Gas Injection Flow Research Articles

Production and optimisation of a well by hybrid artificial activation

This paper focuses on proposing a hybrid activation mechanism for the production and optimisation of a well called X101 (for confidentiality reasons), which has become non-eruptive. Completion, pressure, volume, temperature (PVT), reservoir, and the X101 well profile data are processed by Pipesim and Excel software and integrating a certain number of calculations using nodal and decline curve analysis methods. The activation of the X101 well by an electric submersible pump (ESP) having 450 stages provided an oil production flow rate of 9189.329 stock tank barrels per day with a bottom-hole pressure of 2746.151 psi. Over time, the X101 well activated by the ESP having 450 stages faces a succession of maintenance operations occurring in very short time intervals following the reduction in the efficiency of the ESP. To overcome the problem of frequent maintenance which disrupts production times, the gas lift is added to the X101 well activated by a new ESP having 199 stages. The installation of the gas lift reveals that the adequate gas injection flow rate is 2 million standard ft3 per day and 2 valves must be installed at 4,959 ft and 3,966 ft to suitably meet the production requirements. The X101 well activated by the combination of ESP and gas lift delivered a production flow rate of 7954.601 stock tank barrels per day with a bottom-hole pressure of 2873.623 psi and its optimisation made it possible to obtain a net oil flow rate of 9,035 stock tank barrels per day at the bottom-hole pressure of 2,762 psi. The profitability of the X101 well activated by the combination of ESP and gas lift is USD 73,163,517 for a return on investment after 9 months and 22 days for 13 years of production.

Evaluation of Nong’an oil shale reservoir stimulation based on nitrogen injection

Reservoir stimulation for in-situ oil shale conversion employed hydraulic fracturing, as demonstrated in the Nong’an oil shale in-situ conversion project. This study examines the extent of reservoir stimulation and the associated changes in permeability. Hydraulic fracturing significantly increased the reservoir stimulation volume, raising the permeability in the stimulated area to 324.6 mD. Subsequent water replacement involved injecting lower-temperature nitrogen, which mitigated volume shrinkage and closed microfractures. However, this process reduced permeability by 80.54%, decreasing the seepage area to 2660.7 m3. The gas injection and mining process encompassed two stages: warming and cracking. The former aimed to enhance the drying of the formation in the stimulation area, restoring 22.87% of the permeability of the original area. The latter stage facilitated organic matter decomposition to release hydrocarbons, increasing the permeability of the reformed region to 704.842 mD. The reservoir-stimulated area can be categorized into cracking, high seepage, or low seepage zones, depending on the difficulty of injected gas flow and the extent of high-temperature influence.

Experimental and Numerical Study on the Characteristics of Bubble Motion in a Narrow Channel

Plate fuel elements, known for their compact structure and efficient cooling, are commonly used in the core of nuclear reactors. In these reactors, coolant channels are designed as rectangular narrow slits. Bubble behavior in narrow channels differs significantly from that in conventional channels. This paper investigates the vertical rise of bubbles in narrow slit channels. A gas–liquid two-phase flow experimental rig was constructed using transparent acrylic boards. A high-speed camera captured the bubble formation process during gas injection, and code implemented in Matlab was used to process the images. Numerical simulations were conducted with CFD software under identical conditions and compared with the experimental results, showing a good agreement. The results show that the experimental and simulated bubble movement velocities are in good agreement. In the experiments of this paper, when the width of the narrow gap is below 3 mm, the sidewalls exert a pronounced influence on the dynamics of bubble rise, notably altering both the velocity profile and the trajectory of the bubbles’ ascent. As the gas injection flow rate gradually increases, the bubble rising speed and trajectory change from regular to oscillatory patterns.

Research on Temperature–Pressure Coupling Model of Gas Storage Well during Injection Production

Periodic changes in wellbore temperature and pressure caused by the cyclic injecting and producing of gas storage wells affect wellbore integrity. To explore the distribution and influencing factors of wellbore temperature and pressure during gas storage well injection-production processes, based on energy conservation, momentum theorem, and the transient heat transfer mechanism of the wellbore, a temperature and pressure coupling model for gas storage injection-production wellbores was established, and a piecewise iterative method was used to solve the model equations. Compared with the field data, the predicted relative errors of the wellhead temperature and pressure were 2.30% and 2.07%, respectively, indicating that the coupling model has a high predictive accuracy. The influences of the injection-production conditions, tubing diameter, and overall heat transfer coefficient on the wellbore temperature and pressure distributions were analyzed through an example. When the gas injection flow rate increased by 1.5 times, the bottomhole temperature decreased by 37%. Doubling the overall heat transfer coefficient resulted in a 10% rise in the bottomhole temperature. An increase of 0.3 times in the gas injection pressure led to a 31% increase in bottomhole pressure. With a 1.5-fold increase in the gas production flow rate, the wellhead temperature rose by 28%, and the wellhead pressure dropped by 20%. The research in this paper can serve as a guide for the optimization design and safe operation of gas storage wells.

