Decrease In Fluid Pressure Research Articles

Propagation, proppant transport and the evolution of transport properties of hydraulic fractures

Hydraulic fracturing is a widely used method for well stimulation to enhance hydrocarbon recovery. Permeability, or fluid conductivity, of the hydraulic fracture is a key parameter to determine the fluid production rate, and is principally conditioned by fracture geometry and the distribution of the encased proppant. A numerical model is developed to describe proppant transport within a propagating blade-shaped fracture towards defining the fracture conductivity and reservoir production after fracture closure. Fracture propagation is formulated based on the PKN-formalism coupled with advective transport of an equivalent slurry representing a proppant-laden fluid. Empirical constitutive relations are incorporated to define rheology of the slurry, proppant transport with bulk slurry flow, proppant gravitational settling, and finally the transition from Poiseuille (fracture) flow to Darcy (proppant pack) flow. At the maximum extent of the fluid-driven fracture, as driving pressure is released, a fracture closure model is employed to follow the evolution of fracture conductivity with the decreasing fluid pressure. This model is capable of accommodating the mechanical response of the proppant pack, fracture closure of potentially contacting rough surfaces, proppant embedment into fracture walls, and most importantly flexural displacement of the unsupported spans of the fracture. Results show that reduced fluid viscosity increases the length of the resulting fracture, while rapid leak-off decreases it, with both characteristics minimizing fracture width over converse conditions. Proppant density and size do not significantly influence fracture propagation. Proppant settling ensues throughout fracture advance, and is accelerated by a lower viscosity fluid or greater proppant density or size, resulting in accumulation of a proppant bed at the fracture base. ‘Screen-out’ of proppant at the fracture tip can occur where the fracture aperture is only several times the diameter of the individual proppant particles. After fracture closure, proppant packs comprising larger particles exhibit higher conductivity. More importantly, high-conductivity flow channels are necessarily formed around proppant banks due to the flexural displacement of the fracture walls, which offer preferential flow pathways and significantly influence the distribution of fluid transport. Higher compacting stresses are observed around the edge of proppant banks, resulting in greater depths of proppant embedment into the fracture walls and/or an increased potential for proppant crushing.

Chemical responses to hydraulic fracturing and wolframite precipitation in the vein-type tungsten deposits of southern China

Wolframite is the main ore mineral in the vein-type tungsten deposits of southern China. Much progress has been made on the characteristics of the mineralizing fluids, but the mechanisms of wolframite precipitation remain poorly understood. Hydraulic fracturing driven by high-pressure fluids is a common mechanical process during magmatic-hydrothermal transition, but it is uncertain whether and how this mechanical process may affect chemical equilibrium and cause wolframite precipitation. This paper examines how a hydraulic fracturing process affects solubility of tungsten in CO2-saturated NaCl solutions using a hydro-mechanical numerical model coupled with a multi-component thermodynamic model. The thermodynamic model presented here is in the system of Fe-W-Cl-Na-C-O-H. The modeling results indicate that fluid pressure exerts a significant influence on chemical equilibrium where CO2 solubility in NaCl solutions decreases with decreasing fluid pressure and pH increases with decreasing fluid pressure. An increase in pH reduces the concentrations of the dominant iron-bearing species (FeCl20) and the dominant tungsten-bearing species (HWO4−) in fluids. Tungsten solubility in fluids reaches tens of ppm. Over ten fluctuations of fluid pressure are identified in the numerical experiments of hydraulic fracturing. These pressure fluctuations cause a decrease in solubility of tungsten by over 30% of the maximum solubility. Repeated drops of fluid pressure during hydraulic fracturing processes cause CO2 loss and could be efficient processes for precipitating wolframite from mineralizing fluids. These findings may also offer an insight into the precipitation mechanisms of other metals from CO2-bearing hydrothermal fluids.

