Fracture System Research Articles

Reliability of distal radius fracture classification systems: a CT based study.

To assess the reliability and reproducibility of AO/OTA, Frykman and Fernandez classification systems for distal radius fractures on CT. Four radiologists, including one radiology resident, two musculoskeletal radiology fellows and one radiology consultant independently evaluated CT scans of 115 patients with distal radius fractures and classified the fractures according to AO/OTA, Frykman and Fernandez classification system. To assess reproducibility, a second set of reading was done by two observers after an interval of six weeks. Interobserver reliability was calculated for each classification system using intraclass correlation coefficient (ICC) and using Light's modification of kappa. Intraobserver agreement was calculated using Cohen's kappa. Interobserver reliability using ICC showed fair agreement for AO/OTA (0.447) and Frykman (0.432) classification system and poor agreement for Fernandez (0.196) classification system. Interobserver agreement using kappa was moderate for AO/OTA fracture (0.447) classification into either of three types, while it was only slight for complete classification into type, group and subgroup (0.177). Interobserver agreement using kappa was slight for Fernandez (0.196) classification systems and moderate for Frykman classification system (0.406). Intraobserver agreement for AO/OTA classification system was moderate for observer 1 (0.449) and slight for observer 2 (0.162). Intraobserver agreement for Frykman classification system was substantial for observer 1(0.754) and moderate for observer 2 (0.496). Intraobserver agreement for Fernandez classification system was moderate for both the observers (0.333, 0.320). Currently there is no classification system that is fully reproducible. AO/OTA and Frykman classification systems performed better than Fernandez classification system in terms of interobserver reliability. However, Frykman classification system performed better than both AO/OTA and Fernandez classification system in terms of intraobserver reproducibility. Fernandez classification system had worst inter and intraobserver reliability in present study. Reliability and reproducibility of AO/OTA classification system decreased when fractures were divided into subgroups.

Integrated fracture analysis for improved oil recovery in the reefal limestones of Soğucak formation, Northwest Thrace Basin, Türkiye

Natural fractures play a crucial role in both exploration and development phases in oil and gas industry, as their network and orientation significantly affect flow and recovery strategies. This study highlights the importance of identifying opening-mode fracture systems within a mature Deveçatağı oil field that has been actively producing for nearly half a century. In order to investigate the most effective rock physics parameter to locate oil saturated zones in the field, this study applies detailed rock physics analysis and 2D forward modeling to pinpoint the principal factors affecting production in the Deveçatağı oil field, addressing the challenge posed by the limited shear wave wireline data acquired from only one well within this highly heterogeneous area. Analysis show that acoustic impedance is a crucial elastic property for detecting oil-saturated zones especially in areas with natural fractures. This study successfully integrates drilling-induced fracture (DIF) data, ant tracking maps, and seismic inversion outputs to understand on the issues leading to dry wells and advances in developing more effective exploration and recovery methods in fractured reservoirs. After almost 50 years of operational activities, well stimulation processes, and natural fractures that are present in this field, understanding oil drainage mechanisms in such environments is complex, emphasizing the need for comprehensive analysis to optimize production strategies.

Genesis of an Inorganic CO2 Gas Reservoir in the Dehui–Wangfu Fault Depression, Songliao Basin, China

