Fluid samples

The collection of representative reservoir fluid samples is important in order to establish the PVT properties - phase envelope, bubble point, Rg, B, and the physical properties - composition, density, viscosity. These values are used to determine the initial volumes of fluid in place in stock tank volumes, the flow properties of the fluid both in the reservoir and through the surface facilities, and to identify any components which may require special treatment, such as sulphur compounds. 

Reservoir fluid sampling is usually done early in the field life in order to use the results in the evaluation of the field and in the process facilities design. Once the field has been produced and the reservoir pressure changes, the fluid properties will change as described in the previous section. Early sampling is therefore an opportunity to collect unaltered fluid samples. 

Fluid samples may be collected downhole at near-reservoir conditions, or at surface. Subsurface samples are more expensive to collect, since they require downhole sampling tools, but are more likely to capture a representative sample, since they are targeted at collecting a single phase fluid. A surface sample is inevitably a two phase sample which requires recombining to recreate the reservoir fluid. Both sampling techniques face the same problem of trying to capture a representative sample (i.e. the correct proportion of gas to oil) when the pressure falls below the bubble point. 

Keywords d rec methods, indirect methods, rock properties, coring, core barrel, standard core analysis, special core analysis, slabbed core, sidewall samples, direct indications, microfossils, sonde, logging unit, invasion, mudcake, formation pressure measurement, fluid sampling, measurement while drilling, formation evaluation while drilling. 

A common objective of a data gathering programme is the acquisition of fluid samples. The detailed composition of oil, gas and water is to some degree reguired by almost every discipline involved in field development and production. 

The pressure measurment and fluid sampling procedures can be repealed at multiple depths in the reservoir. 

In exploration wells which show hydrocarbon indications, it is often required to test the productivity of the well, and to capture a fluid sample. This can be used as proof of whether further exploration and appraisal is justified. If the well is unlikely to be used as... 

Fluid samples will be taken using downhole sample bombs or the MDT tool in selected development wells to confirm the PVT properties assumed in the development plan, and to check for areal and vertical variations in the reservoir. In long hydrocarbon columns (say 1000 ft) it is common to observe vertical variation of fluid properties due to gravity segregation. 

The radius R also applies to the entire fluid sample. Since torque equals the product of force and R, canceling out one power of R leaves the shearing force acting on the fluid on the left-hand side of Eq. (2.7). 

Cone—Plate Viscometer. In a cone—plate viscometer (Fig. 28), alow angle (<3°) cone rotates against a flat plate with the fluid sample between them. The cone—plate instmment is a simple, straightforward device that is easy to use and extremely easy to clean. It is well suited to routine work because measurements are rapid and no tedious calculations are necessary. With careful caUbration and good temperature control it can also be used for research. Heated instmments can be used for melt viscosity measurements. 

An on-line supercritical fluid chromatography-capillary gas chromatography (SFC-GC) technique has been demonstrated for the direct transfer of SFC fractions from a packed column SFC system to a GC system. This technique has been applied in the analysis of industrial samples such as aviation fuel (24). This type of coupled technique is sometimes more advantageous than the traditional LC-GC coupled technique since SFC is compatible with GC, because most supercritical fluids decompress into gases at GC conditions and are not detected by flame-ionization detection. The use of solvent evaporation techniques are not necessary. SFC, in the same way as LC, can be used to preseparate a sample into classes of compounds where the individual components can then be analyzed and quantified by GC. The supercritical fluid sample effluent is decompressed through a restrictor directly into a capillary GC injection port. In addition, this technique allows selective or multi-step heart-cutting of various sample peaks as they elute from the supercritical fluid... 

An Alka-Seltzer tablet gives off carbon dioxide when dissolved in aqueous solution. The gas is used to drive hydrogen sulfide out of drilling fluid samples. The H S then reacts with lead acetate paper in the bottle cap. The degree of discoloration is related to hydrogen sulfide concentrations. 

Figure 1.2 High-fleld (aliphatic) region of 500 MHz H Hahn spin-echo NMR spectra of (a) a typical inflammatory synovial fluid sample (b) as (a) but following 7-radiolysis (5.00 kGy). Typical spectra are shown. A, acetate-CHs ...

Further resonances attributable to the CFI3 groups of ketone bodies, predominantly 3-D-hydroxybutyrate, were also found in all synovial fluid samples studied. These data indicate an elevated utilization of frits for energy, despite the overall hypoxic environment of the synovial tissue (Merry et al., 1991 Henderson etal., 1993). 

In inflammatory conditions, activated PMNs may pro-teolytically (by release of lysosomal enzymes) and oxidatively (by release of HOCl) inactivate ai-antitrypsin. Studies of synovial fluid samples from patients with RA showed that a i-antitrypsin was both cleaved and oxidized, resulting in inactivation (Chidwick et al., 1991, 1994). Free-radical attack on ai-antitrypsin and its subsequent inactivation may contribute to the destruction of joint tissues in arthritis due to the imbalance between elastase and its inhibitors. 

An adaptive association of Flehmen with fluid-sampling is shown where related modifications to the stimulus-access system, such as anatomical and behavioural anomalies, appear. The F. sequence is inconspicuous and ducts reduced in two African Alcephaline antelopes the Topi (Damaliscus iunatus) and Coke s Hartebeest (Alcephalus... 

In situ NMR measurements can be made in conjunction with down-hole fluid sampling [5, 6]. The NMR relaxation time and diffusivity can be measured under high-temperature, high-pressure reservoir conditions without loss of dissolved gases due to pressure depletion. In cases when the fluids may be contaminated by invasion of the filtrate from oil-based drilling fluids, the NMR analysis can determine when the fluid composition is approaching that of the formation [5, 6]. 

Fig. 3.7.1 Schematic of the DDIF effect in porous medium. The black areas are solid grains and the white areas are pore space. Diffusing spins in permeating fluid sample the locally variable magnetic field B(r) (solid contours sketched inside pore space) as it diffuses.

Freifield B., Trautz R., et al. The U-tube a novel system for acquiring borehole fluid samples from a deep geologic C02 sequestration experiment. 2005 Journal of Geophysics Reservoir 110 B10203. 

Other even more cunning methods have been devised to suppress the water signal in samples that have a large water content (e.g., bio-fluid samples) such as the WET and the WATERGATE pulse sequences. Other sequences have been devised to cope with signals from carbon-bound hydrogens. Some of these actually collapse the 13C satellites into the main 12C peak prior to suppression. Such a sequence would be useful if you were forced to acquire a spectrum in a nondeuterated solvent. 

Carbon dioxide is another clinically important analyte, but also of highest interest in marine sciences and in context with the greenhouse effect. While sensable , in principle, by IR absorptiometry, this is difficult in case of fluid samples. An indicator-based fiber optic device for CO2 was described... 

As most sensors are limited to single point probing, their application is confined to samples where the investigated point(s) are representative for the sample. Though this is the case for the majority of fluid samples, solid objects may not fulfil this requirement. This is true for high-tech products containing a wide range of different materials as well as e.g. in the food industry, where an item that is analysed as edible at one spot may very well be rotten at a different one. 

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