High Capillary Pressure Research Articles

Noninvasive Cardiac Output Measurement by Inert Gas Rebreathing in Suspected Pulmonary Hypertension

The objective of this study was to evaluate inert gas rebreathing (IGR) reliability in cardiac output (CO) measurement compared with Fick method and thermodilution. IGR is a noninvasive method for CO measurement; CO by IGR is calculated as pulmonary blood flow plus intrapulmonary shunt. IGR may be ideal for follow-up of patients with pulmonary hypertension (PH), sparing the need of repeated invasive right-sided cardiac catheterization. Right-sided cardiac catheterization with CO measurement by thermodilution, Fick method, and IGR was performed in 125 patients with possible PH by echocardiography. Patients were grouped according to right-sided cardiac catheterization-measured mean pulmonary and wedge pressures: normal pulmonary arterial pressure (n = 20, mean pulmonary arterial pressure = 18 ± 3 mm Hg, pulmonary capillary wedge pressure = 11 ± 5 mm Hg), PH and normal pulmonary capillary wedge pressure (PH-NW, n = 37 mean pulmonary arterial pressure = 42 ± 13 mm Hg, pulmonary capillary wedge pressure = 11 ± 6 mm Hg), and PH and high pulmonary capillary wedge pressure (PH-HW, n = 68, mean pulmonary arterial pressure = 37 ± 9 mm Hg, pulmonary capillary wedge pressure = 24 ± 6 mm Hg). Thermodilution and Fick measurements were comparable. Fick and IGR agreement was observed in normal pulmonary arterial pressure (CO = 4.10 ± 1.14 and 4.08 ± 0.97 L/min, respectively), whereas IGR overestimated Fick in patients with PH-NW and those with PH-HW because of intrapulmonary shunting overestimation in hypoxemic patients. When patients with arterial oxygen saturation (SO2) ≤90% were excluded, IGR and Fick agreement improved in PH-NW (CO = 4.90 ± 1.70 and 4.76 ± 1.35 L/min, respectively) and PH-HW (CO = 4.05 ± 1.04 and 4.10 ± 1.17 L/min, respectively). In hypoxemic patients, we estimated pulmonary shunt as Fick - pulmonary blood flow and calculated shunt as: -0.2423 × arterial SO2 + 21.373 L/min. In conclusion, IGR is reliable for CO measurement in patients with PH with arterial SO2 >90%. For patients with arterial SO2 ≤90%, a new formula for shunt calculation is proposed.

Impact of Liquid Loading in Hydraulic Fractures on Well Productivity

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 163837, ’Impact of Liquid Loading in Hydraulic Fractures on Well Productivity,’ by Samarth Agrawal and Mukul M. Sharma, SPE, The University of Texas at Austin, prepared for the 2013 SPE Hydraulic Fracturing Technology Conference, The Woodlands, Texas, USA, 4-6 February. The paper has not been peer reviewed. One of the major challenges in fracturing low-permeability gas formations is the loss of well productivity caused by fluid entrapment in the matrix or fracture. Studies have suggested that this water is trapped in the rock matrix near the fracture face and remains trapped because of the high capillary pressure in the matrix. This study shows that, in regard to hydraulic fractures in horizontal wells, the fluid may also be trapped within the fracture itself and may affect the cleanup as well as productivity. Introduction The loss of fracturing fluid and its impact on the productivity of hydraulically fractured wells have been studied for many years. Conventional wisdom suggests that the liquid is trapped at the fracture face because of capillary effects. This reduces the relative permeability of the hydrocarbon phase during flowback. Most studies published thus far on the subject ignored the accumulation of liquid in the fracture itself and the effect of gravity and fluid segregation in the fracture. In this study, we show that liquid accumulation in the fracture itself can be significant and that this fluid saturation is coupled with the fluid saturation in the matrix, leading to a very different cleanup profile and time scale for cleanup. A 3D reservoir simulator was used to investigate liquid loading in hydraulic fractures in a horizontal well. Generally, hydraulic fractures in horizontal wells range from tens to hundreds of feet in height. If liquid loading takes place in a certain section of the fracture, it will impair the flow of gas there. This will lead to a reduction in the effective producing fracture area, even if the drawdown is greater than the capillary pressure. Liquid Loading Inside the Fracture. The desired lift velocity for unloading liquid and the available gas velocity in a fracture differ by almost two orders of magnitude. It is, therefore, very like-ly that the lower portions of fractures will be filled with liquid when production is initiated. This suggests that concerning load recovery from hydraulically fractured horizontal wells, even if the drawdown is able to overcome the capillary pressures, the inflow gas velocity may not be high enough to lift the liquid against gravity into the wellbore (Fig. 1). Liquid loaded inside the fracture in this way will affect the productivity of the well and the cleanup of the matrix. Understanding the conditions for liquid loading within the fracture will help identify remedial measures, which may be significantly different from remedial measures for reducing liquid blocking at the fracture face.