Geologic structure controls on initial productions of lower Silurian Longmaxi shale in south China

The Lower Silurian Longmaxi shale is the most important marine shale gas play in South China. Several hundred wells have been drilled to date, of which more than 150 wells have obtained high initial production (IP). Outside of the Sichuan Basin, however, wells drilled in the Lower Silurian Longmaxi shale do not reach flow rates that are commercial. Developing an understanding of the key factors controlling the IPs of Longmaxi shale is important in screening shale-resource plays. In this study, the TOC, thermal maturity, porosity, and gas saturation data obtained from Longmaxi shale of southeastern Chongqing area outside Sichuan Basin have been compared with that of Sichuan Basin. The results of this study show that the shales encountered display similar properties including TOC (>2%), thermal maturity (2.5–3.5% EqRo), and total porosity (3–6%). A good correlation between IPs and pressure coefficient suggest that the free gas content of gas shale controls on IPs. Porosity and gas saturation of gas shale are the main factors to control its free gas volume. The gas saturations in Longmaxi shale from high initial production wells in Sichuan Basin mainly range between 50 and 90%, however, that of shale in the southeastern Chongqing area are decreased to 10–30%. This is the directly reason for low IPs of wells. The contrasting gas saturation of Longmaxi shale between Sichuan Basin and the adjacent fold-thrust belts are interpreted to reflect, in part, differences in sealed condition of fluid system. Intensive tectonic movements caused the exhumation, faulting and fracturing, that reduced or destroyed the sealed ability of shale fluid system, which are the major factors for enhancing water saturation, decreasing fluid pressure and IPs. Finally, the study proposes several most favorable zones for Longmaxi shale gas exploration and development.

Three‐dimensional texture of natural pseudotachylyte: Pseudotachylyte formation mechanism in hydrous accretionary complex

AbstractMelt‐origin pseudotachylyte is the most reliable seismogenic fault rock. It is commonly believed that pseudotachylyte generation is rare in the plate subduction zone where interstitial fluids are abundant and can trigger dynamic fault‐weakening mechanisms such as thermal pressurization. Some recent studies, however, have discovered pseudotachylyte‐bearing faults in exhumed ancient accretionary complexes, indicating that frictional melting also occurrs during earthquakes in subduction zones. To clarify the pseudotachylyte generation mechanism and the variation of slip behavior in the plate subduction zone, a pseudotachylyte found in the exhumed fossil accretionary complex (the Shimanto Belt, Nobeoka, Japan) was re‐focused and microscopic and three‐dimensional observations of the pseudotachylyte‐bearing fault were performed based on optical, electron, and X‐ray microscope images. Based on the patterns contained in the fragment, the pseudotachylyte is divided into four domains, although no clear domain boundaries or layering structures are not found. Three‐dimensional observation also suggests that the pseudotachylyte were fragmented or isolated by cataclasite or carbonate breccia. The pseudotachylyte was rather injected into the surrounding carbonate breccia, which is composed of angular fragments of the host rock and a matrix of tiny crystalline carbonate. The pseudotachylyte volume was extracted from the X‐ray microscope image and the heat abundance consumed by the pseudotachylyte generation was estimated at 2.18 MJ/m2, which can be supplied during a slip of approximately 0.5 m. These observations and calculations, together with the results of the previous investigations, suggest hydrofracturing and rapid carbonate precipitation that preceded or accompanied the frictional melting. Dynamic hydrofracturing during a slip can be caused by rapid fluid pressurization, and can induce abrupt decrease in fluid pressure while drastically enhancing the shear strength of the shear zone. Consequently, frictional heating would be reactivated and generate the pseudotachylyte. These deformation processes can explain pseudotachylyte generation in hydrous faults with the impermeable wall rock.

Geology, geochronology and geochemistry of the Dabate Cu–Mo deposit, northern Chinese Tien Shan: Implications for spatial separation of copper and molybdenum mineralization

