Monitor Water Movement Research Articles

Electrical conductivity model for reactive porous media under partially saturated conditions with hysteresis effects

The electrical conductivity of a porous medium is strongly controlled by the structure of the medium at the microscale as the pore configuration governs the distribution of the conductive fluid. The pore structure thus plays a key role since different geometries translate in variations of the fluid distribution, causing different behaviors measurable at the macroscale. In this study, we present a new physically-based analytical model derived under the assumption that the pore structure can be represented by a bundle of tortuous capillary tubes with periodic variations of their radius and a fractal distribution of pore sizes. By upscaling the microscale properties of the porous medium, we obtain expressions to estimate the total and relative electrical conductivity. The proposed pore geometry allows us to include the hysteresis phenomenon in the electrical conductivity estimates. The variations on these estimates caused by pore structure changes due to reactive processes are accounted by assuming a uniform dissolution of the pores. Under this hypothesis, we describe the evolution of the electrical conductivity during reactive processes. The expressions of the proposed model have been tested with published data from different soil textures, showing a satisfactory agreement with the experimental data. Hysteretic behavior and mineral dissolution are also successfully addressed. By including hysteresis and mineral dissolution/precipitation in the estimates of the electrical conductivity, this new analytical model presents an improvement as it relates those macroscopic physical phenomena to its origins at the microscale. This opens up exciting possibilities for studies involving electrical conductivity measurements to monitor water movement, and hysteretic and reactive processes in porous media.

Numerical modeling of self-potential in heterogeneous reservoirs

Monitoring water movement toward production wells through downhole measurements of self-potential (SP) is a promising new technology. However, there are uncertainties about its applicability in heterogeneous, multilayered reservoirs. Using numerical modeling, we investigated the likely magnitude and behavior of SP during oil production supported by water injection in two different models of such reservoirs. We found that the magnitude of the SP signal that would be measured along a production well increased as water approached the well, exceeding an assumed noise level of 0.1 mV before water breakthrough. We also found that, in the reservoir models tested, the maximum value of SP at the well skewed toward the fastest waterfront before water breakthrough. The trend of SP increasing at the well with time, together with the shape of the SP profile, were the prime indicators used to investigate water movement. In the reservoir models tested, before water breakthrough the fastest approaching waterfront could be detected approximately 20 m away from the well. However, subsequent waterfronts approaching the well in other layers could not be detected before breakthrough. The effect of these later waterfronts on the SP profile at the well was only detectable at breakthrough. We attributed this to the fact that the SP generated in these layers is masked by the high SP created by the fastest waterfront. Our findings emphasized the importance of an enhanced understanding of reservoir geology and rock electrical properties for better prediction and interpretation of SP.

Transient moisture profiles in cover-zone concrete during water absorption

A number of sophisticated techniques, such as NMR imaging and γ-ray attenuation, have now been used to study moisture transport in porous construction materials. This paper presents initial developments in the application of discretized, electrical conductivity measurements as a relatively simple technique to monitor water movement within cover-zone concrete. Using a 3-phase model and the Archie relationship for porous rock formations, conductivity measurements are used to evaluate moisture-content profiles during water ingress and, through the use of Boltzmann's transformation, it is shown that these profiles collapse onto a master-curve. Having obtained the master-curve during absorption, the capillary transport coefficient (Dθ) can then be obtained; however, the current work focuses on presenting the methodology as an alternative testing technique.

Miniature External Sapflow Gauges and the Heat Ratio Method for Quantifying Plant Water Loss.

External sapflow sensors are a useful tool in plant ecology and physiology for monitoring water movement within small stems or other small plant organs. These gauges make use of heat as a tracer of water movement through the stem and can be applied in both a laboratory and a field setting to generate data of relatively high temporal resolution. Typical outputs of these data include monitoring plant water use on a diurnal time scale or over a season (e.g., in response to increasing water deficit during drought) to gain insight into plant physiological strategies. This protocol describes how to construct the gauges, how best to install them and some expected data outputs.