Spatial evolution of CO2 storage in depleted natural gas hydrate reservoirs and its synergistic efficiency analysis

Carbon neutrality is now a common strategic target worldwide, with geological storage seen as the mainstream scheme to address CO2 emissions and the greenhouse effect. Depleted natural gas hydrate reservoirs (DNHR), with their high-pressure, low-temperature environment, could capture CO2 in the form of hydrates, being an innovative way for carbon storage. A lab-scale reactor was used in this work to simulate CO2 injection into the reservoir after gas hydrate exploitation. As expected, it was found that the low-temperature environment of the depleted reservoir at the end of gas production provided a high driving force and accelerated the rate of CO2 hydrate formation. Consequently, the maximum gas storage capacity was increased by 66% by optimizing the injection timing and reducing the gas injection flow rate to enable enough hydrate formation. Besides, the formation of CO2 hydrate in the DNHR could also help stabilize the reservoir to achieve a more efficient CH4 production and CO2 storage. This study provides a novel strategy for gas hydrate exploitation as well as subsequent geological storage of CO2 in depleted natural gas hydrate reservoirs by making full use of their favorable conditions.

Application of CO2-Soluble Polymer-Based Blowing Agent to Improve Supercritical CO2 Replacement in Low-Permeability Fractured Reservoirs.

Since reservoirs with permeability less than 10 mD are characterized by high injection difficulty, high-pressure drop loss, and low pore throat mobilization during the water drive process, CO2 is often used for development in actual production to reduce the injection difficulty and carbon emission simultaneously. However, microfractures are usually developed in low-permeability reservoirs, which further reduces the injection difficulty of the driving medium. At the same time, this makes the injected gas flow very fast, while the gas utilization rate is low, resulting in a low degree of recovery. This paper conducted a series of studies on the displacement effect of CO2-soluble foaming systems in low-permeability fractured reservoirs (the permeability of the core matrix is about 0.25 mD). For the two CO2-soluble blowing agents CG-1 and CG-2, the effects of the CO2 phase state, water content, and oil content on static foaming performance were first investigated; then, a more effective blowing agent was preferred for the replacement experiments according to the foaming results; and finally, the effects of the blowing agents on sealing and improving the recovery degree of a fully open fractured core were investigated at different injection rates and concentrations, and the injection parameters were optimized. The results show that CG-1 still has good foaming performance under low water volume and various oil contents and can be used in subsequent fractured core replacement experiments. After selecting the injection rate and concentration, the blowing agent can be used in subsequent fractured cores under injection conditions of 0.6 mL/min and 2.80%. In injection conditions, the foaming agent can achieve an 83.7% blocking rate and improve the extraction degree by 12.02%. The research content of this paper can provide data support for the application effect of a CO2-soluble blowing agent in a fractured core.

Smelting Reduction of HIsarna Slag with Methane

To study the smelting reduction behavior of methane in the HIsarna process, the isothermal reduction experiments of HIsarna slag with 6 wt% of FeO were conducted at the temperatures of 1450, 1475, and 1550 °C, using 5 vol% CH4‐Ar. The effect of the gas injection flow rate on the overall reduction rate was investigated in the range of 0.5–1.5 L min−1. The results confirm that the decomposed carbon black acts as the dominant reductant in the reduction process compared to hydrogen. Increased gas flow rate increases the reaction rate, while temperature shows no significant effect. The reduction process could be described by the JMAEK model: by fixing the gas flow rate at 1.0 L min−1 with different temperatures, the exponent n value is around 1.5, indicating FeO mass transfer is the limiting step since there are sufficient carbon blacks as nucleation sites. The reduction process follows the first‐order model controlled by the reactant concentration with the gas flow rate being at 0.5 L min−1 and in the second reaction stage of the gas flow rate at 1.5 L min−1. The determined activation energy for the methane reduction is 59.8 kJ mol−1.

