Monitoring, Measurement and Verification MMV: A Critical Component in Making the CO2 Sequestration Success

2021 ◽  
Author(s):  
Pankaj Kumar Tiwari ◽  
Debasis Priyadarshan Das ◽  
Parimal Arjun Patil ◽  
Prasanna Chidambaram ◽  
Zoann Low ◽  
...  
Keyword(s):  
Co2 Sequestration ◽  
Fiber Optic Sensor ◽  
Co2 Injection ◽  
Critical Component ◽  
High Co2 ◽  
Plume Migration ◽  
Well Integrity ◽  
Simulation Results ◽  
Co2 Plume ◽  
Gas Fields

Abstract The increasing atmospheric concentration of carbon dioxide (CO2), a greenhouse gas (GHG) is creating environmental imbalance and affecting the climate adversely due to growing industrialization. Global leaders are emphasizing on controlling the production of GHG. However, growing demands of natural gas, industry is embarking on the development of high CO2 contaminant gas fields to meet supply gap. Development and management of contaminated hydrocarbon gas fields add additional dimension of sequestration of CO2 after production and separation in project management. CO2 sequestration is a process for eternity with a possibility of zero-degree failure. Monitoring, measuring and verification (MMV) of injected CO2 volume in sequestration is critical component along with geological site selection, transportation, storage process. The present study discusses all the impacting parameters which makes whole process environment friendly, economically prudent and adhering to national and international regulations. The migration of injected CO2 plume in the reservoir is uncertain and its monitoring is equally challenging. The role of MMV planning is critical in development of high CO2 contaminant fields of offshore Sarawak. It substantiates that injected CO2 in the reservoir is intact and safely stored for hundreds of years after injection and possesses minimum to no risk to HS&E. The deployment of Multi-Fiber Optic Sensor System (M-FOSS) promises a cost-effective solution for monitoring the lateral & vertical migration of CO2 plume by acquiring 4D DAS-VSP (Distributed Acoustic Sensor – Vertical Seismic Profile) survey and for the well integrity by analyzing DAS/DTS (Distributed Temperature Sensor)/DPS (Distributed Pressure Sensor)/DSS (Distributed Strain Sensor) data. Simulation results and injectivity test at laboratory for in-situ CO2 injection has demonstrated the possibility of over 100MMscfd/well injection in aquifer to meet the total CO2 injection of 1.2Bscfd for full field development while maintaining the reservoir integrity. Uncertainty & risk analysis shows possible presence of seismically undistinguished fractures and minor faults, an early breakthrough of injected CO2 cannot be ruled out. The depleted reservoir storage study divulges the containment capacity of identified carbonate reservoirs as well as conformance of potential storage sites. The fault-seal analysis and reservoir integrity studies determine the robustness of the long-term security of the CO2 storage. Injectivity study demonstrates the optimum and maximum possible rates of CO2 injection into these depleted gas reservoirs. VSP simulation results show that a subsurface coverage of 3-4 km2 per well is achievable, which along with simulated CO2 plume extent help to determine the number of wells required to get maximum monitoring coverage for the MMV planning. The deployment of M-FOSS technology is novel and proactive approach to monitor the CO2 plume migration and well integrity. First ever development of MMV Planning for CO2 Sequestration in offshore Sarawak, Malaysia using novel and cutting-edge M-FOSS technology for proactive monitoring of CO2 plume migration and well integrity.

3D DAS-VSP Illumination Modeling for CO2 Plume Migration Monitoring in Offshore Sarawak, Malaysia

2021 ◽  
Author(s):  
Pankaj Kumar Tiwari ◽  
Zoann Low ◽  
Parimal Arjun Patil ◽  
Debasis Priyadarshan Das ◽  
Prasanna Chidambaram ◽  
...  
Keyword(s):  
Dynamic Simulation ◽  
Seismic Velocity ◽  
Time Lapse ◽  
Carbonate Reservoir ◽  
Fiber Optic Sensor ◽  
Co2 Injection ◽  
Storage Site ◽  
Plume Migration ◽  
Co2 Plume ◽  
4D Seismic

