Supercritical CO2 Permeability Research Articles

Supercritical CO2 permeation in polymeric films: Design, characterization, and modeling

This study is concerned with the development of an optimum method for identification of supercritical CO2 permeability in thermoplastic films with moderate to excellent barrier properties namely, High-Density Polyethylene (HDPE), Raised-Temperature Polyethylene (PE-RT), Polyvinylidene Fluoride (PVDF) and aliphatic Polyketone (PK) at elevated temperatures (40 °C−82 °C). A high-temperature/high-pressure permeation cell was designed based on the “closed-volume/variable pressure” standard test method. The identified gas transport properties using the time lag method yielded significant error particularly for PVDF and PK, which was ascribed to the sole reliance on the accumulated pressure-rate in steady-state. This error was minimized using the Non-Linear Regression (NLR) by utilizing the full range of measured data including the transient state. The coefficient of determination between the measured and modeled data using NLR was quantified above 0.99 for all the polymers at the entire examined temperature range. The 1.4 % higher degree of crystallinity and 28.5 % smaller spherulite size caused 13.3 % higher diffusivity and 8.6 % lower solubility in PE-RT when compared with HDPE at 82°C. As a result of this trade-off, PE-RT exhibited only 3.5 % higher permeability than HDPE. The developed generalized temperature-dependent model provided the essential data for design optimization of gas barrier performance in multilayer high-temperature pressure-vessels.

Effect of salinity on supercritical CO2 permeability of caprock in deep saline aquifers: An experimental study

The permanence of injected CO2 in deep saline aquifers mainly depends on caprock permeability. Thus, the main objective of this study is to investigate the effect of salinity level in the formation fluid on permeability of siltstone when advective flow of scCO2 is dominant. Siltstone caprock samples were fully saturated with different synthetic brines, which were similar to natural formation fluids. A chemical analysis was conducted for each saturated rock and brine samples to recognize the geo-chemical equilibrium between the formation fluid and caprock since the identification of final brine composition in rock pores is crucial to predict the possible interactions with scCO2 flow. Interestingly, the results show that the caprock is subjected to dissolution during saturation due to ion exchange between caprock minerals and cations in the pore fluid changing the brine elemental composition. The scCO2 permeability experiments were conducted for each saturated sample using a core flooding apparatus for a series of injection pressures. According to the results, scCO2 permeability significantly reduces at high salinity concentrations in brine due to deposition of different types of evaporites in rock pores which significantly depends on the elemental concentration of brine and caprock-brine interaction. It is known as CO2 dry-out phenomenon.

Effects of Coal Deformation on Different-Phase CO2 Permeability in Sub-Bituminous Coal: An Experimental Investigation

Coal deformation is one of the leading problems for carbon dioxide (CO2) sequestration in coal seams especially with respect to different-phase CO2 injection. In this paper, a series of core flooding tests were conducted under different confining stresses (8–20 MPa), injection pressures (1–15 MPa), and downstream pressures (0.1–10 MPa) at 50 °C temperature to investigate the effects of coal deformation induced by adsorption and effective stress on sub-critical, super-critical, and mixed-phase CO2 permeability. Due to the linear relationship between the mean flow rate and the pressure gradient, Darcy Law was applied on different-phase CO2 flow. Experimental results indicate that: (1) Under the same effective stress, sub-critical CO2 permeability > mixed-phase CO2 permeability > super-critical CO2 permeability. (2) For sub-critical CO2 flow, the initial volumetric strain is mainly attributed to adsorption-induced swelling. A temporary drop in permeability was observed. (3) For super-critical CO2 flow, when the injection pressure is over 10 MPa, effective-stress-generated deformation is dominant over the adsorption-induced strain and mainly contributes to the volumetric strain change. Thus, there is a linear increase of the volumetric strain with mean pore pressure and super-critical CO2 permeability increased with volumetric strain. (4) For mixed-phase CO2 flow, coupling effects of adsorption-induced swelling and effective stress on the volumetric strain were observed but effective stress made more of a contribution. CO2 permeability consistently increased with the volumetric strain. This paper reveals the swelling mechanism of different-phase CO2 injections and its effect on coal permeability.

