Subsurface sample

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. 

Figure 5.25 Subsurface sampling apparatus (after Dake, 1978)...

Sampling saturated reservoirs with this technique requires special care to attempt to obtain a representative sample, and in any case when the flowing bottom hole pressure is lower than the bubble point, the validity of the sample remains doubtful. Multiple subsurface samples are usually taken by running sample bombs in tandem or performing repeat runs. The samples are checked for consistency by measuring their bubble point pressure at surface temperature. Samples whose bubble point lie within 2% of each other may be sent to the laboratory for PVT analysis. 

Biodegradation t, 2(aerobic) = 336-672 h, based on unacclimated grab samples of aerobic soil and a subsurface sample t,( anaerobic) = 1344-2688 h, based on estimated unacclimated aqueous aerobic biodegradation half-life (Howard et al. 1991) ... 

Wade and Quinn [12] measured the hydrocarbon content of sea surface and subsurface samples. Hydrocarbons were extracted from the samples and analysed by thin-layer and gas-liquid chromatography. The hydrocarbon content of the surface micro layer samples ranged from 14 to 599 pg/1 with an average of 155 pg/1, and the concentration in the subsurface samples ranged from 13 to 239 pg/1 and averaged 73 pg/1. Several isolated hydrocarbon fractions were analysed by infrared spectrometry and each fraction was found to contain a minimum of 95% hydrocarbon material, including both alkenes and aromatics. 

Deeley, G.M., Reinhard, M., and Stearns, S.M. Transformation and sorption of l,2-dibromo-2-chloropropane in subsurface samples collected at Fresno, California, J. Environ. Qual, 20(3) 547-556, 1991. 

NOTE Stratum indicates subsurface sampling under the unit... 

PLATE D-3 Sampling strata G, H, I, J, K, L, M—areas outside the munitions demilitarization building. Note Stratum indicates subsurface sampling under the unit. 

Stanton, M. 1973. The role of weathering in trace metal distributions in subsurface samples from the Mayday Mine Dump near Silverton, Colorado. In Church, S. E. (ed) The USGS Preliminary Release of Scientific Reports on the Acidic Drainage in the Animas River watershed San Juan County, Colorado, US Geological Survey, Denver, CO, USA, 77-85. 

Diazinon has been identified in top soil samples (<3 inches deep), subsurface samples (>3 inches deep), soil samples with unspecified depth, and in sediment samples collected at 4, 2, 4, and 4 current or former NPL hazardous waste sites, respectively, where diazinon was detected in some environmental media (HazDat 1996). 

Samples can be obtained in two ways. In one method the well is shut in, and the liquid at the bottom of the wellbore is sampled. This is called a bottom-hole sample or a subsurface sample. 

We use sampling grids mainly for surface soil sampling, however, it is not unusual to place soil borings and collect subsurface samples on a grid pattern. Grids are also used for soil sampling from the bottom and sidewalls of excavation pits and trenches. 

The obvious source of comet samples is by direct collection at a comet with Earth return. Stardust, the first comet sample mission (Brownlee et al., 2000), will collect the positively identified particulate samples from a comet and return them to Earth. Stardust, a NASA Discovery mission, will collect thousands of particles from the coma of SP comet Wild 2 and return them in 2006. Hopefully future sample return missions will, in addition, recover subsurface samples of ice and dust and return them to Earth with cryogenic preservation. 

Using values of apb ranging between 18.6 (value calculated for T = 0°C) and 17.7 (value calculated for T = -2°C) the calculated free ionic Pb concentration ranged from 0.3 to 4.1 pM the minimum values (0.3. 7 pM) were calculated for subsurface samples (10 50 m) collected after 26 December, while the higher values (1.1-4.1 pM) were calculated for samples collected earlier or at greater depths. Considering the uncertainty which may affect evaluation of the ionic concentration, one can conclude that during the summer variations are detectable only for surface layers. 

Major Components—Five phosphogypsum-subsurface samples were obtained from cores by drilling through approximately the bottom 3 m of the phosphogypsum stacks and the tup 3 m of the underlying subsurface soils. Chemical analyses were used to identify the nature of the sample.s and confirm that subsurface levels had been reached. The results of chemical analyses for the major components of the five samples are given in Table 3. fhe approximate mineral compositions of the samples are shown in Table 4. The approximate mineral... 

Minor Components—Tabic 5 gives the concentrations of minor components in the phosphogypsum and in the subsurface samples. Only potassium and chromium had greater concentrations in the subsurface material than in the phosphogypsum, possibly indicating that they were leached from the phosphogypsum. 

The subsurface sample also contained 7.9% carbon dioxide, equivalent to 25% limestone (CaCOd- ... 

TABLE 6—Trace element concentrations in subsurface samples, phosphate rock, and clay. 

Trace Element In Subsurface Samples, In Phosphate Rock In Clay ... 

The same type of comparative projections can be made for the trace elements contained in the clay fraction. The amount of clay present is not as easily or as accurately determined as the phosphate rock. It can be estimated from the iron, magnesium, potassium, silicon, and sodium present, remembering that much of the silicon exists as sand (silicate) and must be excluded from the estimate. The clay fraction was estimated by dividing the concentrations (on a dry basis) of aluminum, iron, magnesium, potassium, and sodium (Tables 3 and 5) by the concentrations of each of these elements in normally occurring clay (Table 6). This produced an average value of 16% clay in the subsurface samples. 

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