Heat front propagation in shale oil reservoirs during air injection: Experimental and numerical studies

Air injection technique for developing shale oil has gained significant attention. However, the ability of the heat front to consistently propagate within the shale during air injection remains uncertain. To address this, we investigated the heat front propagation within oil–detritus mixtures, shale cores, and fractured shale cores using a self-designed combustion tube (CT) and experimental schemes. By integrating the results obtained from high-pressure differential scanning calorimetry and CT, we developed a comprehensive reaction kinetics model to accurately analyze the main factors influencing the heat front propagation within fractured shale. The findings revealed that in the absence of additional fractures, the heat front failed to propagate within the tight shale. The flow of gases and liquids towards the shale core was impeded, resulting in the formation of a high-pressure zone at the front region of the shale. This pressure buildup significantly hindered air injection, leading to inadequate oxygen supply and the extinguishment of the heat front. However, the study demonstrated the stable propagation of the heat front within the oil–detritus mixtures, indicating the good combustion activity of the shale oil. Furthermore, the heat front successfully propagated within the fractured shale, generating a substantial amount of heat that facilitated the creation of fractures and enhanced gas injection and shale oil flow. It was important to note that after the heat front passed through the shale, the combustion intensity decreased. The simulation results indicated that injecting air into the main fracturing layers of the shale oil reservoir enabled the establishment of a stable heat front. Increasing the reservoir temperature (from 63 to 143 °C) and oxygen concentration in the injected gas (from 11% to 21%) promoted notable heat front propagation and increased the average temperature of the heat front. It was concluded that temperature and oxygen concentration had the most important influence on the heat front propagation, followed by pressure and oil saturation.

Numerical Heat Transfer Simulation of Oil Shale Large-Size Downhole Heater

Downhole heaters are critical for effectively achieving in situ oil shale cracking. In this study, we simulate the heat transfer performance of a large-scale helical baffle downhole heater under various operational conditions. The findings indicate that at 160 m3/h and 6 kW the outlet temperature can reach 280 °C. Controlling heating power or increasing the injected gas flow effectively mitigates heat accumulation on the heating rod’s surface. The outlet temperature curve exhibits two phases. Simultaneously, a balance in energy exchange between the injected gas and heating power occurs, mitigating high-temperature hotspots. Consequently, the outlet temperature cannot attain the theoretical maximum temperature, referred to as the actual maximum temperature. Employing h/∆p13 as the indicator to evaluate heat transfer performance, optimal performance occurs at 100 m3/h. Heat transfer performance at 200 m3/h is significantly impacted by heating power, with the former being approximately 6% superior to the latter. Additionally, heat transfer performance is most stable below 160 m3/h. The gas heating process is categorized into three stages based on temperature distribution characteristics within the heater: rapid warming, stable warming, and excessive heating. The simulation findings suggest that the large-size heater can inject a higher flow rate of heat-carrying gas into the subsurface, enabling efficient oil shale in situ cracking.

Analysis of heat transfer performance and system energy efficiency of catalytic combustion heaters for low calorific value waste gas application to oil shale in-situ conversion

In this study, we explore the utilization of low calorific value waste gas for in-situ conversion mining of oil shale. Through simulation, we analyze the effects of variations in the parameters of the catalytic combustion heater's independent variables on the exhaust gas temperature, methane conversion rate, and system energy efficiency (dependent variables). The results demonstrate that larger values of the pore radius, gas injection flow rate, and pulsation flow rate parameters lead to reductions in the corresponding dependent variables. The system's energy efficiency remains stable between 21.94% and 22.46% with increasing gas injection temperature. Furthermore, an increase in the oxygen molar fraction results in elevated methane conversion rates from 0.64% to 58.2% and system energy efficiency from 0.4% to 21.51%. Conversely, an increase in the methane molar fraction causes a decrease in methane conversion from 76.17% to 7.18% and a decline in system energy efficiency from 32.83% to 7.18%. Notably, gas flowback occurs at downhole pressure conditions of 2 MPa. The variation in pressure stabilizes the system's energy efficiency between 21% and 22.10%. The simulation and analysis findings of this study provide significant reference value for subsequent practical testing efforts.