This study systematically examines the origins and formation mechanisms of inorganic CO2 gas reservoirs located within the Dehui–Wangfu Fault in the southeastern uplift region of the Songliao Basin. The research aims to clarify the primary sources of inorganic CO2, along with its migration and accumulation processes. The identification of the Wanjinta gas reservoir within the Dehui–Wangfu Fault Zone, abundant in inorganic CO2, has sparked significant interest in the pivotal roles of volcanism and tectonic activity in gas generation and concentration. To analyze the release characteristics of CO2, this study conducted degassing experiments on volcanic and volcaniclastic rock samples from various boreholes within the fault trap. It evaluated CO2 release behaviors and controlling factors across varying temperatures (150 °C to 600 °C) and particle sizes (20, 40, and 100 µm). The findings indicated a negative correlation between CO2 release and particle size, with a notable transition at 300 °C—marking this temperature as critical for the release of adsorbed and lattice gases. Moreover, volcaniclastic rocks exhibited higher CO2 release compared to volcanic rocks, attributable to their larger specific surface area and higher porosity. At 600 °C, the decomposition of the rock crystal structure results in substantial gas escape. These observations suggest that the inorganic CO2 in this area derives not only from mantle sources but is also influenced by crustal components. Elevated temperatures prompted by tectonic activity and magmatic intrusion facilitated the degassing of the surrounding rocks, allowing released CO2 to migrate upwards through the fracture system and accumulate in the shallow crust, ultimately forming a gas reservoir. This study enhances the understanding of volcanic rock’s roles in inorganic CO2 gas generation and migration, highlighting the fracture system’s critical controlling influence on gas transport and aggregation. The findings indicate that inorganic CO2 gas reservoirs in the Dehui–Wangfu Fault Zone primarily originate from mantle sources with a mixture of crustal gases. This discovery offers new theoretical insights and practical guidance for the exploration and development of gas reservoirs in the Songliao Basin and similar regions.

A space-time mixed finite element method for reduced fracture flow models on nonmatching grids

This paper is concerned with the numerical solution of the flow problem in a fractured porous medium where the fracture is treated as a lower dimensional object embedded in the rock matrix. We consider a space-time mixed variational formulation of such a reduced fracture model with mixed finite element approximations in space and discontinuous Galerkin discretization in time. Different spatial and temporal grids are used in the subdomains and in the fracture to adapt to the heterogeneity of the problem. Analysis of the numerical scheme, including well-posedness of the discrete problem, stability and a priori error estimates, is presented. Using substructuring techniques, the coupled subdomain and fracture system is reduced to a space-time interface problem which is solved iteratively by GMRES. Each GMRES iteration involves solution of time-dependent problems in the subdomains using the method of lines with local spatial and temporal discretizations. The convergence of GMRES is proved by using the field-of-values analysis and the properties of the discrete space-time interface operator. Numerical experiments are carried out to illustrate the performance of the proposed iterative algorithm and the accuracy of the numerical solution.

Development and application of a thermo-hydro-mechanical coupling test system for a single rock fracture

A thermo-hydro-mechanical coupling test system was developed to study the physical and mechanical properties of a single rock fracture under the interaction of multi-physics field. The test system mainly contained a loading system, a shear-flow box and sealing system, a high-temperature environment box and a seepage system. The test system can conduct the normal compression and shear-flow coupling test under complex stress paths within 300 °C. Two load cells were set at both ends of the shear direction to solve problem of inaccurate shear force monitoring. The unique shear-flow box was designed to solve the dynamic sealing problem. To verify the reliability of the test system, the seepage tests during heating–cooling process and a shear-flow coupling test for a single granite fracture under various boundary conditions were carried out. The test system provides research equipment for understanding the interaction mechanism of multi-physical field in deep underground engineering.

Seismic Response of Hectometer‐Scale Fracture Systems to Hydraulic Stimulation in the Bedretto Underground Laboratory, Switzerland

AbstractWe performed a series of hydraulic stimulations at 1.1 km depth in the Bedretto underground laboratory, Switzerland, as part of an overall research strategy attempting to understand induced seismicity on different scales. Using an ultra‐high frequency seismic network we detect seismic events as small as Mw < −4, revealing intricate details of a complex fracture network extending over 100 m from the injection sites. Here, we outline the experimental approach and present seismic catalogs as well as a comparative analysis of event number per injection, magnitudes, b‐values, seismogenic index and reactivation pressures. In our first‐order seismicity analysis, we could make the following observations: The rock volume impacted by the stimulations in different intervals differs significantly with a lateral extent from a few meters to more than 150 m. In most intervals multiple fractures were reactivated. The seismicity typically propagates upwards toward shallower depth on parallel oriented planes that are consistent with the stress field and seem to a large extent associated with preexisting open fractures. This experiment confirms the diversity in seismic behavior independent from the injection protocol. The overall seismicity patterns demonstrate that multi‐stage stimulations using zonal isolation allow developing an extended fracture network in a 3D rock volume, which is necessary for enhanced geothermal systems. Our stimulations covering two orders of magnitude in terms of injected volume will give insights into upscaling of induced seismicity from underground laboratory scale to field scale.

