Transcription of Porosity Measurement - New Mexico Institute of …
1 Porosity MeasurementpVgVbV Measurement of any two of the three volumes allows for the determination of porosityPorosity MeasurementBulk Volume a. linear measurements 10 cm4 cmh2rbV Porosity MeasurementBulk Volume b. displacement method -fluid displaced by sample measured volumetrically or gravimetrically Prevent fluid penetration into pore space by: the rock with paraffin the rock with the fluid into which it is immersed mercury Gravimetric methods observe the loss in weight of the sample when immersed in a fluid, or observe the change in weight of a pycnometerfilled with mercury and filled with Hg and sample. Volumetric methods measure the change in volume when the sample is MeasurementBulk Volume Example displacement methodWeight dryWdry= 20 gmsWeight saturatedWsat= gmsWeight of saturated sample immersed in waterWwet= gmsWeight of water displacedWwtr= Wsat-Wwet= gmsBulk volumeVb= Wwtr/rwtr= ccPorosity MeasurementGrain Volume a.
2 Direct methods i. Dry weight of sample/density of matrix = Vg ii. Destructive methods (Melcher-Nuttingor Russell) -requires sample to be crushed -Vg determined gravimetrically by principle of bouyancy. -not very accurate! b. Gas Expansion methods Boyle s Law porosimeter non-destructive, reasonably accurate Porosity MeasurementBoyle s porosimeter The total moles of gas is constant, thus 21nntn Substituting the ideal gas equation, RTVpRTVpRTfVfp2211 Isothermal conditions prevail, 2211 VpVpfVfp Substituting for the volumes, 22)1(1)21(VpgVVpgVVVfp Rearranging results in an expression for grain volume 1)2(2)1(1pfppfpVpfpVgV ( ) where V1 and V2 are the calibrated chamber volumes. Porosity MeasurementBoyle s porosimeter-exampleV1= 100 ccV2= 80 ccP1= 0 kPaP2= kPaV1= 100 ccV2= 80 ccPf= ) (80) (100ccgV Porosity MeasurementPore Volume Injection methods destructive (contamination of sample) not very accurate Washbum-Bunting, Kobe, Mercury porosimeters(obsolete) Saturation method (See example) non-destructive not suitable for water sensitive rocks, unless use oil very accurate Porosity MeasurementPore Volume 3.
3 Summation of fluids method (Retort method) oil and water volumes calculated by retorting sample up to 1200 F. vapors condense, collected, and measured empirical correlation for coking and cracking of oil Bulk volume and gas volume obtained from adjacent core sample using Hg PUMP displacement at low pressures yields Vb displacement at high pressures yields Vgas Porosity determined from summation of fluids ADV: fast DISADV: dependent on similarity of adjacent samples coking and cracking correlation Porosity MeasurementPore Volume Example fluid saturation methodWeight dryWdry= 20 gmsWeight saturatedWsat= gmsWeight of water in pore spaceWwtr= Wsat-Wdry= gmspore volumeVp= Wwtr/rwtr= ccBulk volume (from previous example)Vb= ccPorosityf= = %
