The Effectiveness of the Continuous and Cyclic Method on CO2-ECBM

This study examines the impact of different CO2 injection methods on coalbed methane recovery. Specifically, this study investigated the effectiveness of continuously injecting CO2 versus injecting CO2 that had been soaked for two weeks. The objective was to ascertain which approach was more successful in enhancing CO2 Enhanced coalbed Methane (CO2-ECBM). The experiment involved injecting 3 MPa of CH4 into dry coal samples, allowing it to adsorb until reaching equilibrium, and then injecting 5 MPa of CO2 to recover adsorbed CH4. The continuous method recovered CH4 without detectable effluent concentration for 5 hours, but desorption efficiency was only 26% due to fast flow. On the other hand, the desorption efficiency of the cyclic method was only 12%, indicating trapped CH4. A comparison of desorption efficiency per unit of time shows the continuous method is more effective than the cyclic method. The results of this study demonstrate the continuous method is more effective for the desorption of CH4, and its efficiency can be improved by briefly soaking CO2 on coal and then reinjecting it to maximize CH4 recovery. It is advisable to limit the soaking time to prevent excessive swelling of the coal matrix, which can hinder seam flow and harm long-term gas production.

Gas Production from Offshore Methane Hydrate Layer and Seabed Subsidence by Depressurization Method

Numerical simulations on consolidation effects have been carried out for gas production from offshore methane hydrates (MH) layers and subsidence at seafloor. MH dissociation is affected by not only MH equilibrium line but also consolidation (mechanical compaction) depended on depressurization in the MH reservoir. Firstly, to confirm present model on consolidation with effective stress, the history matching on gas production and consolidation has been done to the experimental results using with synthetic sand MH core presented by Sakamoto et al. (2009). In addition, the comparisons of numerical simulation results of present and Kurihara et al. (2009) were carried out to check applicability of present models for gas production from MH reservoir in field scale by depressurization method. The delays of pressure propagation in the MH reservoir and elapsed time at peak gas production rate were predicted by considering consolidation effects by depressurization method. Finally, seabed subsidence during gas production from MH reservoirs was numerically simulated. The maximum seabed subsidence has been predicted to be roughly 0.5 to 2 m after 50 days of gas production from MH reservoirs that elastic modulus is 400 to 100 MPa at MH saturation = 0.

Textural Characteristics and Depositional Environment of Ngrayong Sandstone (Middle Miocene) from Rembang Area, Northeast Java, Indonesia

Granulometric analysis of Ngrayong sandstone samples from Rembang area of NE Java (Indonesia) has been carried out to examine the textural characteristics and elucidate depositional environment. The result data from the grain size analysis indicates that the Ngrayong sediments are classified as sand or muddy sands. They are very fine- to medium-grained (phi values: 1.67 to 3.35), moderately- to well-sorted (standard deviation: 0.19 to 0.57), strongly fine-skewed to strongly coarse-skewed (skewness values: 4.82 to −5.97), and very platykurtic to very leptokurtic (kurtosis values: 0.36 to 2.41). Sandstone samples show unimodal grain size distribution. The sediments are interpreted to be transported in all three modes-traction, saltation and suspension, however, suspension and rolling are the major processes during transportation. Discriminant functions indicate diversity in the depositional environment for the sandstones. However, shallow marine is regarded as the dominant depositional environment. The preponderance of fine-grained sediments and lack of coarse sands suggest low to moderate energy conditions during deposition of Ngrayong sediments.

Numerical simulation to evaluate gas diffusion of turbulent flow in mine ventilation system

Tracer gas technique is a method to analyze the airflow path, measure the airflow quantity, and detect any recirculation or leakages in underground mine. In addition, it is also possible to evaluate the axial gas diffusion of gas in turbulent bulk flow by utilizing the tracer gas data. This paper discussed about the measurement using tracer gas technique in Cibaliung Underground Mine, Indonesia and the evaluation of effective axial diffusion coefficient, E, by numerical simulation. In addition, a scheme to treat network flow in mine ventilation system was also proposed. The effective axial diffusion coefficient for each airway was evaluated based on Taylor's theoretical equation. It is found that the evaluated diffusion coefficient agrees well with Taylor's equation by considering that the wall friction factor, f, is higher than those for smooth pipe flow. It also shows that the value of effective diffusion coefficient can be inherently determined and the value is constant when matching with other measurements. Furthermore, there are possibilities to utilize the tracer gas measurement data to evaluate the airway friction factors.

