an alternative theoretical methodology for monitoring the risks of co2 leakage from wellbores

Available online at www.sciencedirect.com Energy Procedia EnergyProcedia Procedia1 00 (2008) 000–000 Energy (2009) 2599–2605 www.elsevier.com/locate/XXX www.elsevier.com/locate/procedia GHGT-9 An Alternative Theoretical Methodology for Monitoring the Risks of CO2 Leakage from Wellbores Jose Condora,b*, Koorosh Asgharib a Energy Technology Innovation Policy, John F Kennedy School of Government, Harvard University 79 JFK St Cambridge, MA 02138, USA b Faculty of Engineering, University of Regina Research Dr Regina, SK S4S 7J7, Canada Elsevier use only: Received date here; revised date here; accepted date here Abstract This paper proposes an alternative theoretical methodology to evaluate the risks of CO2 leakage from reservoirs using a stochastic approach The methodology suggested here makes use of three main concepts: − Features, Events and Processes (FEPs) − Interaction Matrix, IM − Stochastic Representation Both, FEPs and Interaction Matrix have been introduced by other researchers but for different objectives The methodology that is proposed here modifies the original concept of Interaction Matrix in such a way that it may produce probabilistic results as outcome A practical example is given at the end of this paper © Ltd All All rights rights reserved reserved c 2008 2009 Elsevier Elsevier Ltd Keywords: Geological Storage; Risk Assessment; Wellbore Stability; Leakage Scenarios; Safety Criteria; EOR Introduction Several papers have been published in recent years with the objective of evaluating the risk of CO2 leakage from reservoirs[1-5] Some of these researchers have considered the complete geo-sequestration systems, which exhibit high degrees of complexity A geo-sequestration system is a complicated group of elements that has to be modelled in such a way that represents the real system as closely as possible Quintesa elaborated a database with all the applicable Features, Events and Processes (FEPs) for the safe long term storage of CO2[6-8] It was originally proposed as a screening and monitoring tool for the radioactive waste management[9] This database constitutes an excellent source of information, but it does not provide a structured methodology to evaluate the risks of CO2 leakage * Corresponding author Tel.: +1-617-496-2705; fax: +1-617-496-0606 E-mail address: Jose_Condor@ksg.harvard.edu doi:10.1016/j.egypro.2009.02.026 2600 J Condor, K Asghari / Energy Procedia (2009) 2599–2605 Condor, J Asghari, K./ Energy Procedia 00 (2008) 000–000 In 1992, John Hudson published the Rock Engineering Systems explaining in a practical way the value of the Interaction Matrix for the mines engineering[10] His work was useful later on to model engineering systems for storing radioactive waste materials His approach is simple, but practical and basically consists of what the author defined as Interaction Matrix, Expert Semi-Quantitative (ESQ) Code and the Cause-Effect Plot The approach proposed in this paper, for assessing the risk of CO2 leakage, modifies Hudson’s methodology by inclusion of a concept known as Incident Potential Matrix (IPM) instead of the ESQ-Code The inclusion of the IPM concept in the interaction matrix may allow stochastic modelling by the use of probabilistic density functions Also, the interaction matrix can represent different scenarios that make it even more interesting for the modelling purposes in the monitoring phase of CO2 storage projects The first part of this paper will refer to the definitions of Interaction Matrix, Incident Potential Matrix, and the Cause-Effect Plot The second part will present an example applicable for evaluating the risk of CO2 leakage through the wellbores that are used for geological storage of CO2 Concept of Interaction Matrix[10] The Interaction Matrix is a square matrix with a main diagonal containing the components of the system These components are called leading diagonal elements or LDEs The rest of the cells define the interactions and are called off-diagonal elements or ODEs By convention, the interactions between the LDEs and ODEs follow the clockwise direction as it is shown in the Figure In this figure, the main diagonal (dark blue) contains the elements or components of the system and the remaining cells (light blue) define the interactions produced among them Figure A 3X3 Interaction Matrix Element A Interaction B to A Interaction C to A Interaction A to B Element B Interaction C to B Interaction A to C Interaction B to C Element C The interactions for a geo-sequestration system are the result of physical and chemical processes represented by variety of parameters It must be noticed that the matrix is not a symmetric one, which means that Interaction of A to B is not equal to Interaction of B to A Furthermore, certain interactions may not be considered important for the model and then their cells are represented as empty Concept of Incident Potential Matrix, IPM This matrix is mainly used in safety management in order to evaluate risks using a qualitative approach In the IPM, the risk can be defined deterministically