Non-equilibrium solute transport in a fractured rock matrix system under a radial flow pattern

Non-equilibrium solute transport in a fractured rock matrix system under a radial flow pattern

Water flow pattern recognition and fracture characterization in near-surface chalks using time-lapse ground-penetrating radar: An experiment

Predicting subsurface water flow is inherently complex due to the heterogeneity of geological formations. Water infiltration occurs through various pathways, such as pore throats, fractures, or faults, depending on the sediment type. In an effort to enhance our understanding of water flow within heterogeneous, fractured chalks formations, we integrate ground penetrating radar (GPR), acoustic measurements, and photogrammetric surveys to examine the flow patterns. We first conduct a field experiment of injecting water into chalks and monitor the water flow through a time-lapse GPR reflection survey. Then we identify the water-affected zone by analyzing the GPR data, and correlate the water-affected zone with the identified fractures on the exposed strata. Finally, we verify the water effect through measured acoustic velocities of acquired samples. Our analysis of the GPR data encompasses direct subtraction, traveltime delay, electromagnetic (EM) velocity changes, and water saturation variations. These analyses consistently indicate a predominant southeastward flow direction. This finding is corroborated by the fractures identified through photogrammetry, which closely match the water-affected zone, suggesting that water flow is indeed fracture-driven. The measured acoustic velocities are utilized to estimate water saturation using an iso-frame rock physics model, which shows consistency with the saturation estimated through EM velocity, further validating the monitoring results. These findings advance the understanding of fluid flow and its interaction with fracture system in heterogeneous chalks, and provide a reference for future studies by demonstrating the efficacy of integrating photogrammetry-identified fractures, EM velocity, and acoustic velocity to verify monitoring outcomes.

Numerical Optimization of Functionally Graded Ti-HAP Material for Tibial Bone Fixation System.

Functionally graded materials (FGMs) are heterogeneous composites characterized by outstanding properties. They are built from two or more components with a gradient distribution of chemical composition along a given direction. A promising graded material for biomedical engineering as an implant could be a FGM made of titanium (Ti) and hydroxyapatite (HAP). It would allow us to counteract the difference between the stiffness modulus of pure titanium and bone tissue. Moreover, it can be a good solution to the problem of stress shielding for bone fixation plates made of conventional titanium or steel. The presented paper aims to perform micromechanical modeling and optimization of a functionally Ti-HAP graded plate, followed by numerical analysis of a fractured tibia stabilization system under specific boundary conditions. Finite element analysis was performed using ANSYS Workbench 2021 software. The models of the FGM plate and tibial fixation system were made using the Space Claim tool. The ANSYS software allowed the optimization of the model considered and the selection of the appropriate structural parameters of the FGM Ti-HAP material. In general, the results proved that the osteosynthesis plate built of graded Ti-HAP material resulted in lower bone stress compared to titanium and steel plates. The results obtained confirmed the validity of the design and the possibility to use functionally graded Ti-HAP bone fixation plates.

Natural vibrations of fluid in a well connected with the reservoir by a system of radial fractures

The problem of natural vibrations of a fluid in a horizontal well with multiple fractures obtained by hydraulic fracturing is considered. A mathematical model of the natural vibrations of fluid in a horizontal oil well connected to the reservoir by a system of radial hydraulic fractures is constructed and the frequency characteristics of the natural vibrations of fluid as functions of the hydraulic fracture and reservoir parameters are determined. Using a numerical analysis of the frequency characteristics of vibrations, the effect of changes in the fracture width, the number of fractures, and the reservoir permeability on the natural frequencies is demonstrated.

Characteristics and formation of natural fractures in a silica-rich chalk, Coniacian Arnager Limestone Formation, Bornholm, Denmark.

