CO 2 Risk Assessment & Monitoring methodologies

Transcript

1 ΑΝΘΡΩΠΙΝΑ ΔΙΚΤΥΑ ΕΡΕΥΝΗΤΙΚΗΣ ΚΑΙ ΤΕΧΝΟΛΟΓΙΚΗΣ ΕΠΙΜΟΡΦΩΣΗΣ «ΤΕΧΝΟΛΟΓΙΚΟ ΔΥΝΑΜΙΚΟ ΓΙΑ ΤΗΝ ΜΕΙΩΣΗ ΤΩΝ ΕΚΠΟΜΠΩΝ ΔΙΟΞΕΙΔΙΟΥ ΤΟΥ ΑΝΘΡΑΚΑ ΔΥΝΑΤΟΤΗΤΕΣ ΠΡΟΟΠΤΙΚΕΣ ΤΩΝ ΕΛΛΗΝΙΚΩΝ ΕΠΙΧΕΙΡΗΣΕΩΝ» CO 2 Risk Assessment & Monitoring methodologies Δρ. Ν. Κούκουζας Πτολεμαίδα,, 2007

2 Content Risk management Risk assessment Performance assessment Monitoring timeframe and methodologies

3 Risk management provides a comprehensive decision-making processthataidsdecision-makers in identifying, analyzing, evaluating and controlling all types of risks, including risks to health and safety.

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5 The Preparation Phase site characterization (static & dynamic) using a combination of state of the art technologies: seismic, logging, testing, monitoring for geological; geo-mechanical reservoir characterization, determination of aquifer, containment, assessment of unconformities, fracture network, aquifers characterization and connectivity assessment; mapping of old wells and planning for conditioning them against potential leaks the design and completion of smart injection wells and monitoring wells with CO2 compliant cement; the design of a down hole and surface monitoring network for micro-seismic events surveillance during injection and further control of potential leaks and the design of repeat seismic surveys (4D) for CO2 plume tracking.

6 Operational phase includes: a. The modelling of the short term prediction, b. The operation of the plan designed during the preparation phase c. The monitoring of the operation to verify the validity of the short term prediction and take the necessary corrective actions. Abandonment phase includes: a. The update to the long term risk assessment and b. The decision on duration of specific site monitoring.

7 GENERAL METHODOLOGY FOR PERFORMANCE & RISK ANALYSIS

8 Risk Assessment Risk The chance of injury, damage, or loss Risk Assessment for CO2 Storage The process that evaluates the potential for adverse HSE effects resulting from CO2 exposure How to? To evaluate the risks associated with CO2 storage, the potential hazards associated with a specific event must be considered in conjunction with the likelihood of the event happening Risk = probability x unacceptable impact

9 In the risk assessment risk factors are identified and potential impacts are quantified. The complexity of the models used depends on the geological characteristics of the site. The very first step of risk assessment is the definition of the assessment basis, which consists of: Risk acceptance criteria Containment concept Setting of the storage site The outcome of the assessment is used to develop the monitoring plan and the remediation action plan. The results of the monitoring will be used to validate the outcome of the risk assessment, and if necessary adjust the assessment models. Remediation consists of preventive and corrective actions.

10 Performance assessment refers to the process of evaluating the behaviour or performance of an element of a geological storage project relative to one or more performance standards. Performance includes both engineering and safety aspects. Performance = degree to which container leaks (3D flux) Performance assessment Risk management process

11 Scenario analysis (FEPs) Features: physical characteristics or properties of the system, such as lithologies, porosity, permeability, wells, faults and nearby communities Events: discrete occurrences affecting one or more components of the system, such as earthquakes, subsidence, drilling, borehole casing leak and pipe fracture Processes: physico-chemical processes often marked by gradual or continuous changes that influence the evolution of the system such as precipitation of minerals, groundwater flow, CO2 phase behaviour and corrosion of borehole casing

