Microbially induced carbonate precipitation (MICP) is an emerging technique for enhancing the mechanical properties of granular soils. Although several experimental studies have reported increased shear strength in MICP-treated soils at both peak and residual states, other findings have shown reductions in residual strength compared to untreated soils. This study uses the discrete element method (DEM) to investigate the mechanisms governing the residual strength of bio-cemented sands. The results indicate that residual strength may decrease when carbonate precipitates in the form of grain-bridging patterns. In that case, the introduction of carbonates alters the contact network and may induce metastable configurations, particularly when the bonds are weak or non-cohesive. These configurations are prone to strain localisation upon shearing, leading to the development of shear bands and a reduction in residual strength. Conversely, higher cohesive strength enhances microstructural stability, offsetting the weakening effects of localisation. The residual strength of bio-cemented sands is therefore governed by two competing mechanisms, namely bond-induced stabilisation and instability-driven localisation.

Rocks can undergo fatigue failure when subjected to cyclic mechanical, hydraulic, or thermal loadings, or a combination of these. Therefore, accounting for possible fatigue damage is important for subsurface engineering projects, such as the cyclic stimulation of geothermal reservoirs. However, existing models do not simultaneously account for degradation of both tensile strength and stiffness under varying-amplitude loading and coupled thermo-hydro-mechanical (THM) conditions. To address this, a new cohesive zone model is developed to account for the effect of fatigue on tensile strength and stiffness. The model is then used within the framework of zero-thickness interface elements to simulate the response of pre-existing or new fractures. Hydraulic and thermal processes are included in both the cohesive interface elements and the continuum elements, allowing the consideration of coupled thermo-hydro-mechanical processes. The fatigue damage variable is set to evolve with the number and magnitude of cycles according to Palmgren-Miner's rule. The proposed method is validated against three laboratory tests from the literature, including cyclic Brazilian test, cyclic hydraulic fracturing test and cyclic thermal stimulation test. All three validation results show that the fatigue damage or reduced breakdown pressure can be well reproduced. Mesh sensitivity based on the simulation of the Brazilian test, in which interface elements are inserted in-between all the continuum elements, highlights the influence of the mesh orientation and mesh density on the simulation results. In addition, stabilisation of the method is demonstrated by increasing the mechanical viscosity, which must be used with care to avoid predicting a longer fatigue life. The ability of the method to handle varying-amplitude cyclic loading is demonstrated by the simulation of a synthetic cyclic loading scheme based on the Brazilian test. The proposed method can be used to support the design of cyclic thermal stimulation campaigns for geothermal (or other) reservoirs, by being able to simulate the reduction in strength due to fatigue, and thus reducing stimulation pressures needed.

Soft stimulation technologies have been proposed as a means to reduce the breakdown pressure and mitigate the risk of induced seismicity during geothermal reservoir stimulation. Yet, the underlying mechanisms remain poorly understood due to the complexity of the coupled thermo-hydro-mechanical (THM) processes. In this work, a fully coupled THM model is developed to evaluate and compare the performance of different stimulation scenarios (monotonic, stepwise injection rate, cyclic injection rate or temperature, and stepwise combined with cyclic injection rate stimulation) on a synthetic, highly permeable reservoir with near-borehole clogging. Simulation results show that stepwise injection rate stimulation yields the most favourable outcomes, followed by the stepwise injection rate combined with cyclic injection rate stimulation. On the other hand, fatigue effects are seen to play a negligible role in the improved performance since the tensile stress at the fracture tip is relaxed with the continuous fracture growth. In addition, cyclic injection temperature stimulation is generally neither better nor worse than monotonic stimulation, but has slightly different characteristics, creating more local damage controlled by the period of the injection cycle. Cyclic injection rate stimulation can slightly reduce the peak pressure, compared with monotonic stimulation, but only when the injection rate is low. The reduction in peak pressure occurs due to the combination of thermally-induced stresses associated with cooling and incremental damage rather than any influence of fatigue. Stepwise or low-frequency cyclic injection rate stimulation are suggested rather than a high-frequency cyclic injection rate stimulation, while injection with cyclic temperatures is suggested when more local damage is wanted.

