The CO 2 molecules will succeeding start sinking due to gravity). The ability to displace pore fluids from within the trap to surrounding reservoir rocks will govern the value of the storage efficiency.

integrity of seal Given the buoyant nature of CO 2, a reservoir must have an overlying caprock (other terms used are “seal” or “roof”) to be able to store CO 2 effectively. Typical formations with good sealing properties are rocks having low permeability values such as lacustrine and marine mudstones, evaporites, and carbonates. The integrity of the caprock is governed by the thickness of the sealing formation, the absence of faults crossing the formation, as well as the impact of geochemical interactions between the CO 2 and the caprock. Parameters that have influence on the properties of a rock as a seal are described below. The confined rocks that occur between aquifers can be divided into two classes: § aquicludes, which are rocks such as halite that are essentially impermeable if not fractured, and § aquitards, which are rocks such as shales and mudstones that have significant porosity but, because of their very small pore volume and pore throat size, have very low permeability.

what makes a good seal? (cont. ) Basic overburden properties to be evaluated at this stage include stratigraphy (specifically lithology and thickness) and nature of any faulting or fracturing. Favourable overburden properties may include the presence of shallower aquifers that could, through monitoring, provide early warning of upward CO 2 migration. If formation water, and/or CO 2, can leave the storage reservoir only at very low rates (e. g. due to efficient sealing), pore pressure in the reservoir will increase. This may induce hydraulic fracturing of the seal, generating highly efficient pathways for pressure release and potential migration of CO 2 from the reservoir into sea water – hence, particular caution must be taken not to exceed the fracturing pressure of the reservoir. The capillary pressure of the seal is the pressure required to force fluid through the rock. For a good seal, the capillary pressure should be much higher than the intended maximum pressure in the reservoir during and after injection.

integrity of seal (cont. ) permeability As already discussed previously, permeability is a measure of the ability of a material to transmit fluids and in the case of a seal the permeability should therefore be as low as possible thereby hindering the transport of CO 2 through the matrix of the caprock; see “petrophysic reservoir properties” above. seal thickness A thick seal naturally has a positive effect in hindering the leakage of CO 2 through the seal. A thickness less than 20 m is cautionary whereas thickness greater than 100 m is preferable [Chadwick et al. , 2008].

integrity of seal (cont. ) faults and tectonic activity Faults may have several, partly opposing effect on the migration of CO 2. Sealing faults can constitute traps, thereby both trapping CO 2 and constraining its migration pathways. Non-sealing faults in contrast may enable the CO 2 to escape through the seal along faults and thereby potentially escape to the surface and the atmosphere. Seal integrity may also be compromised by fracturing of the caprock, which occurs when the pore pressure of the reservoir is the same value as the least principal stress in the overlying unit [Chiaramonte et al. , 2006]. To avoid a sudden escape of pressurised CO 2 along faults, storage sites should not be located in an area of recent seismic or tectonic activity. Pressurised CO 2 ascending along faults could expand rapidly at sub-critical conditions, reducing the fault strength and opening up pathways for gas to the surface. The injection of large quantities of CO 2 may also change the local stress field and thus trigger seismicity. The history of seismic activity should therefore be checked for potentially storage sites.

integrity of seal (cont. ) heterogeneity of a seal A homogeneous, low permeable seal inhibits the migration of CO 2 through the seal. Abundant in-homogeneities, such as sandstone beds and lenses in a seal of mudstone, increases the risk of CO 2 leakage as the sandstone occurrences may be connected directly or by small faults, thereby forming migration pathways for CO 2. In the unlikely event of leakage beyond the sealing caprock, often secondary caprocks create additional boundaries between the storage reservoir and the surface, hence, increasing safety. geochemical interactions Once CO 2 dissolves into water it form carbonic acid. This will acidify the formation water and potentially attack and alter the caprock and fractures within the caprock. These chemical interactions might change the physical characteristics of parts of the seal and thus potentially enhance CO 2 migration towards the surface. An example is given in the next page.

