Wall Fracture Research Articles

On the cleavage stress promoting crack path deflection and anisotropic fracture in cold drawn pearlitic steel

Crack path deflection is a phenomenon appearing in cold-drawn pearlitic steel wires as a consequence of the pearlite microstructure orientation induced by the manufacturing procedure, the deflection angle being approximately 90º, thereby representing a crack propagation step (fracture wall), a signal of splitting, delamination or debonding in the form of axial cracking (or micro-cracking) by means of a microscopic fracture mode in the form of enlarged and oriented cleavage in the direction of the wire axis (cold drawing direction). The described phenomenon is a signal of anisotropic fracture behaviour (strength anisotropy) associated with mixed-mode propagation. This paper demonstrates that, in addition to the oriented microstructure of the cold drawn pearlitic steels (at the two microstructural levels of pearlite colonies and lamellae), a sufficient level of stress triaxiality (constraint) is required, as in the case of cracked specimens in which a cleavage stress appears as a consequence of the singular stress distribution in the close vicinity of the crack tip (crack tip stress-strain field).

Proppant transport in scaled experiments: Effect of drainage configuration and fracture wall roughness

In recent years, there has been a number of experimental and numerical studies on the transport and settlement of proppant in scaled laboratory fractures that are of interest to understand hydraulic stimulation in hydrocarbon reservoirs. The results from these studies are generally taken with skepticism by the industry. Part of this is due to the perception that results must be very sensitive to the boundary conditions. Small changes in the experimental configuration are expected to lead to very different results. In particular, little is known on how the actual roughness of the fracture walls and the way the slurry is drained from the laboratory cell affect the results. Here, we report experimental results on the proppant transport in a scaled vertical rough cell that mimics a vertical fracture induced during stimulation. We compare results with those obtained in a smooth wall cell, which is more common in laboratory tests. We found that a rough wall allows for a significant increase in the amount of proppant deposited in the cell at high pumping rate. However, the effect of roughness seems to be marginal for low pumping rates, suggesting that most previous studies in the literature which use of a reduced pumping rate were not significantly affected by the use of smooth walls. We also designed different flow configurations at the fracture tip (where the slurry drains form the cell) to study their effect on the way in which the proppant is deposited in the fracture. We found that, in general, the deposited dune is fairly independent of the particular boundary conditions. This suggests that most results reported in the literature are also robust against changes in the selected outflow configuration.

Northwest Africa 6486: Record of large impact events and fluid alteration on the L chondrite asteroid

AbstractWe report the results of petrological, geochemical, and geochronological investigations of the unusual K‐rich L chondrite melt rock Northwest Africa 6486 (NWA 6486). The rock has slightly fractionated siderophile elements and a mostly unfractionated L chondrite pattern of lithophile elements with the exceptions of enrichments in K and Rb and chondritic Sr abundance similar to the K‐rich inclusions found in the ordinary chondrites and indicating a fractionation of alkaline elements through the vapor. We suggest that NWA 6486 and related K‐rich chondritic inclusions were formed in situ on the OC parent bodies and that K and Rb enrichment of these rock most probably is a result of the selective impact evaporation of volatile alkali elements followed by the reaction of a vapor with shock melt. NWA 6486 recorded a breakup event of the L chondrite parent asteroid at 470 Ma during which it was formed. Unusual veins, depleted in K, Na, Ca, and Al relative to the host rock were found in NWA 6486. We suggest that NWA 6486 was affected by aqueous fluids that produced alteration zones depleted in a feldspar component on the walls of opened fractures. The melt veins could be formed during a subsequent impact event by in situ melting of the fracture walls or due to decomposition of an injected supercritical aqueous silicate fluid. The aqueous alteration and the second impact event had no detectable effect on Ar and oxygen isotopic systems. Cosmic ray exposure ages indicate that NWA 6486 was ejected from its parent asteroid ~3–4 Ma ago.

