Fault population

Fault seal prediction in hydrocarbon reservoirs requires an understanding of fault seal mechanisms, fault rock petrophysical properties, the spatial distribution of seals, and seal stability. The properties and evolution of seals within fault zones can be evaluated using the combined results of structural core logging, microstmctural and physical property characterisation, together with information on fault populations from seismic and outcrop studies and well test data. 

Fig. 6b illustrates the type of simple interpretation of the fault structure often used as a basis of fault seal analysis. This interpretation is based on representation of the fault as a single fault plane, where the offset is assumed to be equal to the seismic (cumulative) offset. This is clearly not valid as a representation of throw distributions for use in fault seal analysis. Fig. 6 also illustrates that sub-seismic fault populations can be clustered around larger faults with extensive areas of low fault densities away from the large faults. This has important implications for the spatial distribution of sub-seismic faults and emphasises that uniform distributions of small faults are not always applicable (except perhaps in areas where more uniform straining is associated with doming). The information contained in Fig. 6 reinforces the results of other recent studies which have noted different fault... 

Despite the common assumption of fault sealing in hydrocarbon fields, very few faults have been characterised in the detail needed which allows identification of the sealing mechanism or controls. Without the construction of a robust set of case histories from such analysis, future seal evaluation will remain a high risk venture. These case histories are also needed to integrate seal behaviour with pressure test, production and in situ stress analysis. The paper has highlighted the importance of an integrated approach from micro to macro and stressed the value of core-based studies to quantify fault rock properties, sub-seismic fault populations and sealing mechanisms. 

Knipe, R.J. and McAllister, E. 1996. Fault population analysis identification of fractal characteristics for scaling. J. Struct. Geol., submitted. 

Yielding, G., Needham, T. and Jones, H. 1996. Sampling of fault populations using sub-surface data a review. J. Struct. Geol., 18 135-146. 

Roberts, A.M., Yielding, G., Kusznir, N.J., Walker, I. and Dom-Lopez, D. 1993. Mesozoic extension in the North Sea constraints from flexural backstripping, forward modelling and fault populations. In J.R. Parker (Editor), Petroleum Geology of Northwest Europe Proc. 4th Conf., Geol. Soc. London, pp. 1123-1136. 

Andiesen, A., Steen, 0. and Hartz, E. 1994. Fault populations and fault distributions in rotated fault blocks, Traill 0, East Greenland. In Olsen et al. (Editors), Profit Project Summary Reports, Reservoir Characterization, Near Well Flow, pp. 43-59. 

The risk of leakage, through a fault-connected network of leaky beds (Fig. 2), can be quantified from the number of relatively thick shale beds in the seal and the statistics of the fault population in the trap area, derived from 3-D seismic. In order to model fault-assisted top seal leakage, a basic configuration of identical shale layers of similar thickness, separated by very thin, laterally continuous, leaky beds (siltstones, sandstones), in which a number of... 

Fig. 7. Fault assisted top seal leakage, (a) Probability of top seal leakage. Analytical solution for shale beds of constant thickness /, in which identical faults of maximum throw are randomly dispersed. This relationship for probability of seal leakage also holds approximately for seals in which the shale layers and fault throws are each normally distributed about the same mean t. (b) Determination of the throw-cumulative frequency relationship. Faults in a volume of rock, from a map-based statistical analysis of the fault population. Adding 1 to the slope C2 simulates the addition of the third dimension (Gauthier and Lake, 1993). Here a length/Tfnjx fst o 100 1 was used, (c) Determination of the seal risk. Comparing the number of faults required for leakage with the number of faults in the trap volume determines the seal risk. In the example shown, the probability that the seal is breached lies between 50 and 90%, For points in the sealed field, the effect of increasing fault throw on the number of faults needed for breaching is illustrated.

Dyson s model has been the subject of careful criticism as well as well-meaning agreement. Shneior Lifson (1997) found fault in particular with Dyson s assumption that metabolism (and other properties) could have developed without natural selection. In his third assumption, Dyson postulates that There is no Darwinian selection. Evolution of a molecule population occurs via genetic drift (Dyson, 1999). Lifson (1997) points out that, while Dyson stresses the role of primitive metabolism, its adaptability, error tolerance etc., he himself considers that such properties can only evolve via natural selection. 

Some parts of the bakery industry are in a different situation to others regarding nutritional pressure. The parts of the industry that make bread are largely in the clear. The composition of bread is controlled anyway and bread in moderation is regarded as a healthy staple food. There are those who claim that the general population would be healthier if they ate wholemeal rather than white bread. Well, the industry makes wholemeal bread and the customers are free to buy it. If they choose not to it has to be their fault. The only nutritional pressure regarding the composition of bread has been over the amount of salt added, which the industry has agreed to lower. 

Student s t test statistics and t probability were calculated to quantify the contrast between anomalous and background populations in each extraction method data set (Student 1908 Stanley Noble 2008). Sample sites were designated anomalous based on the projection of mineralization and a fault zone in the cover rocks. For most methods, Zn... 

The adsorption microcalorimetry has been also used to measure the heats of adsorption of ammonia and pyridine at 150°C on zeolites with variable offretite-erionite character [241]. The offretite sample (Si/Al = 3.9) exhibited only one population of sites with adsorption heats of NH3 near 155 kJ/mol. The presence of erionite domains in the crystals provoked the appearance of different acid site strengths and densities, as well as the presence of very strong acid sites attributed to the presence of extra-framework Al. In contrast, when the same adsorption experiments were repeated using pyridine, only crystals free from stacking faults, such as H-offretite, adsorbed this probe molecule. The presence of erionite domains in offretite drastically reduced pyridine adsorption. In crystals with erionite character, pyridine uptake could not be measured. Thus, it appears that chemisorption experiments with pyridine could serve as a diagnostic tool to quickly prove the existence of stacking faults in offretite-type crystals [241]. 

The data were analyzed to determine the feasibility for use in this patient population. The number and percentage of successful and unsuccessful (faults) tests were summarized for each participant. Pupillary data from days when there was no evidence of other recent drug use (urine... 

Not very long after the discovery of the deficiency of isoniazid acetylation, it turned out that the frequency of this phenotypic fault also differed much between the world s populations (47). Today, the reason for this particular interethnic variability is still unknown an influence of geographical latitude and climate is suspected. Such scientific uncertainty is common in this field of research, and it contrasts with the clear-cut findings relating malaria resistance and G-6-PD deficiency (see below). 

Increasing use of hazardous lands (coastal zones, fault zones, flood plains, unstable slopes, fire-prone areas, etc.) in response to both population pressure and demographic preferences. 

All of these materials seem to be equally intolerant of point-defect populations as those described earlier, and others could readily be cited. Thus the conclusion to be drawn from this Section is that phases which accommodate changes in anion to cation stoicheiometry by way of planar fault or intergrowth behaviour comprise a substantial number of inorganic materials, and such phases are in no way the poor relations of defect chemistry compared to systems which are point-defect biased. 

We can finally conclude that the number of chemical systems which appear to reject point-defect populations as a mode of accommodating their non-stoicheiometric behaviour is large and varied and here we have touched upon only a few which make use of planar faults or parallel lamellar or foliar intergrowth structures. The results presented show that physical terms, such as elastic strain, are of importance in controlling the microstructures of such phases, but whether they form or whether they coexist with some form of point-defect clusters may well depend in a sensitive way to the anion-cation bonding within the individual co-ordination polyhedra which made up the structure. The continuing research in this area is certain to produce new and unexpected results before complete answers to the problems posed here are found. 

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