geochemical interactions in the caprock at Sleipner porosity change profile porosity decrease limited to lowest 2 m At the Sleipner storage site, the caprock (seal) reacts with CO 2 and becomes tighter. Note that in other sites, the chemical reactions in the caprock is not necessarily the same, depending on mineralogy and composition of the CO 2 stream and the formation water, the effect might even be opposite [Gaus et al. , 2005].

storage capacity and CO 2 sources All identified storage sites should be capable of storing the lifetime emissions of the selected source point(s). With respect to industrial plants (steel mills, cement factories, power plants, etc. ), the nominal plant lifetimes are feasibly 20 years to 30 years. If a industrial plant as an example has an annual CO 2 emission of 4 million tonnes (Mt) then the storage site should consequently have a minimum capacity of 80 Mt available for utilization. Lifetimes will vary according to different types of industry. As a general rule of thumb, the estimated total storage capacity of a reservoir should be much larger than the total amount from the CO 2 source. Geological parameters which influence the storage capacity include trap type, occurrence of faults, heterogeneity of the reservoir, thickness and areal extent of the reservoir, as described in this e-lecture. In addition, the petrophysical properties of the reservoir naturally also have a large effect on the storage capacity as described above.

storage capacity and trap type CO 2 storage capacity depends not only on the properties of the reservoir itself but also on the nature of its boundaries. As described in [Chadwick et al. , 2008] very little CO 2 can be injected into the water filled pores of a small reservoir with perfectly sealed non-elastic boundaries, as the only space available will be the volume created by the compression of the water and the rock. Furthermore, this may result in an unacceptable increase in reservoir pressure towards the seal, implying that CO 2 may leak through the seal along micro-fractures or faults or migrating through the matrix of the seal, if the pressure overrides the capillary entry pressure of the seal. For significant storage, it is therefore necessary that a significant proportion of the native pore fluid is displaced from the reservoir beyond the duration of the injection period. This may occur either by anthropogenic production of fluids (oil and gas), by deliberate production of formation water, or that the formation water is displaced to the aquifer outside the closure by the injected CO 2. Aquifers, in which formation water is expelled by the injected CO 2, may be divided into trapped aquifers and open aquifers, as described below.

storage capacity and aquifers The majority of suitable structures that can keep CO 2 over long periods of time consist of some sort of three -dimensional structural closures forming different trap types. The ideal convex structure is the isolated dome that dips in all directions radially away from the central high. Eventually all kind of different shapes of those closures will occur in nature, from circular to elongated to more complex structures. A common denominator is, however, that they will be terminated upwards by a highest point that can be measured directly (wells) or indirectly (seismic profiles) as depth to the crest of the structure. In case of complex shaped closures, several crests may be present. Large structures naturally favour the storage capacity compared to minor structures. The better defined the structure is, the more control there is on volume estimates of the aquifer due to the predictable trapping geometries. The majority of suitable structures that can keep CO 2 over long periods of time consist of some sort of three-dimensional structural closures forming different trap types.

heterogeneities and faults Internal barriers within the reservoir, such as faults or lithological inhomogeneities, need to be considered as these may divide the reservoir into separate, unconnected, or poorly connected compartments, which may behave independently of one another. It is therefore easier to estimate the CO 2 storage capacity for non faulted reservoirs with a homogeneous lithology compared to reservoirs, which are heavily faulted and strongly heterogeneous. Furthermore, in the latter type of reservoirs, the injection of CO 2 may require at least one well per compartment [Kirk, 2006] and the dispersal pattern of the injected CO 2 is more difficult to predict. On the other hand, lithological heterogeneity may promote additional “fixing processes” of CO 2 within the reservoir in addition to the structural trapping. Intra-reservoir heterogeneity is therefore likely to increase effective storage capacity in the longer-term by encouraging dissolution of CO 2 into the formation water, promoting “stratigraphical” trapping of CO 2 as an immobile residual phase, and promoting geochemical reaction leading to chemical “fixing” [Chadwick et al. , 2008].

lithological heterogeneity Knowledge of the depositional environment of the reservoir sandstones may give a hint of the lithological heterogeneity. For instance, intercalated mudstone is generally more common in sandstone deposited in a meandering river system compared to sandstone deposited in a braided river system.