Natural fractures are abundant and important components in many carbonate sedimentary rocks globally. In hydrocarbon and groundwater reservoirs of carbonate rocks they can form connected networks and thereby influence the permeability and f luid flow significantly. Outcrop studies of fractured carbonate rocks can provide an essential understanding of 3-dimensional fracture networks, thereby aiding in understanding fracture patterns and connectivity in subsurface carbonate reservoirs. The Arnager Limestone Formation is a naturally fractured silica-rich chalk of Coniacian age exposed in a coastal cliff on the island of Bornholm in the Baltic Sea (Denmark). This study examines the natural fractures in the Arnager Limestone Formation from a structural and geomechanical perspective. The Arnager Limestone Formation forms one, 12–20 m thick, main rock mechanical unit; bedding planes acts as weak interfaces and divides it into near-identical, cm- to dm-thick rock mechanical subuits. Flat-lying (horizontal) or low-angle dipping bedding-parallel fractures are intersected by two near-vertical or steeply dipping fracture systems, a major N–S-trending system and a less prominent W–E-trending fracture system. Rock mechanical analysis of the tensile strength and elastic moduli provides the foundation for discussing maximum burial depth of the Arnager Limestone Formation. The tensile strength gives information on the bedding-parallel fractures, which can have formed due to stress relief during uplift and erosion, possible accentuated by glacial processes. The near-vertical fracture sets are interpreted to have formed in response to tectonic movements.

Improved Fracture Permeability Evaluation Model for Granite Reservoirs in Marine Environments: A Case Study from the South China Sea

Permeability is a crucial parameter in the exploration and development of oil and gas reservoirs, particularly in unconventional ones, where fractures significantly influence storage capacity and fluid flow. This study investigates the fracture permeability of granite reservoirs in the South China Sea, introducing an enhanced evaluation model for planar fracture permeability based on Darcy’s law and Poiseuille’s law. The model incorporates factors such as fracture heterogeneity, tortuosity, angle, and aperture to improve permeability assessments. Building on a single-fracture model, this research integrates mass transfer equations and trigonometric functions to assess intersecting fractures’ permeability. Numerical simulations explore how tortuosity, angle, and aperture affect individual fracture permeability and the influence of relative positioning in intersecting fractures. The model makes key assumptions, including minimal consideration of horizontal stress and the assumption of unidirectional laminar flow in cross-fractures. Granite outcrop samples were systematically collected, followed by full-diameter core drilling. A range of planar models with varying fracture apertures were designed, and permeability measurements were conducted using the AU-TOSCAN-II multifunctional core scanner with a steady-state gas injection method. The results showed consistency between the improved model and experimental findings regarding the effects of fracture aperture and angle on permeability, confirming the model’s accuracy in reflecting the fractures’ influence on reservoir flow capacity. For intersecting fractures, a comparative analysis of core X-ray computed tomography (X-CT) scanning results and experimental outcomes highlighted discrepancies between actual permeability measurements and theoretical simulations based on tortuosity and aperture variations. Limitations exist, particularly for cross-fractures, where quantifying complexity is challenging, leading to potential discrepancies between simulation and experimental results. Further comparisons between core experiments and logging responses are necessary for model refinement. In response to the challenges associated with evaluating absolute permeability in fractured reservoirs, this study presents a novel theoretical assessment model that considers both single and intersecting fractures. The model’s validity is demonstrated through actual core experiments, confirming the effectiveness of the single-fracture model while highlighting the need for further refinement of the dual-fracture model. The findings provide scientific support for the exploration and development of granite reservoirs in the South China Sea and establish a foundation for permeability predictions in other complex fractured reservoir systems, thereby advancing the field of fracture permeability assessment.

Inability to Remove Locking Screws from the Femoral Neck System due to Stripping of the Screwdriver within the Locking Screw Head.