Resource assessment based on 4D seismic and inversion at Ringhorne Field, Norwegian North Sea

Time-lapse (4D) seismic data from Ringhorne Field in the North Sea are used to monitor water movement in both Paleocene- and Jurassic-age reservoir sands, improve existing geologic and simulation models, and enable more cost-effective field operations. The structural complexity of the reservoirs, their proximity to the high-impedance Cretaceous chalk, and a relatively small 4D response has required a significant effort in seismic acquisition and processing which resulted in highly repeatable surveys (Johnston et al., 2010). In addition to the 4D interpretation, VP/VS derived from simultaneous elastic inversion is diagnostic of sand and provides additional constraints on Ringhorne subsurface models. Connected volumes based on VP/VS correlate to areas of water sweep seen in the 4D data and reduce uncertainty in 4D interpretation. Relative P-wave impedance changes calculated from inversion are consistent with presurvey 4D predictions. The 4D seismic data and inversion help explain water breakthrough timing, improve our understanding of field production history, and have resulted in the identification of additional infill well opportunities.

Influence of Machine Setting and Wood Parameters on Crack Formation in Scots Pine Joints Produced by Linear Friction Welding

Previous investigations on linear welded woods have shown that the connections are not sufficiently resistant to water for use in outdoor conditions. Therefore, they are utilized mainly for non-structural use, with only short time exposure to varying humidity. Influences of some welding and wood parameters such as welding pressure, welding time and heartwood or sapwood on crack formation in the weldline of Scots pine (Pinus sylvestris) were investigated. Axial samples measuring 200 mm × 20 mm × 20 mm from Scots pine were welded, placed vertically in 5-mm-deep tap water and were taken out of the water one at a time after each 10 min of water absorption. Then they were scanned and put back into water until the first crack appeared in the weldline. An X-ray Computer Tomography (CT-) scanner was used to monitor water movement and density change in the weldlines during water absorption–desorption. CT-scanning enabled to detect the cracks as they formed in the weldline and could be used in wood welding studies. Data evaluation showed that all the three studied parameters had significant effects on crack formation and that crack occurrence could be postponed by using heartwood samples with 1.3 MPa welding pressure and 1.5 s welding time.

Saturated Lightweight Aggregate for Internal Curing in Low w/c Mixtures: Monitoring Water Movement Using X‐ray Absorption

Abstract: The susceptibility for early‐age shrinkage cracking in low w/c concrete has led to the development of new technologies that can reduce the risk of cracking. Internal curing, one of these new technologies, uses saturated lightweight aggregate to supply ‘curing water’ to low w/c pastes as they hydrate. While significant research has been performed to determine the effects of internal curing on shrinkage and stress development, relatively little detailed information exists on movement of water from the LWA to the paste. The details of when water moves and how far it travels has implications on the volume of aggregate and the aggregate gradation that should be used in mixture proportioning with internal curing. This study examines the timing of the release of water from saturated lightweight aggregate (LWA) and the distance that water can travel. X‐ray absorption is used to determine the time at which water is drawn out of the lightweight aggregate and the loss of water is traced over time. Further, it examines the travel distance of the water into the paste. Experimental details associated with the X‐ray technique are provided to describe the importance of specimen alignment. Further, in sealed specimens, the results indicate little water movement prior to set. After set however, the distance of water movement was as much as 2 mm. The importance of water movement is discussed in terms of mixture proportioning and its influence on shrinkage and stress development.

Influence of Welding Parameters and Wood Properties on the Water Absorption in Scots Pine Joints Induced by Linear Welding

Wood welding is an environmentally-friendly and very quick technique to yield wood joints in just a few minutes and without using any adhesives. The only limitation of welded wood is that the joint is suitable only for interior use. Exterior use, or use in an environment with varying humidity requires water resistance of the welded joints. An investigation was performed to determine the effects of welding parameters and wood properties on water absorption in the weldline and how to reduce it through controlling the production parameters. The influences of welding pressure, welding time, and heartwood/sapwood on water absorption in the weldline of Scots pine (Pinus sylvestris) joints were investigated. Specimens composed of two pieces of heartwood or sapwood, each of dimensions 200 mm × 20 mm × 20 mm, were welded together to form specimens of dimensions 200 mm × 20 mm × 40 mm. The specimens were allowed to stand in 5-mm-deep tap water and then they were taken out of the water one at a time and scanned in 10-min intervals until the first crack appeared in the weldline. An X-ray Computerized Tomography scanner was employed to monitor water movement and density change in weldlines during water absorption–desorption. All three evaluated parameters showed significant effect on water absorption. Samples of heartwood welded by 1.3 MPa welding pressure and 1.5 s welding time showed the lowest water absorption.