This study introduces a small-strain stiffness model for bio-cemented sands, building upon the existing small-strain stiffness model for sands proposed by Wichtmann and Triantafyllidis. The small-strain stiffness of numerical specimens, including sand specimens with different void ratios and bio-cemented specimens with different microscopic features, is evaluated using the discrete element method (DEM). The acquired DEM results are utilised to develop the small-strain stiffness model for bio-cemented sands. The proposed model is able to describe the small-strain stiffness of DEM bio-cemented sands. In particular, different contributions of carbonates in different distribution patterns to G0 enhancement can also be described by the proposed model.

It is clear that to address climate change, an energy transition which makes a large-scale use of the subsurface is needed. The subsurface will play a critical role in this transition, serving as a resource for new sources of energy production and storage, a foundation for energy infrastructure, and a repository for waste by-products from energy production (e.g., radioactive waste disposal, CO2 geo-sequestration). Furthermore, there are challenges in understanding material behaviour due to complex coupled phenomena, measuring material properties and upscaling the physical phenomena to engineering scale structures. Uncertainties, heterogeneities and long timescales offer additional challenges, as does bringing technology ever closer to dense populations. This is the topic of Energy Geotechnics. In the next decade and decades, society needs to complete the energy transition, and to do so the already substantial changes need to be vastly accelerated. This brings many challenges, which academics, consultants, contractors and authorities need to address together. [...]

Argillaceous formations of low permeability have been selected in several countries as geological host rock formation for the disposal of radioactive waste. The general barrier function of the host rock is to retard and attenuate the migration of radionuclides to the biosphere. In this context, understanding porewater chemistry and water-rock interactions in clayey formations is important for the safety assessment of repository systems in clay-rich formations. Porewater chemical conditions and buffering abilities of the rock will control radionuclides concentration in the geological barrier over time. In the Netherlands, poorly indurated clays are viewed as potential host formations in COVRA’s research programme for the disposal of radioactive waste. The properties of these clay layers are poorly characterised, and currently largely inferred from material at shallower depths in Belgium (e.g. 220 m at HADES URL). In Spring 2022, high-quality cores and sediment samples were obtained from the multi-purpose research borehole DAPGEO-02 [1]. The Smet Coring System (SCS), previously applied in Belgium, was employed to extract cores of adequate mechanical quality. 64 cores were extracted at depths between 362 and 415 m beneath Delft, in either PVC or Shelby tube core barrels. The cores were air/light-tight sealed in aluminium bags, and then stored at 4°C. The cored succession belongs to the Miocene age (interval 364.10-390.5 m) and late Paleogene, Thanetian-early Eocene, Ypresian age range (interval 390.5-414.0 m). The lithological stratigraphy fits with four formations: the Diessen formation (364.1-382.95 m), the Groote Heide formation (382.95-390.5 m), the Ieper Member from the Dongen formation (390.5-393.9 m), as well as the Oosteind Member (393.9-402.0 m); and the Liessel Member of the Landen formation (402.0-414.0 m). The mineralogy, geochemistry, and porewater chemistry were analysed from core samples of each formation: DAPGEO-02-C27, DAPGEO-02-C49, DAPGEO-02-C55, DAPGEO-02-C62 and DAPGEO-02-C71. The dry density and water content ranged from 1.54 to 1.62 g/cm3 and 21.5 to 28.1 %, respectively. The porewater was extracted using the squeezing technique at a pressure of 5 MPa, with the water collected inside septum vials to avoid exposure to air. In addition, the porewater was analysed as a function of squeezing pressure up to 50 MPa. The obtained porewater samples were very highly saline waters, with concentrations higher than seawater (SW), and salinity increasing with depth from 0.65 to 0.88 M, except in a transition zone with a sandy layer where the porewater is similar to SW. Br/Cl ratio is similar to SW, but a depletion of sulfate with respect to SW is observed, probably due to sulfate reduction and formation of pyrite, as observed in the rock samples, and according to the reducing conditions of the environment. Mg is also depleted probably due to its involvement in water-rock reactions and formation of smectite clay-rich mineral layers. Anion accessible porosity value is 0.8 for all samples, except in the sandy layer, where the value is 1.