thickness and areal extent The size of the CO 2 storage structure will be defined by the last closing contour at a certain depth. Beneath that depth (spill point) the CO 2 will not be contained within the structure and be allowed to spread uncontrollable. The areal extent of a CO 2 storage site will have impact on the surface area, the so called “footprint”, which will have to be included in further investigations once a storage site is planned. available Space used space free CO 2 spill point brine A schematic picture of a CO 2 storage site.

thickness and areal extent (cont. ) Reservoirs of less than 20 m of cumulative thickness of good reservoir sandstone beds are thought not to be suitable for the storage of large amounts of CO 2 [Chadwick et al. , 2008]. Preferably, the thickness should be larger than 50 m. Naturally, a small thickness can be compensated by a large areal extent of the reservoir. This however, also implies a large “footprint” area, making eventual monitoring of CO 2 leakage to the surface more complicated and expensive. In addition, it requires a large area to be mapped in detail to identify potential leakage pathways (particularly faults). Information on the probable areal extent of a “footprint” can be estimated with the help of geological maps and geological cross sections. Geological maps of the deep surface and seismic profiles will help to define the extent of the structure in more detail, as well as depth structure map displaying the geological succession of interest if existent. Geological maps may also give information of the occurrence of possible fault.

other parameters with implication on storage capacity Apart from the above mentioned parameters, the CO 2 volumes that can be stored in aquifers depend on many commonly poorly-determined parameters and issues as described in Chadwick et al. [2008], including: § Residual saturation trapping, in which capillary forces and adsorption onto the surfaces of mineral grains within the rock matrix immobilise a proportion of the injected CO 2 along its migration path. § Geochemical trapping, in which dissolved CO 2 reacts with the native pore fluid and the minerals making up the rock matrix of the reservoir. CO 2 is incorporated into the reaction products as solid carbonate minerals and aqueous complexes dissolved in the formation water. § Trapping through dissolution, in which the amount of CO 2, which will dissolve into the saline pore fluids will be trapped.

detailed site characterisation and screening process The basic parameter values in pointing out potential CO 2 storage sites in the screening process are listed in the table on the next slide. The parameter values are used as general rules of thumb based on knowledge obtained from several case studies and knowledge from the petroleum industry [Chadwick et al. , 2008]. As exact parameter values commonly lack in the screening process it may be necessary to use derivative parameter values. For example as petrophysic parameter values may not be present in the screening process, a reservoir depth less than 2500 m is used as usable screening criteria to most likely ensure suitable porosity and permeability values in the reservoir. In addition, the lithology of the reservoir and caprocks indirectly reflect porosity and permeability values. The inferred parameter values have to be verified in the detailed site description which follows the screening process. To which degree it is possible to characterise and evaluate the potential storage sites in the screening phase naturally depends on how much relevant data there available and the knowledge of the geological development of the region in question.

key geological indicators characterisation basic, geological related criteria sufficient depth of reservoir petrophysical reservoir properties integrity of seal storage capacity for storage site influential geological criteria to investigate in the screening process and physical parameters positive indicators cautionary indicators pressure temperature porosity permeability lithology porosity permeability thickness faults heterogeneity tectonic activity reservoir: thickness areal extent heterogeneity fault trap type petrophysicalal properties depth of crest of reservoir > 1000 m depth of base of reservoir < 2500 m depth of crest of reservoir < 800 m depth of base of reservoir > 2500 m > 20 % > 300 m. D low permeable lithologies, such as clay > 100 m unfaulted homogeneous no tectonic activity total capacity of reservoir estimated to be much larger than the total amount produced from the CO 2 source. > 50 m well defined unfaulted well defined structures values given above < 10 % < 200 m. D < 20 m faulted heterogeneous tectonic activity total capacity of reservoir estimated to be similar to or less than the total amount produced from the CO 2 source. < 20 m not well defined faulted not well defined values given above after Chadwick et al. [2008]

site characterisation data needs: EC Directive on CCS The EC Directive on CCS “Directive 2009/31/EC of the European Parliament and of the Council of 23 April 2009” covers the following topics: § geology and geophysics § hydrogeology (in particular existence of groundwater intended for consumption) § reservoir engineering (including volumetric calculations of pore volume for CO 2 injection and ultimate storage capacity) § geochemistry (dissolution rates, mineralization rates) § geomechanics (permeability, fracture pressure) § seismicity § presence and condition of natural and man-made pathways including wells and boreholes which could provide leakage pathways.

