Bottom-hole samples

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. 

An oil reservoir must be sampled before reservoir pressure drops below the bubble-point pressure of the reservoir liquid. At reservoir pressures below the bubble point, no sampling method will give a sample representative of the original reservoir mixture. Bottom-hole samples generally will contain less gas than the original liquid since some gas has evolved. Separator samples will be recombined at the wrong ratio because free gas is produced from the reservoir with the reservoir liquid. 

Analysed gases and oils are bottom-hole samples unless otherwise indicated in the text or figures. Bottom-hole samples (BHS) and cores generally predate enhanced oil recovery activity (1979-1984), thus represent original field conditions. Exceptions include multiple dynamic formation test (MDT) oils, repeat formation tester (RFT) oils, sidewall cores (SWC), or separator oil samples from recent wells usually at the periphery of the field. 

The field test consisted of injecting Pusher 700 into a well at four different rates and back producing the polymer fluid. Laboratory measurements were made on location to determine polymer quality. These measurements were made in an oxygen-free environment in order to minimize chemical degradation of the polymer. Both surface and bottom hole sampling techniques were employed. 

Bottom-hole samples were obtained using the Wofford subsurface sampler... 

Table 1 summarizes the results of the field sample analyses standardized for polymer concentration. The quality of the field injection sampled collected both at the well and bottom compared closely to that of a laboratory weighed and dried polymer standard prepared in the field using normal laboratory procedures. This 300 mg/l polymer solution had a measured screen factor of 12. 9 and a viscosity, measured at 115 seconds" shear rate, of 3. 93 cp. Laboratory derived correlations showed that this standard corresponded to a mobility reduction effect, expressed in terms of a resistance factor, of 32. The close comparison between this unsheared standard and field injection samples implied that neither the surface nor bottom hole sampling induced any shear degradation. 

Sixty-eight field samples were transported to the production research laboratory for analysis. Of these, 18 were bottom-hole samples for core displacement experiments. Each sample was opened in a nitrogen tent for solution viscosity and screen factor... 

Surface and bottom hole sampling techniques did not cause shear degradation. 

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. 

This paper deals with the control of weld depth penetration for cylinders in gold-nickel alloy and tantalum. After introducing the experimental set-up and the samples description, the study and the optimization of the testing are presented for single-sided measurements either in a pulse-echo configuration or when the pump and the probe laser beams are shifted (influence of a thermal phenomenon), and for different kind of laser impact (a line or a circular spot). First, the ultrasonic system is used to detect and to size a flat bottom hole in an aluminium plate. Indeed, when the width of the hole is reduced, its shape is nearly similar to the one of a slot. Then, the optimization is accomplished for... 

The col was filled with a bottom hole crude sample and immersed in a thermostatted bath. After one hour at 46°C, the temperature of the bath was gradually decreased at 1.5°C/hr to 4°C and maintained at this temperature for two weeks. After the test period, flow was obtained by applying 0.04 bar (equivalent to 30 psi In field with 5" flowline), indicating that cold start-up would not be a problem ir the field. 

Determination of r and /3. Samples of reservoir oil for analysis are obtained either by recombining surface samples of oil and gas in the proper proportions or by obtaining a sample under reservoir conditions by means of a bottom hole sampler. 

But three facts suggest that Edwards brines today should contain less dissolved silica than when they initially formed (1) the most saline brines we sampled are only saturated with halite, and thus have probably been diluted since they formed (2) cooling to 160°C, the present bottom-hole temperature of the wells, may have caused precipitation of about half the original silica in the deep aquifer and (3) the solubility of silica in near-halite-saturated brines may be lowered significantly because of the reduced activity of water. Clearly the SiO2 values obtained today do not preclude quartz-saturation at the time the brine originally formed. 

Water samples were obtained through downhole sampling (RFT, MDT, bottom hole samplers), well testing (DST, production tests) and actual production. The sampling density for most water samples was one per well with most of these samples obtained from the water-leg. 

There are several gas-well fields that produce hydrocarbon gas associated with very high TDS connate waters. Classical oilfield scale problems (e.g., calcium carbonate, barium sulfate, and calcium sulfate) are minimal in these fields. Halite (NaCl), however, can be precipitated to such an extent that production is lost in hours. As a result, a bottom-hole fluid sample is retrieved from all new wells. Unstable components are "fixed" immediately after sampling, and pH is determined under pressure. A full ionic and physical analysis is also carried out in the laboratory. 

Note All sample except Wellhead were taken with a wireline bottom hole sampler. 

Figure B2.1.7 Transient hole-burned speetra obtained at room temperature with a tetrapyrrole-eontaining light-harvesting protein subunit, the a subunit of C-phyeoeyanin. Top fluoreseenee and absorption speetra of the sample superimposed with die speetnuu of the 80 fs pump pulses used in the experiment, whieh were obtained from an amplified CPM dye laser operating at 620 mn. Bottom absorption-diflferenee speetra obtained at a series of probe time delays.

Another variant (the cone spray) allows the sample solution to flow down the sides of an inverted cone and through a hole at the bottom of which flows a fast stream of argon gas. As the liquid film meets the gas, it is ripped apart into a finely dispersed aerosol (Figure 19.15). 

In cases where wells have a screened or open-hole interval partially submerged below the water table and a pump is going to be used for both purging and sampling, the pump should be placed at the midpoint between the top of the water table and the bottom of the screen. If different equipment is going to be used for purging and sampling of the well, the pump should be placed at the top of the water column. ... 

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