Effect of fracture roughness on transport of suspended particles in fracture during drilling

Fractures with different roughness are important permeable channels in oil and gas reservoirs. However, the drilling fluid is prone to leakage through fractures, resulting in formation damage. Study on the migration behavior of suspended particles with drilling fluid loss is the basis for finding the damage mechanism of solid invasion and drilling fluid loss control measures. From a comprehensive review of the previous studies, the transport behavior of suspended particles considering particle-fluid-fracture interaction hasn't been fully understood and quantified. In this study, we examined flow behavior of the particle-fluid mixture by the unresolved CFD-DEM approach. The effects of particle concentration, particle size, fracture width, drilling fluid loss rate, drilling fluid viscosity and cohesive force on particle transport in different rough fractures were studied. The research suggests that: (1) Increase of particle concentration will not only result in significant increase in fluid-particle velocity, but will also increase the wall mechanical retardation. (2) Particle aggregation near the fracture walls is more serious than in the fracture center. The shape of the agglomeration particle clusters is mainly elongated, with the long axis direction consistent with the flow direction. (3) Rough fracture walls will not only lead to more energy loss due to frequent particle-particle and particle-fracture contact, but also cause more particles to migrate in the fracture center.

Hydrocarbon recovery: Optimized CFD-DEM modeling of proppant transport in rough rock fractures

Proppant distribution in rough rock fractures is a key factor in the evaluation of the effectiveness of a hydraulic fracturing operation. This paper focuses on the study of how fracture roughness influences proppant transport and placement based on improved coupled computational fluid dynamics-discrete element method (CFD-DEM). Laboratory-scale synthetic rough fractures analogous to realistic rock fractures were used to flexibly control fracture geometric parameters. In the numerical model, Magnus force, virtual mass force and Saffman lift force were taken into consideration to precisely describe the interaction between proppant particles and the fracturing fluid. This numerical model was validated by comparison with published experimental results. The distribution of proppant and the transport mechanism in smooth fractures, joint rough fractures and sheared rough fractures were investigated. In addition, the effect of fracture wall’s fractal dimension and fracture inclination on proppant movement and deposition were explored. The study found that proppant settling velocity is slower in fractures with higher fractal dimension. The lateral conveyance of proppant is enhanced by higher fractal dimension of rough fracture walls, and smaller fracture inclination angles. The proppant dune is lower and longer in fractures with greater fractal dimension. When the fracture is close to horizontal, proppant particles show a finger-like distribution instead of generating a sand bed. The results also show that the proppant coverage ratio in fractures increases with increasing fractal dimension, and with decreasing fracture inclination angle. The results provide a better understanding of how fracture roughness and geometry impact proppant transport in rock fractures.

Analytical model for solute transport in discrete fracture networks: 2D spatiotemporal solution with matrix diffusion

A computationally efficient analytical network (AN) model simulating solute transport in discrete fracture networks (DFNs) is developed. The model simulates two-dimensional spatial and temporal distribution of a solute considering advection and hydrodynamic dispersion within the fractures, matrix diffusion, sorption onto the fracture walls and in the matrix, and first order decay for one constituent. The AN model is based on previously developed analytical solutions for a single fracture, and the convolution method is applied to extend these solutions to a DFN. Mass sharing at fracture intersections is calculated using the complete mixing and stream-tube methods. The AN model was verified against numerical models based on the time domain random walk and random walk particle tracking methods using two different fracture networks with a range of properties. In all cases, the AN model solutions showed excellent agreement with the numerical model solutions. The sensitivity of the mass sharing methods to the dominant transport mechanism (i.e., advection or diffusion) was investigated for Peclet numbers ranging from Pe = 3 × 10−6 - 380. Both mass sharing methods give the same results when the transport processes are advection-dominated and matrix diffusion is considered; however, attention must be paid to the mass sharing method employed under other conditions, particularly when the fracture density is small. The AN model was at least 97% more efficient than the numerical models used in this work, and this efficiency will increase with network complexity. The AN model provides a useful reference tool for the verification of numerical dual-porosity fracture network simulations.

