Enhanced gas recovery by CO2 injection : influence of monovalent and divalent brines and their concentrations on CO2 dispersion in porous media

This study aims to experimentally investigate the roles of different brine types and concentrations on the longitudinal dispersion coefficient (KL) during enhanced gas recovery by CO2 injection. Core flooding process was used to simulate the displacement of CH4 by supercritical CO2 in a Buff Berea core sample at a pressure and temperature of 1400 psig and 50oC respectively, and a CO2 injection rate of 0.3 ml/min. Individual NaCl, KCl, CaCl2 and MgCl2 solutions were prepared as test brines with ionic strengths (IS) of 1M, 2M, and 3M. The results revealed that, at lower IS of 1M, MgCl2 and CaCl2 brines had the lowest KL while the monovalent brines showed relatively higher KL. Divalent brines showed a higher degree of salting out effects at higher concentrations resulting in higher KL. The salting and drying out effects of divalent brines were responsible for higher CH4 recovery at 2M IS as CH4 comes out of solution. A hyperbolic-type relationship exists between the two properties (KL and IS), where KL decreases from 0 to 1M IS, and then increases sharply at IS >1M – this behaviour is most pronounced in the divalent brines. Lowest contamination of the recovered CH4 was found to be between formation water salinities of 5-15 wt.%, regardless of salt type, during EGR by CO2 injection and sequestration. This study will not only present new knowledge on EGR process but will also provide an avenue for establishing a screening criterion based on formation water salinity for effective EGR process. This is a first experimental investigation which establishes the relationship between salt types and concentration and the KL in porous media

Role of connate water salinity in gas dispersion during enhanced gas recovery by carbon dioxide injection and sequestration

A better understanding of the factors that influence mixing between CO2 and CH4 in naturalgas reservoirs can provide an avenue to minimise the gas dispersion during Enhanced GasRecovery (EGR). This highlights EGR’s field scale adoption as a potential method forsimultaneously reducing CO2 emissions through sequestration and enhancing natural gasrecovery and, thus, showcases it economic viability. An important aspect of the reservoir isconnate water. So, what is the role of its connate water salinity on mixing during EGR? In this investigation, three (3) different sandstone core samples (Grey Berea, Buff Berea, andBandera Grey) with different petrophysical properties were used in this research. Phase I ofthis study entailed the cleaning and the characterisation of the core samples usingexperimental core analyses to determine the petrophysical properties. A novel practicalapproach to grain diameter determination of the core samples using image analysis wasdeveloped. The measurement showed that Buff Berea had the largest average grain size of165.70 μm amongst the core samples used, followed by Grey Berea with 94.66 μm, and lastlyBandera Grey with 57.15 μm. This facilitated the determination the Peclet number during thedisplacement which helped develop a robust injection strategy for displacement of the CH4with minimum contamination by providing an optimum injection rate ranges for thisapplication. Phase II involved core flooding process to simulate the displacement of CH4 by CO2 that wascarried out at 1300 psig and 50oC with varying injection rates of 0.2, 0.3, 0.4, and 0.5 ml/min.This was performed on dry core samples at different injection orientations –horizontal andvertical - to ascertain the effects of these variations on the displacement efficiency. Theoptimum injection rate was determined based on the dispersion coefficient and the CH4recovery efficiency obtained from testing individual core samples. Grey Berea at 0.3 ml/minin the vertical orientation gave the best results based on the criteria adopted and provided thebenchmark for subsequent sensitivity analyses. The Phase III of the study focused on the impact of connate water salinity of the mixing anddispersion of CO2 into CH4 during the displacement at the simulated reservoir conditionsduring EGR with different brine salinities (0, 5, 10 wt% NaCl) using the optimum conditionsdetermined in Phase II for consistent results. The results from the core flooding processindicated that the dispersion coefficient decreases with increasing salinity, hence the higherthe density of the immobile phase (connate water) the lower the dispersion of CO2 into CH4.This is the first investigation into the relationship between the connate water salinity and thedispersion coefficient in EGR. Consequently, feasibility of the solubility trapping as asecondary mechanism for CO2 storage during EGR was experimentally investigated throughcore flooding process. Solubility trapping was found to increase the CO2 storage capacity ofnatural gas reservoir by about 60% during EGR and the higher the connate water salinity thehigher the sequestration potential of CO2 but lower the CH4 recovery was realised. With this new information, the effect of connate water salinity on EGR is substantial and itsinclusion in simulations studies will be helpful for field scale applications of EGR technique

Experimental investigation on the impact of connate water salinity on dispersion coefficient in consolidated rocks cores during enhanced gas recovery by CO2 injection