as the product of exposure and severity Risk = Exposure × Severity … …… ………………………………………………Equation 2601 J Condor, K Asghari / Energy Procedia (2009) 2599–2605 Condor, J; Asghari, K./ Energy Procedia 00 (2008) 000–000 The IPM is relatively easy to use Its vertical axis corresponds to the exposure or likelihood of occurrence and its horizontal axis represents the severity The intersection between the exposure and severity produces the risk (Figure 2) The right criterion is extremely important in defining the risk A group of experts must assume the values of severity and likelihood Consider for instance the case of an undetected geological fault that can be reactivated The probability of occurrence (exposure) may be very low (A), but the severity can be catastrophic (4) if the location is close to a populated area With these two data, the corresponding value for risk would be A4 (low risk) The colour code for these four kinds of risks allows an easy visualization of the critic interactions In this proposal, four risk categories are identified The very low risk is assigned a value of 1; the low risk, 2; medium risk, 3; and the high risk, The value of zero (0) is applicable when there is absence or undetected risk These values (Table 1) are the input data which later on will define the Cause-Effect plot Figure The Incident Potential Matrix, IPM Exposure or Likelihood (A - E) Very Low Risk= Low Risk = Expos V High (E) High (D) Medium (C) Low (B) V Low (A) Mitigation Prevention High Risk = Medium Risk = E1 E2 E3 E4 E5 D1 D2 D3 D4 D5 C1 C2 C3 C4 C5 B1 B2 B3 B4 B5 A1 A2 A3 A4 A5 Light (1) Serious (2) Major (3) Catastrophic (4) Multi Catastrophic (5) Potential Severity (1 - 5) Table Colour Code for Risk Evaluation Priority No Risk Nil Very Low Low Medium High Description No identified risk Present Interaction – cannot be considered in the initial evaluation, but it has the potential of affecting the system Little influence in other parts of the system Important Interaction – part of the initial evaluation Limited or uncertain influence through this interaction to other parts of the system Very Important Interaction – part of the initial evaluation They have influence in other part of the system Critic Interaction – Part of the initial evaluation High probability of influencing other parts of the system 2602 J Condor, K Asghari / Energy Procedia (2009) 2599–2605 Condor, J Asghari, K./ Energy Procedia 00 (2008) 000–000 Concept of Cause-Effect Plot[10] Once the values for the respective process have been given in the matrix, the next step is to find some mechanism to obtain a quantitative evaluation This is possible by the use of the Cause-Effect Plot The basic idea is to sum all the horizontal and vertical values of the cells corresponding to the interactions of an element The horizontal values are known as causes and the vertical, effects Figure represent the generation of the Cause-Effects coordinates Figure represents the generation of a Plot using the Cause-Effects coordinates The Plot has equidistant lines in an angle of 45º to the axis which represents the intensity of the element, and the perpendicular lines to them represent the domain of the element By using the Cause-Effect Plot it is possible to assign numerical values of intensity and domain of an element Ei in the geo-sequestration system Both, the intensity and domain are defined by simple equations: Ei Intensity : Ei Domain : C+E C−E … …… ………………………………………………Equation … …… …………………………………….…………Equation Figure Cause-Effect Coordinates Interactions in the rest of the cells Column : Influence of other elements on Rows : Influence of on other elements Figure Intensity and Domain of Parameters Intensity ∑I ij in j ( columns ) (CAUSE) (C − E ) / Ei Equidistant intensity lines Cause ∑I in i ( raws ) (C + E ) / ij = E Pj Equidistant domain lines = C Pi Effect Elements in the main diagonal Domain (EFFECT) Example of the Methodology The proposed Interaction Matrix for Long Term Wellbore Stability is made up of fifteen (15) elements (LDEs), but for this example, only six (6) of the elements are considered It is important to emphasize that each geosequestration system has a different matrix depending on its particular features Also the processes and events may vary depending on the scenario analysis, which means that the matrix may take into account different alternatives when modelling[11] Here is where the group of experts play a crucial role in defining the interactions and the values for the incident potential matrix J Condor, K Asghari / Energy Procedia (2009) 2599–2605 Condor, J; Asghari, K./ Energy Procedia 00 (2008) 000–000 2603 The examples showed in the Figures through illustrate the three main stages in evaluating the risks of CO2 leakage from wellbores using this methodology, based on Interaction Matrix, Incident Potential Matrix and the Cause-Effect Plot Figure is a matrix containing six elements and consequently thirty potential cells for interactions Each cell may have none or several interactions and these interactions should come from the list of FEPs Figure is the same interaction matrix after evaluated by