Abstract Monitoring of CO2 plume migration in a depleted carbonate reservoir is challenging and demand comprehensive and trailblazing monitoring technologies. 4D time-lapse seismic exhibits the migration of CO2 plume within geological storage but in the area affected by gas chimney due to poor signal-to-noise ratio (SNR), uncertainty in identifying and interpretation of CO2 plume gets exaggerated. High resolution 3D vertical seismic profile (VSP) survey using distributed acoustic sensor (DAS) technology fulfil the objective of obtaining the detailed subsurface image which include CO2 plume migration, reservoir architecture, sub-seismic faults and fracture networks as well as the caprock. Integration of quantitative geophysics and dynamic simulation with illumination modelling dignify the capabilities of 3D DAS-VSP for CO2 plume migration monitoring. The storage site has been studied in detailed and an integrated coupled dynamic simulation were performed and results were integrated with seismic forward modeling to demonstrate the CO2 plume migration with in reservoir and its impact on seismic amplitude. 3D VSP illumination modelling was carried out by integrating reservoir and overburden interpretations, acoustic logs and seismic velocity to illustrate the subsurface coverage area at top of reservoir. Several acquisition survey geometries were simulated based on different source carpet size for effective surface source contribution for subsurface illumination and results were analyzed to design the 3D VSP survey for early CO2 plume migration monitoring. The illumination simulation was integrated with dynamic simulation for fullfield CO2 plume migration monitoring with 3D DAS-VSP by incorporating Pseudo wells illumination analysis. Results of integrated coupled dynamic simulation and 4D seismic feasibility were analyzed for selection of best well location to deploy the multi fiber optic sensor system (M-FOSS) technology. Amplitude response of synthetic AVO (amplitude vs offsets) gathers at the top of carbonate reservoir were analyzed for near, mid and far angle stacks with respect to pre-production as well as pre-injection reservoir conditions. Observed promising results of distinguishable 25-30% of CO2 saturation in depleted reservoir from 4D time-lapse seismic envisage the application of 3D DAS-VSP acquisition. The source patch analysis of 3D VSP illumination modelling results indicate that a source carpet of 6km×6km would be cos-effectively sufficient to produce a maximum of approximately 2km in diameter subsurface illumination at the top of the reservoir. The Pseudo wells illumination analysis results show that current planned injection wells would probably able to monitor early CO2 injection but for the fullfield monitoring additional monitoring wells or a hybrid survey of VSP and surface seismic would be required. The integrated modeling approach ensures that 4D Seismic in subsurface CO2 plume monitoring is robust. Monitoring pressure build-ups from 3D DAS-VSP will reduce the associated risks.

Offshore MMV Planning for Sustainability of CO2 Storage in a Depleted Carbonate Reservoir, Malaysia

2021 ◽  
Author(s):  
Pankaj Kumar Tiwari ◽  
Debasis Priyadarshan Das ◽  
Parimal Arjun Patil ◽  
Prasanna Chidambaram ◽  
Zoann Low ◽  
...  
Keyword(s):  
Co2 Sequestration ◽  
Co2 Storage ◽  
Carbonate Reservoir ◽  
Co2 Injection ◽  
Storage Site ◽  
Gas Field ◽  
Plume Migration ◽  
Co2 Plume ◽  
The Impact

Abstract CO2 sequestration is a process for eternity with a possibility of zero-degree failure. Monitoring, Measurement and Verification (MMV) planning of CO2 sequestration is crucial along with geological site selection, transportation and injection process. Several geological formations have been evaluated in the past for potential storage site which divulges the containment capacity of identified large, depleted gas reservoirs as well as long term conformance. Offshore environment makes MMV plan challenging and demands rigorous integration of monitoring technologies to optimize project economic and involved logistics. The role of MMV is critical for sustainability of the CO2 storage project as it ensures that injected CO2 in the reservoir is intact and safely stored for hundreds of years post-injection. Field specific MMV technologies for CO2 plume migration with proactive approach were identified after exercising pre-defined screening criteria. Marine CO2 dispersion study is carried out to confirm the impact of any potential leakage along existing wells and faults, and to understand the CO2 behavior in marine environment in the event of leakage. Study incorporates integration of G&G subsurface and Meta-Ocean & Environment data along with other leakage character information. Multi-Fiber Optic Sensors System (M-FOSS) to be installed in injector wells for monitoring well & reservoir integrity, overburden integrity and monitoring of early CO2 plume migration by acquiring & analyzing the distributed sensing data (DTS/DPS/DAS/DSS). Based on 3D couple modeling, a maximum injection rate of approximately 200 MMscfd of permeate stream produced from a high CO2 contaminated gas field can be achieved. Injectivity studies indicate that over 100 MMSCFD of CO2 injection rates into depleted gas reservoir is possible from a single injector. Injectivity results are integrated with dynamic simulation to determine number and location of injector wells. 3D DAS-VSP simulation results show that a subsurface coverage of approximately 3 km2 per well is achievable, which along with simulated CO2 plume extent help to determine the number of wells required to get maximum monitoring coverage for the MMV planning. As planned injector wells are field centric and storage site area is large, DAS-VSP find limited coverage to monitor the CO2 plume. To overcome this challenge, requirement of surface seismic acquisition survey is recommended for full field monitoring. An integrated MMV plan is designed for cost-effective long-term offshore monitoring of CO2 plume migration. The present study discusses the impacting parameters which make the whole process environmentally sustainable, economically viable and adhering to national and international regulations.

