Wall Fracture Research Articles

Slip Backflow of Polymers in Elastic Fractures for Subsurface Heat Recovery

This research delves into the complexities of backflow phenomena in finite-length and flat-walled fractures with elastic walls, specifically focusing on power-law fluids, whose shear-thinning behavior distinguishes them from Newtonian fluids. We model the backflow process under the lubrication approximation and by incorporating the linear Navier slip law. We numerically examine the influence of parameters such as slip length, fluid rheology, and external pressure on the backflow propagation of the carrier fluid. Our findings underscore the significant role played by the rheological index in determining the fracture closure rate. Additionally, our investigations highlight the marked effect of external pressure variations on pressure distribution within the fracture. Notably, the friction coefficient at the fracture walls, as denoted by a dimensionless slip number, exhibits limited influence on the fundamental dynamics of the problem. These insights advance our understanding of power-law fluid backflow and have wide-ranging applications across various engineering disciplines.

Pore-scale insight into the effect of porous walls on fluid flow in rough-walled fractures

This study investigates the influence of porous walls on fluid flow behavior in single rough-walled fractures. A series of direct numerical simulations (DNS) were conducted to examine fluid flow through rough-walled fractures surrounded by porous walls under various hydraulic gradients. The simulation results clearly demonstrate the progressively significant impact of porous walls on flow characteristics as porosity increases. Regression analyses indicate that the Forchheimer's law, which characterizes the nonlinear flow of rock fractures, remains valid in the presence of porous walls. Moreover, increased porosity enhances fluid exchange and leads to an increased ability for single fractures to transmit fluid. Two double-parameter equations were established to quantitatively characterize the effects of porous walls on hydraulic conductivity of the fracture and fluid exchange between porous walls and the fracture. Further analysis revealed that the angle between the fracture profile and main flow direction profoundly influences the inflow/outflow exchange between the fracture and its adjacent porous walls. Moreover, the pore-scale results indicate that it is unreasonable to equate the effect of porous walls with slip boundaries as suggested in previous studies. The results and findings of this study deepen our understanding of flow behavior at the interface between the rough-walled fracture and adjacent porous walls, and they serve as a basis for accurately simulating large-scale fracture networks that consider the hydraulic contribution of fracture walls.

Novel nomogram for predicting paradoxical chest wall movement in patients with flail segment of traumatic rib fracture: a retrospective cohort study

Flail chest is a severe injury to the chest wall and is related to adverse outcomes. A flail chest is classified as the physiologic, paradoxical motion of a chest wall or flail segment of rib fracture (RFX). We hypothesized that patients with paradoxical chest wall movement would present different clinical features from patients with a flail segment. This retrospective observational study included patients with blunt chest trauma who visited our level 1 trauma center between January 2019 and October 2022 and were diagnosed with one or more flail segments by computed tomography. The primary outcome of our study was a clinically diagnosed visible, paradoxical chest wall motion. We used the least absolute shrinkage and selection operator (LASSO) logistic regression model to minimize overfitting. After a feature selection using the LASSO regression model, we constructed a multivariable logistic regression (MLR) model and nomogram. A total of five risk factors were selected in the LASSO model and applied to the multivariable logistic regression model. Of these, four risk factors were statistically significant: the total number of RFX (adjusted OR [aOR], 1.28; 95% confidence interval [CI], 1.09–1.49; p = 0.002), number of segmental RFX including Grade III fractures (aOR, 1.78; 95% CI, 1.14–2.79; p = 0.012), laterally located primary fracture lines (aOR, 4.00; 95% CI, 1.69–9.43; p = 0.002), and anterior–lateral flail segments (aOR, 4.20; 95% CI, 1.60–10.99; p = 0.004). We constructed a nomogram to predict the personalized probability of the flail motion. A novel nomogram was developed in patients with flail segments of traumatic RFX to predict paradoxical chest wall motion. The number of RFX, Grade III segmental RFX, and the location of the RFX were significant risk factors.

