Eric Mackay, Hydra Rodrigues and Dan Arnold, Heriot Watt University

February 18, 2021

Water Alternating Gas (WAG) injection has been applied in Brazilian Pre-salt carbonate reservoirs to reduce residual oil saturation and gas flaring by recycling CO2 that is naturally produced alongside hydrocarbon gas. The original oil contains a high concentration of CO2 contaminant, and the long distance to the shore (up to 300 km) precludes CO2 transportation of any sort. Values of CO2 content in the gas phase can range from 1% to 35% mol/mol in the Santos Basin and with the high gas oil ratios (GOR) of these reservoirs, flaring must be avoided.

However, applying WAG in highly reactive and heterogeneous carbonate rocks can potentially create severe scaling problems. Even with extreme reduction of sulphate scale with seawater desulphation prior to injection, a big risk of calcite scale is still a reality.

The Brazilian Pre-salt carbonate reservoirs, which are limestone and dolomite, are superimposed by thick sealing layers of anhydrite and halite and they can suffer more intense dissolution in high pressure zones, such as at the injection wellbores. When the brine approaches to production wells and it is subjected to large pressure drops, part of the CO2 will gradually be released, raising the pH of the brine. Under these conditions, calcite precipitation may occur, plugging the pores around production wells, tubing and surface facilities.

In this work we use reservoir modelling and simulation tools to investigate how to operate a field in this context to achieve high returns on investment, utilize the CO2 produced sustainably (avoiding flaring) and prevent calcite scale hazards.

Eric Mackay, Hydra Rodrigues and Dan Arnold, Heriot Watt University

February 18, 2021

Water Alternating Gas (WAG) injection has been applied in Brazilian Pre-salt carbonate reservoirs to reduce residual oil saturation and gas flaring by recycling CO2 that is naturally produced alongside hydrocarbon gas. The original oil contains a high concentration of CO2 contaminant, and the long distance to the shore (up to 300 km) precludes CO2 transportation of any sort. Values of CO2 content in the gas phase can range from 1% to 35% mol/mol in the Santos Basin and with the high gas oil ratios (GOR) of these reservoirs, flaring must be avoided.

However, applying WAG in highly reactive and heterogeneous carbonate rocks can potentially create severe scaling problems. Even with extreme reduction of sulphate scale with seawater desulphation prior to injection, a big risk of calcite scale is still a reality.

The Brazilian Pre-salt carbonate reservoirs, which are limestone and dolomite, are superimposed by thick sealing layers of anhydrite and halite and they can suffer more intense dissolution in high pressure zones, such as at the injection wellbores. When the brine approaches to production wells and it is subjected to large pressure drops, part of the CO2 will gradually be released, raising the pH of the brine. Under these conditions, calcite precipitation may occur, plugging the pores around production wells, tubing and surface facilities.

In this work we use reservoir modelling and simulation tools to investigate how to operate a field in this context to achieve high returns on investment, utilize the CO2 produced sustainably (avoiding flaring) and prevent calcite scale hazards.

D. Loeve, E. Peters, S. Belfroid, F. Neele, and S.Hurter, Netherlands Organisation for Applied Scientific Research (TNO)

February 18, 2021

CO2 storage in depleted gas fields in the North Sea are a significant opportunity to reduce Europe’sCO2 emissions. The knowledge and experience gained during operation of such fields provide spatialand temporal data which is lacking for storage projects in saline aquifers. In the absence of strongaquifers, a gas field will terminate production at low pressures. Converting such a field for CO2injection ensures at least the initial capacity for storage. It is possible to maximise storage integrityby placing a constraint of a maximum pressure below the initial reservoir pressure or hydrostaticpressure. This will ensure the injected fluids will tend to remain in the storage container. However,depleted fields have their own challenges. For instance, CO2 will reach the storage field at atemperature much lower than the reservoir pressure. Next, CO2 is to be injected in a low pressurereservoir. The combination of low pressure and low temperature requires careful pipeline-wellmanagement to avoid several issues such as hydration formation in the near wellbore area andthermal stresses due to shrinkage in the rock-cement-well system. Coupled hydro-thermalsimulation of the well-reservoir system is of the utmost importance for both operations andconformance monitoring. Using coupled simulations the operational envelope can be identified forpressure, temperature and composition. First, we present a simple synthetic model with typicalcharacteristics of North Sea depleted gas fields to illustrate the features and challenges of CO2injection in a depleted gas field, focusing on coupled heat and multi-phase fluid flow effects. Thenwe present a workflow that uses reservoir simulation to produce a catalogue of inflow performancecurves / injectivity indices that can be used as input to include the reservoir response in thesimulation of flow in the well and pipeline, which are essential for planning and managing theoperation of CO2 injection and storage in depleted gas fields.

