Development of Porosity Measurement Method in Shale Gas Reservoir Rock

Transcription

1 Journal of Physics: Conference Series PAPER OPEN ACCESS Development of Measurement Method in Shale Gas Reservoir Rock To cite this article: Alita Siswandani and BagusEndar B. Nurhandoko 2016 J. Phys.: Conf. Ser View the article online for updates and enhancements. This content was downloaded from IP address on 03/07/2018 at 12:52

2 Development of Measurement Method in Shale Gas Reservoir Rock Alita Siswandani 1,a), BagusEndar B. Nurhandoko 1,2,b) 1) Faculty of Mathematics and Natural Sciences, Institut Teknologi Bandung 2) Rock Fluid Imaging Lab. a) b) Abstract. The pore scales have impacts on transport mechanisms in shale gas reservoirs. In this research, digital helium porosity meter is used for porosity measurement by considering real condition. Accordingly it is necessary to obtain a good approximation for gas filled porosity. Shale has the typical effective porosity that is changing as a function of time. Effective porosity values for three different shale rocks are analyzed by this proposed measurement. We develop the new measurement method for characterizing porosity phenomena in shale gas as a time function by measuring porosity in a range of minutes using digital helium porosity meter. The porosity of shale rock measured in this experiment are free gas and adsorbed gas porosoty. The pressure change in time shows that porosity of shale contains at least two type porosities: macro scale porosity (fracture porosity) and fine scale porosity (nano scale porosity). We present the estimation of effective porosity values by considering Boyle-Gay Lussaac approximation and Van der Waals approximation. 1. Introduction Today, the most energy that we use is originated from conventional sources of energy such as petroleum, coal, and natural gas [1, 2]. Natural gas based on geological formations can be divided into two terms: conventional and unconventional resources, where the conventional is more accessible to produce than unconventional [2,3]. The differences between conventional and unconventional natural gas are put on the technique and cost for extracting the resources, also geology structure. Shale gas as unconventional resources becomes the interesting topic of research and development of technologies in Indonesia [1]. Indonesia has large storage shale gas reserves [1]. The mining development of unconventional resources needs improvement. It needs specific technologies to reduce production costs, which means increase the revenue cost. Conventional gas is recognized as free gas trapped in porous material and adsorbed gas stored by molecular attraction in the surface of the organic material of the shale [4]. The surface area of the shale is very large to attract natural gas. Therefore, it requires specific measurements and molecular simulation in the laboratory. The pore scale on the surface area of shale has an effect on transport mechanisms in shale gas reservoirs. The amount of gas is trapped in the matrix which depends on the particular properties of the shale reservoir. The quantity of reservoir properties such as porosity is valuable to the storage controlling for gas in place estimation. In this study, digital helium porosity meter is used to quantify the porosity by Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Published under licence by Ltd 1

3 considering real condition. The method adopts Van der Waal equation of real gas. The problem solving of algebraic equations with matrix and root equation are probably used for the calculation. 2. Research methodology Figure 1 shows our methodology which it has two cells. The first valve allows the gas flow to the first cell. The second valve connects the cells. FIGURE 1. Two cells are connected with the second valve using a closed valve condition. (source: Manual Book of Digital Helium Meter by Nurhandoko et al 9 ) A pressure sensor is provided for gas pressure measurement. The pressure readings are displayed in unit Psi and connected to the sensor To calculate the porosity using the helium porosity meter, we must consider the fraction of the volume of voids over the total volume as a percentage between 0 and 100%. 3. Calculation method 3.1. Boyle Gay Lussac Calculation For determining the bulk volume of the porous sample, we must measure dimension of the core sample and applying Boyle's law [5,6,7]. This law states that the product of the pressure and volume will be stay constantly in the constant temperature. Boyle's law is expressed as follows: With ideal assumption, considering that the left part of below equation under is in a close valve and the right part is in under open valve (see figure 1 and 2 ) V 2 is volume in tube in right side or analog with volume of pore or V pore (V p ) 2