Coal Swelling and Permeability Evolutions with Injecting Sub- and Super-Critical Co2 in Sub-Bituminous and Bituminous Coal: An Experimental Study

CO2 sequestration in coalbed is currently identified as one of the promising solutions to reduce CO2 emissions, especially in deep un-minable coal seams, which can easily provide a supercritical condition for CO2. Under in-situ stress conditions, the volumetric expansion of coal mass due to CO2 injection was an important factor to affect CO2 sequestration. Although previous research has investigated the effect of coal swelling on permeability, little attention has been paid to distinguish effects of coal rank on the permeability, especially with respect to coal deformation due to supercritical CO2 injection. Therefore, the main objective of this study is to discover how super-critical CO2 permeability and the volumetric strain vary with CO2 injection in sub-bituminous and bituminous coal under stress-constrained confinements. A series of super-critical CO2 permeability tests were conducted under a range of injection pressures (10-15 MPa) and confinements (16-20MPa) at 50℃. Results indicate that a non-linear increase of volumetric strain was observed at 16 MPa confinement in both sub-bituminous coal and bituminous coal, which resulted in an unexpected drop in permeability at initial supercritical CO2 injection. This is mainly attributed to the coupling effects of adsorption-induced swelling and reduction of compressive strength. After that, the coupling effects due to CO2 saturation fade away, and the volumetric strain increased with the progressive injection pressure mainly due to the decrease of effective stress. Thus, a linear relationship between the volumetric strain and the injection pressure was obtained. Due to difference of coal rank, more dominant variation of volumetric strain and permeability occurred in bituminous coal than sub-bituminous coal after supercritical CO2 injection.

Effect of pore and confining pressure on the supercritical CO2 permeability of sandstone: Implications for the effective pressure law

AbstractThe liquid permeability of rock with distilled water or brine is different from that obtained using gas by variation in the confining pressure Pc and pore pressure Pp. In this study, as part of the research on CO2 geological storage, the permeability of sandstone was measured using supercritical CO2, and the effect of Pc and Pp on this permeability was analyzed. For applying the effective pressure law to the analysis, an effective pressure coefficient for permeability was derived experimentally. In order to utilize supercritical CO2, a non‐Darcy flow test with a high flow rate was conducted, and the permeability was estimated through the Forchheimer equation. We contoured iso‐permeability lines with confining and pore pressure conditions that have identical permeability, and the effective pressure coefficient, χ, was derived from the gradient of the lines following the definition of the effective pressure law. It was identified that the coefficient could be different depending on the pressure conditions. To clarify the variation of the coefficient, we derived the coefficient of χ(Pc, Pp) as a function of pore and confining pressure. The coefficient increased nonlinearly as the difference between Pc and Pp decreased, with a maximum of 1.36 being observed. The correlation between the effective pressure and the permeability were examined by applying empirical models. It was determined that the power law model was appropriate to estimate the change in supercritical CO2 permeability. Especially, it was deduced that the effective pressure with the derived coefficient would be more valid than the Terzaghi effective pressure.

In-situ disposal of CO2: Liquid and supercritical CO2 permeability in coal at multiple down-hole stress conditions

Geological CO2 sequestration is one of the most effective methods to counter global climate change. Coal matrix shrinkage, swelling, gas diffusion and permeability are the key phenomena associated with geological CO2 disposal in coal. In this study, permeability experiments were approached using the supercritical and liquid phases of CO2 (less understood; most likely insitu phases) for naturally fractured bituminous coal. Experiments were performed under triaxial conditions using four sets of various confinement conditions corresponding to variable depths. Injection pressure was varied gradually and the permeability changes were calculated using the Darcy’s equation for subcritical and supercritical CO2 exclusively. Changes in CO2 phases were obtained by changing the system temperature from 26° C for liquid CO2 to 34°C for supercritical CO2. N2 was alternatively injected at the start and between the injections of CO2 to analyze the changes in the permeability from a relatively very less sorptive medium’s perspective. It was observed that the supercritical CO2 flow reduced the permeability significantly and this behavior was greatly attributed to the highly viscous nature of the supercritical phase and the high volumetric deformation or the swelling of coal under supercritical CO2 as compared to liquid CO2. The injection pressures were observed to reduce the effective stress behavior, which in turn pushed the permeability evolution at each confinement to a positive trend. However, the permeability of CO2 reduced exponentially with increasing effective stresses. Two different empirical equations were proposed for permeability of both the phases of CO2 with effective stresses.