Gas-induced fracturing in liquid-saturated clay-rich materials presents challenges in understanding and predicting fracture behaviour, due to the complex mechanical and transport properties of clays and the compressibility of gas. This paper introduces a novel experimental device for visualising fluid-driven cracks in clays. The device allows for the induction and observation of two-dimensional cracks in clay-rich, low-permeability materials through the injection of gas or water. The experimental setup comprises precision instrumentation for measuring compression forces, displacement, and fluid pressure, along with high-resolution imaging capabilities. Preliminary tests with Helium gas injection into Boom clay samples demonstrate the device's ability to track fracture evolution. This innovative experimental tool offers insights into the mechanisms governing fluid-driven fractures in clay-rich materials and provides a means to validate numerical models.

Cold water injection into geothermal reservoirs is a common, sometimes necessary, technique for multiple reasons including the replenishment and stimulation of the reservoirs, and the disposal of waste water. The injection of cold water results in a thermo-hydro-mechanical (THM) impulse, which can cause near-wellbore cracking. A method is presented to simulate coupled thermo-hydro-mechanical processes, including the re-activation of existing fractures and fracturing of the rock matrix. The model is based on the finite element method, and utilises a newly developed cohesive interface element to represent discontinuities. The interface element belongs to the family of zero-thickness elements and is triple-noded. It is developed to allow the simulation of longitudinal and transversal fluid/heat flow. The cubic law is used to simulate the fracture transmissivity as a function of its aperture, while a elasto-damage law is used to characterise the mechanical response of the discontinuity. The method is successfully verified against analytical solutions for hydraulic fracturing (KGD model) and for the thermo-hydraulic response of a single fracture (Lauwerier’s problem). As numerical oscillations are observed due to the high Péclet number, an artificial diffusion is added to stabilise the numerical solution with sufficient accuracy. Qualitative validation is achieved against experimental data of cold water injection in granite samples. Fracture branching is observed in the case with large cooling shock, while a single fracture is induced in the case with smaller cooling shock, as was observed in the experiment. The validation demonstrates the capability of the proposed model to simulate fracturing processes under THM couplings.

The crucial interaction between lessons learned from the study of unsaturated soil mechanics and energy geotechnics was highlighted at the recent third edition of the International Symposium on Energy Geotechnics (SEG23), held in Delft, the Netherlands. This short communication summarises the discussion that revolved around handling the many issues raised by the current energy transition from fossil fuels to more sustainable and renewable resources, and the need to integrate unsaturated soil knowledge into energy geotechnics. The panel discussion at the symposium emphasised how crucial it is to use the fundamental concepts of unsaturated soil mechanics for a range of energy applications to be able to characterise key underlying multi-phase processes and enable efficient design. With representatives from around the world, the panel discussion's goal was to close the gap between theoretical research and real-world applications by fostering a dialogue between academics and industry, thereby advancing creative and sustainable geotechnical solutions. The understandings generated from this conversation highlighted the necessity of ongoing cooperation and knowledge sharing to propel area developments and successfully address the urgent energy and environmental challenges of our time.

Backward erosion piping (BEP), a form of internal soil erosion, often threatens the safety of dykes built on alluvial deposits. To reduce the risk of dyke failure due to piping, reliable and cost-effective mitigation measures are essential. For the first time, this paper proposes the use of nature-inspired low-permeability barriers to mitigate BEP. The potential of this novel solution is demonstrated in a series of laboratory physical tests. Low-permeability barriers are created by mixing sand either with aluminium-organic matter flocs, or clay. The results show that both kinds of barriers can significantly inhibit pipe progression and intercept the erosion channels. The hydraulic gradients required for pipes to reach the barrier are significantly higher than the critical gradient measured in the absence of barriers, ranging from 2·2 to 7·4 times greater than those in sand alone. The associated mitigating mechanisms include the dissipation of flow energy, resistance to internal erosion due to pore space clogging and prevention of sand fluidisation. The mitigating effect is affected by the reduction of hydraulic conductivity, the depths and the heterogeneity of barriers. The findings of this experimental work provide guidance for the design of low-permeability barriers in practice and contribute to the development of numerical models for BEP.