D. Loeve, E. Peters, S. Belfroid, F. Neele, and S.Hurter, Netherlands Organisation for Applied Scientific Research (TNO)

February 18, 2021

CO2 storage in depleted gas fields in the North Sea are a significant opportunity to reduce Europe’sCO2 emissions. The knowledge and experience gained during operation of such fields provide spatialand temporal data which is lacking for storage projects in saline aquifers. In the absence of strongaquifers, a gas field will terminate production at low pressures. Converting such a field for CO2injection ensures at least the initial capacity for storage. It is possible to maximise storage integrityby placing a constraint of a maximum pressure below the initial reservoir pressure or hydrostaticpressure. This will ensure the injected fluids will tend to remain in the storage container. However,depleted fields have their own challenges. For instance, CO2 will reach the storage field at atemperature much lower than the reservoir pressure. Next, CO2 is to be injected in a low pressurereservoir. The combination of low pressure and low temperature requires careful pipeline-wellmanagement to avoid several issues such as hydration formation in the near wellbore area andthermal stresses due to shrinkage in the rock-cement-well system. Coupled hydro-thermalsimulation of the well-reservoir system is of the utmost importance for both operations andconformance monitoring. Using coupled simulations the operational envelope can be identified forpressure, temperature and composition. First, we present a simple synthetic model with typicalcharacteristics of North Sea depleted gas fields to illustrate the features and challenges of CO2injection in a depleted gas field, focusing on coupled heat and multi-phase fluid flow effects. Thenwe present a workflow that uses reservoir simulation to produce a catalogue of inflow performancecurves / injectivity indices that can be used as input to include the reservoir response in thesimulation of flow in the well and pipeline, which are essential for planning and managing theoperation of CO2 injection and storage in depleted gas fields.

Daniel Aramburo, Rowan Haddad, Thijs Huijskes, EBN

February 18, 2021

The Port of Rotterdam CO2 Transport Hub and Offshore Storage (Porthos) project is an innovative carbon capture and storage (CCS) project being prepared at Europe’s biggest port. Porthos will be capable of storing approximately 2.5 million tonnes (Mt) of CO2 per year in the depleted P18 natural gas fields offshore in the Netherlands. The reservoir modelling work included a complete integration from history match, simulation until the end of production which initializes the reservoir model for the CO2 injection period.

The integrated modelling approach allows an optimized injection scenario that satisfies operational as well as commercial requirements and limits. Through our workflow, we address the following challenges:

• Injecting cold (high pressure) CO2 at low reservoir pressure leads to strong Joule-Thomson cooling and phase changes in the wellbore and the reservoir: a simplified coupling approach for steady state between wellbore and reservoir model is demonstrated to capture the full thermodynamics of the injected CO2 and arrive at a safe operational envelope.
• Variation in reservoir stresses during depletion and reinjection due to pressure and temperature changes imposes further uncertainties on the injectivity due to potential fracturing: a coupling approach between geomechanics and reservoir model to evaluate the impact on injectivity will be demonstrated to close the loop with the previously coupled wellbore model.
• Variation in reservoir stresses during depletion and reinjection due to pressure and temperature changes require a fault and cap rock integrity assessment: a coupling approach

Ahmed Elgendy, ENI S.P.A.