Traction images heavily influence lateral wall measurement in trochanteric hip fractures. A prospective study

Introductionhip fracture represents a global health problem, with a high morbidity and mortality rate and an increasing incidence. The treatment of trochanteric fractures is reduction and osteosynthesis, and implant selection depends mainly on the stability of the fracture and lateral wall competence. Lateral wall competence has gained relevance in recent years, which led to the modification of the AO/OTA classification. However, determination of lateral wall integrity is difficult from plain radiographs; the influence of images with traction on its measurement has not been evaluated. Methodsprospective concordance study, emergency and post-traction radiographs of 65 patients with trochanteric fracture were evaluated by six orthopedic surgeons independently, measuring the lateral wall, classifying the fracture according to the AO/OTA 2018 classification and selecting the implant for osteosynthesis. A comparison of incompetent to intact lateral wall proportion between each image set was made. Secondary outcomes were the inter-observer correlation of lateral wall measurement and inter-observer agreement of classification and implant choice. Resultsthe proportion of patients with an incompetent lateral wall in emergency x-ray was 37.43% (CI 95% 0.326–0.422), while the proportion in post-traction fluoroscopy was 15% (CI 95% 0.115–0.185), with a statistically significant difference (p < 0.001). 40.1% of patients with an incompetent lateral wall changed to an intact one. Inter-observer correlation for the lateral wall thickness was 0.399 (CI 95% 0.292–0.519) in emergency x-ray and 0.658 (CI 95% 0.564–0.748) in post-traction fluoroscopy, with a substantial agreement. Inter-observer agreement for the fracture classification was fair to moderate using emergency x-ray (κ 0.369 95%CI 0.330–0.408) and fair to moderate with post-traction fluoroscopy (κ 0.400, 95% CI 0.334–0.466). Conclusiontraction images significantly change the measurement of the lateral wall in trochanteric fractures, changing from an incompetent to a competent wall in 40% of patients. The correct classification of trochanteric fractures is crucial to make the best decision when deciding which implant to use, and the measurement of the lateral wall is determinant in the actual AO/OTA classification. Therefore, traction images appear as necessary for correct decision-making.

A Workflow for Interpretation of Fracture Characteristics Based on Digital Outcrop Models: A Case Study on Ebian XianFeng Profile in Sichuan Basin

Abstract Collecting information about fracture attributes through outcrops measurement is crucial for analyzing the scale, distribution, orientation, and spatial arrangement of fractures. The emergence of digital outcrop models (DOMs) provides a new technology for quantitative interpretation of fractures. However, large-scale DOMs pose additional challenges to the practical application, particularly in the interpretation of geological elements (e.g. fractures). This research proposes a workflow for fracture characteristics interpretation based on DOMs. First, DOMs are generated using light detection and ranging scanning technology. Then, a 3D visualization platform is developed based on OpenSceneGraph. We use level-of-detail technology to reconstruct DOMs for multiscale fast visualization of large-scale models. Finally, in order to realize the quantitative interpretation of fractures, we propose the best-plane fitting and the feature information (orientation, length, spacing, etc.) extraction methods for two types of fractures (exposed fracture walls and fracture traces). The proposed methods are applied to extract attributes of fractures in Dengying Formation (second member), Ebian, Xianfeng, southwest Sichuan Basin, China. The results provide the basis for reservoir evaluation in this area.

Permeability evolution in open fractures during precipitation and dissolution - A phase-field study

In dilated fractures in the Earth’s crust fluid flow in combination with precipitation or dissolution processes can occur, which in turn influences the mechanical and transport properties of the rock system. We use a phase-field modeling framework to investigate these processes of epitaxial crystal growth and dissolution on the fracture walls of crystalline rock systems on microscale. Fluid flow simulations are performed and analyzed during intermediate crystallization and dissolution stages and the obtained hydraulic properties of the partly open fractures are compared to existing literature. The systematic simulation studies show how the rock properties are affected by factors as mineral type with different crystal morphologies, fracture type (inter- vs. transgranular), aperture of the open fracture, and presence of accessory minerals. The results indicate that within the considered parameter space the flow paths remain open until late stages of fracture sealing. Moreover, the long-term permeability and porosity evolution is strongly affected by fracture surface heterogeneities and initial fracture apertures. The simulations enable insights into the evolution of microstructural and fluid flow characteristics and can lay the basis for applications in fractured porous media as groundwater protection, geothermal and hydrocarbon reservoir prediction, water recovery, or storing H2 or CO2 in the subsurface.