Escalating Tumor Dose via Simultaneous Integrated Boost (SIB) Stereotactic Body Radiation Therapy (SBRT) for Large (> 5 cm) Lung Masses

SBRT treatments of large (> 5.0 cm, diameter) lung masses with ablative dose is challenging due to toxicity. We report on a novel centrally-dose-escalated simultaneous integrated boost (SIB) SBRT technique for fast, safe, and effective method that allow for dose escalation to the tumor core while protecting adjacent organs at risk (OAR).Twelve patients with large (mean = 7.0 cm, range: 5.2-7.8 cm, diameter) lung masses from at least Stage II non-small-cell lung cancer (NSCLC) or oligometastatic lung disease from a separate primary site underwent 50 Gy to the planning target volume (PTV) with a 60 Gy SIB to the volume approximately 1 cm interior to the standard gross tumor volume (GTV) margin in 5 fractions. Highly conformal SIB SBRT plans were generated using 3-6 non-coplanar partial VMAT arcs with 6MV-FFF beam and advanced Acuros-based dose engine for tissues heterogeneity corrections. Treatments were delivered every other day using online conebeam CT guidance. Plan quality and treatment delivery efficiency were reported. Outcomes reported include tumor local control (LC), distant failure (DF), lung and rib toxicity. Median follow-up interval was 8 months (1 to 22 months).Mean GTV and PTV was 92.9 ± 40.0 cc and 188.8 ± 45.4 cc. Mean dose to GTV and PTV was 58.1 ± 1.9 Gy and 55.5 ± 1.2 Gy, translating to the corresponding average biological effective dose (BED10, with α/β = 10Gy) of 125 Gy and 117 Gy, respectively. All SIB SBRT plans met RTOG requirements for intermediate dose fall-off and organs at risk (OAR) sparing. Mean values of V20Gy, V10Gy and mean lung dose were 13.6 ± 3.4%, 22.9 ± 6.8%, and 7.5 ± 1.8Gy, respectively. Average maximal doses to OAR were as follows: spinal cord < 12.5 Gy, heart < 33.9 Gy, esophagus < 17.7 Gy, ribs < 48.2 Gy and skin < 23.9 Gy. Average beam-on time was 3.5 ± 0.3 min. Estimated mean treatment time including pre-treatment conebeam CT imaging and patient repositioning was within 15 min. All patients tolerated the SIB-SBRT treatment. 10 patients demonstrated LC, 1 had definite progression, and 1 had ostensible progression with atelectasis complicating the picture. The three patients with oligometastatic disease from stage IV head and neck or sarcoma progressed elsewhere, although the treated site was well controlled. One patient had evidence of grade 2 chest wall pain and treated with NSAIDS; however, 11 patients showed no evidence of rib fracture or chest wall pain. No patients developed grade 2+ pulmonary toxicity or radiation-induced pneumonitis.Escalating core tumor dose via SIB-SBRT (higher than 100Gy BED10) is safe, fast, and efficacious treatment for large lung masses with promising LC rates and no adverse treatment related toxicity. Fast delivery of SIB SBRT treatment could reduce intrafraction motion error due to coughing or pain, making geographic miss unlikely and improving the patient comfort and clinic workflow. Longer clinical follow up results in a larger patient population treated with this approach is warranted.