12 Risk assessment methodology for CO2 storage

13 Assessment basis Assessment criteria Lethality index Groundwater quality index Biodiversity index etc Underground storage concept (containment) Physical trapping Dissolution trapping Mineral trapping etc. Setting of the storage facility Geology Geography/landuse

14 Utilizing the definition of the storage system set out in the assessment basis, the FEPs are ranked and screened in order to identify the FEPs that are likely or very likely to occur. These FEPs are grouped and assigned to specific zones within the geological storage system (compartments). Compartments: Reservoir and its caprock Overburden CO2 exposed zone (shallow saturated and undersaturated zones, marine surface water or atmosphere) Wells and faults

15 Model Development to demonstrate completeness, comprehensiveness or sufficiency in the scope of a performance assessment, usually by seeking to identify and possibly describe, a list of relevant features, events and processes. to decide which FEPs to include in performance assessment. This includes screening of less important FEPs, deciding which FEPs are to be treated in quantitative models of system performance, which FEPs can be handled by scoping calculations and which FEPs should be regarded as the key defining elements of separate scenarios.

16 Model development: Weyburn Base scenario (the expected evolution of the storage system)

17 Model Development: Weyburn Alternative Scenarios (those that illustrate the potential outcomes of uncertainties)

18 Modelling fluxes and concentrations A realisation of CO2 saturation after yrs 100% containment: no CO2 above seal Part of CO2 penetrated seal No signficant mechanical and chemical effects on seal Limited increase of reservoir permeability

19 Consequence Analysis: Consequences

20 Consequence analysis: Level of Risk Consequences by likelihood= Level of risk

21 Consequence Analysis: Likelihood

22 Purpose of monitoring To ensure public health and safety of local environment To verify the amount of CO2 storage To track migration of stored CO2 (simulation models) To confirm reliability of trapping mechanisms To provide early warning of storage failure Risk models can be updated with new data, and updated risk can be calculated. If new risk > risk tolerance, then remedial action.

23 Monitoring from related projects it is clear that there are many monitoring options which are effective in particular circumstances modeling and monitoring is required to demonstrate that despite the initial uncertainties the natural storage system is behaving satisfactorily learning from monitoring will make clear under which conditions long-term CO2 storage can be relied upon

24 Types of monitoring

25 Monitoring group Engineering Geophysical Geochemical Geodetic Biological Εθνικό Κέντρο Έρευνας και Τεχνολογικής Ανάπτυξης / Examples of monitoring techniques Monitoring technologies Pressure, temperature, well tests Seismics (3D), micro seismicity, gravimetry,, electro-magnetic, self- potential, physical well logging Production water & gas analysis, tracers, overburden fluids, direct measurements Geodetic, tilt measurements, satellite interferometry,, airborne sensing Microbial, vegetation changes Compartment Wells Reservoir and back - ground system, wells Reservoir and surface system Surface system Surface and background system Measurements are repeated in time or applied continuously

26 Monitoring timeframe The definition of long-term is based on perceived risk of leakage, which is expected to decrease towards a stable condition as the pressure decays after injection ceases

27 Risks Analysis IEA GHG WEYBURN CO2 MONITORING & STORAGE PROJECT Analysis: Long-term migration pathways of CO2 Effects of CO2 on the hydrochemical and mineralogical properties of the reservoir rocks I. Geological Characterization of the Geosphere and Biosphere. II. Prediction, Monitoring and Verification of CO2 Movements. III. CO2 Storage Capacity and Distribution Predictions and the Application of Economic limits. IV. Long-Term Risk Assessment of the Storage Site

28 Geological Characterization of the Geosphere and Biosphere The Weyburn field is in a tectonically quiet region. The system model within the regional study area of the project Most faults and fracture zones in the greater region are localized disturbances. Larger scale features were also observed, and one fault identified in this study was included in the geological model used in risk assessment but without appearing to affect reservoir integrity in the last 50 million years.