4 FIGURE2. Two cell are connected with second valve with a open valve condition (source: Manual Book of Digital Helium Meter 8 ) Volume of pore as function of pressure and tube is as following: 3.2. Van der Waals calculation J. H. Van der Waals proposed a new equation which attempted to account for the size of the atoms and their interactions. In this experiment we have a new consideration with Van der Waals equation of states. The Van der Waals equation of state is Where n is the mole number, a and b are constants characteristic of a particular gas, and R the gas constant. P, V, and T are respectively the pressure, volume, and temperature. Here, we present the Van der Waals equation in the same condition with the last consideration, open and close valve condition. Then The calculation of the above equation is analog with: 3

5 3.3. Calculation of pore volume with matrix The matrix of the above equations (equation 9) can be expressed as following: = By simplifying the above equation, we can write the following equation: C 1 = C 2 = C 3 =, and C 4 = So that the matrix can be written as following: (11) The volume of pore can be calculated by using equation (13) which derived from (11) and (12), and, V.C = C 4 The value of V p, can be estimated by same strategies: (12) (13) 1. Direct calculation from the value of the matrix V p 2. Average calculation from the value of the matrix V p 2 and V p 3 4

6 3.4. Calculation of pore volume with root equation The following equations show estimating volume of pore through C variables: = (14) if C 1 = C 2 = C 3 =, and C 4 = then (15) Wolframalpha is selected to find the roots of above polynomial equations 3.5. Van der Waals gas constants The parameterized phenomenological equation of Van der Waals contained two adjustable parameters a and b. These two parameters are varied to fit the equation results to the experimental properties of the gas in question. Units: 5

7 1 J m 3 /mol 2 = 1 m 6 Pa/mol 2 = 10 L 2 bar/mol 2 1 L 2 atm/mol 2 = J m 3 /kmol 2 = Pa m 6 /kmol 2 1 dm 3 /mol = 1 L/mol = 1 m 3 /kmol (where kmol is kilomoles = 1000 moles) TABLE1. Van der Waals constants for Argon and Helium Element a b(l/mol) (L 2 atm/mol 2 ) Argon Helium Source: Weast. R. C., Handbook of Chemistry and Physics, Calculation of correction factor The correction factor for calculating losses pressure in pipes by connecting the first tube to the another tube as proposed by equation 5: Thus (17) Let V pore is 0 or porosity is 0% when the second valve is closed thus The porosity could be calculated (20) V pore V correct V total = Pore volume of the core sample. = Correction volume from calibration measurement = Bulk volume of the core sample 6

8 4. Analysis The porosity measurements of three shale samples were done by Digital Helium Meter which connected to PC for storing the pressures changing along with measurement. Three core plugs of shale are showed in figure 4.1, 4.2 and 4.3. Before measurement were done, we had to measure the dimension and weight and also determining duration of experiment. A pressure sensor on Digital Helium Meter provides measurements of gas pressure in unit Psi/minutes. A more detail list of core, dimension, density and duration of experiment is provided in Table 2. TABLE 2. Dimension and duration of experiment of core A, B and C Sample Weight (gr) Height (mm) Diameter (mm) Radius (m) Duration of measurement (minutes) A B C 149, , The other core shale samples are shown by figure 3, 4 and 5 FIGURE 3. Core plug sample A 7

9 FIGURE 4. Core plug sample of B FIGURE 5. Core plug sample of C The calculation of the correction factor is used for estimating the losses pressure in pipes which connecting the first tube to the another tube. In this section, the calibration core measurement is showed in figure 6 which the steel plug is put in the second valve which analogue to the zero porosity. The Digital Helium meter is sensitive to different pressure between the first tube and the second tube. FIGURE 6.Calibration core Figure 7 illustrates the results of correction volume with Boyle-Gay Lussac and Van der Waals calculation. These graphs are obtained from measurement with steel core during 199 minutes. 8