Study on seismic performance test and calculation method of recycled steel fiber reinforced concrete shear wall

SummaryRecycled steel wire is taken from used tires, and by procedures like mechanical cutting and friction treatment, it can be converted into industrial recycled steel fiber that meets precise criteria. Such green fiber may effectively limit the growth of fractures in concrete and diffuse the fracture energy of concrete when incorporated into concrete. An investigation of the effects of materials and horizontal reinforcement spacing on the seismic performance of shear wall specimens is presented in this research. The test and numerical simulation findings indicate that the RSFRC (recycled steel fiber reinforced concrete) shear wall's fracture is substantially narrower than that of a conventional shear wall and that the shear carrying capacity and deformation ductility of the shear wall have been greatly enhanced. The energy dissipation capacity of the RSFRC shear wall specimen with varying horizontal reinforcement spacing is significantly enhanced when compared to the conventional shear wall, and the ultimate displacements are reduced. RSFRC shear wall specimen has higher stiffness in the early stage, and the overall stiffness decreases slowly. With the decrease of fiber volume fraction of RSFRC shear wall in a certain range, the shear bearing capacity and stiffness of the model will decrease slightly, but the ductility will increase significantly. Compared with the RSFRC shear wall with fiber aspect ratio of 40 and 25, the bearing capacity and ductility of the two are close, but the RSFRC shear wall with low aspect ratio is slightly insufficient. When the axial compression ratio is in the range of 0.2–0.4, the horizontal shear capacity of RSFRC shear wall increases with the increase of vertical load, but the maximum horizontal displacement becomes smaller, and the model is damaged by compression. Using theoretical calculation, this work also creates the simplified calculation method and restoring force model for the bearing capacity of the diagonal section of RSFRC shear wall. The observed findings correspond well with the test hysteresis curve and may serve as a benchmark for future study. This study provides a new research direction for the seismic performance of RSFRC structures, as well as a solid theoretical foundation and promotion for future research.

Upscaling solute transport in rough single-fractured media with matrix diffusion using a time fractional advection-dispersion equation

Complex structures in fractures and the rock matrix, which are difficult to map exhaustively at the local scale, can dominate contaminant transport in fractured aquifers. An upscaled model is therefore needed to effectively characterize solute transport in a heterogeneous fracture-matrix system on a large spatiotemporal scale. Most existing upscaling methods, however, do not specifically quantify the influence of matrix diffusion and fracture surface roughness on solute transport, and their upscaling parameters are usually difficult to obtain. To fill this knowledge gap, first, a time fractional advection–dispersion equation (t-FADE) model, which can accurately describe solute transport in straight fractured media, is proposed. Next, the influence of local roughness and tortuosity of fractures on transport is comprehensively considered by introducing trend lines. The t-FADE is used to characterize solute transport in each segment of rough fractures, and an upscaled model describing solute transport in rough fractures is established by averaging the governing equations of each segment. Finally, a time-dependent attenuation function is introduced into the convolutional function of the upscaled model to overcome the error caused by overlapping diffusion regions. Model comparison and analysis reveal that the rough wall of fractures strengthens matrix retention capacity, leading to a delayed peak of the breakthrough curve (BTC) with a lower peak concentration, which can be quantitatively characterized by the ratio of the actual fracture length to its longitudinal length; however, the fracture structure does not affect the solute BTC’s trailing concentration at the constant fracture mean flow velocity without considering mechanical dispersion, so the relatively simple straight fracture model can be used to describe the trailing stage of transport in rough-walled fracture media.

