Residual Capillary Pressure Research Articles

Threshold capillary pressure of caprocks for CO2 storage: Numerical insight on the dynamic and residual method

The dynamic threshold pressure method and the residual capillary pressure method provide an estimate of the threshold capillary pressure for CO2 storage. In the dynamic method, the threshold capillary pressure is determined by comparing the discharge measured when the CO2 starts flowing into the sample with the one measured when only water is flowing. In the residual method, a high CO2 pressure is applied on the vessel at the inlet of a water-saturated sample while water cannot flow from the vessel at its end. The threshold capillary pressure is estimated as the difference between the CO2 and the water pressures at the sample boundaries at equilibrium conditions.Sensitive analyses showed the impact of material properties and experimental conditions on results. Both methods allow estimating the threshold capillary pressure within a few days and the estimates are influenced by the applied pressures. The dynamic method estimate is not precautionary, and it tends to the exact value as the applied CO2 overpressure decreases. The residual method estimate is influenced by the drainage conditions and the volume of the vessels: it is generally precautionary and tends to increase with the volume of the vessels and the applied pressure. Suggestions for test interpretation and planning are also provided.

Insights into gas migration in saturated GMZ bentonite using the RCP technique

In a deep geological repository for disposal of high-level radioactive waste, understanding of gas migration behavior in bentonite materials is one of the most important issues for safety assessment of the repository. This study tries to provide insights into gas transport properties in saturated bentonite tested under a constant-volume condition using the residual capillary pressure (RCP) technique. In this regard, a test setup was developed and gas injection tests were conducted on saturated GaoMiaoZi (GMZ) bentonite specimens using the RCP technique. Among which, some specimens that experienced initial gas breakthrough processes were re-saturated and re-submitted to conduct the subsequent gas injection tests. During the tests, gas permeability and gas breakthrough pressures were measured. Gas migration mechanism at lower gas injection pressures was analyzed and the influence of repetitive breakthroughs on sealing efficiency of saturated GMZ bentonite was discussed. Results show that as dry density increases from 1.3 to 1.7 g/cm3, gas breakthrough pressure increases from 1.37 to 8.56 MPa. Explanations to this conclusion could be that with increasing dry density, the proportion of large pores decreases and the strongly adsorbed water on the surface of minerals increases, leading to harder capillary displacement of pore water and thus a higher gas breakthrough pressure. Meanwhile, both diffusion and advection could play significant roles during the gas migration process at lower injection pressures, while advection could gradually become the dominant transport mechanism as gas injection pressures increase to higher values. Finally, after experienced a gas breakthrough process, the breakthrough pressure of compacted bentonite specimen might not recover to its initial value by re-saturating the specimen, indicating that degradation of sealing capacity of the bentonite materials induced by gas breakthrough process is irreversible.

Investigation of the Gas Breakthrough Pressure of Cement Mortar with Different Experimental Techniques

The gas breakthrough property of cement-based material is an important indicator with which to evaluate the sealing efficiency. Gas breakthrough experiments can be used to obtain the gas breakthrough pressure. However, different techniques for measuring the gas breakthrough pressure usually yield different results. In this paper, three commonly used experimental methods, including the step-by-step approach, the residual capillary pressure approach, and the mercury intrusion porosimetry (MIP) approach, are adopted to investigate the gas breakthrough pressure of mortar samples. The results of the three approaches are analyzed from the perspective of the definition of gas breakthrough, and it shows that the gas breakthrough pressures measured by the step-by-step approach are the most representative values. The MIP approach underestimates the breakthrough pressure due to the lack of confining pressure, and the residual capillary pressure approach represents the gas migration and water reimbibition process after the gas breakthrough. Theoretical analysis and fitting of experimental results show that the gas breakthrough pressure is linear with the permeability on a log-log coordinate.

Gas breakthrough tests on saturated GMZ01 bentonite using RCP technique with consideration of dry density effect

In this study, gas breakthrough tests were conducted on GMZ01 bentonite specimens with dry densities 1.3, 1.5 and 1.7 Mg/m3 under rigid boundary conditions using the residual capillary pressure (RCP) technique. Prior to the gas breakthrough tests, water permeability tests were performed for determining intrinsic water permeability and establishing full water saturation for the follow-up gas breakthrough tests. The intrinsic water permeability measured ranges between 11 and 150 nDarcy (1.10×10-20 and 1.50×10-19 m2). As dry density increases, the residual capillary pressure differences of the initially water-saturated bentonite specimens recorded increase from 0.12 to 0.61 MPa. Meanwhile, the time to breakthrough was recorded to increase sharply as dry density increases. In addition, the maximum effective gas permeability decreases from 8.91×10-18 to 8.92×10-19 m2 as dry density increases from 1.3 to 1.7 Mg/m3. These results indicate that the capillary drainage in the bentonite specimen is highly related to the capillarity effects in the largest pores. The higher dry density, the smaller flow channels, resulting in more difficult for gas phase to dispel water from the interconnected flow pathways and a better sealing capacity with a higher residual capillary pressure.