The Effect of Solvent on Drying Shrinkage of Novolac Xerogels

Three sets of novolac xerogel prepared with various solvents and the effect of solvent on drying shrinkage investigated. The results show that the polarity of solvent has profound effect on microstructure of gel. As the polarity of solvent increases, the ultimate particle size and pore size decrease and consequently, the higher capillary pressure exerts on gel and hence, more shrinkage observed.

Flow boiling phenomena in a single annular flow regime in microchannels (II): Reduced pressure drop and enhanced critical heat flux

In Part II of this study, we report that pressure drop was reduced by approximately 48% and critical heat flux (CHF) was increased by approximately 300% in SiNW microchannels compared to these in smooth wall microchannels. The hydraulic characteristics of the single annular flow were systematically investigated to reveal the mechanisms responsible for the reduced pressure drop and enhanced CHF. In the single annular regime, the liquid and vapor flows were nearly fully separated during the entire flow boiling process (i.e., from the onset of nucleate boiling to the CHF conditions). Moreover, the entrainment droplets were reduced by flattening the profile of the liquid–vapor interfaces using the high capillary pressure generated by SiNWs. These two factors, i.e., flow separation and reduced entrainment droplets, lead to a dramatic reduction of frictional pressure drop. The separation of liquid and vapor flows as well as the improved global and local liquid supply result in a significant CHF enhancement without using inlet restrictors (IR). Reynolds number based the vapor flow at the exit ranged from 0.1 to 2100.

Sealing mechanism for cap beds of shallow-biogenic gas reservoirs in the Qiantang River incised valley, China

Late Quaternary shallow-biogenic gas reservoirs are well-developed in the Qiantang River incised valley, eastern China. They present as sand bodies in the floodplain–estuary facies. Silty clay beds of floodplain–estuary facies and mud beds of estuarine–shallow marine facies serve as the direct and indirect cap beds, respectively, and the former has much better sealing ability. Capillary pressure sealing, pore water pressure sealing, and hydrocarbon concentration sealing contribute to the conservation of shallow-biogenic gas in the reservoirs, in which the pore water pressure sealing may be the most important factor.Here the capillary pressure sealing mechanism is clarified by an indirect method, i.e., the difference of permeability between the cap beds and reservoirs, as the displacement pressure of late Quaternary sediments which is unconsolidated is difficult to be tested. The cap beds have higher capillary pressure than the reservoirs for the far lower permeability. Pore water pressure of cap beds exceeds the total of pore water pressure and original gas pressure of underlying reservoirs. Disequilibrium compaction, swelling of clay minerals and gas generation are responsible for the generation of high pore water pressure. In addition, the hydrocarbon content of the cap beds is higher than that of the reservoirs which could restrain the flow up of gas in the reservoirs.

Controlling effects of the Ordovician carbonate pore structure on hydrocarbon reservoirs in the Tarim Basin, China

The Ordovician carbonate reservoirs in the Tarim Basin with secondary dissolution pores and vugs have complicated pore structures. The weathering crust reservoirs mainly consist of large cavities or vugs connected by fractures, but most of the reef-shoal reservoirs have complex and small throats among matrix pores. The pore structure can be divided into four types: big pore and big throat, big pore but small throat, small pore and small throat, and fracture type. Most of the average throat radius falls between 0.03 and 0.and 0.07 urn, close to that of unconventional reservoirs except in local areas with developed fractures. Fluid driving force analysis shows that the differentiation of fluid is mainly controlled by the throat radius in two kinds of mechanism separated by the critical throat radius about 0.1 urn. There is obvious fluid differentiation and oil/gas/water contact in fracture-cavity reservoirs with big throats. However, most of reservoirs under the critical throat radius have high capillary pressure, which resulted in incomplete differentiation of gas/oil/water, and complicated fluid distribution and fluid properties in the unconventional reservoirs.