Performance evaluation of microemulsion acid for integrated acid fracturing in Middle Eastern carbonate reservoirs

Considering the characteristics of carbonate reservoirs in the Middle East, a low-viscosity microemulsion acid that can be prepared on site and has an appropriate retardation ability was developed. It was compared with four conventional acid systems (hydrochloric acid, gelled acid, emulsified acid and surfactant acid) through experiments of rotating disk, multistage acid fracturing and core flooding with CT scanning. The micro-etching characteristics and conductivity of fracture surfaces were clarified, and the variation of saturation field during water invasion and flowback of spent acid and the recovery of oil phase relative permeability were quantitatively evaluated. The study shows that the addition of negatively charged agent to the oil core of microemulsion acid can enhance its adsorption capacity on the limestone surface and significantly reduce the H+ mass transfer rate. Moreover, the negatively charged oil core is immiscible with the Ca2 + salt, so that the microemulsion acid can keep an overall structure not be damaged by Ca2 + salt generated during reaction, with adjustable adsorption capacity and stable microemulsion structure. With high vertical permeability along the fracture walls, the microemulsion acid can penetrate into deep fracture wall to form network etching, which helps greatly improve the permeability of reservoirs around the fractures and keep a high conductivity under a high closure pressure. The spent microemulsion acid is miscible with crude oil to form microemulsion. The microemulsion, oil and water are in a nearly miscible state, with basically no water block and low flowback resistance, the flowback of spent acid and the relative permeability of oil are recovered to a high degree.

Research Progress of Drilling and Completion Fluid Loss Model in Fractured Reservoir

Well loss and its accompanying reservoir damage is a common and serious problem, which not only greatly restricts the economic benefit, but also seriously affects the correct evaluation of reservoir oil and gas resources in the early stage of exploration. With the exploration and development of deep Marine carbonate oil and gas resources, fracture leakage has gradually become a frontier and hot issue to be studied urgently. Foreign scholars began to study the leakage model of fractured reservoir in the 1990s, but at present, domestic scholars mainly focus on the clastic rock model, focusing on the plugging technology and plugging materials, while ignoring the importance of the dynamic development of the leakage indirectly reflecting the leakage type and the size of the leakage channel. This paper comprehensively analyses the effects of drilling completion fluid rheology, fracture opening variation, fracture wall filtration and other factors on well loss from the time sequence of the establishment of the leakage model, summarizes the research progress of the mathematical model of leakage in fractured reservoirs, and proposes to pay attention to and strengthen the monitoring of the leakage mechanism and the dynamic process of leakage, so as to provide a theoretical basis for the rapid diagnosis of leakage types and the optimization of leakage control.

Clinical Outcomes of Synchronous Lung Stereotactic Body Radiation Therapy Lesions via Single-Isocenter/Multi-Lesion Treatments

