CO2 Storage Functional Requirements Impacts by the CO2 Quality

Transcription

1 CO2 Storage Functional Requirements Impacts by the CO2 Quality Oxyfuel Combustion Working Group Meeting on CO2 Quality Stockholm, 22 nd October Dr. Christian Bernstone, Vattenfall Research and Development AB

2 Why is CO 2 gas quality important? h h h All targeted CO 2 streams that we aim to store contain small amounts of other components but CO 2. The CO 2 quality issue can be seen as an opportunity and a risk: I. An opportunity to co-capture other main pollutants from power plant operations such as SO x and store them together with the CO 2. A concept with near-zero emissions could be created Avoid costly and energy-demanding flue gas cleaning equipment II. A risk that components other than CO 2 could have negative technical and/or HSE effects on the transport and storage system Such components need to be removed. III. Too stringent requirements induce high costs for cleaning of CO 2. The tools for risk assessment and management need to be capable of handling CO 2 streams containing small amounts additional components 2

3 CO 2 Gas Quality Gas quality by The power plant Transportation Saline aquifers Gas fields Oil fields

4 5. Scheme Evaluation/Analysis Transport Gas composition from Capture Storage Is composition conservative? Final composition Environment Regulation Refine gas composition 4

5 CO2 Storage Aspects A CO2 storage site must fulfil requirements, in the short term (operation), and in the long term (closure and abandonment). The technical requirements can be divided into the following functions: High availability of the injection facilities Efficient use of the storage capacity Adequate injection pressure Preservation of seal integrity Requirements on CO2 as a commodity for EOR 5

6 Impact by the Gas Quality on the Availability of the Injection Facilities The injection well shall be designed to minimise risks during both the operation and the abandonment phase: Corrosion: Damages on the well can only with difficulty be replaced with new parts, i.e., corrosion cannot be allowed. The most exposed components of the well that could be exposed to CO 2 with water should be of high-quality steel. For parts not especially exposed to CO 2 with water, the Encap or Dynamis guideline recommendation applies, i.e., 500 ppm. Damages due to formation of hydrates: There is a risk for formation of hydrates at low temperatures and high pressures. Including impurities could consequence that the formation of hydrates can happen at higher temperatures With H 2 S and CH 4, hydrates can form without presence of free water. 6

7 Impact by the gas quality on the Storage Capacity The storage volume is a limited resource, with a certain value. The decreased density caused by impurities in the gas stream can reduce the storage capacity in the range of yearly injection volumes: The volume increase results in additional storage costs The maximum storage capacity is reached faster than it would be by pure CO 2. The additional costs to be compared with the additional costs of CO 2 processing at the power plant. Authorities may regulate how the space is used to ascertain the smallest possible areas are required for CO 2 storage sites 7

8 Impact by the gas quality on the Injection Pressure The injectivity is dependent on phase viscosity of the fluid: Impurities lower the viscosity, and thus improve the injectivity compared to pure CO 2. Additional gas components does not have an adverse effect on the injectivity. The gas-mixture density determines the required static head-pressure: Because additional gas components generally reduce the density of the gas mixtures, the delivery pressure at the wellhead must be increased. The increased compression work results in additional cost, to be compared to the additional costs of CO 2 processing at the power plant. All additions to the CO 2 gas stream result in increased gas-volumes, and increased injection rates: The injection rate is expected to be a limiting parameter, An increased injection rate could require investment in an additional injection well. The additional cost to be compared to the additional costs of CO 2 processing at the power plant. 8

9 Impact by the gas quality on the Injection Pressure, cont. There is only few studies in literature that investigate the impact from injection of CO 2 gas mixture stream into storage formations. The main conclusions are that: In sandstone formations, inclusion of SO 2 can increase mineral dissolution, while H 2 S is expected to not notably affect porosity. Therefore, neither SO 2 nor H 2 S should impact on the injectivity. In carbonate formations, inclusion of H 2 SO 4 and H 2 S can decrease the permeability due to precipitation, thereby possibly damage the injectivity. Geochemical modelling by BRGM: In sandstone formations, there is a SO 2 controlled porosity decrease in the near-well zone (<3%). Whether the porosity decreases will have severe impact in the injectivity or not need to be investigated case-by-case by reservoir modelling. Indicatively, the impact from particulates in the gas stream should not be problematic 9

10 Impact by the gas quality on the seal integrity A literature review has not identified any studies on caprock integrity that involves other substance than CO 2. The knowledge base is very limited. Geochemical modelling by BRGM showed no indication of impact on the cap rocks of two candidate storage sites in Germany. With current knowledge, as long as the injection pressure is controlled within established limits, there is no geo-mechanical impact by gas mixture components on the caprock integrity. 10

11 Requirements on CO 2 as a commodity for EOR Impurities will have effect on oil recovery as they change the solubility of CO 2 in oil and the ability of CO 2 to vaporize oil components by impacting on the MMP (which should be low): Positive additions are: SO 2, SO x, H 2 S, NH 3 Negative additions are: CH 4, Ar, H 2, O 2, N 2, NO, C 2 H 6, CO, [The miscibility of CO 2 in crude oil is strongly affected by pressure. A minimum miscibility pressure is required so that CO 2 becomes fully miscible with oil. At that pressure, the density of CO 2 is similar to that of the crude oil.] There is a certain risk that CO 2 containing O 2 react with the oil and cause negative overheating at the injection point In the event that O 2 -rich fluids reaches extraction wells, the environment would be very corrosive: The reservoir is likely to consume O 2 along the flow pathway. The experience described in literature is very limited, though. The corrosion of equipment and infrastructure at the production-well side of the operation is not additionally severe for CO 2 gas mixtures than for pure CO 2, i.e. it will not affect the CO 2 design specification. 11