Investigation on gas migration in saturated bentonite using the residual capillary pressure technique with consideration of temperature

Determination of parameters for description of gas migration in saturated bentonite is of great importance for the design and construction of artificial barriers in the geological repository for the disposal of high-level radioactive nuclear waste. In this paper, temperature-controlled gas injection tests were conducted on initially water-saturated bentonite specimens using the residual capillary pressure (RCP) technique. Effective gas permeabilities in low injection pressures and the gas breakthrough pressures at temperatures 20, 40 and 60°C were obtained. Results show that: (i) for all the temperatures tested, the intrinsic water permeabilities (kin) range between 3.2 × 10−20 and 5.72 × 10−20 m2, furthermore, those values increase with rising temperature. Meanwhile, the intrinsic water permeabilities derived from the steady state tests are lower than those obtained from the non-steady state tests; (ii) for all the temperatures tested, the effective gas permeabilities (keff) corresponding to the viscous gas flow before gas breakthrough range between 4.81×10-24 and 2.74×10-22 m2, with slight fluctuations with time. The maximum effective gas permeabilities measured at the occurrence of gas breakthrough on the initially water-saturated bentonite specimens extend from 2.27×10-18 up to 3.32×10-17 m2 and increase as temperature increases, while the time required for gas breakthrough decreases as temperature increases; (iii) for all the temperatures tested, the gas breakthrough pressures measured on the initially water-saturated bentonite specimens vary from 2.74 to 4.08 MPa, while the residual capillary pressure differences, also denoted as snap-off pressures (Psnap-off), range from 0.2 to 0.38 MPa. Additionally, the gas breakthrough pressures and the residual capillary pressures decrease as temperature increases.

A laboratory study on capillary sealing efficiency of Iranian shale and anhydrite caprocks

Abstract Caprock has the most important role in the long term safety of formation gas storage. The caprocks trap fluid accumulated beneath, contribute to lateral migration of this fluid and impede its upward migration. The rapid upward passage of invasive plumes due to buoyancy pressure is prevented by capillary pressure within these seal rocks. In the present study, two main seal rocks, from the Zagros basin in the southwest of Iran, a shale core sample of Asmari formation and an anhydrite core sample of Gachsaran formation, were provided. Absolute permeabilities of shale and anhydrite cores, considering the Klinkenberg effect, were measured as 6.09 × 10 −18 and 0.89 × 10 −18 m 2 , respectively. Capillary sealing efficiency of the cores was investigated using gas breakthrough experiments. To do so, two distinct techniques including step by step and residual capillary pressure approaches were performed, using carbon dioxide, nitrogen and methane gases at temperatures of 70 and 90 °C, under confining pressures in the range 24.13–37.92 MPa. In the first technique, it was found that capillary breakthrough pressure of the cores varies in the range from 2.76 to 34.34 MPa. Moreover, the measurements indicated that after capillary breakthrough, gas effective permeabilities lie in range 1.85 × 10 −21 – 1.66 × 10 −19 m 2 . In the second technique, the minimum capillary displacement pressure of shale varied from 0.66 to 1.45 MPa with the maximum effective permeability around 7.76 × 10 −21 – 6.69 × 10 −20 m 2 . The results indicate that anhydrite caprock of the Gachsaran formation provides proper capillary sealing efficacy, suitable for long term storage of the injected CO 2 plumes, due to its higher capillary breakthrough pressure and lower gas effective permeability.

Parametric analysis of caprock integrity in relation with CO2 geosequestration: capillary breakthrough pressure of caprock and gas effective permeability

AbstractCaprock integrity is a primary criterion for evaluating depleted oil and gas reservoirs for long‐term safety of carbon dioxide geosequestration. The occurrence of capillary leakage is inevitable in caprock. This phenomenon occurs whenever the buoyancy pressure due to accumulated CO2 plumes dominates the capillary pressure of caprock, and thereby the plumes intrude into the pore throats. In this study, experimental investigation of the effective parameters, including overburden pressure, ambient temperature, and CO2 impurities in the form of non‐condensable and non‐reactive CH4 and N2 gases on the capability of shale and anhydrite cores to preserve CO2 gas is conducted. In this regard, capillary breakthrough pressure and CO2 gas effective permeability analysis were performed applying two distinct techniques, step by step and residual capillary pressure. Experiments were conducted at the temperatures of 35, 70, and 90 °C and overburden pressures in the range of 3500–5800 psi. Two main seal rocks, including shale and anhydrite core samples, from middle Asmari and Gachsaran formations of the Zagros Basin located in the southwest of Iran were used. Regarding the high capillary breakthrough pressure and low gas effective permeability after outbreak of the leakage, all three parameters have noticeable effects on capillary sealing efficiency of the caprocks. The results indicate that impurities such as CH4 and N2 have a significant effect on capillary breakthrough pressure of caprock and gas effective permeability. © 2015 Society of Chemical Industry and John Wiley & Sons, Ltd

Cap Rock CO2 Breakthrough Pressure Measurement Apparatus and Application in Shenhua CCS Project

Abstract CO 2 breakthrough pressure is a very important factor for cap rock integrity evaluation. It is mainly acquired by laboratory experiments. We developed a set of apparatus to measure CO 2 breakthrough pressure, which was based on pulse decay method (residual capillary pressure approach). Breakthrough pressure measurement experiments were conducted on the mudstone samples derived from four important seal formations in Shenhua CO 2 aquifer storage project located in Ordos basin in China. The main conclusions are listed below based on experiment results and site characterization: 1) the breakthrough pressure of mudstone samples have sufficient capillary pressure to keep the stored CO 2 underground. 2) the mudstones at a deeper burial depth, which may be better consolidated and better diagenetic, tend to have a higher breakthrough pressure. However, mudstones that are too diagenetic may be more likely to generate fractures, which will enhance the permeability and reduce the breakthrough pressure. 3) Breakthrough pressure is just a core scale parameter and site characterization about cap rock thickness, integrity is necessary before a specific formation is selected as a cap rock in CO 2 geological storage. 4) Intercalated sand layers will greatly influence the sealing ability of mudstone formations.