Karl Koerner, 4/15/2012

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1 Determination of Porosity of Rock Samples, Torrefied Biomass, Activated Carbon and Proppant Sand for Usage in Wastewater Treatment and Simulation of Oil Reservoir Analysis using the Barnes Method and Helium Porosimetry Karl Koerner, 4/15/2012 Abstract In industry, the porosity of petrochemical reservoirs is measured frequently by coring and is an important property when trying to determine if a site is appropriate for drilling. Porosity can also be used in waste water treatment in order to determine if a material is ideal for water purification in industrial or residential applications. The purpose of this experiment was to simulate a oil reservoir porosity test using various rock core samples, as well as to test the porosity of activated carbon, biomass, and proppant to determine their efficacy in waste water treatment. This was done by using the Barnes method to determine the porosity of the cores, and the usage of a porosimeter to determine the porosity of the carbon, biomass, and proppant. From this, known values of rock porosity could be compared with the experimental porosity to determine if the rock would be ideal for reservoir drilling, and the values of proppant and biomass porosity could be compared to activated carbon to estimate their efficacy in waste water treatment. It was found that ideally activated carbon, with a porosity of 0.60±0.04 would work best for water treatment, though biomass met the critical diameter specifications of under 0.5mm and could also be used for larger particulates. The results showed that rock core 3, with a porosity of 0.21 (roughly around sandstone) would be a good potential reservoir to drill, however 1, 16, and 111 could also prove useful, as their porosity of 0.12 roughly resembled shale, though might require more processing to be easier to drill. Rock core 7 had a porosity of 0.07, which was also around the value for shale, though more machinery or processing may be required to extract petrochemicals effectively. Rock core 17 had a porosity of 0.00, which could store little to no fluid, making it a bad candidate for drilling. Introduction In modern oil reservoir core analysis properties like porosity, permeability, and saturation, are routinely tested to determine the distribution of hydrocarbons and to control the flow of existing hydrocarbon phases within the reservoir. (1) Knowledge of effective porosity can help to determine the original hydrocarbon volume within the reservoir as well as the ease of extraction of this hydrocarbon. (1) The original porosity of the material is a property of the original material, but induced porosity can result from fractures in the rock structure, or solution cavities in the rock (often found in limestone), adding to the porosity of the material overall. (1) Factors like grain size, grain shape, sorting, clay content, compaction, and cementation all may affect the porosity of a reservoir rock. (2) Low effective porosity, and low permeability in a reservoir may affect the reservoir's commercial viability, requiring more expensive methods of extraction. (2) When cleaning waste water from these reservoirs and from other industrial sources, porosity of the adsorber must also be taken into account. (3) The filling and filtration of water through micro and mesopores in the entire pore system plays a key role in adsorbing industrial hazards such as benzene and toluene from industrial wastewater. (3) In this experiment the porosity of various unknown rock samples was determined using the barnes method, in order to simulate the determination of porosity of oil reservoir cores; helium porosimetry was also used to determine the porosity of torrefied biomass, activated carbon, and proppant sand, for possible usage in wastewater 1

2 treatment applications. Theory The porosity of a material is the ratio of the voids in a material to the bulk volume of the material. (1-2) These voids occur between grains in the rock, whose sizes and distributions can affect the ease of fluid flow within a rock, depending on the isolation of the channels in the rock due to grain cementation. (2) Effective porosity is concerned with the ratio of the non-isolated channels in the rock to the bulk volume of the rock, represented in Equation 1, and is used widely in reservoir engineering. (1-2) Absolute porosity is the ratio of the total pore volume compared to the bulk volume of the material and is represented in Equation 2. (1-2) Based on pore diameter, a material can be microporous at less than 2 nm in pore diameter, mesoporous between 2.0 and 50 nm in pore diameter, or macroporous at greater than 50 nm in diameter. (3) Porosimetry can be used to determine pore diameter, as well as other properties, like pore volume, bulk density, and surface area using a non-wetting liquid or gas (in this case, helium) at high pressures. (4) The pore size (r pore ) is determined by measuring the pressure required to force the non-wetting liquid or gas into a pore versus the surface tension of the non-wetting liquid, represented in Equation 3. The Barnes method involves measuring the initial dry weight of a evacuated sample, then completely saturating pore spaces in the sample by using a suction flask and saturation fluid (originally acetylene tetrachloride, now water), and weighing the amount of fluid adsorbed into the pores to determine pore volume. (5) The weight in grams of the liquid adsorbed, divided by the density of the liquid will yield the pore volume of the sample, which can then be compared with the bulk volume (measured by length and diameter) to determine porosity. (5) Equation 1 Equation 2 Equation 3 where r 1 and r 2 describe the curvature of the interface, γ is the surface tension of the fluid, and θ is the contact angle between the solid and the fluid. Methods To initially demonstrate the concept of porosity on a large scale, a porosity experiment using 25 marbles was performed, to model an ideal circular particle shape with large vacancies. The diameter of each of the 25 marbles was measured with calipers so that the bulk volume could be calculated. The marbles were weighed when dry and water was added, covering the marbles completely. The weight of the marbles with the water was determined and from that the volume of water filling the vacancies could be determined (equivalent to the total pore volume). From this, the porosity of the marbles was determined. Six core samples of various rocks (simulating samples from reservoir sites) of roughly 25 mm in diameter and 35 to 35 mm in length were gathered and placed into an evacuation flask and evacuated for 15 minutes to remove air present in the cores that would impede flow into them. A 2