29 Geological Characterization of the Geosphere and Biosphere The geological setting of the Weyburn oil pool is considered to be highly suitable for the secure longterm storage of CO2. The developed geological model Primary seals enclosing the reservoir appeared to be sound and exhibited only rare discontinuities showing essentially no detectable evidence of fluid conductance. The lack of cross-formulation flow in the Weyburn area indicates that formation fluids as well as any injected fluids such as CO2, will stay within their respective aquifers.

30 Prediction, Monitoring and Verification of CO2 Movements Predictions of the CO2 movement based on flow simulations using the reservoir model of the Weyburn field. Monitoring of the CO2 flood at the Weyburn field includes seismic and geochemical methods. P-wave time-lapse seismic monitoring is highly sensitive to the presence of a CO2-rich gas phase even at low levels of saturation (5-10%), while pressure effects appear as a secondary factor.

31 Prediction, Monitoring and Verification of CO2 Movements Mean CO2 saturation of ~20% over the entire reservoir interval in the areas identified by the P- wave seismic amplitude anomalies. Predicted CO2 saturation at 2 years after start of injection Changes in fluid and gas compositions over time indicate an interaction between reservoir fluids, injected CO2, and reservoir rocks.

32 CO2 Storage Capacity/Distribution, Predictions and the Economic limits Main mechanism for CO2 trapping and storage was phase trapping trapping supercritical CO2 as a separate phase, enhanced by geochemical reactions. Additional storage of CO2: solubility trapping Mt CO2 ionic trapping Mt CO2 mineral trapping Mt CO2. CO2 distribution after 5000 years based on geochemical modelling of 75-pattern simulation EOR

33 Long-Term Risk Assessment of the Storage Site After 5000 years, the total amount of CO2 removed from the EOR area is 26.8% of the initial 21 MT CO2-in in-place at the end of EOR. CO2-rich gas phase movement in the Marly and Vuggy layers 18.2% moves into the geosphere below the reservoir primarily by hydrodynamic forces. 8.6% migrates laterally in the Midale reservoir outside the EOR area. 0.02% diffuses into the Midale Caprock but no CO2 enters the potable aquifer system over the 5000-yr period.

34 SACS - Saline Aquifer CO2 Storage Project Geoscientific characterisation of the reservoir and caprock Typical 2D seismic reflection profile across the Utsira reservoir A regular grid of 2D seismic data over the entire reservoir. A high quality 3D seismic volume over the injection site and adjacent area. The top Utsira Sand surface generally varies quite smoothly in the depth range 550 to 1500 m. Isopachs of the reservoir sand define two main depocentres,, one in the south, where thicknesses range up to more than 300 m, and another some 200 km to the north. On geophysical logs the Utsira Sand characteristically shows a sharp top and base. The peaks on the logs are interpreted as thin (~1m thick) layers of shale or clay which constitute important permeability barriers within the reservoir sand.

35 SACS - Saline Aquifer CO2 Storage Project Properties of the Utsira Sand from core and cuttings Macroscopic and microscopic analysis of core and cuttings samples s show a largely uncemented fine-grained sand, with medium and occasional coarse grains consisting primarily quartz with some feldspar. Shell fragments and sheet silicates are present in small amounts (a few percent). Porosity estimates based on core microscopy range generally from 27% to 31%, locally up to 42%, and from core experiments %. The total pore volume of the Utsira Sand, based on the isopach map and regional assessments of porosity and shale volume, is about 6 x m3.