scholarly journals Numerical Simulation and Optimization of CO2 Sequestration in Saline Aquifers

2012 ◽  
Author(s):  
Zheming Zhang ◽  
Ramesh Agarwal
Keyword(s):  
Numerical Simulation ◽  
Co2 Sequestration ◽  
Storage Capacity ◽  
Co2 Storage ◽  
Injection Well ◽  
Co2 Injection ◽  
Great Promise ◽  
Saline Aquifer ◽  
Simulation And Optimization ◽  
Co2 Plume

With recent concerns on CO2 emissions from coal fired electricity generation plants; there has been major emphasis on the development of safe and economical Carbon Dioxide Capture and Sequestration (CCS) technology worldwide. Saline reservoirs are attractive geological sites for CO2 sequestration because of their huge capacity for sequestration. Over the last decade, numerical simulation codes have been developed in U.S, Europe and Japan to determine a priori the CO2 storage capacity of a saline aquifer and provide risk assessment with reasonable confidence before the actual deployment of CO2 sequestration can proceed with enormous investment. In U.S, TOUGH2 numerical simulator has been widely used for this purpose. However at present it does not have the capability to determine optimal parameters such as injection rate, injection pressure, injection depth for vertical and horizontal wells etc. for optimization of the CO2 storage capacity and for minimizing the leakage potential by confining the plume migration. This paper describes the development of a “Genetic Algorithm (GA)” based optimizer for TOUGH2 that can be used by the industry with good confidence to optimize the CO2 storage capacity in a saline aquifer of interest. This new code including the TOUGH2 and the GA optimizer is designated as “GATOUGH2”. It has been validated by conducting simulations of three widely used benchmark problems by the CCS researchers worldwide: (a) Study of CO2 plume evolution and leakage through an abandoned well, (b) Study of enhanced CH4 recovery in combination with CO2 storage in depleted gas reservoirs, and (c) Study of CO2 injection into a heterogeneous geological formation. Our results of these simulations are in excellent agreement with those of other researchers obtained with different codes. The validated code has been employed to optimize the proposed water-alternating-gas (WAG) injection scheme for (a) a vertical CO2 injection well and (b) a horizontal CO2 injection well, for optimizing the CO2 sequestration capacity of an aquifer. These optimized calculations are compared with the brute force nearly optimized results obtained by performing a large number of calculations. These comparisons demonstrate the significant efficiency and accuracy of GATOUGH2 as an optimizer for TOUGH2. This capability holds a great promise in studying a host of other problems in CO2 sequestration such as how to optimally accelerate the capillary trapping, accelerate the dissolution of CO2 in water or brine, and immobilize the CO2 plume.

Modeling, Simulation, and Optimization of Geological Sequestration of CO2

2019 ◽  
Vol 141 (10) ◽  
Author(s):  
Ramesh K. Agarwal
Keyword(s):  
Fluid Dynamics ◽  
Co2 Sequestration ◽  
Spatial Scales ◽  
The United States ◽  
Co2 Injection ◽  
Temporal Scales ◽  
Simulation And Optimization ◽  
Modeling Simulation ◽  
Plume Migration ◽  
Basic Fluid

With heightened concerns on carbon dioxide (CO2) emissions from coal power plants, there has been a major emphasis in recent years on development of safe and economical geological carbon sequestration (GCS) technology. However, the detailed multiphase fluid dynamics and processes of GCS are not fully understood because various CO2 trapping mechanisms in geological formations have large variations in both spatial and temporal scales. As a result, there remain many uncertainties in determining the sequestration capacity of the reservoir and the safety of sequestered CO2 due to leakage. Furthermore, the sequestration efficiency is highly dependent on the CO2 injection strategy, which includes injection rate, injection pressure, and type of injection well, and its orientation, etc. The goal of GCS is to maximize the sequestration capacity and minimize the plume migration by optimizing the GCS operation. In this paper, first the basic fluid dynamics and trapping mechanisms for CO2 sequestration are briefly discussed. They are followed by a brief summary of current GCS projects worldwide with special emphasis on those in the United States. Majority of the paper is devoted to the numerical modeling, simulation, and optimization of CO2 sequestration in saline aquifers at macro spatial scales of a few to hundreds of kilometers and macro temporal scales of a few to hundreds of years. Examples of numerical simulations of a few large industrial scale projects are presented. The optimization studies include the investigation of various injection and well placement strategies to determine the optimal approach for maximizing the storage and minimizing the plume migration.