Results of the World&s First 4D Microgravity Surveillance of a Waterflood-Prudhoe Bay, Alaska

Summary The world's first 4D surface-gravity surveillance of a1 waterflood has been implemented at Prudhoe Bay, Alaska. This monitoring technique is an essential component of the surveillance program for the Gas Cap Water Injection (GCWI) project. A major factor in the approval process for the waterflood was to show that we could monitor water movement economically where a very limited number of wells penetrated the waterflood area. The drilling of numerous surveillence wells to monitor water movement adequately would have been cost-prohibitive. Field surveys now show conclusively that density changes associated with water replacing gas are being detected readily with high-resolution surface-gravity measurements. The gravity methods used to monitor the water-flood include time-lapse (4D) measurement of surface gravity over the reservoir followed by inversion of the 4D signal for mass-balance calculation and flood-front detection. This paper will focus on field results of time-lapse surface-gravity surveys. Differences in the gravity field over time reflect changes in the reservoir-fluid density. The inversion procedure was formulated and coded to allow for various constraints on model parameters such as density, total mass, and moment of inertia. The gravity survey was designed to permit the inversion for reservoir mass distribution, with resolution on the order of hundreds of meters in the presence of uncorrelated noise of reasonable magnitude (12-μGal standard deviation). Time-differenced gravity-survey results clearly show an increase in surface gravity that is a result of the injected-water mass. Density-change maps deduced from measured gravity change show that water movement is reasonably similar to the reservoir simulations and to the water detected in observation wells. The overall ultimate gravity signal is predicted to increase to approximately 250 μGal, ultimately resulting in accurate maps of the water movement.

4D Microgravity Surveillance of a Waterflood - Prudhoe Bay, Alaska

This article, written by Technology Editor Dennis Denney, contains highlights of paper SPE 101762, "Results of the World's First 4D Microgravity Surveillance of a Waterflood - Prudhoe Bay, Alaska," by J.L. Brady, SPE, BP Exploration Alaska; J.L. Hare, Zonge Engineering; J.F. Ferguson, U. of Texas at Dallas; J.E. Seibert, Seibert & Assocs.; and F.J. Klopping, T. Chen, and T. Niebauer, Micro-g Lacoste, prepared for the 2006 SPE Annual Technical Conference and Exhibition, San Antonio, Texas, 24–27 September. A 4D surface-gravity surveillance of a waterflood was implemented at Prudhoe Bay, Alaska. This monitoring technique is essential for surveillance of the gas-cap water-injection (GCWI) project. Drilling numerous surveillance wells to monitor water movement adequately would have been cost-prohibitive. Field surveys showed conclusively that density changes associated with water replacing gas are readily detected by use of high-resolution surface-gravity measurements. Introduction The fundamental problem in monitoring the GCWI project is sparcity of monitoring wells and lack of producing wells in the gas-cap area of Prudhoe Bay. Distances between some monitoring wells are greater than 10,000 ft, and years would be required for the injected water to propagate these distances. Too few wells exist to monitor the water movement adequately with conventional downhole-logging techniques. Therefore, the Prudhoe Bay surveillance program uses a combination of conventional downhole logging in existing wells and 4D surface-gravity monitoring. The major monitoring concern with the waterflood is to ensure that water added in the gas cap does not prematurely flow downdip into the oil-producing portions of the field, where it could interfere with a highly efficient gravity-drainage mechanism. Surface-gravity instruments measure the Earth's gravitational field at a specific point, or station. With an array of these measurements, local structural traps, stratigraphic traps, or fluid movement can be identified if sufficient density contrast exists between the feature of interest and the surrounding rock. The surface-gravity technique can be applied to any field, depending on reservoir thickness, size, depth of burial, porosity, and density contrast between the fluids. The surface-gravity technique requires that several time-lapse gravity surveys be made over the life of the field. The first survey should be performed before any change occurs in the fluid volumes to obtain baseline data. The baseline survey can be subtracted from future gravity surveys to obtain the gravity anomaly associated with the change in fluid volumes. The technique assumes that any other time-dependent gravity changes can be accounted for by measurement or modeling, and that noise caused by the measurement process and unmodeled (near-surface) density changes has tolerable characteristics.