Thermal comfort characteristics of a catalytic combustion heater under wind-chilled exposure

Heating in wind-chilled environments is a serious task. The catalytic combustion heater (CCH) provides more efficient and cleaner in combustion compared to conventional heaters with high pollutant emission and low energy utilization. In this paper, the heating ability of CCH on human body in a wind-chilled environment (apparent temperatures between −14.8 °C and 12.4 °C) was investigated by collecting skin temperature and subjective thermal evaluation data from 23 subjects. The impact of cold air on localized heating of body parts by CCH was clarified using decision trees and dimensionless correlation coefficients. A human-computer interaction regulation strategy was proposed to simultaneously satisfy the requirements of effective heating, low energy consumption, and low pollution. Finally, CCH and a commercial heater were compared in terms of heating effectiveness and energy consumption in a real outdoor environment. The results showed that CCH effectively solved the problem of excessive cold extremities, and the temperature difference between thoracoabdominal area and extremities was reduced by 57.5–87.9% to within 2 °C. In a strong convective environment, wind speed was the decisive factor (coefficient of 0.95), inducing 46% radiant heat loss. Inputting personnel subjective perception, dynamic environmental parameters, and pollutant thresholds to adjust the injected gas flow enabled intelligent control. In a real cold scenario, the CCH saved 65.9% of energy compared to a commercial heater when achieving the same heating effect. This study provides a reference for the application of catalytic combustion technology in cold outdoor heating and also provides an important theoretical basis for the construction of heating strategies for CCH.

Optimal parameter adjustment of catalytic combustion heaters for oil shale in-situ conversion of low calorific value gases

Oil shale resources are huge, and in order to develop and utilize them rationally, it is crucial to research heaters suitable for downhole in-situ conversion mining. Compared with the problems of short life and multi-stage energy utilization of downhole electric heaters, combustion heaters have advantages such as high thermal efficiency and low cost. The heater uses low calorific value industrial waste gas as the fuel for gas injection, which reduces carbon emissions and environmental pollution and saves gas injection costs. In this paper, we propose to apply catalytic combustion of low calorific value industrial waste gas to generate high temperature exhaust gas suitable for mining, and establish the relationship between gas injection flow rate, combustion chamber parameters and gas injection duration by mathematical methods. The effect of the downhole high-pressure environment on the catalytic combustion characteristics of low calorific gas was simulated and the formula for calculating the content of low calorific gas in the exhaust gas was modified. The results show that the determination of the relational equation solves the problem of excessive axial volume in the design process of downhole heaters. Under high pressure conditions downhole, the exhaust gas temperature and low calorific gas conversion rate are significantly improved. The catalyst ignition temperature ranged from 973 K to 1073 K. Increasing the downhole pressure to 5 MPa increased the conversion of low calorific value gas from 74.56% to 88.22%. The gas injection rate and calorific value range can be calculated by correcting the equation for the content of low calorific gas in the exhaust gas. The conclusion of the study provides a reference basis for the selection of catalytic combustion process parameters for low calorific industrial waste gas, and also provides an important theoretical basis for the construction of the downhole test prototype.

The autothermic pyrolysis in-situ conversion process for oil shale recovery: Effect of gas injection parameters

The scale benefit exploitation of oil shale is of great significance to alleviate the current world energy shortage. The autothermic pyrolysis in-situ conversion process (ATS) method shows the feasibility and broad prospects of in-situ efficient utilization of oil shale resources (Guo et al., 2022) [29]. This study conducts in-situ pyrolysis of oil shale by ATS method with oxygen content and injection gas flow as experimental parameters, further clarifying the energy efficiency mechanism and influence characteristics of oxygen injection amount on the in-situ autothermic pyrolysis. The results showed that the in-situ self-pyrolysis reaction can be successfully triggered at 300 °C under the injection parameters of 12,16,21% oxygen content and 3,5,7 L/min injection gas flow rate. However, neither too low nor too high oxygen injection amount can achieve a good in-situ conversion effect. Within the range of parameters considered in this study, the optimal combination of oxygen injection parameters for in-situ pyrolysis of oil shale by the ATS method is 16% oxygen content and 5 L/min injection gas flow. The recovery rate of its cracked oil is 67.1%, and its energy efficiency is as high as 3.46, which is 6.78 times the energy efficiency of in-situ high-temperature nitrogen pyrolysis, realizing the benefits of the transformation of oil shale resources. Meanwhile, according to the apparent optical characteristics of the sample after the experiment and the evolution of the material components in each reaction region, the in-situ autothermic pyrolysis has a significant regional fingering feature. It is hoped that this study will provide reliable data support for the large-scale application of the ATS method.