10 Calibration Core (P2), (199 Minutes) Pressure (P2) (Psi) y = x R² = Time (Minutes) FIGURE 7. The calibration result by measuring of iron core during 199 minutes In this experiment, porosity is defined as fraction of the void volume from a saturated gas which representative to the volume of void (porosity) of shale to the total volume of the shale sample. The porosity of these cores are obtained from pore volume and corrected by calibration factor shown by figure 7. Core B, Boyle-Gay Lussac (199 Minutes) Boyle-Gay Lussac (%) y = ln(x) R² = Time (Minutes) FIGURE 8. The results of Boyle-Gay Lussaccalculation method of porosity value on core B during 199 minutes Core C (), Van Der Waals (199 Minutes) 4 3.5, Van Der Waals (%) y = 0.202ln(x) R² = Time (Minutes) FIGURE 9.The results of Van Der Waals (matrix) calculation method of porosity value on core C during 199 minutes 9

11 Core C (), Van Der Waals (199 Minutes) 5, Van Der Waals (%) y = ln(x) R² = Time (Minutes) FIGURE 10.The Results Van Der Waals (roots equation) calculation method of porosity valueon a core C in 199 minutes Van der Waals equation of real gases was proposed to calculate the pore pressure by solving the algebraic equations of pore pressure (V p ) and root equation. Flow of gas in shale penetrated initially at the macro pore and then followed by flow in finer porosity (in nano scales). It is represented by graphic and value porosity of shale as a function of time as shown by Figure 9 and 10. The different composition distribution of core sample has a various value of porosity. In the fig. 3, 4, and 5 illustrate the different properties of shale. The plug sample of core A and C have similar general structure. However, they have different value of porosity. The formation of plug sample of core A and C is tighter then core B. TABLE 3.core porosity Values A, B, C to 1 and 155 Core A Core B Core C Time (Minutes) (Boyle- G.L) % (VDW-1) % (VDW-2) % oyle-g.l) % (VDW-1) % (VDW-2) %

12 The value of porosity calculated by Van der Waals equation is lower than Boyle Gay-Lussac equation. This is because Van der Waals equation of states is considered to more parameters in the calculation. As a result Van der Waals proposed to approach real condition with terms a and b as the parameters that depend on the nature of the gas that used in experiment. While the Boyle-Gay Lussac is defined by ignoring these parameters even tough the method is commonly used to calculate the porosity. 5. Conclusions Effective porosity as a function of time can be measured by Helium Digital Meter logged PC. By measuring as function of time, the free gas and adsorbed gas porosity can be estimated precisely. The pressure change in time shows that the shale consists at least two type porosities: macro scale (fracture), and finer scale (nano scale). 6. Acknowledgements I would like to address my gratitude to Rock Fluid Imaging Lab for supporting the facility, and DR Rizal Kurniadi for valuable comments in this manuscript. References [1] Sunarjanto, D., Eksplorasi dan PengembanganMigas Non KonvensionalRamahLingkungan, LEMIGAS, p [2] Euzen, T Shale Gas An Overview, IFP Technologies Canada, p. 8, p.23. [3] Favreau, D. and Rouaud, T Gaz non conventionnels,article Techniques de Lingénieur, p. 2. [4] Ambrose, R., Hartman, R., Diaz Campoz, M., Akkutlu, I. Y., &Sondergeld, C New Pore-scaleConsiderations for shale gas in Place calculation, Journal of SPE International, p. 9. [5] Brouard, B., Castagnède, B., Henry, M., Lafarge, D., & Sahraoui, S Mesure des propriétés acoustiques des matériaux poreux, Article Techniques de Lingénieur, p. 8. [6] Jenkins, R., Accuracy of Determination, CoreLaboratory, INC., p. 3. [7] Wathelet, V., Michaux, C., Fontaine, M., André, J., Jacquemin, D., & Perpète, É., 2008.Paramétrisation d équations d état par la mécanique quantique, Article Techniques de Lingénieur, p. 5. [8] Nurhandoko, B., Budi, M., Abdianto, W., &Kusudiharyo, D., Manual Book of Digital HeliumMeter,RockFluid Imaging Lab, p [9] Weast. R. C. (Ed.), Handbook of Chemistry and Physics (53rd Edn.), Cleveland:ChemicalRubber Co. 11