ABSTRACTPorosity, is a measure of the storage capacity of a reservoir. It is defined as a ratio of the pore volume to the bulk volume and it can be expressed as either in percent or fraction. There are two types of porosity that can be determined which are total or absolute porosity, and effective porosity,. Effective porosity is the ratio of interconnected void spaces to the bulk volume. Thus, the only pores that will contain fluids are the effective porosity that formed from wells. The aim of this experiment is to determine the effective porosity of a porous plug by using liquid brine. Dry core rock sample is heat until fully dried. Then, it is weighed using electronic balance before immersed in a saturated liquid brine for 30 minutes. After that, the saturated sample weight is measured. Base on the recorded data the bulk volume and pore volume can be calculated. This calculation is crucial in determine the effective porosity of the used samples. Result from this experiment shows that the sample core rock 1 has higher percentage of porosity when compared to the core sample 2 which are 0.4510 % and 0.1570 % respectively. This different is due to the arrangement of the grains molecules in both samples together with occurrence of the interconnected void space of the samples. As for conclusion is best to say that core 1 is sandstone and core 2 is limestone as sandstone usually had higher porosity when compared to limestone in the form of sedimentary type rocks.7

1.0 INTRODUCTION(Abu-Khamsin, n.d)measure of storage capacity of a reservoir. It is defined as a ratio of pore volume (VP) to bulk volume (VB) of a reservoir rock and may be expressed in either a percent or a fraction (Abu-Khamsin, n.d). This calculation can be expressed in a form of equation such:

By using this formulae both total or absolute and effective porosity can be calculated. Total porosity is the ratio of all the pores spaces in a rock to the bulk volume of the rock. Effective porosity is the ratio of interconnected void spaces to the bulk volume. Total porosity includes all existing pores regardless of whether they are connected or not. While, effective porosity only includes the interconnected pores. Thus, only the effective porosity contains fluid that can be produced from wells (Chapter 4 : Porosity, n.d). For granular substance like sandstone, the effective porosity may approach total porosity, yet shale and for other highly cemented or vugular rocks like limestone, large variation or pattern may occur between effective and total porosity.2.0 OBJECTIVE

The objective of the experiment is to determine the effective liquid porosity of porousplug by using liquid saturating method in core laboratory.

3.0 THEORY

Due to its origin porosity is classified as either primary or secondary. Primary porosity is referred to porosity in a rock resulting from the sedimentation process. Secondary porosity is defined as a porosity in a rock which happen after sedimentation process like fracturing and recrystallization (Mohd Fauzi Hamid, n.d). These changes in the original pore spaces may be created by ground stresses, water propagation or various types of geological activities after the original sediments were deposited. The original porosity of the rock often increased due to the fracturing or formation of solution cavities.

Porosity is independent of the size of the grains for such a uniform rock grain size. The theoretical maximum porosity for cubic packed rock of uniform size of spherical grains is 48%. These maximum porosity of other packing arrangement can be shown as follows (Glover, n.d).

Figure 2.1 : Ordered packing arrengements.

Table 3.1 : Maximum porosity of different packing arrangementPackingMaximum Porosity (fractional)

Cubic0.476

Hexagonal0.395

Orthorhombic0.395

Rhombohedral0.260

Tetragonal0.302

Triclinic0.260

3.1 Effect of compaction on porosityCompaction is defined as a process of volume reduction resulting from an external applied pressure. For extreme compaction pressure, all materials show some irreversible change in porosity. Generally grain compressibility in most petroleum reservoirs is considered to be negligible. For porous rock, the compressibility is depends on the porosity.Porosity can be estimated through volumetric measurements of core samples or from geological logs (which measure a characteristic of the rock and infer porosity) or from Petro graphic Image Analysis (PIA), which is pore level evaluation of a small sample size. This section is directed towards the measurement of porosity from rock samples or core because it provides the basic concepts for understanding (Porosity, n.d).3.2 Grin sizePorosity is not effected by grains size. Well rounded sediments that are packed into the same arrangement generally have porosities from 26% to 48% depending on the packing (Mohd Fauzi Hamid, n.d).