Experimental study of dual-well gas injection and brine discharge in salt cavern sediment space

Docking Well underground salt cavern storage (DWUSCS) is a novel construction method that enables dual-well to be used for gas injection and brine discharge (GIBD), resulting in improved efficiency, cost savings, and greater utilization of the cavity space. However, the uncertainties of insoluble materials and the discharge patterns have retarded the research status in dual-well GIBD studies. In this study, we analyzed the insoluble materials of the DWUSCS layer, and investigated the factors that affect sediment space injection and discharge in the connecting channel through GIBD simulation experiments. We found that the densities of insoluble mineral components were similar to those of rock salt. Our simulation experiments revealed that the greater the permeability of the sediment space, the larger the void fraction, the more micron-sized particles in the insoluble materials, and the more brine that can be discharged during GIBD. During OIOD, gas injection pressure rises rapidly and then stabilizes before gas discharge. When the gas is discharged with brine, the pressure drops dramatically and finally reaches equilibrium. The gas injection flow rate has an impact on the discharge of brine, flow rate with 10 mL/min can displace more brine than 100 mL/min. The angle of the connecting channel also influences the effect of brine discharge in the sediment space during OIOD. Specifically, when the angle of the channel is 0°, the discharge volume is minimum, but it increases with increasing angle, and the optimal angle relates to permeability. In the case of a horizontal connecting channel, TIOD (the discharge outlet is at the bottom of the channel) (TIOD (bottom)) can discharge the maximum amount of brine. For large GIBD device, TIOD (bottom) will expend more than 50 times experimental periods than OIOD. By using OIOD first and then TIOD (bottom), the construction period can be shortened and the economic cost reduced. These findings provide valuable insights into the GIBD process from on-site DWUSCS.

Controlled Bubble Formation From a Microelectrode Single Bubble Generator

Abstract In this work, a new micro-electrode bubble generator is presented that employs a micro-electrode installed inside a small nozzle enabling the production of bubbles with controllable size and frequency. This bubble generator can be employed as a simple and potentially cheap method for the generation of single bubbles in a liquid, as long as it enables ion exchange, as an alternative to more complicated methods such as timely injection of a gas through a nozzle, which requires sophisticated nozzle design, manufacturing, and monitoring of the injected gas flow rate. A systematic investigation was conducted to assess the effect of the bubble generator dimensions, applied voltage, and electrolyte flow conditions on the size and frequency of the generated bubbles. It was shown that when the micro-electrode is thinly concealed within the nozzle, this bubble generator can successfully produce bubbles covering a wide range of diameters from 0.4 to 1.4 mm with a size distribution standard deviation of about 25%. The mechanism of single and continuous bubbles formation from the proposed bubble generator is also discussed. While this paper introduces this new micro-electrode bubble generator, further work is required to optimize it, enabling more accurate control over bubble size and frequency.

Supervision and Control System of the Operational Variables of a Cluster in a High-Pressure Gas Injection Plant

The objective of this research was to develop a technological architecture proposal that allows for the supervision and control of the operational parameters of gas injection (flow, temperature, and pressure) in a cluster of a high-pressure gas injection plant. The proposal provides a supervision and control system for the HPGIP I high-pressure gas injection plant that includes instrumentation equipment (transmitters and actuators), a remote terminal unit (RTU) as a control device, and the creation of a control logic as the basis for the development of the SCADA GALBA®, through which the operational variables involved in the process of the gas injection plant can be visualized and controlled, allowing the automatic regulation of the flow of gas that enters the deposits. Automatization of the process allows for the elimination of the average error differential that increases from 2 to 5% when the control valve is opened manually. Currently, the MUC-67 and MUC-68 wells that make up cluster 5 require a control valve opening of 20% and 5%, respectively, and this percentage is directly affected by the average valve opening error when performed manually. In addition, there is a savings of around 40 min in the response time by the operators for the adjustment of the opening or closing parameters of the control valve manually. The proposal allows for the different control actions on the variables or parameters of gas injection present in the clump to be carried out from a control room.

