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: i. coating the rock with paraffin ii. saturating the rock with the fluid into which it is immersed iii. using mercury Gravimetric methods observe the loss in weight of the sample when immersed in a fluid, or observe the change in weight of a pycnometer filled with mercury and filled with Hg and sample. Volumetric methods measure the change in volume when the sample is immersed.Porosity MeasurementBulk Volume Example – displacement methodWeight dryWdry= 20 gmsWeight saturatedWsat= 22.5 gmsWeight of saturated sample immersed in waterWwet= 12.6 gmsWeight of water displacedWwtr= Wsat- Wwet= 9.9 gmsBulk volumeVb= Wwtr/rwtr= 9.9 ccPorosity MeasurementGrain Volume a. Direct methods i. Dry weight of sample/density of matrix = Vg ii. Destructive methods (Melcher-Nutting or 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 accuratePorosity MeasurementBoyle’s porosimeter- The total moles of gas is constant, thus 21nntn  - Substituting the ideal gas equation, RTVpRTVpRTfVfp2211 - Isothermal conditions prevail, 2211VpVpfVfp  - Substituting for the volumes, 22)1(1)21( VpgVVpgVVVfp  - Rearranging results in an expression for grain volume 1)2(2)1(1pfppfpVpfpVgV (2.16) where V1 and V2 are the calibrated chamber volumes.Porosity MeasurementBoyle’s porosimeter- exampleV1= 100 ccV2= 80 ccP1= 0 kPaP2= 413.7 kPaV1= 100 ccV2= 80 ccPf= 199.783 kPa.340.140783.199)7.413783.199(80)0783.199(100ccgV Porosity MeasurementPore Volume 1. Mercury Injection methods • destructive (contamination of sample) • not very accurate • Washbum-Bunting, Kobe, Mercury porosimeters (obsolete) 2. Fluid Saturation method (See example) • non-destructive • not suitable for water sensitive rocks, unless use oil • very accuratePorosity MeasurementPore Volume 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 correlationPorosity MeasurementPore Volume Example – fluid saturation methodWeight dryWdry= 20 gmsWeight saturatedWsat= 22.5 gmsWeight of water in pore spaceWwtr= Wsat- Wdry= 2.5 gmspore volumeVp= Wwtr/rwtr= 2.5 ccBulk volume (from previous example)Vb= 9.9 ccPorosityf = 2.5/9.9 = 25.3