4.0 APPARATUS AND MATERIALSApparatus Oven Desiccators with dry silica Electronic balance 100 ml beaker 1000 ml beaker Glass rods Damp cloth Graduated cylinderMaterials Core samples Sodium chloride (NaCl) powder Distilled water5.0 PROCEDURE1. Core sample is dried in an oven at 1000C and then placed in a desiccator with dry silica gel to cool off.2. Weight, Wdry, diameter D, and length L, is measured using electronic balance and vernier caliper respectively.3. Completed dry sample is placed in a container or beaker on a base of glass rods and slowly covered with brine until the sample is totally immersed with about 2cm of brine above it. The sample is saturated with 36 g/l NaCl brine, brine = 1.02 g/cm3.4. The sample is taken out from the container after 30 minutes and blot quickly with a damp cloth to remove surface brine.5. Saturated sample is weighted, Wsat.6. Saturated sample is put in a graduated cylinder filled with brine and the increase in volume on the cylinder is measured. Bulk volume, Vb (cm3), corresponds to the observed increase in the volume of brine measured on the graduated cylinder.7. The test is repeated for the other different sample.

6.0 RESULTCore No: 1 (sandstone)Diameter (cm): 5.45 cmLength / thickness (cm) : 1.4 cmWdry (g)Wsat (g)Wbrine (g)Vp (cm3)Vb (cm3)ee (%)

57.333057.42500.09200.0902200.004510.4510

Core No: 2 (limestone)Diameter (cm): 2.5 cmLength / diameter (cm) : 2.5 cmWdry (g)Wsat (g)Wbrine (g)Vp (cm3)Vb (cm3)ee (%)

60.226560.26650.04000.0392250.00150.1570

7.0 SAMPLE CALCULATIONCore 1 (sandstone)Wbrine= Wsat -WdryWbrine= 57.4250(g) 57.3330(g)= 0.0920(g)Vp = Wbrine / brine = 0.0920(g) / 1.02 (g/cm3)= 0.0902(cm3)Vb = 20mL (1L/1000mL)(0.001m3/1L) = 20cm3

= Vp / Vb = 0.0902(cm3) / 20(cm3)= 0.00451 X 100% = 0.451%Core 2 (limestone)Wbrine = Wsat -Wdry Wbrine = 60.2665 (g) 60.2265 (g)= 0.0400 (g)Vp = Wbrine / brine = 0.0400(g) / 1.02(g/cm3)= 0.0392 (cm3)Vb= 25 mL (1L/1000mL)(0.001m3/1L)= 25cm3 = Vp / Vb = 0.0392 (cm3)/25(cm3)= 0.001570 X 100%= 0.1570%

8.0 DISCUSSIONAny porous materials like rocks are made of solid grains and void space that contains the fluids, water, oil or gas. In this experiment, the observation shows that not all pores of rock sample are filled with brine. This due to the pores properties which do not totally in interconnecting to each other that cause void in some part of the rocks. At certain point, pores contain water or brine that is saturated with mineral in the rock structure.In this experiment, porosity of sample is differ to each other where it is recorded higher in sandstone, 0.451% and low in limestone, 0.1570%. This is due to its different in the arrangement of grains of both samples. The arrangement in sandstone gives more space and it is more interconnected while, limestone give a more compacted arrangement of the grain which resulting less in space and less interconnection. Porosity is one of the most crucial properties of sedimentary rock that is the rock should be porous in order to extract oil and gas. This is due to the only porous media or rock with porosity have the ability to store hydrocarbon within it. Thus, porosity is the main properties of a reservoir rock and without it, rocks have no tendency in storing hydrocarbon which resulting of no occurrence of oil and gas and formation of wells.The principle to employ Boyles Law is that the gas molecules is invade the pore space and not the solid (Boyle's and Charle's Law, 2013). The different in using brine and helium are that the molecules of helium gas is smaller compared to brine molecule. It is easier for the helium gas to penetrate small pore and it is inert does not inert does not absorb on rock surface as air may do. Brine with larger molecule compared to helium yet it still able to enter the pores as it is small enough. This liquid saturation method help in yielding effective porosity, however complete saturation is seldom obtained and therefore porosity is commonly lower than that determined from Boyles Law method.Liquid saturation method is an accurate method of determining the volume of the rock sample that filled with brine when saturated in subsurface (Tatomir, 2007). This accuracy achieve due the characteristic of the reservoir rock subsurface, which already filled with brine. Thus, the volume of the rock can be determined by using volume displacement method. The most significance of applying this method is that the determination of porosity convenient while preparing samples for other tests, and samples can be used for further testing.