Saturation time dependency of liquid and supercritical CO2 permeability of bituminous coals: Implications for carbon storage

Various types of lithospheric geological reservoirs are available for the safe and long-term storage of CO2. The phase of CO2 transitions between liquid and supercritical (mostly supercritical for depths greater than 800m) when injected into the subsurface. This high-density super-critical phase prevents CO2 molecules from upward diffusion toward the surface. Many questions arise in the context of coal seam sequestration with respect to its capacity, injectivity, plume movement, and leakage assessment. This work examines the effect of various saturation periods on the permeability evolution of porous coal. In this triaxial study, liquid and supercritical CO2, along with N2 were injected into a coal sample from the Jharia coal field (Jharkhand state, India). It was observed that the permeability reduction for liquid CO2 was 25%, 13.5% and 1% for 0–20h phase, 20–40h phase and 40–60h phase, respectively. For supercritical CO2, the reduction was observed to be 42.5%, 38.4% and 11%, respectively, for the three saturation cycles. The findings highlight that while high CO2 sorption in supercritical phase stores more of the adsorbate, the reduction in permeability slows down injection operation and the saturation induced coal expansion threatens the overall stability of the system.

A New Device for Measuring the Supercritical CO2 Permeability in Porous Rocks Under Reservoir Conditions

Abstract This paper describes a newly developed device for measuring the CO2 permeability coefficient in porous rocks under reservoir conditions, in which the pressure and temperature of injected CO2 are usually beyond the critical point of 7.38 MPa and 31.8°C. The device consists of a pressure cell, a syringe pump for CO2, a pressure amplifier, a heating unit, and a measurement system. Two buffer tanks are set at the inlet and outlet of the seepage chamber to maintain stable CO2 injection and back pressures during testing. The supercritical CO2 flowing through the rock sample is depressurized to the gaseous phase to measure its flow rate at low pressure. An average flow rate over time is used to calculate the permeability coefficient of CO2 in the rock sample. A performance test was conducted to demonstrate the detailed characteristics of the device. A sample application using silt rock for testing proved that the device can effectively measure the permeability coefficient of supercritical CO2 in porous rock.

A Laboratory Investigation of Permeability of Coal to Supercritical CO2

The kinetics of gas–coal interaction during coalbed methane (CBM) recovery and/or carbon dioxide sequestration in coal has been subject of investigation over past few years. Swelling of coal matrix due to gaseous phase CO2 injection is now well established through laboratory experiments and field validations. Further, fluid exchange or flow in coal alters effective stresses in the underground environment. These significantly affect the permeability characteristics of coal and therefore influence the gas recovery/injection projects. Most research works on coal seam sequestration have been carried out for gas or liquid phase CO2. Considering the pressure–temperature conditions of deep seated coal, studies are now being done on supercritical CO2 flow and adsorption in coal. A newly developed experimental set up was utilized to replicate the underground conditions in laboratory to investigate the (1) initial N2 permeability of coal, (2) supercritical CO2 permeability of coal, (3) effects of CO2 sorption on N2 permeability of coal. The temperature of the set up was maintained at 33 °C while CO2 injection pressures were varied between 11 and 15 MPa at a range of 16–24 MPa confinements, and N2 was used as a relatively neutral medium to estimate the loss in permeability due to supercritical CO2 flow. The results indicate that high adsorption of supercritical CO2 in coal led to significant reduction in permeability. On increasing the confining pressure, further decline in the permeability was recorded. CO2 becomes liquid-like with increasing confining pressures and the coal–fluid interactions change, causing high sorption and matrix swelling, leading to reduced permeability in coal. This explains why substantial decline in the injection rate of CO2 was observed progressively in most CO2 sinks.