36 SACS - Saline Aquifer CO2 Storage Project Characterisation of Utsira caprock Analysis of geophysical logs indicates shale volumes of at least 80%. The thin sandy unit (termed the sand- wedge by SACS) in the lower part of the caprock will provide an important migration conduit (a small dip divergence results in an azimuthal change of some 90 o in predicted migration direction. Sufficient structural closure at the top of the Utsira Sand to trap 20 MT of CO2 within 12 km of the injection site. If most of the CO2 migrates beneath the top of the sand-wedge only 5 MT of CO2 are sufficient for the migration stream to the east. Migration pathways from the Sleipner injection point

37 SACS - Saline Aquifer CO2 Storage Project Monitoring the injection process using time lapse seismic data - 4D seismic Synthetic model of a 2 m thin shale layer with a CO2 accumulation below Suitable because the velocity of sound waves is differentiated between salt water-bearing (higher velocity) and CO2- bearing (lower velocity) sandstones. The seismic response is a composite wavelet caused by interference from sequences of water saturated sand, shale, CO2 saturated sand and water saturated sand. Any major leakage into the overlying caprock could be detected.

38 SACS - Saline Aquifer CO2 Storage Project Time lapse seismic data for the flow distribution of the injected d CO2 at different time steps. Gravitational segregation is the dominant physical mechanism driving the migration. CO2 had reached the top of the sand wedge and then has spread laterally Accumulations at the top of the sand wedge and the top of the Utsira Sand. Chimneys above the injection point form a major vertical migration path which conducts CO2 almost directly to the top of the reservoir An inline through the injection area for the 1994, 1999 and the 2001 surveys In general the 2001 CO2 levels have a larger lateral extent and have been pushed down slightly more compared to the 1999 CO2 levels due to more injected CO2

39 SACS - Saline Aquifer CO2 Storage Project Reservoir simulation in SACS: Verifying the seismic and geological interpretations and predicting the long-term fate of CO2 Simulations suggest that the carbon dioxide mega-bubble may reach its ultimate size after a few hundred years, thereafter shrinking and finally disappearing within a few thousand years Reservoir model of CO2 distribution after three years Simulated dissolution of CO2 in the saline water of the Utsira Formation. Red = supercritical CO2 ; green = CO2 rich brine.

40 SACS - Saline Aquifer CO2 Storage Project Assessing the geochemical impact of CO2 injection The Utsira sand showed only limited reaction with CO2. Most reaction occurred with carbonate phases but these were a very minor proportion (about 3%) of the overall solid material. In terms of geochemical reactions, the Utsira sand appears to be a good reservoir for CO2 storage. Long term diffusion modelling of CO2 into the Nordland Shale cap rock at Sleipner shows that: Due to low diffusion velocities the geochemical impact is limited to the lower section of the cap rock even after thousands of years. Based on the initial mineralogy of the cap rock plagioclase alteration is identified as the most important reaction involving the dissolved CO2, leading to the precipitation of clays and carbonates. A low decrease of porosity (up to a few percentages) can occur in the lowest meters of the cap rock depending on the initial composition of the feldspars present.

41 Future CO2 behavior The In Salah Project The studies demonstrated that the CO2 stream injected into the aquifer a zone of Krechba Carboniferous reservoir will over time migrate back towards the main Hydrocarbon accumulation and into structural trap. It is predicted that during the early years of injection (up to 10 years), the CO2 will be retained within the aquifer zone near the injector locations. Over the long term, as volumes build in the reservoir, the CO2 will w slowly migrate up-dip towards the structural crest of the main gas accumulation, moving into the main field area only after the field is depleted and abandoned. Prediction of the injected CO2 behavior has been modeled both analytically alytically as well as by numerical simulation. The results confirmed that CO2 breakthrough into the main field area would not occur until after field abandonment (after 25 years of production).

42 Conclusions CO2 storage presents risk to human health, and the environment Risk assessment must be used to ensure the safety and acceptability of geological storage as a feasible carbon management option Performance assessment is embedded into risk assessment as its geoengineering component Risk assessment for geological storage is still in development In order to calculate the risk profile of a specific site and monitor its evolution during the injection and post-injection phases, risk tolerance levels are required. Monitoring must be an integral part of any CO2 storage project