Safeguarding CO2 Storage in a Depleted Offshore Gas Field with Adaptive Approach of Monitoring, Measurement and Verification MMV

2021 ◽  
Author(s):  
Pankaj Kumar Tiwari ◽  
Prasanna Chidambaram ◽  
Ahmad Ismail Azahree ◽  
Debasis Priyadarshan Das ◽  
Parimal Arjun Patil ◽  
...  
Keyword(s):  
Co2 Sequestration ◽  
Co2 Storage ◽  
Storage Site ◽  
Injection Wells ◽  
Plume Front ◽  
Plume Migration ◽  
Co2 Plume ◽  
4D Seismic ◽  
And Storage

Abstract CO2 sequestration is a process for eternity with a possibility of zero-degree failure. One of the key components of the CO2 Sequestration Project is to have a site-specific, risk-based and adaptive Monitoring, Measurement and Verification (MMV) plan. The storage site has been studied thoroughly and is understood to be inherently safe for CO2 sequestration. However, it is incumbent on operator to manage and minimize storage risks. MMV planning is critical along with geological site selection, transportation and storage process. Geological evaluation study of the storage site suggests the containment capacity of identified large depleted gas reservoirs as well as long term conformance due to thick interval. The fault-seal analysis and reservoir integrity study contemplate long-term security of the CO2 storage. An integrated 3D reservoir dynamic simulation model coupled with geomechanical and geochemical models were performed. This helps in understanding storage capacity, trapping mechanisms, reservoir integrity, plume migration path, and injectivity. To demonstrate that CO2 plume migration can be mapped from the seismic, a 4D Seismic feasibility study was carried out using well and fluid data. Gassmann fluid substitution was performed in carbonate reservoir at well, and seismic response of several combination of fluid saturation scenarios on synthetic gathers were analyzed. The CO2 dispersion study, which incorporate integration of subsurface, geomatic and metocean & environment data along with leakage character information, was carried out to understand the potential leakage pathway along existing wells and faults which enable to design a monitoring plan accordingly. The monitoring of wells & reservoir integrity, overburden integrity will be carried out by Fiber Optic System to be installed in injection wells. Significant difference in seismic amplitude observed at the reservoir top during 4D seismic feasibility study for varying CO2 saturation suggests that monitoring of CO2 plume migration from seismic is possible. CO2 plume front with as low as 25% saturation can be discriminated provided seismic data has high signal noise ratio (SNR). 3D DAS-VSP acquisition modeling results show that a subsurface coverage of approximately 3 km2 per well is achievable. Laboratory injectivity studies and three-way coupled modelling simulations established that three injection wells will be required to achieve the target injection rate. As planned injection wells are field centric and storage site area is large, DAS-VSP find limited coverage to monitor the CO2 plume front. Hence, surface seismic acquisition will be an integral component of full field monitoring and time-lapsed evaluations for integrated MMV planning to monitor CO2 plume migration. The integrated MMV planning is designed to ensure that injected CO2 in the reservoir is intact and safely stored for hundreds of years after injection. Field specific MMV technologies for CO2 plume migration with proactive approach were identified after exercising pre-defined screening criteria.

Material Selection and Corrosion Rate Analysis for CO2 Injection Well: A Case Study of K1 Field CO2 Sequestration Project

2021 ◽  
Author(s):  
Mohd Azuan Abu Bakar ◽  
Wan Amni Wan Mohamad ◽  
M Wahidullah Moh Wahi ◽  
Muhammad Syafeeq Ebining Amir
Keyword(s):  
Co2 Sequestration ◽  
Material Selection ◽  
Mechanical Damage ◽  
Field Application ◽  
Injection Well ◽  
Co2 Injection ◽  
Base Case ◽  
Operating Life ◽  
Suitable Material ◽  
Well Integrity

