Simplified Gas Porosimeter

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Described is a simple glass apparatus for rapidly obtaining gas porosities of porous rocks. The method consists of fast volume measurements of samples at atmospheric and lower pressures. This method applies basically the same principle as Boyle's law, P1V1 = P2V2, however, volume measurements are obtained at atmospheric pressure and lower in one simple operation. The apparatus is easily built from readily available glass components. A diagram of the glass porosimeter is shown in Fig. 1. The porosimeter has five basic components: two 500-cc glass burettes, a glass sample holder, a three-way glass valve, a 1/4-in. glass tube next to a meter stick and a 500-cc glass leveling bulb containing about 200 cc of mercury. The sample holder can be designed to contain samples of any dimensions; in this case, cores of 1 in. diameter X 3.0 in. long are used. The samples initially were placed in a perforated plastic holder that reduced direct handling of the samples and easily allowed their insertion in and removal from the glass sample holder. A relationship was obtained between the volume drop in cc of Hg and the height drop in cm for the right-hand burette. The value of this slope m is shown in Table 1. The method consists of measuring a new gas volume at a pressure below atmospheric. Briefly, the operational procedure consists of two steps for obtaining the grain volume measurements and a third step for obtaining the bulk volume.The sample is placed inside the glass sample holder with the lid firmly secured (Fig. 1). Initially, the leveling bulb is brought to Position 1 where the mercury level is adjusted to the zero mark on the right burette.The valve to the atmosphere is closed and the leveling bulb is lowered a distance L equal to the room pressure in cm of Hg (read on the meter stick). The new mercury level on the right burette is obtained directly and corresponds to the increase in gas volume in cc at the lower pressure p2. The bulk volume of the sample can be measured from the following step.The leveling bulb is adjusted to Position 3 and the valve to the atmosphere is opened gradually, allowing the mercury to rise slowly and submerge the sample up to the reference mark. The three-way valve is turned slowly to the position connecting the left burette to the right burette. Mercury is drained from the sample holder until the level reaches the zero mark on the right burette. The volume on the left burette v, is obtained directly. Caution must be exercised to prevent any air bubbles from being trapped in the system. All samples are dried TABLE 1-DESCRIPTION AND OPERATIONOF POROSIMETER Calibration Data of Porosimeter Volume of sample holder 79.6 cc Volume of plastic holder 2.6 cc Net volume of sample holder:For grain volume measurements 77.0 ccFor bulk volume measurements 76.2 cc Average value of slope m in cm of Hg per cc of Hg drop1.137 + 0002 Sample Measurements and Calculations True volume of aluminum rod = 36.63 cc Volume increase at p2, = 35.5 cc Atmospheric pressure p1 = 75.88 cm Hg Grain volume of rod = 77.0 P. 335ˆ