Connate water salinity is a vital property of the reservoir and its influence on the displacement efficiency cannot be overemphasised. Despite the numerous analytical literatures on the dispersion behaviour of CO2 in CH4 at different parametric conditions, studies have so far been limited to systematic effects of the process while parameters such as connate water salinity of the reservoir has not been given much attention and this could redefine the CO2-CH4 interactions in the reservoir. This study aims to experimentally determine the effect of connate water salinity on the dispersion coefficient in consolidated porous media under reservoir conditions. A laboratory core flooding experiment depicting the detailed process of the CO2-CH4 displacement using Grey Berea sandstone core sample at a temperature of 50°C and at a pressure of 1300 psig was carried out to determine the optimum injection rate, from 0.2-0.5 ml/min, for the experimentation based on dispersion coefficients and methane recovery in the horizontal orientation. This was established to be 0.3 ml/min. At the same conditions, the effects of connate water saturation of 10% and a salinity of 0 (distilled water), 5, and 10% wt. with a CO2 injection rate of 0.3 ml/min on the dispersion coefficients was investigated. The results from the core flooding process indicated that the dispersion coefficient decreases with increasing salinity, hence the higher the density of the immobile phase (connate water) the lower the dispersion of CO2 into CH4. This is a significant finding given that the inclusion of the connate water and its salinity have an effect on the mixing of the gases in the core sample and should be given importance and included during simulation studies for field scale applications of Enhanced Gas Recovery (EGR). This is the first experimental investigation into the relationship between the connate water salinity and the dispersion coefficient in consolidated porous media. Keywords: Enhanced Gas Recovery; Dispersion Coefficient; Connate water Salinity; CO2 sequestratio

Effects of pressure decay on Non-Methane Volatile Organic Compounds (NMVOC) species distribution in domestic aerosol sprays with LPG propellants

Conventional aerosols sprays contain different Volatile Organic Compounds (VOC). These organic compounds have different properties and can have detrimental impact on air quality. This study investigated the spray performance and variation of the types of Non-Methane VOCs (NMVOCs) expelled over the life of pressurised aerosol spray can. Three types of aerosol sprays – hair sprays, deodorants, and antiperspirants were selected from the solvent-based cosmetic products. Mass Ratio (MR) of solvent (ethanol) to propellant (LPG) for all the products was analysed at pressure decay sequences of 4, 3, 2, and 1.5 bar. It was found that the MR in hair sprays expelled was significantly higher than that of antiperspirants and body sprays by 53% and 54% respectively at 4 bar. As the pressure depleted, however, the antiperspirant and body sprays’ MR decreased while that of the hair spray increased. At the lower pressures (2 bar), the hair spray had the highest MR and antiperspirant had the lowest. This finding is important in evaluating the performance of the delivery pathways of aerosol spray products and will provide insight into the effective design of atomisers with alternative “green” propellants like compressed air replacing LPG as the primary propellant in spray products

Experimental study on the interplay between different brine types/concentrations and CO2 injectivity for effective CO2 storage in deep saline aquifers

Salt precipitation during CO2 storage in deep saline aquifers can have severe consequences on injectivity during carbon storage. Extensive studies have been carried out on CO2 solubility with individual or mixed salt solutions; however, to the best of authors’ knowledge, there is no substantial study to consider pressure decay rate, as a function of CO2 solubility in brine, and the range of brine concentration for effective CO2 storage. This study presents an experimental core flooding of the Bentheimer sandstone sample under simulated reservoir conditions to examine the effect of four different types of brine at a various range of salt concentration (5 to 25 wt.%) on CO2 storage. Results indicate that porosity and permeability reduction as well as salt precipitation is higher in divalent brines. It is also found that, at 10 to 20 wt.% brine concentrations in both monovalent and divalent brines, substantial volume of CO2 is sequestered which indicates the optimum concentration ranges for storage purposes. Hence, the magnitude of CO2 injectivity impairment depends on both the concentration and type of salt species. The findings from this study are directly relevant to CO2 sequestration in deep saline aquifers as well as screening criteria for carbon storage with enhanced gas and oil recovery processes

Experimental study on the interplay between different brine types/concentrations and CO2 injectivity for effective CO2 storage in deep saline aquifers

Salt precipitation during CO2 storage in deep saline aquifers can have severe consequences on injectivity during carbon storage. Extensive studies have been carried out on CO2 solubility with individual or mixed salt solutions; however, to the best of authors’ knowledge, there is no substantial study to consider pressure decay rate, as a function of CO2 solubility in brine, and the range of brine concentration for effective CO2 storage. This study presents an experimental core flooding of the Bentheimer sandstone sample under simulated reservoir conditions to examine the effect of four different types of brine at a various range of salt concentration (5 to 25 wt.%) on CO2 storage. Results indicate that porosity and permeability reduction as well as salt precipitation is higher in divalent brines. It is also found that, at 10 to 20 wt.% brine concentrations in both monovalent and divalent brines, substantial volume of CO2 is sequestered which indicates the optimum concentration ranges for storage purposes. Hence, the magnitude of CO2 injectivity impairment depends on both the concentration and type of salt species. The findings from this study are directly relevant to CO2 sequestration in deep saline aquifers as well as screening criteria for carbon storage with enhanced gas and oil recovery processes