The strategic study “HLW Repository optimisation including closure (OPTI)” has recently been launched as part of EURAD 2 program. The study is motivated by the fact that the first HLW (high-level waste) repository projects are entering the licensing, construction and operation phases and that optimisation is becoming increasingly important to ensure that repository designs are not only technically robust but also economically efficient, environmentally sustainable, and socially acceptable. Furthermore, the discussion of optimisation is justified by the long-term nature scales of repository projects in general. Within each national program, changing boundary conditions (e.g. new waste types, updated regulatory frameworks, evolving societal expectations, etc.), technological developments, or the process adaptations based on operational experience will justify and require optimisation. The term “optimisation” covers a wide range of socio-technical and economic aspects. The term is further relevant for all steps of the repository programme, including site selection, design, construction, operation, closure, and post-closure monitoring. Optimisation in preparation of the safety case and licensing is an established engineering process ensuring compliance with regulatory requirements and enhancing the overall safety of repository systems. Optimisation after licensing or during construction and operation may have a different focus as safety is already demonstrated and a reduction of conservative assumptions is more important. In general, optimisation promises improvements in technical and economic aspects as well as with regard to flexibility and robustness. As such, optimisation is a process that should involve all stakeholders (e.g. research entities, regulators, waste management organizations), including the civil society. Different stakeholders will have different objectives and strategies for optimisation. OPTI will develop mutual understanding and provide recommendations on methods and further activities for the design and optimisation of specific HLW repository systems, structures and components (SSCs), and processes. For mutual understanding, it is important to know e.g. what are the main drivers for optimisation? At which points in the programme is optimisation required, recommended, not reasonable, or maybe even limited or restricted by regulatory requirements? The work package creates a platform to share best practice for optimisation strategies and processes. The results will notably help both advanced and emerging programmes. Knowledge transfer from advanced to developing ones will be facilitated. R&D needs for specific SSCs and procedures that could be further optimised will be identified.

Bio-cemented soils can exhibit various types of microstructure depending on the relative position of the carbonate crystals with respect to the host granular skeleton. Different microstructures can have different effects on the mechanical and hydraulic responses of the material, hence it is important to develop the capacity to model these microstructures. The discrete element method (DEM) is a powerful numerical method for studying the mechanical behaviour of granular materials considering grain-scale features. This paper presents a toolbox that can be used to generate 3D DEM samples of bio-cemented soils with specific microstructures. It provides the flexibility of modelling bio-cemented soils with precipitates in the form of contact cementing, grain bridging and coating, and combinations of these distribution patterns. The algorithm is described in detail in this paper, and the impact of the precipitated carbonates on the soil microstructure is evaluated. The results indicate that carbonates precipitated in different distribution patterns affect the soil microstructure differently, suggesting the importance of modelling the microstructure of bio-cemented soils.

Utilizing existing deep mining systems for geothermal extraction not only facilitates the development of geothermal systems but also helps meeting the cooling requirements for deep mining operations. In this study, a thermo-hydro-mechanical model of geothermal extraction in deep mines is developed to investigate the evolution of mine galleries stability and temperature, and the temperature changes in geothermal production wells. The uncertainty in system responses is predicted through the Bayesian Evidential Learning framework. Due to our limited understanding of the material properties and the scarcity of measurement data, uncertainties emerge in the forward simulations. Ideally, a comprehensive uncertainty analysis would be conducted to predict all possible outcomes and assess any risks. However, In light of the intractability of performing comprehensive uncertainty analyses in scenarios with vast unknown data, particularly due to the computational overhead of multiple inverse problemsolving, we employ the Bayesian Evidential Learning framework, which provides a feasible and rapid alternative for approximating prediction post-distributions and choosing the most informative data sets. Before implementing BEL, we employed Latin Hypercube Sampling to create 500 sets of realizations for forward simulations, and subsequently utilized global sensitivity analysis to evaluate the data's informational value, aiming to diminish the uncertainty in predictions. In this paper, the BEL framework is utilized to achieve two: firstly, to stochastically predict the responses of the system (stability and temperature) within the BEL framework, using machine learning to discover direct correlations between predictors (sensitive parameters) and targets (system responses). Subsequently, newly collected data can be utilized to predict the approximate posterior distributions of the corresponding gallery stability, temperature, and production well temperature, thus circumventing traditional data inversion steps. This framework can be adjusted to accommodate any predictions related to subsurface conditions; hence, our second goal involves predicting the system's long-term responses within the BEL based on shortterm data collection, forecasting posterior distributions from the acquired short-term data, and validating the efficacy of this approach. Our study indicates that in practical engineering, by (1) obtaining data of material properties and (2) key responses of short-term simulation, it is possible to predict the critical responses of the system in long-term geothermal extraction, thereby maximizing the information content of any measurement data while minimizing budget constraints and computational costs.

