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AbstractPetrophysics is the study of rock properties and their interactions with fluids (gases, liquid hydrocarbons, and aqueous solutions). The geologic material forming a reservoir for the accumulation of hydrocarbons in the subsurface must contain a three-dimensional network of interconnected pores in order to store the fluids and allow for their movement within the reservoir. Thus the porosity of the reservoir rocks and their permeability are the most fundamental physical properties with respect to the storage and transmission of fluidsRock core analysis in the laboratory is used to determine the petrophysical properties of rocks. Rock core analysis procedure basically consists of two parts, they are routine rock core analysis and special rock core analysis. Routine rock core analysis porosity in general is about porosity measurement, absolute permeability measurement and fluid saturation measurement. Whereas special rock core analysis can be grouped into two, they are the measurements in static condition and measurements in dynamic conditions. Measurements in static conditions including capillary pressure, electrical properties and the speed of sound propagation, grain density, wettability, rock compressibility, permeability and porosity function of pressure (net over burden) and petrographic studies. And the measurements on dynamic conditions include: the relative permeability, thermal recovery, residual gas, water flood evaluations, liquid permeability (completion evaluation, work-over and the injection fluid includes surfactant and polymer).From the laboratory experiments that we did, there is the some results. The are measurements of porosity, permeability, saturation, acid solutibility of formation samples. Core that we used for research was limestone because limestone is a carbonate rock that will react with acid, and it is also porous rock according to the physical properties of reservoir rocks in the field. We took that core in the Wonosari area, because Wonosari is an area of limestone mountains.

Keywords : Porosity, Saturation, Permeability, Acidizing.1. PREFACE1.1. Background Issues Rock core analysis is the analysis steps after core sampel of formation in the subsurface, obtained in which the purpose of the rock core analysis is to determine directly the information of the physical properties of rocks to be carried out exploration. Core analysis is divided into two activities, The are Routine Core Anaysis and Special Core Analysis. Routine Core Analysis include the measurement of porosity, saturation and permeability. Porosity measurements or samples of reservoir rocks is to know the size of the cavity in the rock by rock bulk volume and pore volume of the rock. Measurement of Fluid Saturation aim to determine the pore space of reservoir rocks containing fluid especially oil. Permeability measurements to determine the ability of a fluid reservoir rocks passed without damaging the structure of the constituent rocks. Determination of Levels of Sample Solution Formation in Acid Solution, determine the concentration of acid-soluble formations in solution, in order to obtain important information prior to stimulation.

1.2. Methodology The method used to determine the porosity is Mercury Method Injection Pump, with materials used Hg or mercury as a guide. It is also used weighing method. But we only use the weighing method. The method used for the measurement of saturation is a method of distillation and retort method. But this time only just introduced distillation method. To determine the permeability of a reservoir rock that is supported by a tool consisting of a liquid permeameter and gas permeameter. This tool can only identify a single fluid, the rest of this tool can not be read. For samples soluble levels, we calculate the solubility as% by weight and material dissolved in 5N HCl. In experiments sieve analysis, we determined the type of screen or filter to be used to fix the sand problem.

2. THEORETICAL 2.1. Porosity Discussed from the point of reservoir engineering, porosity divided into two, namely: Absolute porosity, defined as the ratio between the whole pore volume to the total volume of rock, or can be written:abs=Vp/Vbx100%........................ (1)abs = (Vb-Vg)/Vb x 100 % ..........(2)

Vp = volume of rock pores, cm3 Vb = the total rock volume, cm3 Vg = volume of grain, cm3

Effective porosity, defined as the ratio of the pore volume is related to the total volume of rock or written:

eff = (Vp related)/Vb x 100 % ....(3)

Therefore, the oil can only flow through interconnected pores. So that is important in the petroleum industry and that we measured in this experiment is the effective porosity. In general, the amount of porosity ranging between 5-30%. Theoretically, the magnitude of the porosity of not more than 48%. On the field, we can get an estimate visually, which is semi-quantitative determination and is used as the following scale: 0%- 5%very bad porosity (can be ignored)5%- 10%bad porosity 10%- 15%sufficent porosity 15%- 20%well porosity > 25% excellent porosity2.2. Saturation Reservoir fluid saturation is defined as the ratio between the volume of a particular fluid (water, oil, or gas) to total pore volume. Generally, the formation of the water content in the oil zone is called interstitial formation water or connate water. Water saturation is defined as:


Oil saturation is defined as: .......................(5)

Gas saturation is defined as:


Sw + So + Sg = 1 ..................(7)

2.3. PermeabilityBasis for determining the permeability of the rock is from trials conducted by Darcy. In the experiments, Henry Darcy using sandstone that is not compact by flowing water. The porous sandstone saturated with 100% fluid viscosity, cross-sectional area A, length L. Then, by applying pressure P1 entrance at one end, then the flow occurs at a rate of q, while the external pressure P2. In this experiment it can be shown that q is constant and will be equal to the price of the rock permeability is independent of the fluid, the pressure difference and the dimensions of the rock used. Because Henry is considered a pioneer darcy permeabilitys investigation then is Darcy permeability for the unit. Permeability itself is divided into two, namely: 1. Absolut Permeability is the permeability where fluid flow in porous media consists of only one phase, ex: only gas, oil, or water. 2. Effective Permeability is a permeability where fluid is flowing through a porous medium is more than one phase, ex: oil and water, oil and gas, water and gas, or all three. 3. Relative Permeability is the ratio between the effective permeability to absolute permeability.

Definition API to 1 Darcy is a porous medium having a permeability of 1 Darcy if single phase fluid with viscosity 1 cp, flowing with a speed of 1 cm / sec, through the cross-sectional area of 1 cm at a hydraulic gradient of 1 atm (76.00 mmHg) per cm and the liquid fills the medium. Mathematically it can be written as follows: ................. (8)Where in:K = permeability, Darcyq = flow rate, cc/sec = Viscosity, cpA = cross-sectional area, cmL = length, cmP1P2 = pressure difference, atm

In Darcy's law itself there are assumptions that are used, as follows: a) linear flow. b) in compressible fluid (can not breath / full because if crowded / full it does not cause the volume decreases. c) steady flow conditions (no change in the P and T). d) homogeneous and isotropic porous media. In units of the field K is expressed in miliDarcy. In the field estimate can also be made semi-cumulative giving to the permeability (K scale), they are:1.Tight: < 5 md2.Fair: 5 10 md3.Good: 10 100 md4.Very good : 100 1000 md

2.4. Acid solutibilityAcidizing is the way to stimulate the reservoir consisting of limestone or dolomite reservoir rocks and acid dissolvable rock. This is done by injecting acid into the reservoir to get the price of the permeability and porosity of the larger or more commercial in an oil field. The acid used is 15% of the acid chloride reacts with carbonate rocks according to the equation:

CaCO3 + 2 HCl CaCl2 + H2O + CO2Prior to stimulation with acidizing must be planned precisely laboratory data obtained from samples of formation fluid and the fluid reservoir stimulation so that the information obtained from the laboratory can be used to plan operations with proper stimulation. And, in turn, increase the productivity of the formation can be obtained as expected. One of the required information is the solubility of the acid rock samples (acid solubility). This method uses a gravimetric technique for determining the reactivity of the acid formation. Acidification method (Acidizing) can be divided into two kinds:

1. Matrix Acidizing, in this method, the acidic solution is pumped or injected in order to dissolve the rock and sediment formations around the wellbore. The pressure used is smaller than the fracturing pressure of the formation. Thus, the acid can react with the walls of the pores of the rock and eventually will enlarge pores. The maximum radial penetration and acid solution is dependent on the speed of the acid in the pores. Some of the assumptions used in the implementation of this method are as follows: a. Homogeneous formationb. Uniform pore size c. Penetration of acid solution uniformly and radially d. Reaction speed decreases uniformly with decreasing acid concentration e. The weight of limestone is dissolved on any additional distance decreases uniformly until all the acid used. Based on the above assumptions, the radial distance of