Quantification of hydrodynamic effects on capillary seal capacity

Whether a reduction in overpressure across a hydrocarbon column and its seal will reduce the column height that the seal is capable of supporting has been much debated. Recent studies have focused on measuring water relative permeability at high capillary pressure, and have concluded that hydrocarbon columns may be sufficiently permeable to water for the seal capacity to be unaffected by hydrodynamic flow in most situations. A new method for estimating the capillary seal capacity is developed which properly takes into account viscous as well as gravity and capillary forces. A reassessment of existing analyses indicates that hydrodynamic flow has a greater influence on the seal capacity than previously thought. Sets of sensitivity models, including a range of reservoir and seal geometrical and petrophysical characteristics, indicate that – as a general rule – hydrodynamic flow should not be neglected when assessing capillary seal capacity. The sealing capacity of thick top seals above reservoirs with a basal aquifer are least likely to be affected by hydrodynamic flow. The sealing capacity of membrane fault seals, irrespective of whether they have a basal or edge aquifer, may be influenced by realistic overpressure differences. Simple end-member equations define the possible influence of hydrodynamic flow in a particular situation, and only if this is significant should a more comprehensive evaluation be considered.

Insight into petrophysical properties of deformed sandstone reservoirs

We use samples from undeformed and deformed sandstones (single deformation band, deformation band cluster, slip-surface cataclasite, and fault core slip zone) to characterize their petrophysical properties (porosity, permeability, and capillary pressure). Relationships between permeability and porosity are described by power-law regressions where the power-law exponent (D) decreases with the increasing degree of deformation (strain) experienced by the sample from host rock (D, ∼9) to fault core (D, ∼5). The approaches introduced in this work will allow geologists to use permeability and/or porosity measurements to estimate the capillary pressures and sealing capacity of different fault-related rocks without requiring direct laboratory measurements of capillary pressure. Results show that fault core slip zones have the highest theoretical sealing capacity (>140-m [459-ft] oil column in extreme cases), although our calculations suggest that deformation bands can locally act as efficiently as fault core slip zones in sealing nonwetting fluids (in this study, oil and CO2). Higher interfacial tension between brine and CO2 (because of the sensitivity of CO2 to temperature and pressure) results in higher capillary pressure and sealing capacity in a brine and CO2 system than a brine and oil system for the same samples.

Evaporative Heat Transfer Analysis of a Heat Pipe With Hybrid Axial Groove

Through the application of thin film evaporation theory and the fundamental operating principles of heat pipes, a hybrid axial groove has been developed that can greatly enhance the performance characteristics of conventional heat pipes. This hybrid axial groove is composed of a V-shaped channel connected with a circular channel through a very narrow longitudinal slot. During the operation, the V-shaped channel can provide high capillary pressure to drive the fluid flow and still maintain a large evaporative heat transfer coefficient. The large circular channel serves as the main path for the condensate return from the condenser to the evaporator and results in a very low flow resistance. The combination of a high evaporative heat transfer coefficient and a low flow resistance results in considerable enhancement in the heat transport capability of conventional heat pipes. In the present work, a detailed mathematical model for the evaporative heat transfer of a single groove has been established based on the conservation principles for mass, momentum and energy, and the modeling results quantitatively verify that this particular configuration has an enhanced evaporative heat transfer performance compared with that of conventional rectangular groove, due to the considerable reduction in the liquid film thickness and a corresponding increase in the evaporative heat transfer area in both the evaporating liquid film region and the meniscus region.

Experimental Study on Reducing Water Phase Trapping in Tight Gas Reservoirs

This document explains and demonstrates how to reduce water phase trapping in tight gas reservoirs during drilling. The water phase trapping laboratory device and experiment method has been studied, through the experiments on reservoir water phase trapping of western Sichuan Basin in China, Knowing that the damage is very serious, water self absorption experiments with different periods show that porosity and permeability of cores are basically above 50%. for the reason, the high capillary pressure and low water saturation are the main factors. Water phase trapping damage prevention measures has been put forward, including avoiding using water-based operating fluid as much as possible, minimizing or even avoiding the invasion of water-based operating fluid, and reducing interfacial tension and promote smooth operating fluid flow back.