February 19, 2021

Cap rock integrity and thermally induced fractures (TIF) are two key issues to be evaluated when dealing with CO2 sequestration projects. We will present the current status of geomechanical modelling strategy for CO2 disposal projects, the actual developments towards a single integrated modelling environment (CMG-GEM). The presentation shall include several comparisons (case studies):

1. ECL-ABAQUS Vs CMG-GEM for subsidence prediction (PUNQ-S3)
2. COMSOL Vs CMG-GEM for TIF evaluation (Perkins analytical model)
3. COMSOL Vs CMG-GEM for TIF evaluation (Real case study)

Geochemical investigation in CCS operation: a new perspective

In the framework of Carbon Capture and Storage (CCS), geochemical investigation plays an important role in the assessment of the main physical and the chemical phenomena occurring during and after the CO2 injection in sedimentary formations. To increase the reliability and specificity of the investigation a strong integration between experimental analysis and numerical modelling is nowadays mandatory. Under this theme we shall present:

1. An integrated workflow starting from real samples, couples lab activities and numerical simulations
2. Comparative analysis between PHREEQC-3 and CMG-GEM via 0D (batch) models
3. CO2 injection in 2D multi-layered radial model (including site-specific minerals)

Ahmed Elgendy, ENI S.P.A.

February 19, 2021

Cap rock integrity and thermally induced fractures (TIF) are two key issues to be evaluated when dealing with CO2 sequestration projects. We will present the current status of geomechanical modelling strategy for CO2 disposal projects, the actual developments towards a single integrated modelling environment (CMG-GEM). The presentation shall include several comparisons (case studies):

1. ECL-ABAQUS Vs CMG-GEM for subsidence prediction (PUNQ-S3)
2. COMSOL Vs CMG-GEM for TIF evaluation (Perkins analytical model)
3. COMSOL Vs CMG-GEM for TIF evaluation (Real case study)

Geochemical investigation in CCS operation: a new perspective

In the framework of Carbon Capture and Storage (CCS), geochemical investigation plays an important role in the assessment of the main physical and the chemical phenomena occurring during and after the CO2 injection in sedimentary formations. To increase the reliability and specificity of the investigation a strong integration between experimental analysis and numerical modelling is nowadays mandatory. Under this theme we shall present:

1. An integrated workflow starting from real samples, couples lab activities and numerical simulations
2. Comparative analysis between PHREEQC-3 and CMG-GEM via 0D (batch) models
3. CO2 injection in 2D multi-layered radial model (including site-specific minerals)

Pedram Mahzari, University College London

February 19, 2021

The Husmuli zone of SW-Iceland Hellisheidi geothermal field is currently being used for re-injection of geothermal fluids and geothermal CO2 for permanent storage in the form of carbonate minerals. The production and re-injection of geothermal fluids into this reservoir can cause permeability variations due to local changes in effective stress. Using CMG-GEM, fully coupled hydro-thermo-mechanical-chemical numerical modelling was employed to investigate the coupled impacts of these complex processes on calibration of the fluid flow paths.

Employing a combination of high-resolution fault mapping with laboratory measurements of stress dependent permeability coupled into a dual porosity field-scale model, the flow paths were calibrated using results of tracer tests performed at the site using stress-dependent permeability tensors. As the upward flow streamlines manifest, deep geological layers can also deviate the fluid flow towards the shallower layers provoking the vertical flow of geothermal fluids, which highlights the sweet spot for sustainable flow and heat extraction in vicinity of faults intercepting the geological layers at depth of 1100 m.

Having sensitised the impact stress-dependent properties, it was shown that the inclusion of the geomechanical calculations in history matching of the tracer test can lead to significant improvements in fluid flow path characterisation. Results of an independent tracer test were used to validate the model and demonstrated a reliable predictive capability for the calibrated model, which verifies the consistency of our methodology to incorporate the stress-dependent permeability. To assess the performance of CARBFIX project and the associated dissolution and precipitation rates of minerals, geochemical module of CMG was incorporated into the calibrated model. The long-term fixation of CO2 and H2S was studied using geochemical modelling. It was identified that the model can reproduce the field observations such as tracer concentration and CO2-related aqueous ions with reasonable accuracies, which indicated the robustness of the modelling methodology.