3 saturation fluid, in this case water, was introduced to the evacuation flask with the samples still present, and the saturation fluid was left to adsorb into the cores for 15 minutes. After 15 minutes the cores were weighed and the porosity was calculated based on the density of the saturation fluid. A porosimeter was calibrated by removing up to three disks (disk one was removed, then both one and two, then one two and three were removed) of fixed volume, one of cm 3, cm 3 and cm 3, and recording initial and final pressures in triplicate for each subsequently removed disk. A biomass, proppant, and activated carbon sample was then measured at weights between 0.3 and 0.7 g. These samples were placed individually into the porosimeter and pressureized to 100 psi, closed and then P1 was recorded. Then the sample value was allowed to expand and P2 was recorded. This was repeated in triplicate for each sample, and the effective porosity was determined. Results and Discussion The marbles in the first experiment, though performing as an effective demonstration of porosity calculation, were outliers in terms of porosity, yielding a value of 1.8, never seen in real-world reservoir analysis. If a value like this were to be seen for effective porosity, it would be more than ideal for petrochemical recovery, as the petrochemicals would already be freely flowing through the rock, an unrealistic circumstance. The low porosity and limited surface area would make this a very poor water treatment material, as most hazardous chemicals would flow through freely as well. The core samples and activated carbon, proppant, and biomass samples were much more realistic representation of porous rock found at reservoir sites and materials found in industrial water treatment, respectively. The porosity of the activated carbon greatly overshadowed the other materials, as seen in Figure 1. Due to its classification as a microporous material, this elevated porosity of 0.60±0.04 was expected. The microporosity of the activated carbon lends it to greater adsorption capacity due to the increased surface area, making it ideal for industrial water treatment.(3) Biomass had a porosity very close to that of the proppant, both being around 0.35±0.01. This is close to sandstone porosity values, which range from about 0.15 to (6) In water treatment biomass has a critical diameter of 0.5 mm, and must be less than that diameter in order to be effective (7). Our sample did range in this diameter and had a relatively high porosity, meaning that it would most likely be useful for water treatment applications. Rock cores 1, 16, and 111 had porosities of roughly 0.12, suggesting a close resemblance to shale, a good conductor of fluid in a reservoir. (6) Rock core 3 had a porosity of 0.21, closer to limestone or a mid-range sandstone, ideal for a reservoir. Rock core 7 had a porosity of 0.07, a less than ideal porosity for a reservoir, though still around the values for shale, more machinery or processing may be required to extract petrochemicals effectively. Rock core 17 was an outlier with a porosity of 0.00, which can not possibly store any fluid. Overall, ideally activated carbon would work best for water treatment, and rock core 3 would be a good potential reservoir to drill, however 1, 16, and 111 could also prove useful given further study and possible processing. 3

4 Figure 1: A graph comparing the porosities of activated carbon, proppant, biomass, and various rock cores. Conclusions The routine usage of porosity in petrochemical reservoir analysis makes it an important property when trying to determine if a site is appropriate for drilling. Porosity can also be used to determine if a material is ideal for usage in water treatment. Overall it was found that rock core 3, with a porosity of 0.21 would be the best site for drilling, though cores 1, 16, and 11 could be useful with a porosity of roughly 0.12, with possible slight adjustments to drilling. Core 17 had 0.00 porosity and would not hold enough, if any, petrochemicals to be worth drilling, core 7 had a porosity of 0.07 and would probably not be very effective either. The micropores of activated carbon make it ideal for waste water treatment and purification, and account for the high porosity of 0.60±0.04 recorded for this experiment. Materials like proppant sand and biomass could possibly be used in waste water treatment, with a decent surface area and porosity of 0.35±0.01, however, they would not as effectively treat smaller microparticles that activated carbon could. Separate Answers to Provided Questions 1) The absolute porosity is defined as the ratio of pore space in the material to the bulk volume of that material, whereas the effective porosity is the ratio of interconnected pore space in the material to the bulk volume of the material. (1) Due to the large particle size of the marbles, the pore space was also very large, resulting in all of the pores being interconnected to some extent. Assuming the pores were all interconnected, the absolute porosity would be equal to the effective porosity, though in materials 4