Physical Properties and Main Controlling Factors of Low-Permeability Sandstone Gas Reservoir

In order to guide the resource prediction and exploration evaluation of low-permeability sandstone gas reservoir, the physical properties of this kind of gas reservoir are summarized from such aspects as lithology, porosity, permeability and the characteristics of capillary force, and the main controlling factors of the gas reservoir are analyzed. The analysis show that low-permeability sandstone gas reservoir is mainly characteristic of high capillary pressure, high bound water saturation, low and high porosity as well as low permeability. Rock composition and structural characteristics of the reservoir is the basis of the factors that can affect the compactness of the reservoir. The formation of the reservoir is mainly affected by deposition, diagenesis and late tectogenesis: deposition can affect the composition of minerals, the original physical properties of clastic sediments and others; diagenesis is the main stages of the densification of reservoir, where compaction, pressure solution, cementation and late dissolution are the causes of the densification of reservoir. Dissolution and rim chlorite cementation improve reservoir property; tectonization can have an effect of late transformation on the physical properties of clastic reservoir. At the same time, the fluid characteristics in the reservoir can also affect the permeability of reservoirs.

TOUGH2 code를 이용한 처분장 절리암반 내 벤토나이트 완충재의 포화도 변화

This paper briefly introduces the scope and objectives of SKB Task 8, which is an international cooperative research project. In addition, the hydraulic behaviors of bentonite buffer focusing on the interactions between bentonite and a rock mass with a joint were investigated using TOUGH2 code as part of a sub-mission of Task 8a. The effects of a rock joint and high capillary pressure of bentonite on the re-saturation properties and pressure distribution in a buffer were identified and successfully incorporated in the TOUGH2 code. Based on the numerical results, it was found that the speed of re-saturation in bentonite surrounded by a rock mass with a joint is 2.5 to 12 times faster than that in a condition without a rock joint, while the degree of saturation in the lower part of the buffer material is generally higher than in the upper part in both the cases of with and without a joint. It can be anticipated that the results obtained from this study can be applied to an estimation of the full saturation time and a determination of optimum thickness with regard to the design of the bentonite buffer in a high level waste disposal system.

Role of the fragility of the pulmonary blood-gas barrier in the evolution of the pulmonary circulation

In 1953 Frank Low published the first high-resolution electron micrographs of the human pulmonary blood-gas barrier. These showed that a structure only 0.3-μm thick separated the capillary blood from the alveolar gas, immediately suggesting that the barrier might be vulnerable to mechanical failure if the capillary pressure increased. However, it was 38 years before stress failure was recognized. Initially it was implicated in the pathogenesis of High Altitude Pulmonary Edema, but it was soon clear that stress failure of pulmonary capillaries is common. The vulnerability of the blood-gas barrier is a key factor in the evolution of the pulmonary circulation. As evolution progressed from the ancestors of fishes to amphibians, reptiles, and finally birds and mammals, two factors challenged the integrity of the barrier. One was the requirement for the barrier to become increasingly thin because of the greater oxygen consumption. The other was the high pulmonary capillary pressures that were inevitable before there was complete separation of the pulmonary and systemic circulations.

Reservoir characterization: Evaluation for the channel deposits sequence – Upper part using scanning electron microscope (SEM) and mercury injection (MICP): Case of tight reservoirs (North Sea)