site characterisation: saline formations, examples from Denmark Within the Danish Basin the site characterisation listed in the previous table [Anthonsen et al. , 2014] have attempted to: § identify formations with reservoir potential § map their distribution and depths – structural maps at top reservoir level § identify traps within the suitable depth window approximately 800 m to 2500 m § identify regional seal geometry and quality § identify match of regional reservoir and seal geometry § interpret structural regime; consider faults and fractures § estimate effective storage capacity § (match CO 2 point sources and traps).

examples from the Danish Basin Legend Geological map and profile line (stippled line) [Anthonsen et al. , 2014].

sedimentary units Diapir Ringkøbing-Fyn High Sorgenfrei-Tornquist Zone Skagerrak-Kattegat Platform Domes with 4 -way closure Norwegian-Danish Basin Geological profile, for position, see geological map on previous slide [Anthonsen et al. , 2014].

distribution of five reservoir formations within the suitable depth interval between 800 m and 2500 m s [Anthonsen et al. , 2014]

matching reservoir and seal mappings [Anthonsen et al. , 2014]

identifying reservoir potential, close up on possible structures, see next slides [Anthonsen et al. , 2014]

top Trias ↔ top Gassum formation, close up on possible structures © Map of top Trias (from DGU map series no. 30).

top Trias ↔ top Gassum formation, close up on possible structures © Once potential storage sites have been identified and ranked during the basin-scale assessment stage of investigation, a prospective site has to be further evaluated through a process of detailed site Characterisation.

exercise site selection + characterisation

exercise Your task is to find the location (field) which is the best option concerning depth and storage capacity. § Consider also an acceptable injectivity (fluid permeability) by means of a good flow of water or CO 2 through beds of sand (measured in Darcy or millidarcy). § Consider if there is a good seal to keep CO 2 in the reservoir. § Consider if there are other issues to be taking into account, e. g. quality of data, conflicts between interests, hazard, etc. § What type of storage is possible (e. g. volumetric aquifer storage, EOR)? § Rank the four different storage sites (table). § Remember costs in general will increase with increasing storage depth. Note that amount and quality of data from the four storage sites varies, as in the real world.

CO 2 site selection For the exercise consider if there is information on § reservoir geology + rock properties: geological structure, rock type, caprocks, and reservoirs, mineralogy, porosity, permeability, capillary pressure, wettability, and fluid distribution; § basic reservoir concepts: reservoir pressure, reservoir temperature, storage capacity estimation, fluid flow through porous media; § storage concept and mechanism: CO 2 plume, dissolution, diffusion, CO 2 solubility rate, mineralization, geochemical aspects, injection, pressure build up; § environment, health + safety: governing regulations, risk; § CO 2 storage cost.

what needs to be characterised considering CO 2 storage geology § reservoirs, trap type § integrity of seal § depth geometry of layers § lateral continuity, sheet-, wedge-, lens-shaped § thickness petrophysical reservoir properties § permeability and porosity – storage capacity mineralogy and geochemistry § types of minerals: interaction of CO 2 with rocks and pore fluids § geochemical simulations reservoir and caprock properties § cores and outcrop analogies stress regime and tectonic activity § faults, fractures.

what needs to be characterised considering CO 2 storage, additional consideration § § § § § worst case, expected, best case reservoirs size permeability and porosity storage capacity economic limitations hazards onshore offshore regulatory limitations public perception and acceptance.