The Husmuli zone of SW-Iceland Hellisheidi geothermal field is currently being used for re-injection of geothermal fluids and CO2 for permanent storage in the form of carbonate minerals. The production and re-injection of geothermal fluids into this reservoir can cause permeability variations due to local changes in effective stress. Using GEM’s fully coupled hydro-thermo-mechanical-chemical numerical modelling technology, GEM was used to investigate the coupled impacts of these complex processes by calibrating fluid flow paths. The model reproduced field observations such as tracer concentration and CO2-related aqueous ions with reasonable accuracies, which indicated the robustness of the modelling methodology.

Injection in a depleted gas field, focusing on coupled heat and multi-phase fluid flow effects. Thenwe present a workflow that uses reservoir simulation to produce a catalogue of inflow performancecurves / injectivity indices that can be used as input to include the reservoir response in thesimulation of flow in the well and pipeline, which are essential for planning and managing theoperation of CO2 injection and storage in depleted gas fields.

Pedram Mahzari, University College London

February 19, 2021

Abstract

The Husmuli zone of SW-Iceland Hellisheidi geothermal field is currently being used for re-injection of geothermal fluids and geothermal CO2 for permanent storage in the form of carbonate minerals. The production and re-injection of geothermal fluids into this reservoir can cause permeability variations due to local changes in effective stress. Using CMG-GEM, fully coupled hydro-thermo-mechanical-chemical numerical modelling was employed to investigate the coupled impacts of these complex processes on calibration of the fluid flow paths.

Employing a combination of high-resolution fault mapping with laboratory measurements of stress dependent permeability coupled into a dual porosity field-scale model, the flow paths were calibrated using results of tracer tests performed at the site using stress-dependent permeability tensors. As the upward flow streamlines manifest, deep geological layers can also deviate the fluid flow towards the shallower layers provoking the vertical flow of geothermal fluids, which highlights the sweet spot for sustainable flow and heat extraction in vicinity of faults intercepting the geological layers at depth of 1100 m.

Having sensitised the impact stress-dependent properties, it was shown that the inclusion of the geomechanical calculations in history matching of the tracer test can lead to significant improvements in fluid flow path characterisation. Results of an independent tracer test were used to validate the model and demonstrated a reliable predictive capability for the calibrated model, which verifies the consistency of our methodology to incorporate the stress-dependent permeability. To assess the performance of CARBFIX project and the associated dissolution and precipitation rates of minerals, geochemical module of CMG was incorporated into the calibrated model. The long-term fixation of CO2 and H2S was studied using geochemical modelling. It was identified that the model can reproduce the field observations such as tracer concentration and CO2-related aqueous ions with reasonable accuracies, which indicated the robustness of the modelling methodology.

Nazika Moeininia, Hagen Bueltemeier. DBI Gas- und Umwelttechnik GmbH

February 19, 2021

Introduction and background:

Based on the long-term storage operation experience of a UGS facility, the geological and technical reservoir conditions are assessed for their potential of underground bio-methanation (UBM) and thus, develop a case for a utilization of this UGS facility that allows the integration of fluctuating renewable energy and re-cycles CO2 from industrial processes. According to the most suitable compartment of the reservoir, a target area for application of the UBM process is selected.

Reservoir simulation utilizing CMG STARS is used to evaluate the UBM potential and to determine possible operation regimes and surface facility design. Thus, the most important mechanisms of the gas conversion process as Methanogenesis reaction

and bio-reactive transport

are implemented in the reservoir simulation model, utilizing following options in STARS.

Modeling of bacterial growth, products and decay:

• Chemical Reaction
• Reaction Kinetics

Diffusion / Dispersity Models

• Effective Molecular Diffusion Coefficients
• Mechanical dispersion

Laboratory microbiological analysis currently assesses the microbial kinetic parameters under in-situ conditions. Subsequently, results from laboratory experiments in the form of batch and dynamic tests are incorporated for model calibration and validation purposes.

The UBM process will be optimized regarding H2- and CO2- injection volumes, injection-production rates, necessary shut-in time to stimulate the conversion process and well spacing. A sensitivity analysis was carried out to determine the parameters having the largest impact on the bio-methanation process.

As a preliminary achievement, a numerical simulation model capable of simulating complex UBM process has been established based on the most contributing effects (Methanogenesis and bio-reactive transport). The developed workflow in CMG STARS can be successfully applied for modeling bacterial transport, growth, decay and gas conversion processes and is verifiable in the UGS application.

