Integrated CO2 Modeling Studies to Assess CO2 Sequestration Prospect in a Depleted Carbonate Gas Reservoir, Malaysia

This paper presented an integrated CO2 injection and sequestration modelling study performed on a depleted carbonate gas reservoir, which has been identified as one of potential CO2 sequestration site candidate in conjunction with nearby high CO2 gas fields development and commercialization effort to monetize the fields. 3D compositional modelling, geomechanical and geochemical assessment were conducted to strategize optimum subsurface CO2 injection and sequestration development concept for project execution. Available history matched black oil simulation model was converted into compositional model. Sensitivity analyses on optimum injection rate, number and types of injectors, solubility of CO2 in water, injection locations and impact of hysteresis to plume distribution were investigated. Different types of CO2 trapping mechanisms including hydrodynamic, residual/capillary, solubility and mineral trapping were studied in detailed. Coupled modelling study was performed on base case scenario to assess geomechnical and geochemical risks associated with CO2 injection and sequestration process before-, during- and post- CO2 injection operation to provide assurance for a safe and long-term CO2 sequestration in the field. Available history matched black oil model was successfully converted into compositional model, in which CO2 is treated and can be tracked as a separate component in the reservoir throughout the production and injection processes. Integrating all the results obtained from sensitivities analyses, the proposed optimum subsurface CO2 injection and sequestration development concept for the field is to inject up to 400 MMscf/D of CO2 rate via four injectors. CO2 injection rate is forecasted to sustain more than 3 years from injection start date before declining with time. In terms of CO2 storage capacity, constraining injection pressure up to initial reservoir pressure, maximum CO2 storage capacity is estimated ~65 Million tonnes. Nevertheless, considering maximum allowable CO2 injection pressure estimated from coupled modelling study and operational safety factor, the field is capable to accommodate a total of ~77 Million tonnes of CO2, whereby 73% of total CO2 injected will exists in mobile phase and trapped underneath caprock whilst the other 24% and 3% will be trapped as residual/capillary and dissolved in water respectively. Changes of minerals and porosity were observed from 3D geochemical modelling, however, changes are negligible due to the fact that geochemical reaction is a very slow process. This paper highlights and shares simulation results obtained from CO2 injection and sequestration studies performed on 3D compositional model to generate an optimum subsurface CO2 injection and sequestration development concept for project execution in future. Integration with geomechanical and geochemical modelling studies are crucial to assess site's capability to accommodate CO2 within the geological formation and provide assurance for a safe and long-term CO2 sequestration.

Converting Development Wells to Observations Wells to Aid Reservoir and Overburden Monitoring for CO2 Sequestration in a Depleted Carbonate Field

Measurement, Monitoring & Verification (MMV) is crucial to ascertain both containment and conformance in Carbon Capture & Storage (CCS) projects. The magnitude of parameters to be monitored along with the technologies to be adopted could be very cost intensive and impact overall project Net Present value (NPV). To rationalize the associated costs and maximize the value propositions of existing infrastructure, the development wells in depleted field provide the opportunity to reduce the MMV cost by converting them into observation wells. However, the wells are to be analyzed for their strategic location in the reservoir, fit for purpose plug & abandonment plan and the apt technologies that can be implemented for both reservoir & overburden monitoring. Development wells in the identified depleted field are 30-40 years old and were not designed considering high CO2 concentration. In consequence, the possibility of well leakage due to accelerated corrosion channeling, cracks, along the wellbore cannot be ignored and requires careful evaluation. Rigorous process has been adopted in assessing the feasibility for converting existing producers into observation wells. Wells basis of designs disparity between the producer and the required observation well governs the selection for conversion to observation wells or plugging and abandonment. The reservoir simulation and coupled modelling predict that CO2 plume will reach all wells penetrating the storage reservoir during the initial injection phase. Out of 9 available producers, 2 strategically located wells have been evaluated for conversion based on end injection reservoir pressure of ∼3450psi. Quantitative CO2 leakage through the observation wells has been numerically computed based on all possible pathways for risk characterization. The permeable/perforated zones in these two wells are to be isolated along with the cap-rock restoration technique at deepest depth of ∼4000ft TVDSS. This will ensure the wells are safe & accessible for monitoring CO2 plume migration, CO2 leakage and well integrity by analyzing acquired DAS-VSP, DTS, DPS data and well logs. This paper elaborates unique challenges associated with identifying strategic wells for conversion to observation wells. Minimum plug setting depths, ranging from 3720-3880ft TVDSS, for abandonment of 9 development wells are derived based on fracture gradient and maximum horizontal stress. 2 observation wells require deeper plug setting depth to make caprock accessible at ∼4000ft TVDSS to be restored by utilizing either perforate-wash-cement (PWC) or section milling. Based on the subsurface illumination modelling, deployment of fiber-optics sensors in observation wells promises a cost-effective solution for monitoring CO2 plume migration and leakage by acquiring 4D DAS-VSP survey. Conversion of producers to observation wells promises cost effective MMV application for CO2 plume migration and leakage monitoring along with periodic temperature, pressure, and CO2 concentration measurement in overburden.