four different settings The storage sites considered were the Oilfield Complex 1 and Oilfield Complex 2, Coal Complex and Deep Saline Aquifer Complex. 1. Oilfield complex 1 has a storage capacity to be approximately 14 Mt to 29 Mt, of these fields, the largest potential oilfield has the storage capacity of 5 Mt to 10 Mt CO 2. Oilfield Complex 2 has a storage capacity of 288 Mt to 577 Mt using the CSLF-based methodology (see lecture 4), depending on remaining oil reserves in the oilfields, as the most recent publicly available data are from the year 2000. The largest potential oilfield has a storage capacity of 80 Mt to 160 Mt. § The potential for recovering additional oil from the Oilfield Complex 2 was also investigated; CO 2 can assist recovery by dissolving into the oil reducing viscosity or by pushing oil towards the production boreholes. The additional oil which could be recovered by EOR was calculated to be approximately 23 Mt to 112 Mt using yield rates of 2 % to 10 %.

four different settings (cont. )

four different settings (cont. )

storage capacity estimation § For simplification, we would like to define the term storage efficiency as the ratio of used space over available space. § Effective regional storage capacity estimates based on bulk volume of aquifers and applying a storage efficiency factor as a supplement to regional estimates based on the sum of capacity in individual identified traps.

oilfield complex 1 Overview The exploration area covers about 18698 km 2, exploration began in 1955. Geological conditions and resource distribution of the Oilfield Complex 1 § Geological conditions in the Oilfield Complex 1 are very complicated. Multiphase tectonic movements and fault activity have resulted in the formation of numerous petroleum generative depressions, multiple sets of hydrocarbon reservoir assemblages, many types of reservoir rocks and numerous hydrocarbon traps, which comprise an oil and gas resource area Characterised a wide range of reservoir horizons across the region and multiple oil-bearing layers in vertical profile. § Oilfield Complex 1 lies in a basin which is a rift-subsidence basin which was divided into numerous fault blocks by frequent tectonic movement during the Cenozoic Era. Structurally it is very complex.

CO 2 storage capacity of oilfield complex 1 To summarize, the main oil reservoir characteristics are as follows: § reservoir type: complex block reservoir § production method: Water injection § wells: more than 700 § rock type: sandstone § sedimentary deposits: fluvial facies (meandering stream, braided stream) § production layer: 50 stratigraphic layers, with more 100 sand layers § single sand layer thickness: 2 m to 10 m (mostly 3 m to 5 m) § average net pay thickness: 14. 7 m § average porosity: 31% § permeability: 1000 m. D § well spacing: 150 m to 200 m § geologic reserve: 87 million tonnes The structure of the oilfield is very complicated, the sandstone reservoir has more than 100 mudstone interbeds. The oil field is penetrated by more than 700 wells and the estimated CO 2 storage capacity is quite small, making it unsuitable for CO 2 storage.

oilfield complex 2 § The basin is connected with a fault zone. There are many troughs and intertrough highs, with restrained pattern. § The basin is divided into five structural layers by regional angular unconformities and disconformities between the stratigraphic layers, it can be described by the situation of strata distribution, fold and fracture, combined with regional geological information.

oilfield complex 2 (cont. ) system lithologic character thickness [m] quaternary unconsolidated loess stratum 200 to 400 brown-red mudstone inter-bedded with brown-yellow siltstone 800 to 900 grey, pebbled sandstone, sandstone intercalated with grey, green, purple mudstone 300 to 900 grey, grey-green mudstone with sandstone, pebbly sandstone alternating beds 700 to 1000 dark grey mudstone and linen sandstone intercalated with carbonatite and oil shale > 2000 brown-red and crimson sandstone, mudstone intercalated with grey sandstone, mudstone > 1000 upper tertiary lower tertiary purple, variegated gravel, pebbled sandstone, sandstone and mudstone cretaceous grey andesite and purple sand-shale > 700 variegated pebbled sandstone intercalated with grey sandstone, greygreen mudstone jurassic purple mudstone intercalated with linen mudstone, sandstone, gravel 250 dark, purple, grey-green mudstone, sandstone intercalated coal seam 90 to 200