9.0 CONCLUSIONGenerally, sedimentary rocks have the highest percentage of porosity compared to the metamorphic rocks and igneous rocks (Salman Bloch, 2002). In this experiment sandstone and limestone used as sample are both from the types of sedimentary rocks.Sandstone is usually more porous than limestone as it arrangement of grains is based on the grains size while, limestone normally undergo further compaction and dissolution of minerals. This compaction and dissolution of minerals result in lowering the porosity of the limestone. Compaction is the process of volume reduction resulting from an externally applied pressure. All materials show some irreversible change in porosity for the extreme compaction pressure. This is because of the distortion and crushing of the grain or matrix elements of the materials and in some recrystallization cases (Yuyuan Zhao, 2004).In this experiment core 1 has higher percentage of porosity compared to core 2 which are 0.4510 % and 0.1570 % respectively. The different is calculated to be 0.294 % and thus it can be say that core 1 is sandstone as it gain higher in porosity while core 2 is limestone as it porosity is lower.10.0 RECOMMENDATION1. The rock samples used in this experiment had been repeatedly heated many time and also used by other groups. This situation may actually help in giving some error to the actual result for the carried experiment. The theoretical value will be slightly differ from the actual result as the structure of stratification of the rock may be damaged due to repeat heating applied. Thus, it is recommended that in proceeding this experiment, it would be wise to use a different rock sample for every different experiment.2. When lifting the core sample from brine solution it is advised to use some helping device like clipper in order to avoid an error resulting from the polluted solution as non-proper method used.3. When, weighed the dry core and saturated core, used the electronic balance so that the value observe and recorded will be more precise as it consist of long decimal places. Using the covered electronic balance would also help in getting more accurate reading as it get rid the effect of the wind to weighing system.4. The eyes position must be perpendicular to the scale of graduated cylinder so that parallax or misreading error can be avoided. This will help in reducing error in this experiment.REFFERENCES

Abu-Khamsin, D. S. (n.d). Basic Properties of Reservoir Rocks. 1-102.Boyle's and Charle's Law. (2013). Lear extra live, 1-3.Chapter 4 : Porosity. (n.d). 1-7.Glover, D. P. (n.d). Porosity. Petrophysics MSc Course Notes, 1-11.Mohd Fauzi Hamid, W. R. (n.d). Rock and Fluid Properties. Fundamentals Of Petroleum Engineering, 1-52.n.d. (n.d). Chapter 4: Porosity. 1-7.Porosity. (n.d). Chapter 2, 1-8.Salman Bloch, R. H. (2002). Origin and predictability. Anomalously high porosity and permeability in deeply buried sandstone reservoirs, 1-28.Tatomir, A.-B. (2007). Saturation Determination for Multiphase Systems in Porous Medium Using Light Transmission Method. 1-74.Yuyuan Zhao, F. H. (2004). Optimisation of compaction and liquid-state sintering in sintering and dissolution process for manufacturing Al foams. Materials Science and Engineering, 117-125.http://petrowiki.org/Porosity_determination

APPENDICES

Figure 2 : Core Sample 2Figure 1 : Core Sample 1

Figure 3 : Immersed Core Sample 2 with Brine solutionFigure 3 : Immersed Core Sample 1 with Brine solution