Effect of different mix compositions on apparent carbon dioxide (CO2) permeability of geopolymer: Suitability as well cement for CO2 sequestration wells

The wellbore integrity is a key factor for a successful oil, gas and carbon capture and storage (CCS) projects and the durability of the cement used in the wellbore plays a vital role in the long term safety of those projects. To date, Ordinary Portland cement (OPC) has been used in the wells used in oil and gas industry, and it is found to be unstable under down-hole pressures and temperatures conditions. Therefore, this research work intends investigating an alkali activated inorganic binder, geopolymer, as well cement and study the apparent CO2 permeability of different types of geopolymer. Three different types of geopolymer was prepared by adding 0%, 8% and 15% of alkali activated slag (by mass) with fly ash, and existing class G oil cement was tested for the comparison of results. Sub and supercritical CO2 permeability was experimented at different injection and confining pressures expected under deep down-hole environment. The experimental results reveal that the apparent CO2 permeability of geopolymers (0.0005–0.002μD) is two to three orders lower than class G cement (0.12–2.6μD) depending on the mix compositions of geopolymer. The addition of 15% slag reduces the permeability by approx. 10times compared to fly ash based geopolymer and 1000times compared to class G cement. Alkali activated geopolymer materials can be a good replacement for existing OPC based cement as they have lower CO2 permeability, and can be employed in shallow and deeper depths of injection wells by changing the mix composition.

Sub- and super-critical carbon dioxide permeability of wellbore materials under geological sequestration conditions: An experimental study

Carbon capture and storage has attracted attention as a feasible solution to global warming caused by anthropogenic emissions of greenhouse gases. The injection wells and well cement provide the wellbore integrity necessary for the long-term storage of carbon dioxide (CO2). To date, ordinary Portland cement (OPC) has been used in injection wells, and its survival has been questioned as it is unstable in CO2-rich environments. Therefore, an experimental study was conducted to study geopolymer (G) as well cement and sandstone (S) as formation material. The sub- and super-critical CO2 permeability of geopolymer, sandstone and G–S composites were studied using the high pressure triaxial set-up in the Department of Civil Engineering, Monash University. The undrained triaxial experiment was conducted at confining pressures from 14 to 26 MPa, and inlet pressures from 6 to 20 MPa to study the sub- and super-critical CO2 permeability of wellbore materials. Based on the experimental results, the apparent CO2 permeability of sandstone (0.8–30 μD) is approx. 1000 times higher than that of geopolymer (0.002–0.02 μD). The increase in pore pressure reduces the permeability of geopolymer, sandstone and G–S composite materials, and this is related to Klinkenberg's slip flow. In addition, the apparent permeability of CO2 reduces due to pore volume shrinkage caused by the increase in confining pressure. The percentage permeability reduction (per 1 MPa increase in downstream pressure) of geopolymer, sandstone and G–S composite materials reduces with increase in pore pressure, and the reduction is significant from sub-critical to super-critical CO2 pressure conditions. This observation shows the significance of super-critical CO2 pressure conditions for effective and leak-free storage of CO2 in deep underground reservoirs.

Sub- and super-critical carbon dioxide flow behavior in naturally fractured black coal: An experimental study

A proper understanding of super-critical carbon dioxide (CO2) flow behavior in coal is essential, as CO2 normally exists in its super-critical state in deep coal seams and studies are lacking. The main objective of this study is to distinguish the permeability behavior of coal for sub-critical and super-critical CO2 flows. Therefore, a series of triaxial experiments was conducted on naturally fractured black coal specimens. Permeability tests were carried out for 15, 20 and 25MPa confinements at 33.5°C temperature. Three test scenarios were conducted to investigate, (1) variation of the permeability behavior of coal with CO2 phase condition, (2) the swelling effect on sub- and super-critical CO2 permeability patterns, and (3) the potential of nitrogen (N2) to reverse CO2-induced swelling. According to the test results, the permeability of super-critical CO2 is significantly lower than sub-critical CO2 due to the higher viscosity and swelling associated with super-critical CO2. Moreover, at super-critical state there is a higher decline of CO2 permeability with increasing injecting pressure due to the higher increments in the associated viscosity and swelling. Although CO2 adsorption-induced swelling causes permeability of both CO2 and N2 to be reduced at low injection pressures the poro-elastic effect becomes more dominant and may cause CO2 permeability to increase for higher injecting pressures, because CO2 flow behavior may transfer from super-critical to sub-critical after the swelling due to the decline of downstream pressure development. Moreover, N2 has the potential to reverse some swelling effects due to CO2 adsorption, and this recovery rate is higher at lower injecting pressures and higher confining pressures.