The Dabate deposit is a porphyry Cu–Mo deposit located in the Sailimu Block, northern Chinese Tien Shan. The deposit shows a clear separation of Cu and Mo mineralization, with Cu mineralization occurring along the edge of the rhyolitic porphyry, and Mo mineralization in the inner part of the rhyolitic porphyry. Sm-Nd isotopic analyses of six fluorite samples from the Cu sulfides–fluorite veins yield an isochron age of 298.1 ± 5.0 Ma, and Re-Os isotopic analyses of four molybdenite samples from the molybdenite–quartz veins yield an isochron age of 299.6 ± 3.2 Ma. These geochronological data and accompanying geologic evidence indicate that the Cu and Mo mineralization belongs to the same hydrothermal system and are closely related to the rhyolitic porphyry, which has a youngest zircon 206Pb/238U age of 297.3 ± 8.0 Ma.Rare earth element (REE) and fluid inclusion studies were carried out for fluorite in the Cu ores. The fluorite related to Cu mineralization have high ΣREE (63.4–216.9 ppm) and show generally similar REE patterns with the rhyolitic porphyry, suggesting that the fluid of Cu mineralization is closely related to the rhyolitic porphyry. The slight LREE-depletion and Ce-depletion of fluorite relative to the rhyolitic porphyry may be due to preferential partitioning of HREE into the fluid in neutral to weak alkaline conditions and to mixing with meteoric water which is characterized by Ce-depletion. Three types of fluid inclusions were recognized in the fluorite from the Cu sulfides–fluorite veins: liquid–vapor (LV-type), CO2-bearing (C-type) and solid mineral-bearing (S-type). The LV-type inclusions have homogenization (vapor to liquid) temperatures from 175 to 328 °C and salinities of 0.4∼14.9 wt% NaCl eqv. (mode at 0∼8 wt% NaCl eqv.), and is of H2O + NaCl composition. The C-type inclusions have homogenization (vapor to liquid) temperatures from 206 to 279 °C and salinities of 1.6∼8.5 wt% NaCl eqv., and is of H2O + CO2 + NaCl + CH4 composition. The S-type inclusions have partial homogenization (vapor to liquid) temperatures of 173–233 °C and salinities of 1.2–7.9 wt% NaCl eqv., and is of H2O + NaCl composition. The solid particle in S-type inclusions did not change during heating up to 550 °C, indicating that the solid is not daughter mineral and the S-type inclusions are actually the same as the LV-type inclusions. The LV-type inclusions have microthermometric attributes similar to those typically found in the late stages of porphyry deposits, whereas the C-type inclusions have similar compositions as the inclusions in the Mo ores as documented in previous studies at Dabate. The presence of both LV-type and C-type inclusions suggests that the Cu mineralization may be related to mixing between meteoric water and magmatic fluids, as is also indicated by the REE of fluorite.Comparing with data from Mo ores reported in previous studies, it is suggested that the Mo-stage fluids were more reduced and acidic and Mo mineralization may be mainly related to fluid pressure decrease and immiscibility, whereas the Cu-stage fluids were more oxidized, neutral to weakly alkaline and Cu mineralization may be mainly controlled by mixing and cooling. The vapor phase produced by fluid immiscibility in the deep area may have carried Cu, As, Ag, HF, CO2 and migrated to the outer part of the porphyry, precipitated Cu sulfides, arsenopyrite and fluorite by mixing with meteoric water from the country rocks. Whereas the liquid phase produced by fluid immiscibility at depth may have carried Mo, NaCl and migrated to the middle-west part of the rhyolitic porphyry, become immiscible and precipitated molybdenite.

Influence of faulting on the distribution and development of cold seep-related dolomitic conduit concretions at East Cape, New Zealand

An intertidal shore platform in bathyal mudstones of the Late Miocene Pohutu Formation near East Cape, North Island, New Zealand, hosts many impressive dolomitic conduit concretions having predominantly doughnut morphologies up to 6 m across. Carbon isotope values (δ 13 C + 6 to + 9‰ PDB) are interpreted to show that the carbon for dolomite precipitation was derived from extensive anaerobic oxidation of thermogenic methane, while oxygen isotope values (δ 18 O + 2 to + 6‰ PDB) implicate the dissociation of gas hydrates at the time of carbonate precipitation. The concretions are inferred to mark the shallow sub-seafloor locations of upward migrating hydrocarbon-enriched fluids in a fossil cold seep system on a convergent margin. The distribution of concretions and faults are intimately associated. We propose that doughnut concretion growth was related to a periodically active fault-valve mechanism involving fluid pressure increase, fault rupture and fluid discharge, followed by fluid pressure decrease, mineral precipitation and fault sealing.