The purposes of this study were to investigate the frequency of screwdriver stripping in the head of the locking screw that attaches to the side plate to the femur shaft among the patients who underwent implant removal after Femoral Neck System (FNS) for femoral neck fracture, to determine the risk factors for locking head screw stripping in FNS treatment of femoral neck fracture, and to suggest a surgical tip that removes FNS, which is difficult to remove due to screw stripping. Design: Retrospective cohort study. Eight Urban tertiary referral academic hospitals. Included were patients with OTA/AO 31-B1, 31-B2, and 31-B3 femoral neck fractures who underwent surgical fixation with FNS from Nov 2019 to Feb 2023. The frequency of locking head screw stripping of FNS during the implant removal was evaluated. Among the 47 patients (18 (38%) men and 29 (62%) women) who met the inclusion criteria with average age of 59.2 years (range, 28 to 94 years), 13 (27.7%) experienced screwdriver stripping in the head of the distal locking screw during FNS removal surgery. A higher BMI showed a borderline significant association with the stripping in the adjusted model (OR = 1.233; 95% CI: 0.988-1.539; p = 0.064). No other variables showed significant association with the stripped locking head screw (p>0.05). Stripping of the screwdriver within the head of the distal locking screw occurred in over one quarter of cases. While a higher BMI demonstrated a borderline significant association, none of the other variables examined showed a statistically significant relationship with the stripped locking head screw. Level III (retrospective cohort study).

Epidemiology, Classification and Treatment of Femur and Tibia Fractures around Total Knee Arthroplasty (Literature Review)

Summary. Periprosthetic fractures around total knee arthroplasty (TKA) are difficult to treat due to complex fracture morphology, high proportions of injuries associated with osteopenia, and the variability of injury patterns. Periprosthetic fractures associated with TKA are defined as fractures around the knee joint (femur, tibia, or patella) occurring within 5 cm of the intramedullary stem of the prosthesis or 15 cm of the joint. The incidence is estimated to be between 0.3% and 2.5% after primary TKA and up to 28% after revision TKA. There are several surgical and nonsurgical risk factors associated with postoperative periprosthetic fractures. Distal femoral periprosthetic fractures following TKA are the most common and reported to occur in 0.2–1.8% of patients after primary TKA. Tibial periprosthetic fractures have a reported prevalence of 0.07–0.1% in primary and 0.36% in revision knee arthroplasties. Patella fractures are the second most common periprosthetic fractures following TKA, with prevalence ranging from 0.68% to 1.19%, and are usually associated with a resurfaced patella. Several classification systems of periprosthetic fractures around TKA have been published and some treatment recommendations have been provided. However, most systems are subject to criticism and use different classification systems for the tibia, patella, and the femur.A variety of treatment methods are available for periprosthetic fractures. Conservative treatment can include protected weight bearing, splinting, or traction. Surgical treatment commonly involves closed intramedullary nailing or open reduction and internal fixation by plates. In cases of significant bone loss, a revision TKA may be indicated. In general, treatment must be guided based on the stability of the implant and the remaining bone quality, as determined by the presence of osteolysis and the location of the fracture.

An inception framework hypothesis for karst development in the Burren, Ireland

The Inception Horizon Hypothesis (IHH) postulates that certain stratigraphic horizons in a limestone sequence, combined with structural surfaces such as joints, provide a framework for cave development. Although subsurface and surface karst landforms are fundamentally linked, the IHH has not yet been extended to surface karstification. We tested this extension of the IHH in the world-renowned Burren karst due to its stratigraphic and structural simplicity. We used very high-resolution remote sensing datasets and detailed fieldwork to develop an updated map of the Burren's surface karst features, combined with a 3D geological model containing over 60 km of mapped cave passages.Our analysis shows that karstic connectivity between the surface and subsurface is primarily provided by a suite of vertically-persistent calcite and silica-rich veins, which form a non-stratabound fracture system across the Burren. The flow pathways provided by these veins then intersect the following inception horizons: (i) boundaries between distinct lithological units in the limestone sequence; (ii) crinoidal cycle tops, and more sporadically chert lenses, within one of those units (the Slievenaglasha Formation); (iii) thin horizons of non‑carbonates (‘clay wayboards’) within another unit (the Aillwee member). At the surface, the same horizons have been preferentially exploited by glacial processes, creating surfaces from which meteoric waters now recharge the subsurface and form new surface karst depressions and other karst landforms. Our new inception framework for karstification thus provides a new basis for understanding surface and subsurface connectivity in the karst critical zone in the Burren landscape, and it provides new geological insight into the functioning of carbonate critical zones more generally.