Geothermal energy extraction through deep mine systems offers the potential to reduce the cost of geothermal systems while meeting the cooling needs of deep mines. However, the injection of cold water into the subsurface triggers strongly coupled thermo-hydro-mechanical (THM) processes that can affect the stability of underground excavations. This study evaluates the impact of geothermal energy extraction on the temperature and stability of a deep mine. By quantifying the sensitivity of the mine temperature and stability to various parameters, we propose a scheme to optimize geothermal energy production, while achieving rapid mine cooling and maintaining stability. We first evaluate the impact of geothermal operations on mine temperature and stability through THM numerical modeling. The simulations show that poro-elastic stress quickly affects mine stability, while thermal stress has a more significant impact on the long-term stability. We then use Distance-based Generalized Sensitivity Analysis (DGSA) to quantify parameter sensitivity. The analysis identifies the distance between the mine system and the geothermal system as the most influential factor. Other important parameters include the injection rate, injection temperature, well spacing, coefficient of thermal expansion, permeability, Young's modulus, and heat capacity. Finally, we propose a DGSA-based optimization framework that accounts for subsurface uncertainty and validate the optimized results. Our results indicate that, with favorable geological conditions, a rational selection of system design parameters can enhance geothermal energy production while ensuring rapid mine cooling and stability. This study provides essential insights for the optimization of deep mine geothermal systems and supports effective decision-making.

Bio-mediated methods, such as microbially induced carbonate precipitation, are promising techniques for soil stabilisation. However, uncertainty about the spatial distribution of the minerals formed and the mechanical improvements impedes bio-mediated methods from being translated widely into practice. To bolster confidence in bio-treatment, non-destructive characterisation is desired. Seismic methods offer the possibility to monitor the effectiveness and mechanical efficiency of bio-treatment both in the laboratory and in the field. To aid the interpretation of shear wave velocity measurements, this study uses the discrete element method to examine the small-strain stiffness of bio-cemented sands. Bio-cemented specimens with different characteristics, including properties of the host sand (void ratio, uniformity of particle size distribution) and properties of the precipitated minerals (distribution pattern, content, Young’s modulus), are modelled and subjected to static probing. The mechanisms affecting the small-strain properties of cemented soils are investigated from microscopic observations. The results identify two mechanisms controlling the mechanical reinforcement associated with bio-cementation, namely the number of effective bonds and the ability of a single bond to improve stiffness. The results show that the dominant mechanism varies with the properties of the host sand. These results support the use of seismic measurements to assess the mechanical efficiency and effectiveness of bio-mediated treatment.

Nitrogen undergoes multiple biogeochemical transformations during waste degradation, which depend on speciation, prevailing geochemical boundary conditions, and waste surface properties. This study developed a waste biodegradation model with high flexibility in accommodating reaction pathways to assess different process dynamics. The model was applied to landfill simulator reactors operating anaerobically. Model results show that dilution with adsorption matches the experimental dissolved NH4+ concentration (C/N=25) at the early experimental stages. Also, NH4+ binding decreases
due to competition with Ca2+, and the model better captures the dissolved NH4+ behavior when CaSO4 is present in solution. Mass removal due to sampling and posterior dilution are the main mechanisms to reduce NH4+ concentration in the leachate. The model highlights the role of nitrogen sorption as the main
mechanism for nitrogen accumulation in the solid phase of municipal solid waste.

In geothermal projects, reinjection of produced water has been widely applied for disposing wastewater, supplying heat exchange media and maintaining reservoir pressure. Accordingly, it is a key process for environmental and well performance assessment, which partly controls the success of projects. However, the injectivity, a measure of how easily fluids can be reinjected into reservoirs, is influenced by various processes throughout installation and operation. Both injectivity decline and enhancement have been reported during reinjection operations, while most current studies tend to only focus on one aspect. This review aims to provide a comprehensive discussion on how the injectivity can be influenced during reinjection, both positively and negatively. This includes a detailed overview of the different clogging mechanisms, in which decreasing reservoir temperature plays a major role, leading to injectivity decline. Strategies to avoid and recover from injectivity reduction are also introduced. Followed is an overview of mechanisms underlying injectivity enhancement during reinjection, wherein re-opening/shearing of pre-existing fractures and thermal cracking have been identified as the main contributors. In practice, nevertheless, mixed-mechanism processes play a key role during reinjection. Finally, this review provides an outlook on future research directions that can enhance the understanding of injectivity-related issues.