Influence of faulting on the distribution and development of cold seep-related dolomitic conduit concretions at East Cape, New Zealand

ABSTRACTAn intertidal shore platform in bathyal mudstones of the Late Miocene Pohutu Formation near East Cape, North Island, New Zealand, hosts many impressive dolomitic conduit concretions having predominantly doughnut morphologies up to 6 m across. Carbon isotope values (δ13C + 6 to + 9‰ PDB) are interpreted to show that the carbon for dolomite precipitation was derived from extensive anaerobic oxidation of thermogenic methane, while oxygen isotope values (δ18O + 2 to + 6‰ PDB) implicate the dissociation of gas hydrates at the time of carbonate precipitation. The concretions are inferred to mark the shallow sub-seafloor locations of upward migrating hydrocarbon-enriched fluids in a fossil cold seep system on a convergent margin. The distribution of concretions and faults are intimately associated. We propose that doughnut concretion growth was related to a periodically active fault-valve mechanism involving fluid pressure increase, fault rupture and fluid discharge, followed by fluid pressure decrease, mineral precipitation and fault sealing.

Reaction-induced grain boundary cracking and anisotropic fluid flow during prograde devolatilization reactions within subduction zones

Devolatilization reactions during prograde metamorphism are a key control on the fluid distribution within subduction zones. Garnets in Mn-rich quartz schist within the Sanbagawa metamorphic belt of Japan are characterized by skeletal structures containing abundant quartz inclusions. Each quartz inclusion was angular-shaped, and showed random crystallographic orientations, suggesting that these quartz inclusions were trapped via grain boundary cracking during garnet growth. Such skeletal garnet within the quartz schist formed related to decarbonation reactions with a positive total volume change (∆V t > 0), whereas the euhedral garnet within the pelitic schists formed as a result of dehydration reaction with negative ∆V t values. Coupled hydrological–chemical–mechanical processes during metamorphic devolatilization reactions were investigated by a distinct element method (DEM) numerical simulation on a foliated rock that contained reactive minerals and non-reactive matrix minerals. Negative ∆V t reactions cause a decrease in fluid pressure and do not produce fractures within the matrix. In contrast, a fluid pressure increase by positive ∆V t reactions results in hydrofracturing of the matrix. This fracturing preferentially occurs along grain boundaries and causes episodic fluid pulses associated with the development of the fracture network. The precipitation of garnet within grain boundary fractures could explain the formation of the skeletal garnet. Our DEM model also suggests a strong influence of reaction-induced fracturing on anisotropic fluid flow, meaning that dominant fluid flow directions could easily change in response to changes in stress configuration and the magnitude of differential stress during prograde metamorphism within a subduction zone.

Emergence and seismological implications of phase transition and universality in a system with interaction between thermal pressurization and dilatancy.

A dynamic earthquake source process is modeled by assuming interaction among frictional heat, fluid pressure, and inelastic porosity. In particular, fluid pressure increase due to frictional heating (thermal pressurization effect) and fluid pressure decrease due to inelastic porosity increase (dilatancy effect) play important roles in this process. Two nullclines become exactly the same in the system of governing equations, which generates non-isolated fixed points in the phase space. These lead to a type of phase transition, which produces a universality described by the power law between the initial value of one variable and the final value of the other variable. The universal critical exponent is found to be 1/2, which is independent of the details of the porosity evolution law. We can regard the dynamic earthquake slip process as a phase transition by considering the final porosity or slip as the order parameter. Physical prediction of phase emergence is difficult because the porosity evolution law has uncertainties, and the final slip amount is difficult to predict because of the universality. Finally, nonlinear mathematical application of the result is also discussed.

Mechanisms of Serpentinization Utilizing Olivine–Plagioclase–H2O System under Hydrothermal Conditions

Silica activity influences the reaction pathways that may occur during serpentinization. At the crust–mantle boundary, silica activity and mass transfer are expected to increase. In this study, hydrothermal ‘tube-in-tube’ experiments utilizing the olivine–plagioclase–H2O system were conducted to assess silica-related mechanisms of hydrothermal alternation at the crust–mantle boundary. Experimental conditions were 230 ˚C and 2.80 MPa (i.e., vapor–saturated pressure) with run times up to 7,980 hours.Reaction products in the olivine zone varied with increasing distance from the olivine–plagioclase boundary, primarily changing from Al–serpentine to serpentine ± brucite + magnetite. No secondary minerals were apparent in the plagioclase zone. Total H2O content in the products was greatest at the boundary compared to the inner tube, where total H2O became homogeneous after the appearance of brucite at 3,184 h. During the experiments, olivine hydration and metasomatic reactions proceeded simultaneously. In contrast to talc-forming metasomatic reactions in olivine–quartz experiments, metasomatic reactions involving plagioclase–buffered fluids led to a decrease in fluid pressure. These reactions suggest that contrasting effects between quartz-buffered and plagioclase-buffered fluids on the chemical and mechanical behavior of the crust–mantle boundary.