Statistical characterization of the interfacial behavior captured by a novel image processing algorithm during the gas/liquid counter-current two-phase flow in a 1/3 scaled down of PWR hot leg

This study addresses a statistical characterization of the interfacial behaviors during gas/liquid counter-current flow in a large scale of pressurized water reactor’s hot leg typical geometry on the basis of both time and frequency domain analyses. Here, the visualizations were captured by high-speed cameras. Furthermore, the image processing algorithm on the basis of pixel identification was developed to identify the time-series interfacial dynamics of the liquid holdup fluctuations, comprising the wave growth and its movement. The obtained data were further analyzed by using various advanced statistical tools comprising the probability density function, power spectral density function, and also discrete wavelet transform. Additionally, chaotic levels of the flow were obtained through the Kolmogorov-entropy analysis.Particular results reveal that a typical mechanism of flooding begins with the appearance of a wavy interface which further develops into either a roll or large wave, and later blocks the entire cross-sectional area of the conduit around the bend region. This later stage indicates the inception of flooding which is characterized by the increase of the water level close to the bend region. Next, the higher the pressure of system, the higher the frequency occurrence of slugging, while the injected gas flow rate obtained a different trend. However, the Kolmogorov entropy enables to correlate the stabilizing effect due to the fluid resistance which corresponds to either the pressure of the system or the physical properties of the fluid. In addition, there were no significant differences between the flooding mechanisms for both the air/water and steam/water flows.

Enhancement of Electromagnetic Wave Shielding Effectiveness by the Incorporation of Carbon Nanofibers-Carbon Microcoils Hybrid into Commercial Carbon Paste for Heating Films.

Carbon microcoils (CMCs) were formed on stainless steel substrates using C2H2 + SF6 gas flows in a thermal chemical vapor deposition (CVD) system. The manipulation of the SF6 gas flow rate and the SF6 gas flow injection time was carried out to obtain controllable CMC geometries. The change in CMC geometry, especially CMC diameter as a function of SF6 gas flow injection time, was remarkable. In addition, the incorporation of H2 gas into the C2H2 + SF6 gas flow system with cyclic SF6 gas flow caused the formation of the hybrid of carbon nanofibers-carbon microcoils (CNFs-CMCs). The hybrid of CNFs-CMCs was composed of numerous small-sized CNFs, which formed on the CMCs surfaces. The electromagnetic wave shielding effectiveness (SE) of the heating film, made by the hybrids of CNFs-CMCs incorporated carbon paste film, was investigated across operating frequencies in the 1.5-40 GHz range. It was compared to heating films made from commercial carbon paste or the controllable CMCs incorporated carbon paste. Although the electrical conductivity of the native commercial carbon paste was lowered by both the incorporation of the CMCs and the hybrids of CNFs-CMCs, the total SE values of the manufactured heating film increased following the incorporation of these materials. Considering the thickness of the heating film, the presently measured values rank highly among the previously reported total SE values. This dramatic improvement in the total SE values was mainly ascribed to the intrinsic characteristics of CMC and/or the hybrid of CNFs-CMCs contributing to the absorption shielding route of electromagnetic waves.

Dynamic Criteria for Physical Modeling of Oil Displacement by Gas Injection

In this work, slim tube displacement tests for minimum miscibility pressure MMP were carried out. Based on the displacement data, the MMP was calculated by statistical regression using linear and quadratic extrapolation with threshold values of 90% and 95% oil recovery as well as the intersection of trend lines for immiscible and miscible displacement regimes. The obtained data show a significant variation in the range of MMP values depending on the calculation method. To clarify the MMP value, an analysis of displacement dynamics was carried out. The ratio of the volume flow rate of reservoir oil to the volume flow rate of the injected gas—flow rates ratio (FFR)—was used as a new parameter. The MMP value calculated from the FRR value extrapolation was determined as 37.09 MPa. According to the results obtained, the proposed methodology based on the displacement dynamics can be useful as a criterion for clarifying the MMP value in slim tube displacement experiments.

3D Simulations of gas injection on callovo-oxfordian claystone assuming spatial heterogeneity and anisotropy

A series of gas injection tests on Callovo-Oxfordian (COx) claystone from the Bure underground research laboratory (URL) in France were carried out at the British Geological Survey (BGS). The tests were performed using a triaxial apparatus specifically designed to capture small volumetric strains induced by the injected gas flow and consequent material dilatancy. The long-duration experiments were monitored throughout. Measurements also included pressure, stresses (axial and radial stresses prescribed for each test stage), rate of gas inflow, gas outflow volume as well as pore-pressures observed at various points of the sample. A coupled hydro-gas-mechanical 3D numerical model has been developed to simulate the tests. Initial permeability is assumed heterogeneous throughout the specimen and embedded fractures are incorporated in the formulation. Gas pressure-induced deformations during the test lead to variations of permeability due to changes in matrix porosity and, especially, fracture aperture as well as fracture orientation due to material anisotropy. A programme of sensitivity analyses involving the variation of different aspects and parameters of the model contributes to a better understanding of the phenomena and highlights its complexity. The model is able to reproduce the observed behaviour of the tests.