Textural and structural facies analysis in the Buchan Field (North Sea) has provided an important potential database for the assessment of parameters controlling the reservoir quality. Nowadays, significant research effort in oilfield reservoirs focused on pore-scale petrophysics, grain distribution, pore geometry and distribution besides the fluid flow circulation. The investigation, we are conducting, is aimed to determine the reservoir type, based on qualitative and quantitative evaluation. This study deals with the upper part of the defined upward channel sequence in the Buchan oilfield (North Sea). In this view, determination of pore geometry and pore aperture sizes which are related to grain size, sorting and packing becomes essential. The pore geometry size and distribution are present but at a microscopical-scale. They constitute the main petrophysical properties of the studied reservoir, since these selected parts of the reservoirs can be qualified as tight or unconventional material type. These investigated deposits are characterized by very low permeability with the presence of reduced pores leading to the probable existence of important interfacial tension forces as well as high capillary pressure. These properties are directly affecting fluid circulation by trapping considerable amount of residual oil leading to a lesser reservoir recovery. In the case study, examination and assessment of this type of reservoirs and their characteristics, responsible for the H/C accumulations and circulation can only be accomplished by the use of very refined equipments such as the Micro-CT or the SEM. Support for this investigation can be credited to the Autopore use.Accordingly, this paper presents the results of a combination of reservoir characteristics determination, the use of the SEM. petrographical investigation for the purpose of detailed examination as well as the MICP application for the physical properties appraisal. The overall will lead to better understanding of the studied section coupled to other reservoir attributes identification.

A Hybrid Method Employing Breakdown Anodization and Electrophoretic Deposition for Superhydrophilic Surfaces

A fabrication method is developed for superhydrophilic surfaces with high capillary pressure and fast spreading speed. The fabrication method consists of electrophoretic deposition (EPD) and breakdown anodization (BDA). Nanopores and micropores were produced on titanium plates by EPD and BDA, respectively. In EPD, TiO(2) nanoparticles were used to enhance the surface energy and create nanoporous structures, while BDA was employed to produce microporous structures. Capillary rise measurements (CRM) were utilized to characterize superhydrophilic surfaces in terms of capillary pressure and spreading speed. From CRM, it was revealed that microporous structures play a dominant role in determining transport properties, and nanoporous structures affect local wettability without significantly reducing spreading speed. By combining BDA and EPD into a hybrid method, dual-scale (nano and micro) porous structures were produced on titanium plates. The methods presented offer the potential to vary the transport characteristics of superhydrophilic surfaces by altering the nanoscale and microscale features independently. As an example, surfaces with unconventional capillary flows were produced by the hybrid method. This method provides additional opportunities to investigate wetting phenomena while offering a potentially low cost process for industrial applications.

Study on Heat Transfer Characteristics of Heat Pipe with Axial “Ω”-Shaped Microgrooves

Heat pipes are devices capable of very high heat transfer and have been widely used in many thermal management applications. Heat pipe with axial ‘‘Ω”-shaped grooves combines a high capillary pumping pressure with a low axial pressure drop in the liquid. An experimental investigation of thermal characteristics of heat pipe with axial ‘‘Ω”-shaped grooves was presented in this paper. The experimental results showed that the work temperatures affect the equivalent heat transfer coefficients obviously, and 20 °C is chosen to be the most appropriate working temperature for heat pipe in present study. The working temperature affects the operational characteristic of heat pipe significantly. When the working temperature is 20 °C, the most efficient working input power is from 80 to 140W. The tilt angles affect the equivalent heat transfer coefficients not so obviously.

Study of structural failure of the blood‐gas barrier and the epithelial‐epithelial cell contacts in rested and exercised chicken, Gallus domesticus

In birds, high pulmonary capillary blood pressure (PCBP) greatly challenges the structural integrity of the blood‐gas barrier (BGB). Among air‐breathing vertebrates, birds interestingly have thinnest BGBs. To reconcile presence of thin BGB with high PCBP, failure of the BGB and the epithelial‐epithelial cell contacts (E‐ECCs) in rested and exercised chickens was investigated. The number of red blood cells (nRBCs) and protein concentration (PC) were determined in the lavaged fluid. The numbers of E‐ECC breaks (nE‐ECCBs) and those of the BGB (nBGBBs) were counted in the regions supplied by the four branches of the pulmonary artery (PA). The blood lactate concentration increased 4‐fold between rest and highest level of treadmill exercise (speed 2.95 m/s) while the nRBCs and the PC increased gradually, tending to level at higher workloads. Indicating their relative fragility, the nE‐ECCBs surpassed the nBGBBs. In resting birds, there were no breaks in the cranial region. In exercised birds, differences in number of breaks only occurred at 0.66 m/s where the lowest and highest counts respectively occurred in the cranial‐ and caudomedial regions whereas at all other levels of exercise, the numbers of breaks were comparable.Funded by the National Research Foundation (NRF)