Influences of Hydraulic Fracturing on Fluid Flow and Mineralization at the Vein-Type Tungsten Deposits in Southern China

Wolframite is the main ore mineral at the vein-type tungsten deposits in the Nanling Range, which is a world-class tungsten province. It is disputed how wolframite is precipitated at these deposits and no one has yet studied the links of the mechanical processes to fluid flow and mineralization. Finite element-based numerical experiments are used to investigate the influences of a hydraulic fracturing process on fluid flow and solubility of CO2and quartz. The fluids are aqueous NaCl solutions and fluid pressure is the only variable controlling solubility of CO2and quartz in the numerical experiments. Significant fluctuations of fluid pressure and high-velocity hydrothermal pulse are found once rock is fractured by high-pressure fluids. The fluid pressure drop induced by hydraulic fracturing could cause a 9% decrease of quartz solubility. This amount of quartz deposition may not cause a significant decrease in rock permeability. The fluid pressure decrease after hydraulic fracturing also reduces solubility of CO2by 36% and increases pH. Because an increase in pH would cause a major decrease in solubility of tungsten, the fluid pressure drop accompanying a hydraulic fracturing process facilitates wolframite precipitation. Our numerical experiments provide insight into the mechanisms precipitating wolframite at the tungsten deposits in the Nanling Range as well as other metals whose solubility is strongly dependent on pH.

Formation and destruction mechanism as well as major controlling factors of the Silurian shale gas overpressure in the Sichuan Basin, China

Taking the Well JY1 and Well PY1 in the Eastern Sichuan Basin as examples, the formation mechanism of shale gas overpressure was studied by using the cross plot of acoustic versus density logging data. During the processes of hydrocarbon generation and the uplifting, the pressure evolution of fluids in shale gas layers was reconstructed by fluid inclusions and PVTSIM software. The major factors controlling the evolution of shale gas overpressure were established according to the study of fracture, the timing of the uplifting, and episodes of tectonic deformation. Our results showed that the main mechanism of overpressure in the Silurian shale gas reservoirs in the Sichuan Basin was the fluid expansion, which was caused by hydrocarbon generation. Since the Yanshanian, the strata were uplifted and fluid pressure generally showed a decreasing trend. However, due to the low compression rebound ratio of shale gas reservoir rocks, poor connectivity of reservoir rocks, and low content of formation water and so on, such factors made fluid pressure decrease, but these would not be enough to make up the effects of strata erosion resulting in a further increase in fluid pressure in shale gas reservoirs during the whole uplifting processes. Since the Yanshanian, the Well PY1 zone had been reconstructed by at least three episodes of tectonic movement. The initial timing of the uplifting is 130 Ma. Compared to the former, the Well JY1 zone was firstly uplifted at 90 Ma, which was weakly reconstructed. As a result, low-angle fractures and few high resistance fractures developed in the Well JY1, while high-angle fractures and many high resistance fractures developed in the Well PY1. In totality, the factors controlling the overpressure preservation in shale gas reservoirs during the late periods include timing of late uplifting, superposition and reconstruction of stress fields, and development of high-angle fractures.

Coupling changes in densities and porosity to fluid pressure variations in reactive porous fluid flow: Local thermodynamic equilibrium

