Permeability values

Next, in the 2nd run the horizontal permeabilities of all 15 layers were estimated by using the value of 200 md as initial guess. It required 12 iterations to converge to the optimal permeability values. 

It was also attempted to estimate permeability values for eight zones but it was not successful. It was concluded that in order to extent the reservoir that can be identified from measurements one needs observation data over a longer history. Finally, in another run, it was shown that the porosities of layers 5 to 10 could be readily estimated within 10 iterations. However, it was not possible to estimate the porosity values for eight layers due to the same reason as the permeabilities. 

In practice when reservoir parameters such as porosities and permeabilities are estimated by matching reservoir model calculated values to field data, one has some prior information about the parameter values. For example, porosity and permeability values may be available from core data analysis and well test analysis. In addiction, the parameter values are known to be within certain bounds for a particular area. All this information can be incorporated in the estimation method of the simulator by introducing prior parameter distributions and by imposing constraints on the parameters (Tan and Kalogerakis, 1993). 

Fig. 4.1.8 Determined permeability distribution for the thin Bentheimer sample. The vertical axis represents the permeability value for the corresponding point.

These suggested factors for standardization of the Caco-2 model might also be reasons for the variability in published permeability values obtained from different laboratories [86]. Clearly, data from different publications or laboratories should not be mixed without prior harmonization of the experimental protocols. 

Compounds absorbed by active uptake mechanisms (e.g., glucose and Gly-Pro) and compounds known to be substrates for efflux transport (e.g., digoxin, verapamil) were also included in the list. The applied concentration (10-500 pM) only had minor effects on the permeability values. Thus, the choice of concentration was not critical for this set of compounds with respect to the relationship between permeability and fraction absorbed in humans. Changing the pH on the apical donor side had significant effects on the Papp values of several compounds, the effects being in agreement with the acid-base properties of the compounds. The... 

Fig. 7.7. Human in vivo permeability values (Peff) can be determined using a single-pass perfusion technique (Loc-I-Gut) in humans. These human Peff values correlated very well...

In order to avoid a lack of consistent literature-based data, the Caco-2 permeability values of our selected compounds were transformed according to the following scheme the majority of compounds with Papp < 4 x 10 6 cm s 1 were classified as poorly absorbed and assigned a score of —1 compounds with Papp > 8 x 10 6 cm s 1 were classified as well-absorbed and assigned a score of +1. Different assumptions were made in special cases, when the experimental protocols were different or no internal standard compounds were used. 

We have used these indicators to estimate permeability values for surface soils in Spokane County, WA. A general soil map of this county is shown in Figure 5. The spatial extent of two soil associations, the Naff-Larkin-Ereeman association (area 1) and the Garrison-Marble-Springdale association (area 2), are shaded in the figure, and detailed estimates of air permeability for these two association have been made, as described briefly below. More information is given in Nazaroff el al.r (1986). 

Radon concentrations were determined using an RM-2 portable soil radon monitoring system while in situ soil permeability values were determined using Radon-JOK portable sampling equipment. 

Similar reductions in permeability were found for C02 and N2. Apparently this treatment method creates a universal gas barrier and is seemingly universal for polymers with a high hydrocarbon content. It is anticipated that by optimizing this approach, 02 permeability values for PE of less than 50 cm7m2 per 24 h will be achieved. 

In Figs 11.4 and 11.5, permeability is shown as a percentage of a predefined permeability value. 

FIGURE 3.11 Range of hydraulic conductivity and permeability values. (After Freeze and Cherry, 1979.)... 

H D-glucose Actively transported via the Na+/D-glucose co-transporter Steady-state permeability values for D-glucose indicate that active transport processes are operational (typically at concentration >100 mM). At low concentrations (e.g. 1 mM), absorption is assumed to be ABL controlled and hence at these concentration can serve as marker for resistance of the ABL... 

Antipyrine Passively transported compound Steady-state permeability values for antipyrine indicate that passive transport processes are operational. Stable transmucosal transport of antipyrine during the experiment indicates that the mesenteric blood flow is stable [33, 60]... 

Wohnsland and Faller ([175] performed measurements using a thin (9-10 //in) supported, phospholipid-free hexadecane layer. To validate their model, they used 32 well-characterized chemically diverse compounds. The permeability values obtained with their model could be correlated with known human absorption values if the maximum permeability obtained at different pH was taken into account. However, several disadvantages are related to this method. For hydrophilic drugs, hexadecane by itself has an increased barrier function in comparison with membranes. In addition, the hexadecane layers are not very stable, which makes this assay difficult to apply as a routine screening method. The advantage of this PAMPA setup is that it appears to be a satisfactory substitute for obtaining alkane-water partition coefficients, which are usually very difficult to measure directly, due to the poor solubility of drug molecules in alkanes. 

The more viable the segment is the better is the quality of the results. Based on the tissue viability data, extremes in permeability values can be discarded from the data set, resulting in better and more reliable results and a better overall understanding of drug transport [108],... 

In a limited independent evaluation of GastroPlus , Hendriksen et al. [22] used literature data on solubility together with calculated human permeability values to predict the human Fabs for 21 drugs for which observed human FabS... 

---