Reflectance spectrometry and multispectral data for mapping fractures and hydrothermal alterations in the northern edge of the eastern High Atlas, Morocco

The Marginal Folds, in the north-western axis of Moroccan eastern High Atlas, are mainly composed of the Infra-Cenomanian terrains. These latter contain continental detrital deposits (red beds) and are characterized by a network of fractures. These marginal folds host significant concentrations of metallic minerals, such as Cu, Pb, Ag, and Zn, particularly at the Merija (Cu) and Bou Sellam (Pb-Zn) sites.Several techniques were applied to the Landsat-8 Oli images to improve the clarity and visibility of the linear features. Radiometric and atmospheric corrections, color compositions, directional filters, and principal component analysis were adopted. The lineaments resulting from automatic extraction, as well as their statistical analysis were validated by visual interpretation and field investigations. Statistical analysis revealed three dominants fracture systems: N-S, NE-SW, and E-W; the first two systems show a high density in the study area.The mineral alteration of the outcropping rocks is well described by ASTER multispectral imaging techniques. In this work, the effectiveness of this techniques for mineral alteration mapping was demonstrated on the Merija area. Several occurrences of mineral alteration were highlighted, using a combination of false color and band ratios, the principal component analysis (PCA), and the band ratios. This research was completed by reflectance spectrometry, covering the visible, near-infrared (VNIR), and short-wave infrared (SWIR) domains, to identify mineral alteration.Hydrothermal alteration in the Merija region includes clay, phyllite, carbonate, and phyllosilicate alteration, such as kaolinite, illite, montmorillonite, palygorskite, and vermiculite. Regarding to oxidation, as evidenced by the presence of goethite, jarosite, and hematite, it is widespread in most of the analyzed samples, resulting from the alteration of pyrite, followed by jarosite and goethite.

Experimental study on the influence of horizontal stress difference coefficient on coal rock fracture

Hydraulic fracturing is a pressure-relief and permeability-enhancing technique widely used in the mining of low-permeability coal seams. The horizontal stress difference coefficient is an important factor that affects the fracture propagation during the fracturing. To study the mechanism of the hydraulic fracturing process, in this paper, the initiation and propagation of cracks under horizontal stress difference coefficient are studied by using the developed true triaxial hydraulic fracturing system. The fracture surface morphology was obtained by 3D scanner. The experimental results are verified by the mathematical model. The results show that the fracture pressure and the peak values of AE count rate and b value increase and the cumulative AE count decreases with the increase of the horizontal stress difference coefficient. After the first pressure drop, the “pressure built-up” in the specimen increases and the peak value of AE count rate decreases with the increased horizontal stress difference coefficient. The 3D scanning results show that when the horizontal stress difference coefficient is larger, the hydraulic fracture propagation is straighter and the fracture surface area is smaller. The experimental results are in good agreement with the theoretical values. The experimental results provide a basis for engineering practice.

A multi-level Stress–Strain relationship and hydraulic characteristics for supporting grain-porous rock fracture system