AbstractMineralogical reactions which generate or consume fluids play a key role during fluid flow in porous media. Such reactions are linked to changes in density, porosity, permeability, and fluid pressure which influence fluid flow and rock deformation. To understand such a coupled system, equations were derived from mass conservation and local thermodynamic equilibrium. The presented mass conservative modeling approach describes the relationships among evolving fluid pressure, porosity, fluid and solid density, and devolatilization reactions in multicomponent systems with solid solutions. This first step serves as a framework for future models including aqueous speciation and transport. The complexity of univariant and multivariant reactions is treated by calculating lookup tables from thermodynamic equilibrium calculations. Simplified cases were also investigated to understand previously studied formulations. For nondeforming systems or systems divided into phases of constant density, the equations can be reduced to porosity wave equations with addition of a reactive term taking the volume change of reaction into account. For closed systems, an expression for the volume change of reaction and the associated pressure increase can be obtained. The key equations were solved numerically for the case of devolatilization of three different rock types that may enter a subduction zone. Reactions with positive Clapeyron slope lead to an increase in porosity and permeability with decreasing fluid pressure resulting in sharp fluid pressure gradients around a negative pressure anomaly. The opposite trend is obtained for reactions having a negative Clapeyron slope during which sharp fluid pressure gradients were only generated around a positive pressure anomaly. Coupling of reaction with elastic deformation induces a more efficient fluid flow for reactions with negative Clapeyron slope than for reactions with positive Clapeyron slope.

Post-Spinal a Rare Complication and Treatment: Tinnitus and Epidural Blood Patch.

Dear Editor, Rare auditory symptoms such as tinnitus after spinal anaesthesia have been observed (1–4). It can be accompanied by headache (1, 4) and can become chronic and affect a patient’s quality of life. In this case, we aimed to present our clinical experience regarding the relief of symptoms by an epidural blood patch in a patient who developed headache and bilateral tinnitus following spinal anaesthesia. A 31-year-old female patient, who was 58 kg in weight and 169 cm in height, was scheduled for operation under spinal anaesthesia due to venous stasis. Informed written consent was obtained. The spinal space was accessed with a 25-G Quincke needle on the first try through the L4–5 interspinous space. On observing a clear cerebrospinal fluid leak, 12.5 mg of hyperbaric bupivacaine and 15 μg of fentanyl were intrathecally administered in a volume of approximately 3 mL. The patient was admitted to the hospital on the first postoperative day due to severe headache that started from the nape of the neck and that involved the entire head. The headache was accompanied by tinnitus (ringing in both ears and motor noise) and nausea–vomiting and was more prominent in the standing and sitting positions. The patient was chiefly discomforted by the tinnitus. The headache diminished while in the lying position, but the tinnitus did not subside. An intravenous access was established in the patient, and she was hydrated. An oral caffeinated analgesic and antiemetic were started. The headache alleviated on the second day of admission, but the tinnitus remained. The patient was unable to sleep and expressed that she was extremely discomforted by this. Given that it was accompanied by headache, we thought that the patient could benefit from an epidural blood patch. Following appropriate site cleaning, approximately 12 mL of the blood patch was epidurally administered by accessing the same space. The tinnitus in the left ear immediately improved following the injection, while it disappeared within approximately 12 h in the right ear. Additionally, the complaint of pain, which lost its severity with the medical treatment, completely disappeared. Aetiology regarding symptoms related to hearing following spinal anaesthesia is not very clear. One of the proposed hypotheses is the decrease in intra-labyrinth pressure. The cochlear duct provides an anatomical connection between the cochlea and the subarachnoid distance. The composition of the perilymph in the cochlea closely resembles the cerebrospinal fluid. One of the proposed views is that a decrease in cerebrospinal fluid pressure causes a decrease in intra-labyrinth pressure and that this causes functional inability in the ear in transmitting sounds (5). Symptoms could spontaneously subside; however, there are patients who became chronic. The relationship of chronic cases with spinal anaesthesia can only be revealed by obtaining a good medical history. These patients can benefit from an epidural blood patch (1, 2, 4). In a patient who developed tinnitus following spinal anaesthesia (4 years), it was learned, upon obtaining medical history by the ear, nose and throat specialist, that the complaint started 24 h after spinal anaesthesia, and the patient was directed to an anaesthetist. The tinnitus was successfully treated by administering 20 mL of an epidural blood patch to the patient (2). A patient with postspinal 8 years tinnitus complaint underwent epidural anaesthesia for another surgical operation. The tinnitus recovered by the epidural administration of 27 mL of bolus, followed by a local anaesthetic performed by continuous infusion (3). Due to the high rate of success and ease of application, an epidural blood patch is the accepted gold standard treatment in treating postspinal headache when conservative treatments have failed. It is a treatment whose major side effects are (usually temporary) rare, and it is safe and effective. Side effects are low back pain or radicular pain during injection, generally related to the administered volume (6). For evaluating these cases, the epidural administration of any application-blood, normal saline or local anaesthetics-appears to be effective in improving auditory symptoms. In conclusion, the accompaniment of nausea–vomiting and tinnitus with headache that develops after spinal anaesthesia negatively affects the quality of life. Therefore, we think that administering an epidural blood patch without delay in the presence of auditory symptoms accompanying headache will improve the comfort of patients.

