Fluid Sampling From Porous Rock to Determine Filtrate Contamination Profiles Around a Well Bore

Drilling fluid filtrate invades the pores of rock surrounding a well bore during drilling of the well, and contaminates the pore fluid originally within the rock pores. Models for the flow of contaminated pore fluid towards a sampling tool within the well bore are investigated, assuming that the filtrate has the same viscosity as the original pore fluid and that the wellbore radius is small compared to the depth of filtrate invasion. If the filtrate contamination in the fluid withdrawn from the rock is monitored as a function of the volume withdrawn, then it is shown that results can be inverted to give the radial distribution of filtrate around the well bore. A new generation of guarded sampling probes is then considered, and it is shown that the radial distribution of filtrate can be obtained by means of such a probe if the fraction of flow entering the central sampling region of the probe is small compared to that entering the concentric annular guard probe. The effects of dispersion, non-zero wellbore radius and anisotropic hydraulic permeability of the rock are also studied, and numerical simulations are used to give some indication of the effect of the ratio of the filtrate viscosity to that of the original pore fluid.     

Controlled-dispersion flow analysis : Flow-injection analysis applied to clinical chemistry

Mechanisation came early to clinical chemistry and has passed through a number of phases. Selective multichannel machines, usually discrete analysers with their associated mechanical complexities, have become popular; the simplicity and reliability of flow analysers has been lost. Flow injection offers new opportunities to develop simple selective machines. Sample waste is avoided in the controlled-dispersion flow analyser; the slug of sample is picked up by a probe, the volume being metered by the peristaltic pump driven by a stepping motor under computer control. Reagent waste is avoided by a similar system and use of merging zones. Very economical operation is thus possible and acceptable precision is attained. Various features of the technique, including prolonged incubation, use of kinetic methods to minimise the need for blanks, and application of different detectors are discussed in the context of clinical assays. Anomalous behaviour of particulate matter in flow streams and the changing shape of sample slugs in stationary streams are described. The application of flow-injection systems in clinical chemistry is extremely promising.     

Covering arrays of higher strength from permutation vectors

A covering array CA(N;t,k,v) is an N × k array such that every N × t sub‐array contains all t‐tuples from v symbols at least once, where t is the strength of the array. Covering arrays are used to generate software test suites to cover all t‐sets of component interactions. We introduce a combinatorial technique for their construction, focussing on covering arrays of strength 3 and 4. With a computer search, covering arrays with improved parameters have been found. © 2005 Wiley Periodicals, Inc. J Combin Designs 14: 202–213, 2006