Abstract The CO2 sequestration project is becoming increasingly attractive due to tax exemption benefits and as an initiative to reduce the global warming effect (D'Alesio, P., Poloni, R., Valente, P., & Magarini, P. A.2010). One of the major challenges in CO2 sequestration project is to ensure that the injection well integrity is intact throughout the well operating life. CO2 gas leakage to the surface or sea is unacceptable. Therefore, the considerations of using exotic/premium tubing materials are usually considered as the base case for continuous long-term operations (Baklid, A., Korbol, R., & Owren, G.1996). Typical materials used for CO2 injector wells are either Corrosion Resistant Alloy (CRA) or epoxy lined tubulars. The most widely adopted CRA material is 25 Cr (L. Smith, M.A. Billingham, C.-H. Lee, D. Milanovic, 2011). Selection of 25 Cr material is considered as conservative and may well be overdesigning. The main drawback is the high well cost associated with the application of 25 Cr tubing. Meanwhile, alternative materials such as epoxy lined tubulars are exposed to high temperature and pressure blistering effects and prone to mechanical damage caused by wireline activities, hauling, running, and pulling off the tubing (Newton, L. E., & McClay, R. A, 1977). Application of materials other than 25 Cr for CO2 injector wells, such as 22 Cr, Super 17 Cr, Super 15 Cr, Super 13 Cr, 13 Cr and carbon steel are uncommon but may be fit for purpose. Detailed studies using analytical method and physical tests are required to further qualify these materials for application in CO2 injector wells. These studies should cover all possible conditions throughout the well life such as injection, shut-in, flowback and by considering surface and bottom hole conditions which may contribute to increase in the corrosion rates for different types of materials. Other tests warranted before selecting the suitable material for field application include physical coupon, Sulfide Stress Cracking (SSC) and Stress Corrosion Cracking (SCC) tests. This paper describes the material selection methodology and corrosion studies performed in the K1 field CO2 sequestration project using the other materials mentioned above as an effort to optimize well costs and improve overall project economics without jeopardizing the CO2 injector well integrity.

Preliminary results of numerical simulation in a small-scale CO2 injection pilot site: 1. Prediction of CO2 plume migration

2015 ◽  
Vol 51 (5) ◽  
pp. 487 ◽  
Author(s):  
Byoung-Young Choi ◽  
Yong-Chan Park ◽  
Young-Jae Shin ◽  
Kue-Young Kim ◽  
Gi-Tak Chae ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Co2 Injection ◽  
Small Scale ◽  
Pilot Site ◽  
Preliminary Results ◽  
Plume Migration ◽  
Co2 Plume

4D Seismic in Subsurface CO2 Plume Monitoring – Why It Matters?

2021 ◽  
Author(s):  
Pankaj Kumar Tiwari ◽  
Debasis Priyadarshan Das ◽  
Parimal Arjun Patil ◽  
Prasanna Chidambaram ◽  
Prasanna Kumar Chandran ◽  
...  
Keyword(s):  
Dynamic Simulation ◽  
Time Lapse ◽  
Carbonate Reservoir ◽  
Acoustic Properties ◽  
Co2 Injection ◽  
Seismic Amplitude ◽  
Plume Migration ◽  
Fluid Properties ◽  
Co2 Plume ◽  
4D Seismic

Abstract CO2 sequestration in depleted carbonate reservoir stipulate incorporation of comprehensive and trailblazing monitoring technologies. 4D time-lapse seismic is sine qua non for Monitoring, Measurement and Verification (MMV) planning to demonstrate the migration of CO2 plume within geological storage. An ingenious, adaptive and site specific MMV plan for monitoring CO2 plume is paramount to minimize possible subsurface and project integrity risks. Integration of dynamic simulation with seismic forward modeling aggrandize the capabilities of 4D seismic in CO2 sequestration projects. Depleted carbonate reservoir has been thoroughly studied and its geomechanical and geochemical modeling results were coupled into dynamic simulation. Reservoir porosity and fluid properties along with CO2 saturation and injection pressure distribution within each reservoir level were generated. The dynamic simulation results were integrated with seismic forward modeling to demonstrate the CO2 plume migration and its impact on seismic amplitude. Fluid acoustic properties were computed for carbonate reservoir using FLAG method. Selection of wells was based on availability of superior quality acoustic logs as well as those representing the reservoir best. Gassmann fluid substitution exercise was carried using dry rock modeling. Several scenarios were generated, and results were analyzed to demonstrate the effect of CO2 saturation and pressure build-ups within reservoir on the seismic amplitude due to continuous CO2 injection. Synthetic seismic AVO gathers were generated for angles ranging from 5 to 50 degree. Near, Mid and Far seismic amplitude response at the top of carbonate reservoir were analyzed with respect to in-situ condition for each scenario. Results reveal that CO2 saturation as low as 25 - 30% in depleted carbonate reservoir can be distinguished from 4D time-lapse seismic. With continuous CO2 injection, the reservoir pressure increases and this in turn controls the properties of both in-situ and injected fluids. The gradual changes in fluid properties and their impact on bulk acoustic properties of reservoir were modeled to assess the feasibility of using 4D seismic as a predictive tool for detection of localized and provincial pressure build-ups. Modeling results show that although observed changes in amplitude on synthetic gathers were subtle, it is expected that 4D seismic with high signal-to-noise ratio possibly be able to image such localized pressure build-ups. To monitor CO2 plume migration as well as localized pressure build-ups, we recommend acquiring multi-azimuth (MAZ) surface seismic in combination with 3D DAS-VSP for superior subsurface imaging. The integrated modeling approach ensures that 4D Seismic in subsurface CO2 plume monitoring is robust. Monitoring pressure build-ups from MAZ surface seismic and 3D DAS-VSP will reduce the associated risks.