an Incident Potential Matrix The code colour constitutes an easy way to see the critical interactions The numbers in the right and bellow the matrix are resulted from the summation of the values of the interactions in the horizontal rows and vertical columns, respectively These numbers are the coordinates that provide the input for the Cause-Effect Plot Finally, Figure plots all the elements of the system identifying their domains and intensities In this particular example, it is the cement plug which holds the highest values for domain (9.90) The highest values for intensity correspond to both cement plug and water composition (16.97) The interpretation for this particular example is that under certain assumptions, cement plug constitutes the element in the geo-sequestration system with the highest risk for CO2 leakage This information can be used for the initial evaluation of the system and consequently for devising mitigation plans to reduce their risks Also, later on, this same matrix may be used during the monitoring phase Figure Section of an interaction matrix (The numbers in the brackets corresponds to the names of the cells and not their numerical values) 2604 J Condor, K Asghari / Energy Procedia (2009) 2599–2605 Condor, J Asghari, K./ Energy Procedia 00 (2008) 000–000 Figure The Interaction Matrix after giving numerical values to the interaction cells The red numbers (right and bellow the matrix) correspond to the sum of the horizontal and vertical values of the interaction cells These numbers are the coordinates for the Cause-Effect Plot (Figure 7) Figure The Cause-Effect Plot for the Interaction Matrix In this particular example, is the element cement plug which has the highest values for intensity and domain and consequently it is the element in the geo-sequestration system with the highest risk to provide a pathway for the CO2 leakage J Condor, K Asghari / Energy Procedia (2009) 2599–2605 Condor, J; Asghari, K./ Energy Procedia 00 (2008) 000–000 2605 Conclusions and Recommendations This methodology has a great potential of being used in the probabilistic risk assessment and monitoring phases of wellbores and other components of geo-sequestration systems used for geological storage of CO2 Its major advantage consists in its simplicity and practical results Further studies may include the stochastic representation in the Incident Potential Matrix In such a way, instead of having a fixed number for risk, probability density functions can incorporate the uncertainty Acknowledgements The funding for this work was provided by Natural Resources Canada, NRCan, T&I projects, and the Petroleum Technology Research Centre, PTRC and the University of Regina References [1] Nordbotten, J.M., Celia, M.A., Bachu, S., Dahle, H.K Semianalytical Solution for CO2 Leakage through an Abandoned Well Environmental science & technology 2005 Jan 15;39(2):602-11 [2] M.A Celia, S Bachu, J.M Nordbotten, S.E Gasda, H.K Dahle Quantitative Estimation of CO2 Leakage from Geological Storage: Analytical Models, Numerical Models, and Data Needs Paper 228, presented at 7th International Conference on Greenhouse Gas Control Technologies [3] F.J Moreno, R Chalaturnyk, J Jimenez Methodology for Assessing Integrity of Bounding Seals (Wells and Caprock) for Geological Storage of CO2 7th Int Conf on Greenhouse Gas Control Technologies (eds Rubin, E.S Keith, D.W & Gilboy, C.F.), vol pp 731–740, Oxford, UK: Elsevier [4] K Tammaoto, O Kitamura, K Itaoka, M Akai A Risk Analysis Scheme of the CO2 Leakage from Geological Sequestration Presented at 7th International Conference on Greenhouse Gas Control Technologies [5] K Yamamoto, K Itaoka, C Yoshigahara, M Akai Simple Estimation Methodology of Leakage from Geologic Storage of CO2 Presented at 7th International Conference on Greenhouse Gas Control Technologies [6] Quintessa Limited CO2 FEP Database Available in internet [www.quintessa.org/co2fepdb] [7] Maul, P, Savage, D, Benbow, S, Walke, R, Bruin, R Development of a FEP Database for the Geological Storage of Carbon Dioxide Presented at 7th International Conference on Greenhouse Gas Control Technologies [8] The Netherlands Institute of Applied Geoscience TNO – National Geological Survey Risk Assessment using FEPs May 2003/7.53 [9] The Swedish Nuclear Fuel and Waste Management Co., SKB [www.skb.se] [10] John A Hudson Rock Engineering Systems: Theory and Practice Ellis Horwood, 1992 University of Michigan [11] Swedish Nuclear Fuel and Waste Management Co Project SAFE Scenario and system analysis Report R-0113  ... with the highest risk for CO2 leakage This information can be used for the initial evaluation of the system and consequently for devising mitigation plans to reduce their risks Also, later on,... represent the generation of the Cause-Effects coordinates Figure represents the generation of a Plot using the Cause-Effects coordinates The Plot has equidistant lines in an angle of 45º to the axis... represents the intensity of the element, and the perpendicular lines to them represent the domain of the element By using the Cause-Effect Plot it is possible to assign numerical values of intensity and