Estimation of axisymmetric spatial distributions of permeability and porosity from pressure-transient data acquired with in situ permanent sensors

Oil-producing companies have shown increased interest in instrumenting their hydrocarbon fields with in situ pressure sensors. As opposed to standard bottom-hole permanent pressure gauges, in situ pressure sensors are deployed behind casing to remain in direct hydraulic communication with rock formations. Prototype deployments have been tested in field operations that included intelligent completions. In situ pressure sensors allow the possibility of monitoring real-time dynamic variations of reservoir conditions due to primary or enhanced recovery. In consequence, a feedback loop can be enforced to modify the production scheme in a way that optimizes the recovery of existing hydrocarbon assets. While a great deal of laboratory and field work has been undertaken to advance hardware prototypes, relatively little has been done to quantify the spatial resolution and reliability of in situ permanent pressure data to detecting hydrocarbon reservoir properties. In this paper, we consider the inverse problem of simultaneously estimating spatial distributions of absolute permeability and porosity from transient measurements of pressure acquired with in situ permanent sensors. We pose the inverse problem as the minimization of a quadratic cost function that quantifies the misfit between the measured and numerically simulated data. A modified Gauss–Newton nonlinear optimization technique is used to minimize the quadratic cost function subject to physical constraints. We also make use of a dual-grid approach that alternates the use of coarse and fine finite difference grids to accelerate the inversion. Several examples of inversion are performed with noise-free and noisy synthetic measurements aimed at understanding the role played by the flow rate function and the location, spacing, and number of permanent sensors into the accuracy and stability of the inverted spatial distributions of permeability. Following these proof-of-concept exercises of applicability, the inversion algorithm is used for the simultaneous estimation of spatial distributions of permeability and porosity. Results indicate that in situ permanent pressure measurements exhibit significantly more sensitivity than bottom-hole pressure sensors to detecting spatial variations of permeability and porosity. However, because of their diffusive nature, the spatial resolution and distance of penetration of noisy in situ pressure measurements rapidly decreases with increasing distances from the sensor and flow rate pulse locations. Finally, the dual-grid inversion technique is utilized for the quantitative interpretation of time records of pressure acquired during an experimental field deployment of in situ permanent sensors. The field experiment was conducted to demonstrate the feasibility of electrical, pressure, and fiber optic measurement technologies to monitoring water movement between an injection and an observation well. Only transient wellbore pressure measurements acquired in the injection well were deemed consistent with the assumptions of the forward model used in this paper. The absence of in situ pressure data severely reduced the sensitivity of the measurements to spatial variations of permeability and porosity in the reservoir. In consequence, the estimated distributions of permeability and porosity reflected only large-scale effective medium properties of the formation of interest.

An Integrative Approach for Monitoring Water Movement in the Vadose Zone

Electrical resistivity tomography (ERT), during the past few years, has emerged as a potentially cost-effective, noninvasive tool for imaging changes of moisture content in the vadose zone. The accuracy of ERT surveys, however, has been the subject of debate because of its nonunique inverse solution and spatial variability in the constitutive relation between resistivity and moisture content. In this paper, an integrative inverse approach for ERT, based on a stochastic information fusion concept of Yeh and Simůnek, was developed to derive the best unbiased estimate of the moisture content distribution. Unlike classical ERT inversion approaches, this new approach assimilates prior information about the geological and moisture content structures in a given geological medium, as well as sparse point measurements of the moisture content, electrical resistivity, and electric potential. Using these types of data and considering the spatial variability of the resistivity–moisture content relation, the new approach directly estimates three-dimensional moisture content distributions instead of simply changes in moisture content in the vadose zone. Numerical experiments were conducted to investigate the effect of uncertainties in the prior information on the estimate. The effects of spatial variability in the constitutive relation were then examined on the interpretation of the change in moisture content, based on the change in electrical resistivity from the ERT survey. Finally, the ability of the integrative approach was tested by directly estimating moisture distributions in three-dimensional, heterogeneous vadose zones. Results show that the integrative approach can produce accurate estimates of the moisture content distributions and that incorporating some measurements of the moisture content is essential to improve the estimate.