5 that are not interconnected in such a manner the values would be significantly different. In reservoir engineering, effective porosity is extremely useful, as it represents the interconnected pore space that contains the recoverable hydrocarbons in the rock. (1) 2) Packing geometry and efficiency play a key role in the laminar flow of fluids through porous media, and can be described using Darcy's law. (8) In Darcy's law, the permeability, K, of a porous object depends only on the geometry of the pore space, which can be represented by the Kozeny-Carman Equation, seen in Equation 4. (8) This equation can represent an idealized gapless random packing of adjacent perfect spheres, these spheres can be grouped into random tetrahedral arrangements, which can then be used to calculate a mean frequency distribution and porosity of each tetrahedral unit, which can then be averaged to calculate the overall porosity of the object. (8) In this method, the variability of particle size is not taken into account. In a real case, the porosity and permeability would be effected by smaller particles filling gaps in between larger particles, reducing the permeability and porosity. (8) Equation 4 where h, is the Kozeny constant (about 5), ε is the porosity of the packing, and S 0 is the specific surface. 3) Zeolites are aluminosilicate minerals such as faujasite, mordenite, offretite, ferrierite, erionite and chabazite used for catalysis in various industrial processes. (9) The introduction of faujasites in fluid catalytic cracking of petroleum distillates increased the yield of gasoline significantly when compared to previously used silica-alumina catalysts. (9) Zeolites are also used in hydrocracking of heavy petroleum distillates, increasing octane number of gasoline by isomerization, and the formation of styrene and polystyrene via ethylbenzene synthesis and the Mobil-Badger process. (9) Precious metals, like platinum, suspended in zeolites facilitate the conversion of straight chain hydrocarbons into branched isomers, increasing octane number. (10) Zeolites can catalyze these processes due to their structure of SiO 4 and AlO 4 tetrahedra, linked via oxygen atoms. (9) This structure allows for strictly uniform pore diameters in a microporous material, which can aid in shape-selective catalysis with a large amount of reaction sites, allowing for a large quantity of a certain reaction mechanism to take place. (9) 4) The baled density of certain biomasses (particularly switchgrass and miscanthus) ranges from kg/m 3, whereas coal's baled density is around kg/m 3 depending on rank. (11) This large variation in density results in different heating, drying, and storage characteristics, which impact the combustion process as well as the economic viability of cofiring coal with biomass. (12) Due to smaller overall fuel density as well as energy density, biomass requires a disproportionate amount of shipping, storage, and handling when compared to coal, all for a high cost when compared to coal's much greater heat contribution. (12) 5

6 References (1)Ahmed, T.(2010). Reservoir Engineering Handbook. Amsterdam: Gulf Professional Publishing. Pp (2)Dandekar, A. (2006). Petroleum Reservoir Rock and Fluid Properties. Boca Raton: CRC Press. Pp (3)Asenjo, N., Alvarez, P., Granda, M., Clara, B., Santamaria, R., Menendez, R. (2011) High Performance Activated Carbon for Benzene/Toluene Adsorption From Industrial Wastewater. Journal of Hazardous Materials 192(3) pp (4)Giesche, H. (2005) Mercury Porosimetry: A General (Practical) Overview. Part. Part. Syst. Charact. 23(1) pp (5)Barnes, K. (1931) A Method for Determining The Effective Porosity of A Reservoir-Rock. State College, PA: School of Mineral Industries. Pp 1-13 (6)U.S. Department of Energy. (2012) Argonne National Laboratory: Total Porosity. Retrieved 4/15/2012 via (7)Tay, J., Tay, V. Ivanov, S., Pan, H., Jiang, L. Liu, Q. (2003) Biomass and Porosity Profiles in Microbial Granules Used for Aerobic Wastewater Treatment. Letters in Applied Microbiology. 36 (1) pp (8)Leitzelement, M., Seng, C. Dodds, J. (1984). Porosity and Permeability of Ternary Mixtures of Particles. Power Technology 41 (1), pp (9)Weitkamp, J. (2000). Zeolites and Catalysis. Solid State Ionics 131 (1) pp (10)Gary, J., Handwerk, G, Kaiser, J. (2007) Petroleum Refining: Technology and Economics. Boca Raton: CRC Press. (11)Scurlock, J. (1994). Biomass Energy Data Book: U.S. Department of Energy. Retrieved 4/15/2012 via (12)Baxter, L., Koppejan, J. (2004) Biomass-coal Co-combustion: Opportunity for Affordable Renewable Energy. Retrieved 4/15/2012 via 6