Hydraulic fracturing fracture propagation in tight sandstone reservoir

The tight sandstone reservoir of Shaximiao Formation of Middle Jurassic in Qiulin block of central Sichuan Basin, with a burial depth about 2200 to 2300 m, is characterized by undeveloped natural fractures. It is difficult to form complex fracture network during the implementation of traditional volume fracturing technology, affecting the benefit of tight sandstone gas development. A series of true triaxial hydraulic fracturing tests were conducted on the sandstone outcrop (dimensions: 300 mm × 300 mm × 300 mm), collected from this block, to investigate the initiation and propagation law of hydraulic fracture in tight sandstone reservoir under different conditions. Experimental results indicate that the peak value disturbance and increasing stress shadow in the back section of the pump pressure curve of staged multi-cluster fracturing in horizontal wells of sandstone reservoir will dominate the fracture morphology. The small interval leads to the increase in dynamic hydrostatic pressure on the fracture wall and increase in the deflection angle and degree of multi-cluster fractures, and it is easy to form crosscut fractures. The symmetrical middle segment perforation cluster inhibits the initiation and expansion of fractures, and the fractures will extend perpendicular to the maximum horizontal in situ stress direction and gradually approach the fractures on both sides and finally stop expanding. High-viscosity fracturing fluid is easy to form high hydrostatic pressure in the perforated section, reducing the difficulty of fracture initiation. The angle between the borehole and the minimum horizontal in situ stress ( σ h) will affect the propagation direction of hydraulic fractures. When the angle is large, the propagation direction of fractures is easily affected by the natural weak surface and induced stress field, resulting in fracture diversion. This study has mastered the initiation and propagation mechanism of artificial hydraulic fractures in tight sandstone reservoir, established the optimization chart of fracturing parameters in sandstone reservoir, and has certain guiding significance for the establishment of on-site fine optimization fracturing scheme design.

Association of the lateral wall integrity with clinical outcomes in older patients with intertrochanteric hip fractures treated with the proximal femoral nail anti-rotation-Asia.

The purpose of this study is to assess the role of the lateral wall in post-operative clinical outcomes in patients with intertrochanteric fractures treated with the proximal femoral nail anti-rotation-Asia (PFNA-II). A cohort of 466 patients (OTA type 31A1 or A2) was divided into two groups: one was intact lateral wall group, and the other was fractured lateral wall group. Radiographic outcomes were measured by using the loss of neck-shaft angle (NSA), femoral neck shortening (FNS), and offset shortening (OS). Functional outcomes were assessed by using the Harris score and SF-36 Physical Component Summary (SF-36 PCS). Post-operative complications were recorded. The fractured lateral wall group had a greater loss of NSA (mean [SD], fractured group (8.7°) [2.7°] vs intact group (4.8°) [2.8°]; mean difference, 3.3° [95% CI 2.9 to 3.8]; P < 0.001) compared with the intact lateral wall group. Similar results were found for FNS and OS. The fractured lateral wall group had a worse Harris scores at the threemonth follow-up (mean [SD] score, fractured group (66.6) [5.2] points vs intact group (71.3) [5.8] points; mean difference, - 3.3 points [95% CI - 3.9 to - 2.7]; P < 0.001) compared with the intact lateral wall group. Similar results were observed for Harris scores at the threeand 12-month follow-ups and SF-36 PCS at the three, six and 12-month follow-ups. The fractured lateral wall group had a higher risk of post-operative complications compared with the intact lateral wall group. Among older patients with intertrochanteric fractures, the fractured lateral wall was associated with worse clinical outcomes compared with the intact lateral wall. Clinicians should pay attention to the lateral wall integrity in patients with intertrochanteric fractures treated with the PFNA-II.

Prediction of fracture initiation and propagation in pelvic bones

The objective is developing an XFEM model that is capable of predicting different types of fracture in the pelvic bone under various loading conditions. Previously published mechanical and failure characteristics of cortical and cancellous tissues were implemented and assigned to an intact pelvic bone with specified cortical and cancellous tissues. Various loading conditions, including combined load directions, were applied to the acetabulum to model different types of fracture (e.g., anterior/posterior wall fracture and transverse fracture) in the pelvic bone. The predicated types of fracture and the maximum force at fracture were compared to those acquired from previously published experimental tests. Anterior/posterior wall fracture and transverse fracture were the most common types of fractures determined in the simulations. The XFEM simulations were able to predict similar fractures to those reported in the experimental tests. The maximum fracture force in the XFEM model was found to be 18.6 kN compared to 8.85 kN reported in the previous experimental tests. The results revealed that different types of fracture in the pelvic bones can be caused by the various loading conditions in unstable high-rate impact loads. Using proper mechanical and failure behaviors of cortical and cancellous tissues, XFEM modeling of pelvic bone is capable of predicting bone fracture. In future work, the XFEM models of cancellous and cortical tissues can be assigned to other bones in human body skeleton so that the failure mechanism in such bones can be investigated.