aquifer complex The aquifer complex was selected as there is little hydrocarbon exploration here, and so this reduces the potential for leakage from boreholes and the potential for conflict of interest with oil and gas extraction. The volume of each of the aquifer layers has been calculated. In the Table below the corresponding theoretical and effective storage capacity has been calculated using average estimates of CO 2 density of 0. 2 t/m 3 and 0. 65 t/m 3 and an estimated average porosity of 0. 25. The effective storage capacity has been calculated using a storage efficiency factor of 2 %. aquifer Volu Net/gr Porosity CO Theoretical Storage Effective Theoretical versus effective Theoretical capacity estimates assuming that the entire available pore volume can be filled with CO 2 are regarded unrealistic. For the Aquifer Complex a theoretical storage capacity of 1092 Gt has been calculated based on the bulk volume of four regional aquifer layers. This should be compared to an effective storage capacity of 20 Gt (using a storage efficiency factor of 2 %. formations me (V) (109 m 3) oss ratio (NG) 2 (Φ) density (ρCO 2) (t/ m 3) regional CO 2 storage capacity (MCO 2) (Gt) efficiency factor (Seff) regional CO 2 storage capacity (Gt) 1 aquifer layer 4, 200 0. 25 0. 65 205 0. 02 3 2 aquifer layer 5, 950 0. 25 0. 65 205 0. 02 4 3 aquifer layer 14, 000 0. 25 0. 65 455 0. 02 9 4 aquifer layer 5, 950 0. 25 0. 65 227 0. 02 4 Total estimated regional CO 2 storage capacity (Gt) 1092 20

aquifer complex (cont. ) The aquifer layers is located in a downfaulted basin. The basin has been exposed to multi-tectonic processes and periods of non-deposition. The whole stratum in the aquifer complex can be divided into four sets of aquifer layers: 1. The Palaeozoic aquifer layers consist of the marine carbonate. 2. The Mesozoic aquifer layers are mainly volcanic lava and volcanoclastic rocks. 3. The Palaeogene aquifer layers. 4. The Miocene aquifer layers. § The depth of burial of the Miocene group is more than 1000 metres. The aquifer space comprises the semi-cemented-porespaces and fractures of gravel-rich rocks. The sediments are widely distributed with great thickness and contain large quantities of sandstone. The connectivity of the aquifers is good. The formation waters condensed into the salt water continually and their hydrochemical character is stable.

coalfield complex Geologic background § The mine has a long development history. § The thickness of Carboniferous-Permian stratum is 490 m to 530 m, which includes 15 to 20 coal beds. § The thickness of a coal beds is 20 m to 28 m, and coal containing coefficient is 3. 91 % to 5. 57 %. § Coalbeds Numbers 8, 9, 12 and 14 are the main coal seams being mined and § Seams 5, 6, 7, 11, 12 and downwards are being mined in some places, § Seam number 3 is not being mined § The coalbed methane (CBM) exploitation area is 900 km 2 and uses coalseams at depths of up to 2000 m in the K 1 mining area. § Total estimated CBM reserves are 71. 9 billion m 3. § The CBM reserves at depths below 1500 m are 35. 2 billion and the § Forecast reserves between the depth of 1500 m and 2000 m is 36. 7 billion m 3. § Adsorption experiments carried out on coal samples.

coalfield complex (cont. ) Coal porosity and permeability characteristics in the Coalfield 4 § The coal bed porosity ranges from 3 % to 13. 29 % in Coalfield 4 § Coal porosity in other areas is generally higher than these values. § Permeability are highly variable § Average coalbed permeability in this area is 3. 5 m. D. § Sealing properties of the overlying stratigraphy