Lung cancer patients with synchronous primary or oligometastatic (< 5 lesions) with associated co-morbidities may not retain their treatment position for the extended stereotactic body radiotherapy (SBRT) treatment times with individual isocenter plans for each lesion due to discomfort or shortness of breath. SBRT using a single-isocenter/multi-lesion (SIML) volumetric arc therapy (VMAT) plan with flattening filter free (FFF) beam could significantly shorten overall treatment time, improve patient comfort and compliance and clinic efficiency. We report clinical results of treating multiple lung metastases or synchronous primary lung cancers with SIML lung SBRT. Eighty patients with synchronous primary lung cancers or oligometastatic lung tumors (two, n = 61; three, n = 10; four, n = 4; five n = 5; total treated lesions, n = 193) were simulated with abdominal compression and/or 4D-CT MIP images and treated with a highly-conformal SIML VMAT lung SBRT plans via 3-4 non-coplanar arcs. Common prescriptions were 50-55 Gy/5 fractions and 54 Gy/3 fractions prescribed 70-80% isodose line to the each PTV. Acuros dose calculation for 6MV-FFF beam was used for tissue heterogeneity corrections. RTOG-0618/0813 criteria were used to dose constraints to organs at risk (OAR) and target conformality. Treatment was delivered every other day or twice weekly with CBCT-guidance, adjustments made with 6DOF couch corrections on a medical linear accelerator, and treatment delivery time within 15 minutes. Local control rates and toxicity profile was evaluated using CTCAE v. 5.0 grading for pneumonitis, rib fracture and chest wall pain. All plans met RTOG-0618/0813 requirements for each tumor coverage, dose to OAR including normal lung and ribs. Mean follow up after last fraction of treatment was 16.9 months (range, 1.0-54.2 months). PTV volume ranged from 2.17 to 167.8 cc with mean volume of 16.1 cc. Of the 80 patients treated, 71 had adequate post-treatment thoracic CT imaging to assess local control. Local control was achieved in 167/175 (95.4%) of treated and followed lesions. CTCAE grade 1 asymptomatic pneumonitis was noted on thoracic CT scans in 42/71 (59.2%) of patients and occurred, on average 4.8 months after SBRT. Symptomatic pneumonitis and rib fracture did not occur in any patient. CTCAE grade 2 chest wall pain occurred in 4/80 (5.0%) treated patients and was managed conservatively with over-the-counter NSAIDS or acetaminophen. SIML lung SBRT for synchronous primary lung cancers or multiple lung metastases can be used as a variant to traditional multiple isocenter SBRT or chronologically separate treatment courses, and has excellent local control rates and low toxicity profile in our patient population. It can help improve comfort and compliance of the patients who have difficulty lying still for an extended treatment course, and significantly reduces treatment time via isocenter shifts/repeated CBCTs for image guidance, thus improving clinic efficiency.

Characterization of mineral precipitation in artificially fractured chalk during flooding experiments for IOR research

Natural fractures in carbonate reservoirs are essential to effectively transport hydrocarbon in an otherwise low permeable matrix. However, they can reduce the wanted effect of water injection and Improved Oil Recovery (IOR), as the injected water mainly runs through the fractures. We have investigated chemical and textural alteration in and adjacent to an artificial fracture with an aperture of 2.25 (±0.05) mm in Upper Cretaceous chalk from the St. Vaast Formation (Mons Basin, Belgium). The sample has been injected mainly with 0.219 M MgCl₂ under reservoir conditions over two months. The fracture aperture reduced averagely by 76%. The analysis performed by Transmission Electron Microscopy (TEM) and X-ray Diffraction (XRD) show that, magnesite is the dominating precipitate in the fracture with sizes ranging from 0.5 to 5 μm. The abundance of magnesium phases in the fracture fill was also confirmed by Scanning Electron Microscopy (SEM) coupled with Energy-dispersive X-ray spectroscopy (EDS) and bulk geochemistry (Inductively Coupled Plasma Mass Spectrometry ICP-MS). Besides magnesite, phyllosilicates were observed by TEM and Helium Ion Microscopy combined with Secondary Ion Mass Spectrometry (HIM-SIMS). The newly formed material, precipitates, and possible reworked minerals are characterized by magnesite crystals being covered occasionally by phyllosilicates. This material has formed a distinct area bounded to the surrounding matrix. The final diameter of the precipitate measures about 2.75 (±0.15) mm, which indicates an incremental widening of the original fracture aperture. Calcite along fracture wall dissolved. Effluent concentration supports dissolution by an increase in Ca2⁺ and precipitation of magnesite by the loss of Mg2+. As either silica or aluminium is a component of the fluids, the origin of these elements is necessarily from the matrix of the chalk. It is yet unknown if phyllosilicates precipitated or was reworked, or both. Formation and concentration of magnesite and phyllosilicates in reservoir fractures can reduce fracture permeability over time and lead to subsequent propagation through the matrix of the reservoir rock. This in-depth mineralogical study of artificial fracture changes has the utmost importance for the implementation of techniques in fractured reservoirs.