Transnasal Surgical Treatment Of Patients With A Fracture Of The Medial Wall Of The Orbit

The article presents the method of transnasal surgical treatment of patients with a fracture of the medial wall of the orbit using the Volkov elevator as a repositioning tool and an iodine tampon as a fixation material, which allows efficient fixation of the medial orbit wall fragments and its soft tissue components, allowing to reduce the trauma of surgical intervention, to restore the eyeball position, and to eliminate the cause of emphysema and dynamic correction of postoperative diplopia in one-time operation.

Surgical Fixation With Only Fibrin Glue in the Isolated Anterior Wall of the Maxillary Sinus Fracture.

When isolated anterior wall fractures of the maxilla occur, there is a high possibility that a comminuted fracture also exists. Because of thin and small fracture fragments and the associated damage to the mucosa, treating these fractures using conventional methods is difficult. The authors considered a surgical method that utilizes only fibrin glue after reduction. This method was also compared with the use of absorbable mesh. in total, 30 patients were diagnosed with an isolated anterior wall fracture of the maxilla between January 2013 and December 2018 in a single hospital. From these, 19 patients underwent fractured fragment reconstruction using only fibrin glue after reduction. The remaining patients underwent reconstruction using an absorbable mesh. Patient demographics, trauma vector, length of hospital stay, follow-up period, and acute/chronic complication rates of the two groups were investigated and statistically analyzed. The group using only fibrin glue showed better results with regard to the length of hospital stay and acute complication rates. Therefore, the surgical method using only fibrin glue after reduction can be recommended as a viable treatment method for these fractures.

Disproportionate filtration behaviors of polymer/chromium gel used for fracture plugging

Polymer/chromium gel is commonly used for fracture plugging in naturally or hydraulic fractured formation. At present study, the filtration behavior of polymer gelant in fracture was investigated. According to the results of gelant analysis, the filtration degree of Cr3+ is obviously higher than that of polymer molecules, which verifies the disproportionate filtration behaviors of gel components. Polymer has great impact on the filtration behavior of Cr3+. Because of the thickening, entrapping and cross-linking effects, the filtration degree of Cr3+ can be greatly decreased by polymer molecules. Moreover, the adsorption layer of polymer molecules on fracture wall, the accumulation layer near the adsorption layer, and the retention layer in the matrix can also significantly hinder the filtration of Cr3+ from fracture into matrix. Results of fractured core flowing experiments show that both the filtration depth of gelant and the filtration degree of Cr3+ from fracture into matrix are reduced with the increase of polymer concentration. In addition, high injection pressure differential contributes to high filtration degree of Cr3+, which further results in the intense disproportionate filtration of gel components. What’s more, with the fracture width increasing and matrix permeability decreasing, the filtration degree of Cr3+ is greatly declined. Research results can provide theoretical reference for improving the water plugging performance of polymer gel in hydraulic fractured formation.