Focal cartilage defect compromises fluid-pressure dependent load support in the knee joint.

A focal cartilage defect involves tissue loss or rupture. Altered mechanics in the affected joint may play an essential role in the onset and progression of osteoarthritis. The objective of the present study was to determine the compromised load support in the human knee joint during defect progression from the cartilage surface to the cartilage-bone interface. Ten normal and defect cases were simulated with a previously tested 3D finite element model of the knee. The focal defects were considered in both condyles within high load-bearing regions. Fluid pressurization, anisotropic fibril-reinforcement, and depth-dependent mechanical properties were considered for the articular cartilages and menisci. The results showed that a small cartilage defect could cause 25% reduction in the load support of the knee joint due to a reduced capacity of fluid pressurization in the defect cartilage. A partial-thickness defect could cause a fluid pressure decrease or increase in the remaining underlying cartilage depending on the defect depth. A cartilage defect also increased the shear strain at the cartilage-bone interface, which was more significant with a full-thickness defect. The effect of cartilage defect on the fluid pressurization also depended on the defect sites and contact conditions. In conclusion, a focal cartilage defect causes a fluid-pressure dependent load reallocation and a compromised load support in the joint, which depend on the defect depth, site, and contact condition.

Blood Vessel Maturation in Health and Disease and its Implications for Vascularization of Engineered Tissues.

Engineered blood vessels have often been found to be immature and unstable. Similarly, numerous pathologies such as diabetic retinopathy and cancer are characterized by highly abnormal, defective, hypervascular networks, consisting of immature, leaky, and irregular vessels with a marked loss of perivascular cell coverage. An emerging therapeutic concept in treatment of such vascular diseases and their management is the potential to normalize blood vessels by strengthening the cellular components that form the vascular network. Vessel normalization is characterized by the reduction in the number and size of immature vessels, a decrease in interstitial fluid pressure, and increase in perivascular cell coverage. Understanding the molecular and cellular defects associated with abnormal blood vessels will allow us to find appropriate treatment options that can promote normal blood vessel development. These, in turn, can be applied to improve vessel maturation in engineered tissues. In this review, we describe the major perivascular abnormalities associated with various human diseases and engineered vasculatures and the major advances in obtaining mature vasculatures for translational applications.

Neurogenic Shock Immediately following Posterior Lumbar Interbody Fusion: Report of Two Cases

Study Design Case report. Objective To present two cases of neurogenic shock that occurred immediately following posterior lumbar interbody fusion (PLIF) and that appeared to have been caused by the vasovagal reflex after dural injury and incarceration of the cauda equina. Case Report We present two cases of neurogenic shock that occurred immediately following PLIF. One patient had bradycardia, and the other developed cardiac arrest just after closing the surgical incision and opening the drainage tube. Cardiopulmonary resuscitation was performed immediately, and the patients recovered successfully, but they showed severe motor loss after awakening. The results of laboratory data, chest X-ray, electrocardiogram, computed tomography, and echocardiography ruled out pulmonary embolism, hemorrhagic shock, and cardiogenic shock. Although the reasons for the postoperative shock were obscure, reoperation was performed to explore the cause of paralysis. At reoperation, a cerebrospinal fluid collection and the incarceration of multiple cauda equina rootlets through a small dural tear were observed. The incarcerated cauda equina rootlets were reduced, and the dural defect was closed. In both cases, the reoperation was uneventful. From the intraoperative findings at reoperation, it was thought that the pathology was neurogenic shock via the vasovagal reflex. Conclusion Incarceration of multiple cauda equina rootlets following the accidental dural tear by suction drainage caused a sudden decrease of cerebrospinal fluid pressure and traction of the cauda equina, which may have led to the vasovagal reflex.

