Science-Based Risk Assessment and Wellbores and in a CO 2 Storage System

Transcription

1 Science-Based Risk Assessment and Wellbores and in a CO 2 Storage System Wellbores Factors in CCS Operations Placement of CO 2 economic (number of wellbores needed; maintenance, P&A, etc.) Potential release of CO 2 (penetration through primary seal) poor completion or abandonment mechanical damage chemical damage (corrosion of cement; corrosion of casing) George Guthrie Fossil Energy & Environment Programs Los Alamos National Laboratory Potential conduits/fastpaths for CO 2 movement within the geologic site must address phase-change effects

2 Wellbore integrity is important in long-term CO 2 storage. Wellbores are typically completed & plugged with portland-based cement hydrated portland cements contain calcium hydroxide (a base) and other acid sensitive materials Portland cements can degrade in the presence of CO 2 & water CO 2 + water => carbonic acid batch experiments suggest rapid degradation by carbonic acid

3 How can we scale fundamental processes to system-level behavior? chemical reactions involving fluids and solids in a heterogeneous porous medium coupled to fluid flow field kinetics often differ from lab determined? CO 2 +brine dissolves hydrated cement

4 Quantitative risk assessment is a formal process to minimize potential consequences of long-term storage. atmosphere; anthropogenic systems groundwater system CO 2 storage reservoir Risk assessment must consider the potential for CO 2 release and subsequent movement from storage reservoir to various receptors.

5 CO 2 -PENS is a probabilistic system model relying on several modules associated with wellbore release. CO 2 Capture at Power Plants CO 2 Transport and Injection CO 2 Storage in Geologic Reservoir CO 2 Movement from Reservoir CO 2 CO 2 CO 2 Storage System Potential Release Mechanism Transport Potential Receptors Lateral Migration Saturated Porous Flow Unsaturated Porous Flow Other Reservoirs Carbonate Reservoir Seal Release Fracture Flow Water Wells Well Bore Release Well Bore Flow Atmospheric Systems

6 Science based prediction of natural system performance requires system-level probabilities based on process level phenomena. Wellbore Permeability i iii ii iv time time Possible scenarios for wellbore fate i. wellbores degrade rapidly ii. wellbores degrade slowly iii. wellbores improve over time iv. wellbores are unaffected by CO 2 +brine theory, experiment, computation observation (analog sites)

7 Several pathways have the potential to contribute to CO 2 release from wellbores. 0. dissolution/corrosion of cement 1. flow between cement & casing (Gasda et al. mechanisms A & B) 2a. diffusion through cement (Gasda et al. mechanism C) 2b. fracture flow through cement (Gasda et al. mechanism E) 3. flow between cement & shale (Gasda et al. mechanism F) Gasda, Bachu, Celia, 2004 Princeton CMI

8 CO 2 -EOR operations routinely utilize wellbore technology to place (and to contain) fluids within the reservoir SACROC is one of several industrial-scale examples in the Permian Basin ~13.5 million tonnes of CO 2 /yr injected (~6-7 million t/yr of new CO 2 ) ~ 70 million tonnes CO 2 accumulated (>30 million tonnes anthropogenic) CO 2 injection since 1972 Carey et al., 2007

9 Whipstock drilling at SACROC 49-6 provided recovery of core through cemented annulus to within 12 of top of pay. Drilled/completed 1950 Water flood initiated 1954 First direct CO 2 exposure yrs as injector; 7 yrs as producer Top of Pay Carey et al., 2005, SPE; Guthrie et al., 2005, Midland CO 2 Conf.

10 Observations suggest initial flow along interfaces followed by precipitation of silica and carbonate phases. fluid flow along interface into sandy unit in shale precipitation of silica and carbonate from brine along interfacial zones diffusive carbonation of cement to form orange zone wellbore shale caprock casing silica-carbonate precipitation pristine cement carbonated cement Guthrie et al., 2005, Midland CO 2 Conf.; Carey et al., 2007 shale fragment zone

11 Cement sample from SACROC 49-6 (6550 near top of pay) was exposed to CO 2 for ~ 30 years (~110,000 tonnes). pristine hydrated cement (portlandite (Ca(OH) 2 ) in matrix/veins) limits both complete dissolution & Gasda et al. mechanisms C&E thin carbonated zone between cement and casing (Gasda et al. mechanism A) orange carbonated cement ( popcorn texture) (Gasda et al. mech.s C&F) gray carbonated vein fluid flow followed by precipitation of silica/carbonate wellbore shale caprock casing silica-carbonate precipitation pristine cement carbonated cement Carey et al., 2007, Int. J. GHG Control, 1:75-85 shale fragment zone