Posterior femoral head dislocation with ipsilateral posterior wall and anterior column acetabular fracture: a case report and review of the literature

Posterior femoral head dislocation with ipsilateral posterior wall and anterior column acetabular fracture: a case report and review of the literature

Microscopic characteristics of water invasion and residual gas distribution in carbonate gas reservoirs

AbstractWe used the nuclear magnetic resonance online detection method to analyze the water invasion mechanism and residual gas distribution of a carbonate rock gas reservoir. The T2 spectra obtained by using the Carr‐Purcell‐Meiboom‐Gill (CPMG) pulse sequence were applied to characterize the invasion water and residual gas distribution. The results showed that (a) in the pore‐type gas reservoir, the water first invades the meso–macropores and then the small pores as the pressure decreases further. The fracture distribution in a fracture‐pore‐type gas reservoir has an effect on the water invasion mode. The water can enter the pores through the fracture wall after the water invades the fracture. (b) In the pore‐type gas reservoir, 37.7% of the residual gas resides in the small pores, while the rest resides in the macropores. While in the fracture‐pore‐type gas reservoir, 4.8% ~ 26.8% of the residual gas is in the smaller pores and 69.2% ~ 95.7% in the macropores. Barely, any residual gas resides in the fractures. The residual gas in the small pores is difficult to produce. (c) The residual gas is controlled by the fracture penetration, amount of bottom water, fracture width, and production rate. It is suggested the production rate decreased to induce the water to invade the meso–macropores after the gas well begins to produce water to reduce the amount of residual gas in the meso–macropores.

Numerical study of long-time growth of hydraulic fractures in a line drive

This work concerns detailed numerical modelling of injection fracturing in chalk formations under 2–3 km burial. The conditions and properties are chosen to resemble field conditions as typically found in oil fields subject to water injection in the Central Graben in the North Sea off-shore Denmark, Norway and the UK, but the studied phenomena are general to injection fracturing irrespective of geographical location and technological application. The complexity of reality is a challenging factor when mathematical models of hydraulic fractures in the subsurface are formulated. To this end the finite element method and a multi physics approach is instrumental, and data from fields developed and operated under conditions prudent for modelling are equally important. In the present study, a poroelastic finite element model is applied and used under plane strain conditions for a linear fracture mechanics investigation. This approach is suitable for analysing fracturing in arrays of parallel and horizontal wells as can be found in many oil fields undergoing water-flooding. Based on realistic field data, e.g. reservoir properties and rate and pressure scenarios representative for typical fields in the North Sea region, fracture initiation and fracture growth are analysed in details in a realistic field setting. Using a formulation of the J-integral, that includes Functionally Graded Material and poroelastic effects, it is demonstrated that formation fracture toughness determines fracture initiation and fracture height. The fracture propagation speed is controlled by continuity, e.g. the injection rate must balance the leak-off from the fracture wall. By combining the fields of geotechnical engineering, petroleum engineering and mechanical engineering with realistic data measurements, this study provides a novel realistic study of how the producer and injector pressure influence the fracturing process for induced hydraulic fractures in a line drive.

A corrected cubic law for single-phase laminar flow through rough-walled fractures

Hydraulic properties of natural fractures are essential parameters for the modeling of fluid flow and transport in subsurface fractured porous media. The cubic law, based on the parallel-plate concept, has been traditionally used to estimate the hydraulic properties of individual fractures. This upscaling approach, however, is known to overestimate the fractures hydraulic properties. Dozens of methods have been proposed in the literature to improve the accuracy of the cubic law. The relative performance of these various methods is not well understood. In this work, a comprehensive review and benchmark of almost all commonly used cubic law-based approaches in the literature, covering 43 methods is provided. We propose a new corrected cubic law for incompressible, single-phase laminar flow through rough-walled fractures. The proposed model incorporates corrections to the hydraulic fracture aperture based on the flow tortuosity and local roughness of the fracture walls. We identify geometric rules relative to the local characteristic of the fracture and apply an efficient algorithm to subdivide the fracture into segments, accordingly. High-resolution simulations for Navier-Stokes equations, computed in parallel, for synthetic fractures with various ranges of surface roughness and apertures are then performed. The numerical solutions are used to assess the accuracy of the proposed model and compare it with the other 43 approaches, where we demonstrate its superior accuracy. The proposed model retains the simplicity and efficiency of the cubic law but with pronounced improvement to its accuracy. The data set used in the benchmark, including more than 7500 fractures, is provided in open-access.