4 different settings, summary Ranking criteria Oilfield Complex 1 Oilfield G Oil Complex 2 Aquifer Complex Coalfield Complex Depth 1035 – 2639 m 900 to 3200 m 1000 – 2200 m 800 – 1500 m Storage capacity 5 – 10 Mt CO 2 using (20 – 40 % Seff) 268 – 535 Mt CO 2 (20 – 40 % Seff) 717 Mt CO 2 (using 2 % Seff) 689 Gt CO 2 Injectivity - must be able to store > 100 kt/year CO 2 Porosity 31 % Permeability 975 m. D Liquid production 5. 2 Mt/year Reservoir formation 28 – 36 % porosity, permeability 1520 – 3118 m. D. Many reservoirs within each field No data, assumed to be similar to Oilfield Complex 2 Coal bed porosity ranges from 3 % to 13. 29 % Permeability 0. 002 – 3. 4 m. D. Seal integrity - capillary pressure/faulting Highly compartmentalised, large faults (with oil reservoirs so may be sealing), more than 700 wells Highly compartmentalised, large faults (with oil reservoirs so may be sealing), , Major faults and minor faults, uncertainty how much data are available Seal permeability 0. 089× 10 -3μm 2; 2) Porosity is 1. 97 %; 3) Breakthrough pressure is 20. 67 MPa; 4) Diffusion coefficient is 1. 33× 10 -5

ranking basic site selection criteria Your task is to find the location (field) which is the best option concerning depth and storage capacity § Rank the 4 different storage sites (use the weighting in the table to right and insert in the table next slide § In the following slide, you will find a proposal for ranking Weighti ng Explanation +++ data from several boreholes, seismic data ++ some average values + some data estimated - many estimates -- only few data --- no data

ranking, basic site selection criteria Oilfield Complex 1 Oilfield G Ranking criteria Depth Value (m) data quality * Storage capacity Value (Mt CO 2) data quality Permeability Value (m. D) data quality Seal integrity - capillary Value pressure/faulting data quality Value data quality Data availability implying confidence Rank Oil Complex 2 Aquifer Complex Coalfield Complex

suggested results of exercise Note that there is no definite answer to the exercise. The final selection depends on the actual situation.

4 different settings, suggested results Ranking criteria Depth Storage capacity Injectivity - must be able to store > 100 kt/year CO 2 Oilfield Complex 1 Oilfield G Oil Complex 2 Aquifer Complex Coalfield Complex 1035 – 2639 m 900 to 3200 m 1000 – 2200 m 800 – 1500 m ++ +++ ++ 5 – 10 Mt CO 2 (20 – 40 % Seff) 268 – 535 Mt CO 2 (20 – 40 % Seff) 717 Mt CO 2 (2 % Seff) 689 Gt CO 2 ++ - -- + Porosity 31 % Permeability 975 m. D Liquid production 5. 2 Mt/year Reservoir formation 28 – 36 % porosity, permeability 1520 – 3118 m. D. Many reservoirs within each field No data, assumed to be similar to Oilfield Complex 2 Coal bed porosity ranges from 3 % to 13. 29 % Permeability 0. 002 – 3. 4 m. D. ++ + --- +++ Highly compartmentalised, large faults (with oil reservoirs so may be sealing), more than 700 wells Highly compartmentalised, large faults (with oil reservoirs so may be sealing), , Major faults and minor faults, uncertainty how much data are available Seal permeability 0. 089× 10 -3μm 2; 2) Porosity is 1. 97 %; 3) Breakthrough pressure is 20. 67 MPa; 4) Diffusion coefficient is 1. 33× 10 -5 + + - +++ Rank 3 2 1 4 Seal integrity - capillary pressure/fa ulting

storage sites summary § Oilfield Complex 1: geology and number of boreholes make this unfavourable for large-scale storage, maybe a small-scale EOR § Oilfield Complex 2: some of the oilfields within Oilfield 2 may be suitable for storage. § Aquifer Complex: data is difficult to obtain about the aquifers, the data used for this study is mainly based on geological publications. Large potential storage capacity, but more uncertainty than for the oilfields. § Coalfield Complex: Storage potential in the coalfield is small due to low permeability. However, there may some potential for enhanced coalbed methane recovery though care would have to be taken not to contaminate future energy resources and to avoid risk of leakage.