Seismic precursors linked to highly compressible fluids at oceanic transform faults

Earthquakes on oceanic transform faults are often preceded by foreshock swarms. A theoretical model suggests that circulating hydrothermal fluids, which compress as the fault rocks expand and deform, cause this precursor seismic activity. Large earthquakes on mid-ocean ridge transform faults are commonly preceded by foreshocks1,2,3 and changes in the seismic properties of the fault zone3. These seismic precursors could be linked to fluid-related processes2,3. Hydrothermal fluids within young, hot crust near the intersection of oceanic transform faults become significantly more compressible with decreasing pressure, with potential impacts on fault behaviour. Here we use a theoretical model to show that oceanic transform faults can switch from dilatant and progressive deformation to rupture in response to fluid-related processes. We assume that the fault core material behaves according to a dilatant and strain-softening or contractant and strain-hardening constitutive law (Cam-clay-type4), depending on the effective stress state. According to our model, after the initial purely rigid-elastic phase, dilatancy is found to occur within the fault core, causing pore pressure to decrease, hence fluid compressibility to increase. The plastic regime starts with a stable phase, with effective stresses gradually increasing over a timescale of years in response to tectonic loading. The fault then evolves into a metastable phase, lasting a few days, as the pore pressure decreases, inducing large variations or even a discontinuous jump in fluid compressibility, depending on fluid properties. This in turn triggers fault-slip instability that creates foreshock swarms. In the final phase, the fault fails in the mainshock rupture. Our results imply that seismic precursors are caused by the decrease in fluid pressure which results in an increase in fluid compressibility, in response to fault core dilatancy just before rupture.

Pressure Transient Modeling in Geothermal Reservoir by Using Picard-McLaurin Iteration

Exploitation of geothermal resource results the decrease of fluid pressure in geothermal reservoir. In production process, the analysis of reservoir condition is made by observing the pressure state. When the fluid is pumped into the reservoir, the value of pressure varies with time which is called as transient state. The plot of pressure versus time will create a curve with a certain slope. From the graph of the pressure the reservoir condition can be analyzed. The solution of the pressure transient is identified as exponential integral equation Ei(x). When the input to the function is really small for example at x < 0.01, the equation will form an asymptotic curve. Analytical solution involves logarithm natural and Euler constant (γ). In this paper we try to approach the solution of exponential integral equation by numerical integration. The objective of this study is to make a numerical model of the pressure change in a geothermal reservoir and to compare the result between numerical method and analytic. There are two methods used in this study, first is Picard-McLaurin iteration to solve the ordinary differential equations (ODE), and the second is trapezoidal integration to calculate the function of Ei(x). The modeling shows that the result of the calculation with the numerical method matched with the analytic with the range of error between 0.0008 to 4.5 % for drawdown test and 0.19 to 7.7 % for buildup test.

Physicochemical impacts associated with natural gas development on methanogenesis in deep sand aquifers.

The Minami-Kanto gas field, where gases are dissolved in formation water, is a potential analogue for a marine gas hydrate area because both areas are characterized by the accumulation of microbial methane in marine turbidite sand layers interbedded with mud layers. This study examined the physicochemical impacts associated with natural gas production and well drilling on the methanogenic activity and composition in this gas field. Twenty-four gas-associated formation water samples were collected from confined sand aquifers through production wells. The stable isotopic compositions of methane in the gases indicated their origin to be biogenic via the carbonate reduction pathway. Consistent with this classification, methanogenic activity measurements using radiotracers, culturing experiments and molecular analysis of formation water samples indicated the predominance of hydrogenotrophic methanogenesis. The cultivation of water samples amended only with methanogenic substrates resulted in significant increases in microbial cells along with high-yield methane production, indicating the restricted availability of substrates in the aquifers. Hydrogenotrophic methanogenic activity increased with increasing natural gas production from the corresponding wells, suggesting that the flux of substrates from organic-rich mudstones to adjacent sand aquifers is enhanced by the decrease in fluid pressure in sand layers associated with natural gas/water production. The transient predominance of methylotrophic methanogens, observed for a few years after well drilling, also suggested the stimulation of the methanogens by the exposure of unutilized organic matter through well drilling. These results provide an insight into the physicochemical impacts on the methanogenic activity in biogenic gas deposits including marine gas hydrates.