The influence of fracture surface morphology on nonuniform etching in limestone acid fracturing

The success of acid fracturing in tight limestone reservoirs relies on the formation of nonuniform etching on the fracture wall. However, almost all acid fracturing models neglect the effect of fracture surface morphology on nonuniform etching. In this study, a three-dimensional acid fracturing mathematical model is developed to quantify and analyze the influence of rough fracture surface morphology on nonuniform etching for the first time by defining a morphology coefficient to describe the degree of local and overall morphological undulations of the fracture surface from a three-dimensional scale. The model uses the moving mesh partial differential equation (MMPDE) method to describe the flow field and spatial variation in the fracture as the fracture surface is continuously dissolved with the acid during acid fracturing, and the MMPDE moving mesh is coupled with the flow field, mass transfer, acid-rock reaction and fracture width variation. Based on the model, the effects of flow pattern, morphology coefficient, initial fracture width and fracture type on the nonuniform etching are studied. The simulation results demonstrate that the rough fracture surface can disturb the flow field and make the acid distribution more turbulent, which is conducive to the formation of nonuniform etching on the fracture surface. This phenomenon of flow rate differentiation can enhance the acid transfer distance. The local etching degree of the fracture surface decreases with the increase of the morphology coefficient of the area, and the strongly etching areas will appear around it. When the morphology coefficient of the local fracture area is larger than 1.2218, the area can appear obvious strongly etching areas and weakly etching areas after acid etching. The larger the initial fracture width is, the smaller the degree of nonuniform etching on the fracture surface. The prediction model constructed based on multiple linear regression was highly accurate (R2 = 0.9268) for the standard deviation of facture width (StdWidth) after acid etching. The critical value of StdWidth is recommended to be 0.6 as the criterion for judging the nonuniform etching ability. When the nonuniformity of the fracture surface is greater than this value, it is considered that the nonuniform etching ability is strong. In addition, the fracture with shear damage can produce relative sliding distance, which makes the fracture morphology on both sides of the fracture surface unevenly distributed and thus disturbs the flow field, which enhances the degree of nonuniform etching on the fracture surface. As the sliding distance increase, the magnitude of this enhancement also increases gradually. This study proposes a new three-dimensional characterization method for rough fracture surface morphology, solves the issue of mismatching flow field due to dynamic change in fracture width during acid fracturing.

Proppant transport law in multi-branched fractures induced by volume fracturing

To further clarify the proppant transport and placement law in multi-branched fractures induced by volume fracturing, proppant transport simulation experiments were performed with different fracture shapes, sand ratios, branched fracture opening time and injection sequence of proppants in varied particle sizes. The results show that the settled proppant height increases and the placement length decreases in main fractures as the fracturing fluid diverts gradually to the branched fractures at different positions. The flow rate in branched fractures is the main factor affecting their filling. The diverion to branched fractures leads to low flow rate and poor filling of far-wellbore branched fractures. The inclined fracture wall exerts a frictional force on the proppant to slow its settlement, thus enhancing the vertical proppant distribution in the fracture. The increase of sand ratio can improve the filling of near-wellbore main fracture and far-wellbore branched fracture and also increase the settled proppant height in main fracture. Due to the limitation of fracture height, when the sand ratio increases to a certain level, the increment of fracture filling decreases. When branched fracture is always open (or extends continuously), the supporting effect on the branched fractures is the best, but the proppant placement length within the main fractures is shorter. The fractures support effect is better when it is first closed and then opened (or extends in late stage) than when it is first opened and then closed (or extends in early stage). Injecting proppants with different particle sizes in a specific sequence can improve the placement lengths of main fracture and branched fracture. Injection of proppants in an ascending order of particle size improves the near-wellbore fracture filling, to a better extent than that in a descending order of particle size.

Effect of proppant sizes and injection modes on proppant transportation and distribution in the tortuous fracture model