A Case of Endoscopic Reduction of Isolated Maxillary Sinus Posterior Wall Fracture Using Foley Catheter

The surgical goal for reduction of maxillofacial fracture has been focused on the reconstruction of facial buttresses. If there is fracture-displacement at non-buttress area, it close observation used to be the choice of treatment. It is not easy to have access to the posterior part of maxilla with conventional approach. But with the endoscopic sinus surgery technique, posterior wall of maxillary sinus is easily approachable and can be manipulated. This report presents a case of a 38-year-old male with isolated posterior wall of maxillary sinus fracture. Inward comminuted fracture-displacement of the posterior wall of maxillary sinus with retroantral fat and soft tissue was herniated into the maxillary sinus and extruded out through the natural ostium of maxillary sinus. Using endoscopic approach and Foley catheter inflation, the maxillary sinus posterior wall was successfully repaired without complications. This report thus suggests endoscopic approach with the Foley catheter for the posterior maxillary sinus wall fracture.

Hydromechanical Investigations on the Self-propping Potential of Fractures in Tight Sandstones

The hydromechanical properties of single self-propping fractures under stress are of fundamental interest for fractured-rock hydrology and a large number of geotechnical applications. This experimental study investigates fracture closure and hydraulic aperture changes of displaced tensile fractures, aligned tensile fractures, and saw-cut fractures for two types of sandstone (i.e., Flechtinger and Fontainebleau) with contrasting mechanical properties, cycling confining pressure between 5 and 30 MPa. Emphasis is placed on how surface roughness, fracture wall offset, and the mechanical properties of the contact asperities affect the self-propping potential of these fractures under normal stress. A relative fracture wall displacement can significantly increase fracture aperture and hydraulic conductivity, but the degree of increase strongly depends on the fracture surface roughness. For smooth fractures, surface roughness remains scale-independent as long as the fracture area is larger than a roll-off wavelength and thus any further displacement does not affect fracture aperture. For rough tensile fractures, these are self-affine over a larger scale so that an incremental fracture wall offset likely leads to an increase in fracture aperture. X-ray microtomography of the fractures indicates that the contact area ratio of the tensile fractures after the confining pressure cycle inversely correlates with the fracture wall offset yielding values in the range of about 3–25%, depending, first, on the respective surface roughness and, second, on the strength of the asperities in contact. Moreover, the contact asperities mainly occur isolated and tend to be preferentially oriented in the direction perpendicular to the fracture wall displacement which, in turn, may induce flow anisotropy. This, overall, implies that relatively harder sedimentary rocks have a higher self-propping potential for sustainable fluid flow through fractures in comparison to relatively soft rocks when specific conditions regarding surface roughness and fracture wall offset are met.

Investigating Fracture Network Deformation Using Noble Gas Release

We investigate deformation mechanics of fracture networks in unsaturated fractured rocks from subsurface conventional detonation using dynamic noble gas measurements and changes in air permeability. We dynamically measured the noble gas isotopic composition and helium exhalation of downhole gas before and after a large subsurface conventional detonation. These noble gas measurements were combined with measurements of the subsurface permeability field from 64 discrete sampling intervals before and after the detonation and subsurface mapping of fractures in borehole walls before well completion. We saw no observable increase in radiogenic noble gas release from either an isotopic composition or a helium exhalation point of view. Large increases in permeability were observed in 13 of 64 discrete sampling intervals. Of the sampling intervals which saw large increases in flow, only two locations did not have preexisting fractures mapped at the site. Given the lack of noble gas release and a clear increase in permeability, we infer that most of the strain accommodation of the fractured media occurred along previously existing fractures, rather than the creation of new fractures, even for a high strain rate event. These results have significant implications for how we conceptualize the deformation of rocks with fracture networks above the percolation threshold, with application to a variety of geologic and geological engineering problems.