12 Summary of major processes occurring at wellbore dissolution/corrosion of cement 1. flow between cement & casing (Gasda et al. mechanisms A & B) precipitation along interface 2a. diffusion through cement (Gasda et al. mechanism C) minimal Ca(OH) 2 preserved 2b. fracture flow through cement (Gasda et al. mechanism E) minimal Ca(OH) 2 along fractures Gasda, Bachu, Celia, 2004 Princeton CMI 3. flow between cement & shale (Gasda et al. mechanism F) cement alteration; precipitation filling voids

13 Field observations have elucidated fluid-rock reactions, some of which can now be modeled at the continuum scale. Carey et al., 2007, Int. J. GHG Control, 1:75-85 Lichtner & Carey, 2006, GCA, 70:

14 Field observations have elucidated fluid-rock reactions, some of which can now be modeled at the continuum scale. Relative Permeability (md; air dried) (B. Svec, NMT) Upper Cement (~5160 ) 0.09 Lower Cement (~6550 ) Carey et al., 2007, Int. J. GHG Control, 1:75-85 Lichtner & Carey, 2006, GCA, 70: Orange Zone (~6550 )

15 Flow-through experimental models can reproduce many of the observations from the field samples. Orange Zone Mineralization cement alteration zone Mineralization along casing-cement interface Wigand, Carey, Hollis, Kaszuba, 2007 (LA-UR )

16 Assessing Wellbore Integrity Following CO 2 Exposure by a Combination of Field, Experiment, Theory, and Computation Analysis of field samples of cement exposed to CO 2 (in collaboration with Kinder-Morgan CO 2 company) Laboratory experiments on cement exposure to CO 2 Numerical simulation of cement degradation Field observations on gas migration through wellbore cements in Alberta (in collaboration with Alberta Electric Utilities Board) Application of non-linear acoustic methods to detect fractures in wellbore cements

17 Approximations used in traditional approaches preclude the ability to capture coupled wellbore-reservoir processes in large simulations. Finite Element Heat & Mass (FEHM) numerical simulator Multi-dimensional, multi-phase porous media heat & mass transfer simulator (brine,water, CO2, methane hydrates) Coupled flow, reactive transport, and stress capabilities Finite volume method captures complex geology Incorporation of wellbores and near-wellbore radial flow computationally efficient 60 km 60 km Modeling of reservoir-scale observations can be used to assess effective permeability. Pawar, 2007 (LA-UR )

18 Example application of CO 2 -PENS: Impact of release through wellbores Permeable layer : 5 m thick Impermeable layer : 200 m thick Primary CO 2 storage reservoir: 20 m thick Hypothetical Sequestration Site Injection well Pawar, 2007 (LA-UR )

19 CO 2 Fraction near Wellbore in Hypothetical Storage System (Base Case) 50 years In top aquifer Mass of CO 2 (% of injected CO 2 ) Time (years) In reservoir Pawar, 2007 (LA-UR )

20 Numerous variables can impact the processes that control wellbore integrity. Hydration State of Cement (porosity, permeability, mineralogy) slurry characteristics (cement type; admixtures; fluids; water:cement ratio; drilling muds) hydration conditions (reservoir fluids; P, T, time) Physical State of Wellbore System wellbore fractures and flow pathways effective permeability of wellbore (cement permeability; flow along interfaces and fractures) materials properties (rock, casing, hydrated cement) P, T, Chemical and Biological State of Wellbore System fluid chemistry (P CO2, T, brine composition, reservoir rocks, ) sulfur cycle?

21 Cements used in well completions have varied over time. first oil well first use of cement slurry first use of pozzolans first standards committee additives; 4 cement types 38 additives; 8 cement types 3 additives; 2 cement types no additives; 1 cement type first portland cement in U.S. after Smith (1976)

22 Additives can have a profound impact on cement properties. Accelerating agents salts (CaCl 2, NaCl) Dispersing agents sulfonates lignin High density additives barite hematite Retarding agents lignosulfonates phosphonates CMHEC diesel Low density additives bentonites Na-silicates pozzolans (e.g., fly ash, tuff, diatomaceous earth) walnut shells coal cellophane

23 Reservoir fluid chemistries can impact the hydration of cement and subsequent carbonated-brine interactions.

24 Summary Wellbores are critical components of a CO 2 storage system Placement of CO 2 Potential release pathways from reservoir Potential conduits/fastpaths for CO 2 movement Predicting the integrity of wellbores/cement requires integration of experiments, field observations, theory to upscale fundamental processes to system level field, field, field more observations needed In some examples, CO 2 +brine+cement interactions may improve integrity of wellbore