With the increasing demand for mineral and alternative energy resources, as well as the gradual depletion of shallow resources, the exploitation and utilization of mineral resources and geothermal energy in deep strata is an effective way to solve the problem of resource shortage [1]. In recent years, as a new type of resource mining mode, the co-mining of deep mineral and geothermal energy has developed rapidly [2, 3]. This method can make use of the original equipment of the mine for geothermal exploitation. However, the deep co-mining system faces two significant challenges: the first is the significant uncertainty inherent in subsurface properties, while the second is the high levels of geostress and temperature associated with deep mining. These challenges are adding some constraints on the practicality of exploiting such systems and limit the feasibility of deep resource co-mining, so that modelling efforts are needed for actual risk assessment.
Consequently, we developed a Thermo-Hydro-Mechanical (THM) coupling framework for geothermal energy exploitation in deep mines using COMSOL to quantitatively characterize the temperature field of the geothermal system and predict the stress field of the mining system, considering the joint effects of large uncertainties and THM coupling. Through SGeMS, the uncertainty and spatial heterogeneity distribution of porosity are first generated. Then, the uncertainty of the hydraulic parameter [4] (permeability), mechanical parameter [5] (elastic modulus), and thermal parameter [6] (heat capacity and heat conductivity) was derived from the porosity. 500 samples were generated within a given uncertainty range, by means of Monte Carlo simulations. The spatial and temporal distributions of the temperature field of the geothermal system, and the stress field of the mining system were simulated, for each sample with COMSOL. Using the distance-based global sensitivity analysis [6], the most sensitive parameters for deep mining are identified, the heat storage capacity of the system and evolution of the maximum stress ratio are evaluated, including uncertainty.

Geological Disposal Facilities (GDF) for radioactive waste will generally rely on clay-rich materials as a host geological formation and/or engineered barrier. Gas will be produced within the GDF, which can build up significant gas pressure and will activate the migration of gas through the clay materials via different transport mechanisms. These transport mechanisms are usually investigated in laboratory tests on small clay samples of a few centimetres. In this paper, a new Pneumo-Hydro-Mechanical (PHM) Finite Element model to simulate gas migration in saturated clay samples of this scale is presented. In the proposed modelling approach, continuum elements are used to represent the mechanical and flow processes in the bulk clay material, while zero-thickness interface elements are used to represent existing or induced discontinuities (cracks). A new triple-node PHM interface element is presented to achieve this. The performance of model is illustrated with synthetic benchmark examples which show the ability of the model to reproduce observed PHM mechanisms leading to propagation of cracks due to the gas pressure (gas fracturing).

The injection of gas in a liquid-saturated clay-rich material may lead to the formation of narrow channels or fractures created by the mechanical action of gas pressure. However, the complexity of the mechanical and transport properties of clays, combined with the high compressibility of gases, makes it challenging to understand and address this phenomenon. Gas fracturing can occur in a range of engineered processes, for instance the stimulation of sensitive hydro-carbon reservoirs, carbon dioxide injection and storage in subsurface reservoirs, pneumatic fracturing for enhanced remediation of contaminated soils, or gas transport through natural and engineered clay barriers in geological disposal facilities for radioactive waste. Despite the multiple environmental and economic implications associated with gas fracturing it remains difficult to predict and control due to the lack of fundamental scientific insight. One of the most challenging aspects of understanding gas-driven cracking in clays is the difficulty in visualising the crack formation in real time. In recent years, a new experimental setup has been proposed by the British Geological Survey, which makes it possible to induce and observe the formation of 'two dimensional' cracks in clay-rich low-permeability materials by the injection of gas or water. In order to aid the interpretation of the results obtained with this new device, the authors have carried out a series of numerical simulations performed with a finite element approach recently published, and compared them to experimental data. The model uses a fully coupled Pneumo-Hydro-Mechanical (PHM) formulation in 2D, and is implemented in the code LAGAMINE. These simulations show that the model proposed can reproduce the experimental results, providing valuable insights into the factors controlling the onset and propagation of the gas fractures. These insights have the potential to enhance the performance and safety of projects involving gas fracturing processes.