Continuous Hydrolysis and Liquid–Liquid Phase Separation of an Active Pharmaceutical Ingredient Intermediate Using a Miniscale Hydrophobic Membrane Separator

Continuous hydrolysis of an active pharmaceutical ingredient intermediate, and subsequent liquid–liquid (L-L) separation of the resulting organic and aqueous phases, have been achieved using a simple PTFE tube reactor connected to a miniscale hydrophobic membrane separator. An alkoxide product, obtained in continuous mode by a Grignard reaction in THF, reacted with acidic water to produce partially miscible organic and aqueous phases containing Mg salts. Despite the partial THF–water miscibility, the two phases could be separated at total flow rates up to 40 mL/min at different flow ratios, using a PTFE membrane with 28 cm2 of active area. A less challenging separation of water and toluene was achieved at total flow rates as high as 80 mL/min, with potential to achieve even higher flow rates. The operability and flexibility of the membrane separator and a plate coalescer were compared experimentally as well as from a physical viewpoint. Surface tension-driven L-L separation was analyzed in general terms, critically evaluating different designs. It was shown that microporous membrane L-L separation can offer very large operating windows compared to other separation devices thanks to a high capillary pressure (Laplace pressure) combined with a large number of pores per unit area offering low pressure drop. The separation device can easily be operated by means of a back-pressure regulator ensuring flow-independent separation efficiency. Simple monitoring and control strategies as well as scaling-up/out approaches are proposed, concluding that membrane-based L-L separation may become a standard unit operation for continuous pharmaceutical manufacturing.

Pulmonary circulation at exercise.

The pulmonary circulation is a high-flow and low-pressure circuit, with an average resistance of 1 mmHg/min/L in young adults, increasing to 2.5 mmHg/min/L over four to six decades of life. Pulmonary vascular mechanics at exercise are best described by distensible models. Exercise does not appear to affect the time constant of the pulmonary circulation or the longitudinal distribution of resistances. Very high flows are associated with high capillary pressures, up to a 20 to 25 mmHg threshold associated with interstitial lung edema and altered ventilation/perfusion relationships. Pulmonary artery pressures of 40 to 50 mmHg, which can be achieved at maximal exercise, may correspond to the extreme of tolerable right ventricular afterload. Distension of capillaries that decrease resistance may be of adaptative value during exercise, but this is limited by hypoxemia from altered diffusion/perfusion relationships. Exercise in hypoxia is associated with higher pulmonary vascular pressures and lower maximal cardiac output, with increased likelihood of right ventricular function limitation and altered gas exchange by interstitial lung edema. Pharmacological interventions aimed at the reduction of pulmonary vascular tone have little effect on pulmonary vascular pressure-flow relationships in normoxia, but may decrease resistance in hypoxia, unloading the right ventricle and thereby improving exercise capacity. Exercise in patients with pulmonary hypertension is associated with sharp increases in pulmonary artery pressure and a right ventricular limitation of aerobic capacity. Exercise stress testing to determine multipoint pulmonary vascular pressures-flow relationships may uncover early stage pulmonary vascular disease.

Transport properties of unconventional gas systems

An overview is given of the mechanisms and processes (viscous flow, diffusion, sorption, desorption) affecting transport in unconventional reservoir rocks. Processes are described, terms and definitions are given, and selected literature data are presented to document the state of knowledge and the data situation on gas, water and two-phase flow in low-permeable lithotypes.Gas transport in the matrix of shales and coals is controlled by and may be restricted to diffusion. Depending on the gas type (e.g. methane or carbon dioxide), transport may be strongly affected by sorption. In many instances, high capillary threshold pressures prevent gas from moving as a continuous phase through the conducting pore network. In contrast, tight sandstone reservoir rocks allow for capillary-controlled viscous flow of a gas phase. Because in these rocks the determination of the water saturation at the prevailing flow conditions is difficult or impossible, we propose to directly use the relationship between effective gas permeability and capillary pressure for the description of two-phase (gas/water) flow in these rocks. In ongoing studies this relationship is being studied systematically for both, steady state and non-steady state saturation conditions.