An Integrative Approach for Monitoring Water Movement in the Vadose Zone

Electrical resistivity tomography (ERT), during the past few years, has emerged as a potentially cost‐effective, noninvasive tool for imaging changes of moisture content in the vadose zone. The accuracy of ERT surveys, however, has been the subject of debate because of its nonunique inverse solution and spatial variability in the constitutive relation between resistivity and moisture content. In this paper, an integrative inverse approach for ERT, based on a stochastic information fusion concept of Yeh and Šimůnek, was developed to derive the best unbiased estimate of the moisture content distribution. Unlike classical ERT inversion approaches, this new approach assimilates prior information about the geological and moisture content structures in a given geological medium, as well as sparse point measurements of the moisture content, electrical resistivity, and electric potential. Using these types of data and considering the spatial variability of the resistivity–moisture content relation, the new approach directly estimates three‐dimensional moisture content distributions instead of simply changes in moisture content in the vadose zone. Numerical experiments were conducted to investigate the effect of uncertainties in the prior information on the estimate. The effects of spatial variability in the constitutive relation were then examined on the interpretation of the change in moisture content, based on the change in electrical resistivity from the ERT survey. Finally, the ability of the integrative approach was tested by directly estimating moisture distributions in three‐dimensional, heterogeneous vadose zones. Results show that the integrative approach can produce accurate estimates of the moisture content distributions and that incorporating some measurements of the moisture content is essential to improve the estimate.

Interpreting INEEL Vadose Zone Water Movement on the Basis of Large‐Scale Field Tests and Long‐Term Vadose Zone Monitoring Results

A review of the results from two large‐scale field tests and vadose zone monitoring data at two facilities at the Idaho National Engineering and Environmental Laboratory (INEEL) has provided information to support development of a conceptual model of water movement in the highly heterogeneous vadose zone beneath two INEEL facilities. Both of the large‐scale field tests were ponded water infiltration tests that approached the size of the two facilities. An assembly of perched water wells, neutron access tubes, and tensiometers have been used to monitor water movement beneath these sites. Once water has percolated through the surficial sediment at these facilities, the presence of the surficial sediment–basalt interface results in some perching of the percolated water with limited lateral movement. Water movement in basalt formations is mainly gravity‐dominated in preferential fracture pathways and rubble zones and results in rapid vertical flow especially frequently under conditions of positive hydrostatic head. Detection of wetting front advance is typically not sequential with depth and has been shown to vary between episodic infiltration events. At the basalt–sediment interface of the interbeds, perched water is often detected and has resulted in more lateral spreading of recharge than at the surficial sediment–basalt interface. Gaps in the sedimentary interbeds will allow some of the recharge water to bypass the interbeds and rapidly continue toward the aquifer. This complex water movement in the vadose zone beneath the INEEL supports the need to control surface infiltration, identify gaps and the lateral continuity of the interbeds, and investigate the influence of nearby surface water sources on perched water movement beneath these two facilities.

Interpreting INEEL Vadose Zone Water Movement on the Basis of Large-Scale Field Tests and Long-Term Vadose Zone Monitoring Results

A review of the results from two large-scale field tests and vadose zone monitoring data at two facilities at the Idaho National Engineering and Environmental Laboratory (INEEL) has provided information to support development of a conceptual model of water movement in the highly heterogeneous vadose zone beneath two INEEL facilities. Both of the large-scale field tests were ponded water infiltration tests that approached the size of the two facilities. An assembly of perched water wells, neutron access tubes, and tensiometers have been used to monitor water movement beneath these sites. Once water has percolated through the surficial sediment at these facilities, the presence of the surficial sediment–basalt interface results in some perching of the percolated water with limited lateral movement. Water movement in basalt formations is mainly gravity-dominated in preferential fracture pathways and rubble zones and results in rapid vertical flow especially frequently under conditions of positive hydrostatic head. Detection of wetting front advance is typically not sequential with depth and has been shown to vary between episodic infiltration events. At the basalt–sediment interface of the interbeds, perched water is often detected and has resulted in more lateral spreading of recharge than at the surficial sediment–basalt interface. Gaps in the sedimentary interbeds will allow some of the recharge water to bypass the interbeds and rapidly continue toward the aquifer. This complex water movement in the vadose zone beneath the INEEL supports the need to control surface infiltration, identify gaps and the lateral continuity of the interbeds, and investigate the influence of nearby surface water sources on perched water movement beneath these two facilities.