Experimental and Modeling Study of Salt Precipitation During Injection of CO2 Contaminated With H2S Into Depleted Gas Fields in the Northeast of the Netherlands

SPE Journal ◽  
2014 ◽  
Vol 19 (06) ◽  
pp. 1058-1068 ◽  
Author(s):  
P.. Bolourinejad ◽  
R.. Herber
Keyword(s):  
The Netherlands ◽  
Carbonic Acid ◽  
Co2 Storage ◽  
Mineral Dissolution ◽  
Co2 Injection ◽  
Salt Precipitation ◽  
Geological Time ◽  
Core Samples ◽  
Carbon Dioxide Co2 ◽  
Gas Fields

Summary Depleted gas fields are among the most probable candidates for subsurface storage of carbon dioxide (CO2). With proven reservoir and qualified seal, these fields have retained gas over geological time scales. However, unlike methane, injection of CO2 changes the pH of the brine because of the formation of carbonic acid. Subsequent dissolution/precipitation of minerals changes the porosity/permeability of reservoir and caprock. Thus, for adequate, safe, and effective CO2 storage, the subsurface system needs to be fully understood. An important aspect for subsurface storage of CO2 is purity of this gas, which influences risk and cost of the process. To investigate the effects of CO2 plus impurities in a real case example, we have carried out medium-term (30-day) laboratory experiments (300 bar, 100°C) on reservoir and caprock core samples from gas fields in the northeast of the Netherlands. In addition, we attempted to determine the maximum allowable concentration of one of the possible impurities in the CO2 stream [hydrogen sulfide (H2S)] in these fields. The injected gases—CO2, CO2+100 ppm H2S, and CO2+5,000 ppm H2S—were reacting with core samples and brine (81 g/L Na+, 173 g/L Cl−, 22 g/L Ca2+, 23 g/L Mg2+, 1.5 g/L K+, and 0.2 g/L SO42−). Before and after the experiments, the core samples were analyzed by scanning electron microscope (SEM) and X-ray diffraction (XRD) for mineralogical variations. The permeability of the samples was also measured. After the experiments, dissolution of feldspars, carbonates, and kaolinite was observed as expected. In addition, we observed fresh precipitation of kaolinite. However, two significant results were obtained when adding H2S to the CO2 stream. First, we observed precipitation of sulfate minerals (anhydrite and pyrite). This differs from results after pure CO2 injection, where dissolution of anhydrite was dominant in the samples. Second, severe salt precipitation took place in the presence of H2S. This is mainly caused by the nucleation of anhydrite and pyrite, which enabled halite precipitation, and to a lesser degree by the higher solubility of H2S in water and higher water content of the gas phase in the presence of H2S. This was confirmed by the use of CMG-GEM (CMG 2011) modeling software. The precipitation of halite, anhydrite, and pyrite affects the permeability of the samples in different ways. After pure CO2 and CO2+100 ppm H2S injection, permeability of the reservoir samples increased by 10–30% and ≤3%, respectively. In caprock samples, permeability increased by a factor of 3–10 and 1.3, respectively. However, after addition of 5,000 ppm H2S, the permeability of all samples decreased significantly. In the case of CO2+100 ppm H2S, halite, anhydrite, and pyrite precipitation did balance mineral dissolution, causing minimal variation in the permeability of samples.

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