Facies and Reservoir Characteristics of the Ngrayong Sandstone in the Rembang Area, Northeast Java (Indonesia)

The Rembang area is a well-known prospective region for oil and gas exploration in Northeast Java, Indonesia. In this study, the reservoir characteristics of the Ngrayong Sandstone were investigated based on outcrops in the Rembang area. Petrological, mineralogical, petrophysical and sedimentological facies analyses were conducted. These sandstones are grain- and matrix-supported, and composed of very fine to medium, sub-angular to poorly-rounded, moderately- to very well-sorted sand grains. These sandstones are mainly composed of quartz, orthoclase, plagioclase, and micas with minor amounts of clay minerals, and therefore are predominantly classified as sub-lithic arenite and sub-felds pathicarenite. Petrographic observations and grain size data indicate that these sandstones are texturally quite mature, based on their good-sorting and the occurrence of minor amounts of matrix clays. Common clays in the samples include illite, smectite, kaolinite, and gibbsite. The porosity of the Ngrayong sandstones ranges from 25.97% to 40.21%, and the permeability ranges from 94.6 to 3385 millidarcies. Thus, these sandstones exhibit well to excellent reservoir qualities. Eight lithofacies were identified from five measured stratigraphic sections, and are dominated by foreshore and tide-dominated shoreface facies. The Ngrayong sequence shows a single transgressive-regressive cycle. Cross-bedded sandstone and massive sandstone are identified as the most promising potential reservoir facies based on their characteristics in outcrops, their lateral and vertical distributions, their sedimentological characteristics and their petrophysical properties.

Swelling Measurements of a Low Rank Coal in Supercritical CO₂

Coal swelling in the presence of water as well as CO2 is a well-known phenomenon, and these may affect the permeability of coal. Quantifying swelling effects is becoming an important issue to verify the suitability of particular coal seams for CO2-enhanced coal bed methane recovery projects. In this report, coal swelling experiments using a visualization method in the CO2 supercritical conditions were conducted on crushed coal samples. The measurement apparatus was designed specifically for the present swelling experiment using a visualization method. Crushed coal samples were used instead of block coal samples to shorten equilibrium time and to solve the problem of limited availability of core coal samples. Dry and wet coal samples were used in the experiments because there is relatively limited information about how the swelling of coal by CO2 is affected by water saturation. Moreover, some coal seams are saturated with water in initial reservoir conditions. The maximum volumetric swelling was around 3% at 10 MPa for dry samples and almost half that at the same pressure for wet samples. The wet samples showed lower volumetric swelling than dry ones because the wet coal samples were already swollen by water. Experimental results obtained for swelling were comparable with other reports. Our visualization method using crushed samples has advantages in terms of sample preparation and experimental execution compared with the other methods used to measure coal swelling using block samples.

Discrete Tracer Point Method to Evaluate Turbulent Diffusion in Circular Pipe Flow

Diffusion of a solute in turbulent flows through a circular pipe or tunnel is an important aspect of environmental safety. In this study, the diffusion coefficient of turbulent flow in circular pipe has been simulated by the Discrete Tracer Point Method (DTPM). The DTPM is a Lagrangian numerical method by a number of imaginary point displacement which satisfy turbulent mixing by velocity fluctuations, Reynolds stress, average velocity profile and a turbulent stochastic model. Numerical simulation results of points’ distribution by DTPM have been compared with the analytical solution for turbulent plug-flow. For the case of turbulent circular pipe flow, the appropriate DTPM calculation time step has been investigated using a constantβ, which represents the ratio between average mixing lengths over diameter of circular pipe. The evaluated values of diffusion coefficient by DTPM have been found to be in good agreement with Taylor’s analytical equation for turbulent circular pipe flow by givingβ=0.04 to 0.045. Further, history matching of experimental tracer gas measurement through turbulent smooth-straight pipe flow has been presented and the results showed good agreement.

Experimental Study on Seismic Attenuation and Permeability of Large Porosity Rock

The large porosity areas widely present in the underground resulting from natural hazards or artificial damages. The porosity and permeability are suggested to be capable of estimating the mechanical and air flow conditions inside the porous layer in the underground. To accurately measure the porosity and permeability in the porous area is imperative. To address this issue, we experimentally modeled some porous samples in large porosities by using sandstone particles sieved to different sizes. Ultrasonic was employed to apply on the porous sandstone samples to characterize the seismic velocity and attenuation. Permeability was also measured simultaneously to find a correlation with the porosity. The results showed the seismic attenuation decrease as the reduction of frequency and increasing particle size at the same porosity. Seismic attenuation was strongly correlated to porosity and particle size. Velocity showed a good relationship with the porosity change. Permeability was highly dependent on the particle size especially in the higher porosity range. The results indicated that it is possible to find a relationship between the permeability and seismic attenuation via the porosity and particle size.

Evaluation of SrBr2 Hydration Reaction Rate with Repeated Cycling

In this study, we evaluated the SrBr2 hydration reaction rate on repeated cycling. It was estimated that hydrated SrBr2 particles were expanded by hydration and condensed to form secondary particles;thus, the hydration reaction was reduced by repeated cycles. Using volumetric methods, we examined the effect of repetition on the reaction rate for 900 cycles during hydration and dehydration and analyzed the reaction rate using the unreacted core-shell model. From the experimental and calculated results, we confirmed that reaction rate decreased and the sample particles formed secondary particles after 900 repeated cycles. By analyzing the unreacted core-shell model, we found that the coefficient of H2O diffusion in the particles exponentially decreased with increasing repeated cycles. The value of the diffusion coefficient after 900 cycles was five times lower than that of the first cycle. To achieve stable repeated hydration cycles, technology to control the formation of secondary particles must be investigated.