Interpreting INEEL Vadose Zone Water Movement on the Basis of Large-Scale Field Tests and Long-Term Vadose Zone Monitoring Results

A review of the results from two large-scale field tests and vadose zone monitoring data at two facilities at the Idaho National Engineering and Environmental Laboratory (INEEL) has provided information to support development of a conceptual model of water movement in the highly heterogeneous vadose zone beneath two INEEL facilities. Both of the large-scale field tests were ponded water infiltration tests that approached the size of the two facilities. An assembly of perched water wells, neutron access tubes, and tensiometers have been used to monitor water movement beneath these sites. Once water has percolated through the surficial sediment at these facilities, the presence of the surficial sediment–basalt interface results in some perching of the percolated water with limited lateral movement. Water movement in basalt formations is mainly gravity-dominated in preferential fracture pathways and rubble zones and results in rapid vertical flow especially frequently under conditions of positive hydrostatic head. Detection of wetting front advance is typically not sequential with depth and has been shown to vary between episodic infiltration events. At the basalt–sediment interface of the interbeds, perched water is often detected and has resulted in more lateral spreading of recharge than at the surficial sediment–basalt interface. Gaps in the sedimentary interbeds will allow some of the recharge water to bypass the interbeds and rapidly continue toward the aquifer. This complex water movement in the vadose zone beneath the INEEL supports the need to control surface infiltration, identify gaps and the lateral continuity of the interbeds, and investigate the influence of nearby surface water sources on perched water movement beneath these two facilities.

An Application of Cemented Resistivity Arrays To Monitor Waterflooding of the Mansfield Sandstone, Indiana, U.S.A.

Summary In 1999, an oilfield experiment was initiated to test the application of electrical measurement technologies to permanent reservoir monitoring. The principal objective of the experiment was to demonstrate the feasibility of monitoring water movement between an injection and an observation well. This paper describes the interpretation of the data provided by the resistivity arrays and discusses the data quality and reliability of the measurements. Two wells were drilled into the Mansfield sandstone reservoir in Indiana, U.S.A. The D-8 injector well was located in the center of four development wells. The OB-1 monitoring well was offset 233 ft to the southwest in a location midway between the D-8 injector and the No. 3 production well. The injector was instrumented with a 16-electrode resistivity array that was run on the outside of insulated casing and cemented into the annulus of the well. A similar array was cemented into the annulus of the monitoring well. In March 1999, the D-8 well was perforated and acidized. A surface gauge was used to monitor injection rates and pressures. Initially, injection proceeded at a rate of approximately 20 B/D, increasing to 90 B/D after fracture stimulation. The D-8 array records responses to wellbore operations and injection. It clearly distinguishes the movement of the waterfront in different zones. The OB-1 electrical array clearly indicates early water breakthrough by means of an induced fracture. The data show good signal-to-noise ratio and high reciprocity. The experiment has demonstrated the viability of using permanently installed resistivity arrays to monitor the movement of oil/ water contacts and salinity fronts that are some tens of feet away from the wellbore. Results demonstrate the feasibility of using such arrays to monitor oil/water contact movements remote from injection, monitoring, and production wells.