Other relevant reactions for UBM catalysed by hydrogenotrophic species (bacteria and archea) are acetogenesis, sulfate reduction, Iron(III)-reduction and additionally pore plugging will be incorporated to the bio-methanation simulation workflow in future steps.

This research and development project was funded by the German Federal Ministry for Economic Affairs and Energy (BMWi) under the fund number 03EI3021D.

Nazika Moeininia, Hagen Bueltemeier. DBI Gas- und Umwelttechnik GmbH

February 19, 2021

Introduction and background:

Based on the long-term storage operation experience of a UGS facility, the geological and technical reservoir conditions are assessed for their potential of underground bio-methanation (UBM) and thus, develop a case for a utilization of this UGS facility that allows the integration of fluctuating renewable energy and re-cycles CO2 from industrial processes. According to the most suitable compartment of the reservoir, a target area for application of the UBM process is selected.

Reservoir simulation utilizing CMG STARS is used to evaluate the UBM potential and to determine possible operation regimes and surface facility design. Thus, the most important mechanisms of the gas conversion process as Methanogenesis reaction

and bio-reactive transport

are implemented in the reservoir simulation model, utilizing following options in STARS.

Modeling of bacterial growth, products and decay:

• Chemical Reaction
• Reaction Kinetics

Diffusion / Dispersity Models

• Effective Molecular Diffusion Coefficients
• Mechanical dispersion

Laboratory microbiological analysis currently assesses the microbial kinetic parameters under in-situ conditions. Subsequently, results from laboratory experiments in the form of batch and dynamic tests are incorporated for model calibration and validation purposes.

The UBM process will be optimized regarding H2- and CO2- injection volumes, injection-production rates, necessary shut-in time to stimulate the conversion process and well spacing. A sensitivity analysis was carried out to determine the parameters having the largest impact on the bio-methanation process.

As a preliminary achievement, a numerical simulation model capable of simulating complex UBM process has been established based on the most contributing effects (Methanogenesis and bio-reactive transport). The developed workflow in CMG STARS can be successfully applied for modeling bacterial transport, growth, decay and gas conversion processes and is verifiable in the UGS application.

Other relevant reactions for UBM catalysed by hydrogenotrophic species (bacteria and archea) are acetogenesis, sulfate reduction, Iron(III)-reduction and additionally pore plugging will be incorporated to the bio-methanation simulation workflow in future steps.

This research and development project was funded by the German Federal Ministry for Economic Affairs and Energy (BMWi) under the fund number 03EI3021D.

Walter Eikelenboom and Thijs Huijskes, EBN

February 19, 2021

All around the world countries have started the transition from fossil fuels towards more clean sources. In the Netherlands the future energy system will include a lot of solar and wind energy, which will result in a fluctuating supply. To balance demand and supply of energy, large scale energy storage will be required. For the Netherlands it was assessed that the demand for hydrogen storage by the year 2050 is probably larger than what can be achieved by developing salt cavern storage only. This has been the main driver to study hydrogen storage in gas fields.

GEM was used to build a portfolio of conceptual reservoir models and evaluate the production and injection behaviour with different reservoir characteristics and operating constraints. A base case radial model was constructed with initial conditions comparable to a typical methane gas field. The objective of the conceptual dynamic reservoir modelling is to understand the effect of the individual parameters, so that suitable candidates can be chosen from the Dutch natural gas portfolio. These candidates will ultimately be studied in more detailed and realistic reservoir models.

All models were setup under similar conditions, having a methane residual cushion volume equivalent to 10% of the initial reservoir pressure and on top of that hydrogen up to 90% of the initial reservoir pressure. Subsequently, hydrogen production until depletion was used to evaluate the effect of a range of reservoir characteristics.

To compare the results of the various simulations the working gas and cushion gas volume ratios (WV:CV) were determined based on the ability of the reservoir to produce under two constraints: a minimum rate and a minimum hydrogen mole fraction. One of the conclusions is that the transmissivity (kh) is the dominant factor influencing WV:CV. There is however an upper limit, because at a certain kh, early methane breakthrough will take place, resulting the produced hydrogen-methane mix to be out-of-spec.