Influence of the local urban environment on the thermo-radiative and hydrological behaviour of a garden lawn

Several urban canopy models now incorporate urban vegetation to represent local urban cooling related to natural soils and plants evapotranspiration. Nevertheless, little is known about the realism of simulating these processes and turbulent exchanges within the urban canopy. Here, the coupled modelling of thermal and hydrological exchanges was investigated for a lawn located in an urban environment, and for which soil temperature and water content measurements were available. The ISBA-DF surface-vegetation-atmosphere transfer model is inline coupled to the TEB urban canopy model to model mixed urban environments. For the present case study, ISBA-DF was applied to the lawn and first evaluated in its default configuration. Particular attention was then paid to the parameterization of turbulent exchanges above the lawn, and to the description of soil characteristics. The results highlighted the importance of taking into account local roughness related to surrounding obstacles for computing the turbulent exchanges over the lawn, and simulating realistic surface and soil temperatures. The soil nature and texture vertical heterogeneity are also key properties for simulating the soil water content evolution and water exchanges.

Inter-Model Comparison for Tsunami Debris Simulation

Assessing the risk of tsunami-driven debris has increasingly been recognized as an important design consideration. The recent ASCE/SEI7-16 standard Chapter 6 requires all the areas included within a 22.5° spreading angle from the debris source to consider the debris impact. However, it would be more reasonable to estimate the risks using numerical simulation models. Although a number of simulation models to predict tsunami debris transport have been proposed individually, comparative studies for these simulation models have rarely been conducted. Thus, in the present study, an inter-model comparison for tsunami debris simulation model was performed as a part of the virtual Tsunami Hackathon held in Japan from September 1 to 3 in 2020. The blind benchmarking experiment, which recorded the transport of three container models under a tsunami-like bore, was conducted to generate a unique dataset. Then, four different numerical models were applied to reproduce the experiments. Simulated results demonstrated considerable differences among the simulation models. Essentially, the importance of accurate modelling of a flow field, especially a tsunami front, was confirmed to be important in simulating debris motion. Parametric studies performed in each model and comparisons between different models also confirmed that a drag coefficient and inertia coefficient would influence the simulated debris trajectory and velocity. It was also shown that two-way coupled modelling to express the interaction between debris and a tsunami is important to accurately model the debris motion.

Importance of 3-Way Coupled Modelling for Carbon Dioxide Sequestration in Depleted Reservoir

Carbon sequestration is the process of capturing and storage of atmospheric carbon dioxide. The objective of any carbon sequestration project is to store CO2 safely for hundreds or thousands of years with a goal of reducing global climate change. A depleted hydrocarbon reservoir is one of the potential storage sites being considered for long-term CO2 storage. The dynamic, geochemical, and geomechanics changes that occur during CO2 injection are inter-related. For example, when injected CO2 causes dissolution of reservoir rock, on one hand, porosity increases while rock strength decreases. On the other hand, reduced rock strength could cause additional compaction thus reducing porosity, whereas increase in pressure due to injection could cause dilation. Hence, it is critical to have an integrated model that captures effect of all changes on the storage capacity and integrity of the reservoir. Three major depleted gas reservoirs in Central Luconia field, located offshore Sarawak, are being evaluated for future CO2 storage. A 3-way coupled modelling approach that integrates dynamic model, geochemistry model, and geomechanics model is utilized to obtain cumulative effect of all three changes. This integrated model provides a more accurate estimate of 1) CO2 storage capacity, 2) Caprock integrity evaluation, 3) CO2 plume migration path, and 4) Volume of CO2 stored through different storage mechanisms (viz. hydrodynamic trapping, capillary trapping, solubility trapping, and mineral trapping). Apart from providing storage capacity, this model also provides inputs for evaluating integrity of caprock, fault reactivation study, MMV (Measurement, Monitoring, and Verification) planning, and estimating potential leak rates through plugged and abandoned wells. Using a 3-way coupled model, it is estimated that there is an average reduction in porosity of 5-10% (of initial porosity). This translates to an equivalent reduction in CO2 storage capacity of 5-10% compared to dynamic model. It is observed that pore collapse as a result of pressure depletion is primarily responsible for this reduction in porosity. It has also been observed that the injection can be continued till initial reservoir pressure is reached without breaching caprock integrity. CO2 plume migration path significantly affects MMV planning. Potential leak rate estimation is critical in mitigation and contingency planning.