Performance of Geocomposite Membrane as Pavement Moisture Barrier

With the advance in electromagnetic techniques, measuring and monitoring the moisture content in pavement systems appears feasible, and the contribution of geosynthetics to the drainage system can be verified. To investigate the performance of a geocomposite membrane (a lowmodulus polyvinyl chloride layer sandwiched between two nonwoven geotextiles), two sections at the Virginia Smart Road were instrumented and constructed to quantify the effectiveness of the geocomposite membrane as a moisture barrier and as a strain energy absorber. All layers were instrumented for stress and strain measurements as well as for environmental effects (temperature, frost, and moisture). The moisture variation in the subbase aggregate layer over different precipitations was continuously monitored by using time domain reflectometry (TDR). Ground penetrating radar (GPR) was used periodically to monitor water movement in the pavement sections. Results of the GPR surveys indicated that use of a geocomposite membrane underneath a drainage layer forms a water barrier, preventing the saturation of underlying layers and facilitating the lateral drain of water. Results of TDR moisture sensors validated the effectiveness of the geocomposite membrane in abating water infiltration into the subbase layer even in the event of heavy rain.

A three-compartment model of osmotic water exchange in the lung microvasculature.

A bolus injection of hypertonic NaCl into the pulmonary arterial circulation of an isolated perfused dog lung causes the osmotic movement of water first into, and then out of the capillary. The associated changes in blood constituent concentrations and density are referred to as the osmotic transient (OT). Measurement of the sound conduction velocity of effluent blood during an OT is a highly sensitive way to monitor water movement between the vascular and extravascular spaces. It was our objective to develop a mathematical model that adequately describes this transient change in the sound conduction velocity and evaluate its application under conditions of homogeneous and heterogeneous capillary flow distributions. The model accounts for osmotic water exchange between the capillary and two parallel extravascular compartments, and includes as parameters the osmotic conductances (sigmaK1 ,sigmaK2) of the two compartments. The osmotic conductance parameters incorporate the filtration coefficient for water and reflection coefficient for salt for the two pathways of water exchange. The partition of total extravascular lung water (EVLW) between the two extravascular compartments is a third parameter of the model. The homogeneous model parameter estimates (per gram wet lung weight +/-95% confidence limits) from the best-fit analysis of a typical curve were sigmaK1=2.15 +/-0.07, sigmaK2 = 0.03 + 0.00 [ml h(-1) (mosmol/liter)(-1) g(-1)] and V1 = 23.83+/-0.12 ml, with a coefficient of variation (CV) of 0.08. The heterogeneous parameter estimates for a capillary transit time distribution with mean transit time (MTTc) = 1.72 s, and relative dispersion (RDc) = 0.35 were KI = 2.38+/-0.05, or K2 = 0.03+/-0.00 [ml h(-1) (mosmol/liter)(-1) g(-1)], V1 = 23.91+/-0.08 ml, and CV=0.05. EVLW was 42.1 ml for both models. We conclude that the three-compartment mathematical model adequately describes a typical OT under both homogeneous and heterogeneous blood flow assumptions.

Absorption of valproic acid from the gastrointestinal tract of the piglet.

Valproic acid is a commonly used drug for the treatment of epilepsy. Since valproic acid can only be given orally, its absorption from the gastrointestinal (GI) tract especially in patients with short bowel syndrome (SBS) and in neonates is important. The specific sites of absorption for valproic acid in the small intestine and colon have not been investigated. It is currently unknown whether these patients are able to absorb oral valproic acid sufficiently to maintain a therapeutic serum concentration. The primary objectives of the study were to: (a) determine the relative absorption of valproic acid from specific sites in the GI tract; and (b) investigate the influence of intestinal development on valproic acid absorption using the newborn piglet as a model. Two groups were studied: Group I included 5 piglets 18-21 days of age, and Group II included 5 piglets 1-3 days of age. A valproic acid solution was simultaneously perfused through 5 partitioned segments of the gastrointestinal tract: the duodenum, jejunum, ileum, right colon and left colon. Tritiated [3H] polyethylene glycol was co-administered to monitor water movement across the GI mucosa. Following steady state, samples were collected from each segment, and analyzed by a specific enzyme-mediated immunoassay. The absorption rates (micrograms/min/cm) of valproic acid in Group I were as follows: 9.96 +/- 2.8 duodenum; 11.28 +/- 2.79, jejunum; 9.42 +/- 3.34, ileum; 10.88 +/- 3.35, right colon; 10.96 +/- 2.92, left colon.(ABSTRACT TRUNCATED AT 250 WORDS)