Particle-fluid transport and placement mechanism in tortuous fracture played a crucial role in unconventional reservoirs. Currently, most studies focused on mono-size proppant with fluid transport processes in tortuous fractures. However, the mixture-size proppant with fluid movement mechanism in tortuous fracture was still uncommon. Therefore, this study designed and applied a series of experiments with a physical analog model of a tortuous fracture with 120° and 90°-angled bends and combined high-speed camera-based equipment. This experimental system was used to track different-mixture-sized proppant particle motion trajectories for a series of proppant injection schemes; The following conclusions were drawn from this study:1. The pile-up processes mechanism in all investigated schemes were similar and could be reduced to four main stages. 2. The packing structure at both sides of the fracture wall had different variation rates, which were controlled by the mix ratio (change from 1:1–1:5) of proppant size. 3. Some new packing patterns, such as Zebra Stripe, had occurred, controlled by the different proppant injection sequences. 4. Small-sized mono-proppant (30/50 mesh) had the highest transport efficiency in the tortuous fracture, followed by the mixed-sized multi-proppant (10/20 mesh:30/50 mesh), large-sized proppant (10/20 mesh) was the worst. 5. An optimized alternating injection mode was recommended as injecting small-sized proppant first (30/50 mesh) and followed by mixed-sized multi-proppant (10/20 mesh:30/50 mesh), which could contribute to obtaining the optimal both proppant packing height and travel distance in tortuous fracture.6. Two correlations were developed for predicting the proppant packing height and transportation distance.

Diffusion characteristics of shale mixed gases on the wall of microscale fractures

Shale reservoirs are rich in organic and inorganic matter, causing a large amount of gas to exist on the surface of microscale cracks in an adsorbed state. Revealing the surface diffusion characteristics of adsorbed gas is of great significance for the microscale numerical simulation of shale gas reservoir. In this paper, the unconventional gas reservoir is taken as the research object, and the characteristics of gas surface diffusion on surface wall of microscale fractures is systematically studied. There are two innovations in this paper: (a) the characteristics of gas surface diffusion inside the planar microscale fractures are analyzed; (b) The influence of mixed gas effect on gas surface diffusion is considered. Research results show that: (a) when the fracture opening is 2 nm or 5 nm, the influence of the opening of microscale fractures on the thickness of adsorption layer can be ignored. (b) The interaction between components refers to the frictional force generated by the relative motion of molecules. (c). The magnitude of frictional force is related to the Maxwell Stefan diffusion term and is proportional to the velocity difference. Due to the interaction between components, fast-moving molecules will accelerate the movement of slow-moving molecules.

Functional outcome of type 4 Pipkin classification of femoral head fracture operated by open reduction internal fixation by ganz safe surgical dislocation approach management: a case report

Fracture of the femoral head is a severe, relatively uncommon injury; typically, it may have associated with traumatic posterior dislocation of the hip joint with or without acetabulum fracture. The Pipkin classification is the most commonly used classification system. Controversies include the preferred surgical approach (anterior versus posterior) versus ganz safe surgical dislocation approach and whether to perform femoral head fragment excision or internal fixation. Presenting a case report of 28 years old young male with a motor vehicle road traffic accident and suffered a head of femur fracture on right hip joint with posterior wall of right acetabulum fracture with Judet-Letournel type posterior wall and type 4 Pipkin’s classification of femoral head fracture. This patient was undergone for emergency surgical intervention of open reduction, internal fixation through Ganz approach and insertion of Herbert screws for femoral head and interfragmentary screw for trochanteric osteotomy. The patient was followed up for 1 year and have a complete range of motion at hip joint with painless daily lifestyle. Type 4 Pipkin classification of femoral head fracture managed timely and with surgical intervention by ganz safe surgical dislocation approach provides visualization to femoral head and whole acetabulum with internal fixation of femur head by herbert screw which preserves normal anatomic contour of femoral head shows appropriate reduction of fracture fragments and it may also avoid hemiarthroplasty surgeries. Fracture of the femoral head has been associated with a relatively poor functional outcome and requires timely management and surgical intervention. Specially type 4 Pipkin classification of femoral head fracture treated by ganz safe surgical dislocation approach with internal fixation of femur head by herbert screw shows better outcome and avoid risk of AVN of femoral head. Complications associated with fracture of the femoral head and subsequent treatment include osteonecrosis, post-traumatic osteoarthritis, heterotopic ossification and implant failure.

Cross-Scale Seepage Characteristics of Fractured Horizontal Wells in Tight Gas Reservoirs.