Location Structure description Basic site selection criteria sufficient depth for supercritical dense phase (> ) sufficient injectivity to be economically viable (kg/s) integrity of seal in terms of faults/capillary pressure (permeability has to be checked) Geological Parameters trap type storage type (e. g. hydrocarbon field/aquifer) reservoir lithology type heterogeneity of system areal extent thickness of reservoir (min-max) (m) depth to crest (max-min) (m) depth to base of reservoir (max-min) (m) porosity (max-min) (%) permeability (max-min) (m. D) pore volume (km 3) pressure (k. Pa/m) fracture pressure temperature (K/km (temperature gradient)) seal lithology type seal permeability seal capillary pressure seal pore entry pressure (can estimate if perm. is known) faulting in seal tectonically active availability of data conflicts of interest Ranking criteria depth (m) storage capacity (Mt CO 2 ) injectivity - must be able to store > 100 Kt/year CO 2 (kg/s) seal integrity - capillary pressure/faulting (fault permeability has to be checked) tectonically stable area data availability implying confidence our y f no tio lua a v e ur o y h wit hoice? u o re y f best c e w eld o dent i i f f n co w o H Data quality

summary A large knowledge based on existing data implies that it is possible to make a well qualified choice of suitable sites in the screening process. The amount of supplementary investigations in the following site characterisation may, depending on the amount and quality of existing data available for the screening process, result in several potential storage sites which will need to be investigated further before the most suitable site can be chosen. As it can be very expensive to produce the necessary data from several sites it may be appropriate to investigate the sites one by one until a suitable site is found. The order in which the sites should be investigated could then be determined by non-geological criteria. For example, it may be appropriate first to investigate the site which is closest to the CO 2 source, thereby keeping the installation costs down (short pipeline) if the investigations show that the site is suitable for CO 2 storage.

summary (cont. ) A basic set of criteria has been evaluated for the assessment and ranking of sedimentary basins in terms of their suitability for CO 2 storage. A sedimentary basin assessment and a site characterisation for CO 2 geological storage are dependent to different degrees to data availability and their essential characteristics. The screening process is to identify predictable, laterally continuous, suitable permeable reservoir rocks overlain by good quality caprocks at a suitable depth based on existing data. By screening an overview can be obtained of which sites there are best fulfil the storage criteria. The screening therefore narrows the search at an early stage so that costly and time-consuming investigations can be limited to potentially prospective areas only.

glossary CCS Carbon Dioxide Capture and Storage CSLF Carbon Sequestration Leadership Forum Darcy A darcy (D) or Darcy unit and millidarcy (md or m. D) are units of permeability, named after Henry Darcy. Permeability in fluid mechanics and the earth sciences is a measure of the ability of a porous material (often, a rock or an unconsolidated material) to allow fluids to pass through it. DOE U. S. Department of Energy ECBM enhanced coal bed methane recovery ENOS Enabling Onshore CO 2 Storage in Europe EOR Enhanced oil recovery: implementation of various techniques for increasing the amount of crude oil that can be extracted from an oil field, e. g. through injection of CO 2 IEA International Energy Agency - https: //www. iea. org/

glossary (cont. ) κ, or k Permeability is commonly symbolized as κ, or k (measured in millidarcy) is megapascal MPa 1, 000 equals MPa Megapascals. The 1 Pressure Unit. mainly used describe pressure to the ranges hydraulic ratings and of systems. The Pascal (symbol: Pa) the is unit of pressure used to quantify internal pressure. is It defined as one newton per square metre. It is named after the French polymath Blaise Pascal. The unit of measurement called standard atmosphere (atm) is defined as 101, 325 Pa and approximates to the average pressure at sea-level at the latitude 45° N. The internationally recognized standard measure 0. 101325 MPa = 101. 325 k. Pa = 1013. 25 h. Pa = 1 atm, which roughly corresponds to the average pressure at the ocean surface on Earth. Mt Mega tonnes

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acknowledgement + disclaimer This lecture was completed with the support of the European Commission and European Union’s Horizon 2020 research and innovation programme under grant agreement No 653718. The contents of this publication do not necessarily reflect the Commission's own position. The document reflects only the author's views and the European Union and its institutions are not liable for any use that may be made of the information contained here. Lecture template by Dorothee Rebscher (BGR)

Carbon Capture and Storage e-book

Carbon Capture and Storage e-book