Fracturing technology, essential for enhancing permeability within oil and gas reservoirs, relies on supported particles to maintain fracture conductivity. A comprehensive understanding of the stress-strain relationships and hydraulic properties of Supported Grain-Porous Media Fracture System (SG-PMFS) is crucial for optimizing hydrocarbon extraction and advancing geomechanical modeling. In this study, we introduced a multilevel spring compression deformation model that categorized SG-PMFS deformation into an equivalent tensile component in matrix pores of the far-field region, equivalent compressive components in matrix pores of the near-field region and fractures, and multilevel compressive components in supporting grains. We derived distributed uniaxial/triaxial stress-strain relationships to quantitatively characterize these multilevel deformation behaviors across distinct characteristic regions. Digital image correlation strain measurement was employed for experimental validation, confirming the model's accuracy. The experimental results identified five distinct characteristic regions within SG-PMFS, with the distribution factors of each deformation component decreasing with distance from the fracture. Self-supported grains significantly enhanced the correlation coefficient of experimental data, reducing the fracture-related bulk modulus from 11.99 MPa to 1 MPa. The degree of grain crushing was directly proportional to the bulk modulus of the corresponding multilevel compressive component. Furthermore, we established constitutive relationships between stress and key hydraulic properties: fracture aperture, compressibility, and porosity. The model predictions and experimental results consistently characterized the relationship between hydraulic properties and stress across different regions. The hydraulic behavior of SG-PMFS under stress was segmented into three stages: porous rock fracture-dominated deformation (0–2.2 MPa), first-level particle crushing (2.2–4.6 MPa), and second-level particle crushing (4.6–25 MPa). The contribution of grain crushing to porosity changes consistently exceeded 50%, making it the dominant factor in the porosity variation of SG-PMFS.

Environmentally friendly production of petroleum systems with high CO2 content

Natural gas hydrates represents a huge source of energy. At the same time substantial leakages of natural gas from hydrates contributes significantly to climate changes. One of the most important reasons for these natural gas fluxes is leakage of seawater in to the hydrates from seafloor, through fracture systems. Hydrate dissociates if surrounding seawater is less than hydrate stability limit. Another interesting aspect of natural gas hydrates is the potential for safe CO2 storage. These different aspects of hydrates in natural sediments put demands on thermodynamic models. In addition to accurate description of pressure temperature hydrate stability there also a need to describe hydrate dissociation in concentration gradients towards surrounding water or surrounding gas as two examples. In this work we present new experimental data and an extensive thermodynamic model for hydrate. In contrast to conventional thermodynamic models for hydrate the model is consistent since all thermodynamic properties are derived from the Gibbs free energy. In this work we examine mixtures of CH4, C2H6, N2, CO2 from the China Sea and some synthetic mixtures, using this model. Maximum CO2 content in these mixtures are 60 mol% and the rest is dominated by CH4. Agreement between experimental data and model calculations are generally good and average deviations are below 5.5% for all the systems and conditions examined. Another aspect of the model is the ability for incorporation of effects of mineral surfaces. Specifically it is illustrated that adsorption of water on rust dominates liquid water drop out from gas as compared to water dew-point. Production of natural gas with such high CO2 content requires a strategy for CO2 separation and storage. It is proposed that the CH4 is separated from the C2H6, CO2 and N2 and cracked to H2 and CO2 using steam. Thermodynamic analysis indicates a significant potential for safe CO2 storage in natural gas hydrate and H2 as the only export product.

Research on Numerical Simulation Methods for Water Invasion Dynamics in Fractured Gas Reservoirs with Water Content

Abstract Fractured gas reservoirs with water have complex gas-water relationship, large permeability difference between matrix and fracture, complex gas-water percolation mode, rapid production decline, short stable production period and large reduction of recovery factor due to water production of gas wells, which poses great challenges to efficient development of gas fields. The fracture system is the main channel for the edge and bottom water channeling of gas reservoirs. It is the core issue to understand the water invasion dynamic characteristics of such gas reservoirs to accurately depict the fracture geometry occurrence and truly simulate the gas-water two-phase flow mechanism in the fracture-matrix dual media. Taking the Jia-2 gas reservoir in Moxi gas field as an example, a discrete fracture model construction method that explicitly characterizes the fracture system is proposed. Based on the discrete fracture model, a mathematical model of gas-water two-phase flow in the fracture-matrix dual system is constructed and numerically solved. The influence mechanism of fracture opening, length, density and occurrence on the water invasion performance of multi-layer gas reservoirs is discussed, and the main control factors of the water invasion and water channeling law of fractured water gas reservoirs are identified. The application shows that the water invasion dynamics of gas reservoirs based on the discrete fracture model are more consistent with the actual conditions of the mine, providing a theoretical basis for deepening the understanding of water invasion dynamics of this type of gas reservoirs, optimizing the gas well working system, and formulating targeted water control countermeasures..