Tight gas reservoirs are rich in microscale pores and fractures. The effect of microscale gas seepage in tight sandstone matrix on gas well productivity cannot be ignored. At present, the effect of microscale gas flow on the well testing model of fractured horizontal wells has not been systematically studied. In this paper, first, the coupling influence mechanism of "multicomponent gas effect-fracture geometry characteristics" is expounded, second, a seepage model coupling the flow in the fracture and the flow in the gas reservoir is established on the fracture wall surface, and third, an unsteady pressure analysis model for fractured horizontal wells in tight gas reservoirs is established. Results show that (a) when the microscale fracture is at a quite small level, the Knudsen diffusion plays a dominant role at a wide range of pressures; (b) the mass transfer rate of multicomponent shale gas through macrofractures increases with increasing CO2 fraction; (c) the unsteady flow process is divided into six stages in turn: microscale diffusion stage, linear flow stage in fractures, linear flow stage between fractures, early radial flow stage in gas reservoirs, linear flow stage in gas reservoirs, and late radial flow stage in gas reservoirs; and (d) with an increase of dimensionless bottom-hole storage coefficient, the second and third stages of flow are gradually covered up.

Geochemistry of syntaxial calcite veins in ultra-deep sandstone reservoirs from the Kuqa depression, western China

Extensional fractures filled with calcite are widespread in the ultra-deep reservoir sandstones of the Cretaceous Bashijiqike Formation (>6000 m) in the Kuqa Depression, western China. Microstructures of calcite veins provide an excellent opportunity for investigating fracture opening processes in a tectonically active, ultra-deep foreland basin setting. The syntaxial calcite vein is the dominant type and is formed through a single crack-seal event. Calcite crystals in fractures show blocky and elongated blocky shapes. The textural and geochemical characteristics of syntaxial calcite veins were investigated in detail using optical cathodoluminescence, trace element distributions and stable carbon and oxygen isotopes. Calcite veins were inferred to have precipitated from a mixture of seawater and meteoric water. ∑REE + Y and elemental concentrations of Mg2+, Mn2+, Fe2+ and Sr2+ both increase from fracture walls to the center. This process was controlled by temperature, crystal growth rate and variations in elemental concentration in a relatively closed environment. Medium REE-bulge patterns after Post Archean Average Shale (PAAS) normalization, negative δCe and positive δEu anomalies all indicate that calcite wall-rock cements and veins may inherit constituents from seawater and from meteoric water containing feldspar-weathering components, respectively. Both 13δCPDB and 18δOSMOW of the parent fluids imply that calcite veins were primarily precipitated from seawater under a relatively closed diagenetic environment. Considering the scope and timing of the transgression of the Tethyan Ocean in the study area, meteoric water may have been retained prior to the seawater invasion (65 Ma). The mixing of meteoric water and seawater within the reservoir could be the primary origin of the fluids forming the calcite veins.

Proppant transport in rough fractures of unconventional oil and gas reservoirs

A method to generate fractures with rough surfaces was proposed according to the fractal interpolation theory. Considering the particle-particle, particle-wall and particle-fluid interactions, a proppant-fracturing fluid two-phase flow model based on computational fluid dynamics (CFD)-discrete element method (DEM) coupling was established. The simulation results were verified with relevant experimental data. It was proved that the model can match transport and accumulation of proppants in rough fractures well. Several cases of numerical simulations were carried out. Compared with proppant transport in smooth flat fractures, bulge on the rough fracture wall affects transport and settlement of proppants significantly in proppant transportation in rough fractures. The higher the roughness of fracture, the faster the settlement of proppant particles near the fracture inlet, the shorter the horizontal transport distance, and the more likely to accumulate near the fracture inlet to form a sand plugging in a short time. Fracture wall roughness could control the migration path of fracturing fluid to a certain degree and change the path of proppant filling in the fracture. On the one hand, the rough wall bulge raises the proppant transport path and the proppants flow out of the fracture, reducing the proppant sweep area. On the other hand, the sand-carrying fluid is prone to change flow direction near the contact point of bulge, thus expanding the proppant sweep area.