A methodology to improve nanosilica based cements used in CO2 sequestration sites

Attempts to reduce the amount of greenhouse gases released into the atmosphere in recent years have led to the development of Carbon Capture and Sequestration(CCS)technology.However,there have been many studies reporting leakages form CO2 storage sites as a result of cement degradation induced by generation of an acidic environment in the storage site.Although there are a number of approaches proposed to enhance the efficiency of the cement,the degradation issue has not been totally resolved yet perhaps due to the excessive corrosives nature of carbonic acid and supercritical CO2.The aim of this study is to propose a methodology to improve the physical and mechanical characteristics of the cement by nanomodification such that a consistent rheology,constant density and a good strength development can be achieved.A new dispersion technique was proposed to ensure that the cement formulation gives a consistent result.The results obtained indicated that unlike the literature mixing,cement slurries prepared by the new mixing technique are very consistent in their rheology,regardless of the sonication parameters chosen.The measurements of the compressive strength performed at the reservoir condition revealed that nanosilica contributes in the strength development up to a certain point.Thermogravimetric Analysis(TGA)conducted at the last stage indicated that the amount of Portlandite left in the cement by adding nanosilica is decreased due to the pozzolanic reaction,which would help the cement to have a higher chance of survival in a storage site.However,cautions must be taken to maintain a certain amount of Portlandite in the cement for slowing down the carbonation rate,as otherwise the matrix of the cement is attacked directly and the cement will be degraded very fast.

Well selection in depleted oil and gas fields for a safe CO_(2) storage practice: A case study from Malaysia

Carbon capture and sequestration technology is recognized as a successful approach taken to mitigate the amount of greenhouse gases released into the atmosphere.However,having a successful storage practice requires wise selection of suitable wells in depleted oil or gas fields to reduce the risk of leakage and contamination of subsurface resources.The aim of this paper is to present a guideline which can be followed to provide a better understanding of sophisticated wells chosen for injection and storage practices.Reviewing recent studies carried out on different aspects of geosequestration indicated that the fracture pressure of seals and borehole conditions such as cement-sheath integrity,distance from faults and fractures together with the depth of wells are important parameters,which should be part of the analysis for well selection in depleted reservoirs.A workflow was then designed covering these aspects and it was applied to a depleted gas field in Malaysia.The results obtained indicated that Well B in the field may have the potential of being a suitable conduit for injection.Although more studies are required to consider other aspects of well selections,it is recommended to employ the formation integrity analysis as part of the caprock assessment before making any decisions.

CO_(2) storage in depleted gas reservoirs:A study on the effect of residual gas saturation

Depleted gas reservoirs are recognized as the most promising candidate for carbon dioxide storage.Primary gas production followed by injection of carbon dioxide after depletion is the strategy adopted for secondary gas recovery and storage practices.This strategy,however,depends on the injection strategy,reservoir characteristics and operational parameters.There have been many studies to-date discussing critical factors influencing the storage performance in depleted gas reservoirs while little attention was given to the effect of residual gas.In this paper,an attempt was made to highlight the importance of residual gas on the capacity,injectivity,reservoir pressurization,and trapping mechanisms of storage sites through the use of numerical simulation.The results obtained indicated that the storage performance is proportionally linked to the amount of residual gas in the medium and reservoirs with low residual fluids are a better choice for storage purposes.Therefore,it would be wise to perform the secondary recovery before storage in order to have the least amount of residual gas in the medium.Although the results of this study are useful to screen depleted gas reservoirs for the storage purpose,more studies are required to confirm the finding presented in this paper.

Preliminary assessment of CO_(2) injectivity in carbonate storage sites

Depleted gas reservoirs are used for a large-scale carbon dioxide(CO_(2))storage and reduction of the greenhouse gas released into the atmosphere.To identify a suitable depleted reservoir,it is essential to do a preliminary and comprehensive assessment of key storage factors such as storage capacity,injectivity,trapping mechanisms,and containment.However,there are a limited number of studies providing a preliminary assessment of CO_(2) injectivity potential in depleted gas reservoirs prior to a CO_(2) storage operation.The aim of this study is to provide a preliminary assessment of a gas field located in Malaysia for its storage potential based on subsurface characterization prior to injection.Evaluation of the reservoir interval based on the facies,cores,and wireline log data of a well located in the field indicated that the pore type and fabrics analysis is very beneficial to identify suitable locations for a successful storage practice.Although the results obtained are promising,it is recommended to combine this preliminary assessment with the fluid-mineral interactions analysis before making any judgment about reliability of storage sites.