Correlation of petrophysics to determine the potency of carbonate rock from Kemadang, Wonosari.Anugrah Hadi Pratama, Delta Cahyaputri, Harrymawan Pasca N, Indra Bayu, Johanes Halasan Sirait, Khrisna Agung P, Moh. Fauzan Akbar A, Persadan Canisius Kaban, Widya S, M. Zain. as members of a Team Research Chevron, Department of Petroleum Engineering,UPN “Veteran” Yogyakarta.

AbstractRock properties are determined by performing laboratory analyses on sample cores from the reservoir to be evaluated. And sample of carbonate rock in this research was taken from Kemadang, Wonosari, because there are many lithologies carbonate rock and in this area, the carbonate rocks are easy to find because it has the deposition of carbonates. Rock sample that we have had a good react with HCL solution that proves if the sample in this experiment is a carbonate rock. The reaction was marked by the foam from the rock. Then the rock sample first was cut into cubes 8cm3 before analyzed as many as 8 cubes. This research focused on the Routine Core Analysis of the rock sample, including the measurement of effective porosity, saturation measurement, measurement of absolute permeability, and rock solubility in acid. Porosity and saturation measurement was performed to determine the amount of hydrocarbon reserves filling rock formations with the calculation of OOIP and OGIP. Permeability analysis aimed to determine the flow rate of fluid which can be produced. which in this experiment we get the results of permeability of liquid 0,06676 and permeability of gas 0,31058. While the analysis of the sample solubility in acid was performed as a reference in the acidizing stimulation. This stimulation is necessary to enhance the production of wells that has started to decline.

IntroductionThe definition of Petroleum is a mixture

of naturally occurring hydrocarbons which may exist in the solid, liquid, or gaseous states, depending upon the conditionsof pressure and temperatures to which it is subjected.Virtually all petroleum is produced from the earth in either liquid or gaseous form, and commonly, this material canbe referred to as either crude oil or natural gas, depending upon the state of the hydrocarbon mixture.

The material of which a petroleum reservoir rock may be composed can range from very loose and unconsolidated sand to a very hard and dense sandstone, limestone, or dolomite. The grains may be bonded together with a number of materials, the most common of which are silica, calcite, or clay. Knowledge of the physical properties of the rock and the existing interaction between the hydrocarbon system and the formation is essential in understanding and evaluating the performance of given reservoir.

Rock properties are determined by performing laboratory analyses on cores from the reservoir to be evaluated. The cores are taken from the reservoir environment, with subsequent changes in the core bulk volume, pore volume, reservoir fluid saturations, and, sometimes, formation wettability. The effect of these changes on rock properties may range from negligible to substantial, depending on characteristics of the formation and property of interest, and should be evaluated in the testing program. There are basically two main categories of core analysis tests that are performed on core samples regarding physical properties of reservoir rocks.

We got the carbonate rock which will be used in this observation from Kemadang, Wonosari. In this area, the carbonate rocks are easy to find because it has the deposition of carbonates. Based on the law of uniformitarianism that the geological expansion history of Wonosari is formed from the sea which is lifted become the landing. The routine core analysis that we do are to find the value of effective porosity, saturation, permeability, and the rock solubility on acid.

The porosity of a rock is a measure of the storage capacity (pore volume) that is capable of holding fluids. Quantitatively, the porosity is the ratio of the pore volume to the total volume (bulk volume). This important rock property is determined mathematically by the following generalized relationship:

Ø = porevolumebulkvolume

Where: Ø is porosity

As the sediments were deposited and the rocks were being formed during past geological times, some void spaces that developed became isolated from the other

void spaces by excessive cementation. Thus, many of the void spaces are interconnected while some of the pore spaces are completely isolated. The effective porosity is the value that is used in all reservoir engineering calculations because it represents the interconnected pore space that contains the recoverable hydrocarbon fluids.

ϕeff =interconnected pore volume

bulk volumeX 100 %

Saturation is defined as that fraction, or percent, of the pore volume occupied by a particular fluid (oil, gas, or water). This observation of saturation used distillation method by using dean and stark distillation apparatus. This property is expressed mathematically by the following relationship:

Saturation=Pore volume filled wit hcertain fluidTotal pore volume

Permeability measurements aimed to determine the ability of the rock to drain the fluid. Just as effective porosity, permeability is also affected by the uniformity of grain size, cementation and compaction of rock. This permeability measurement used two methods, which are permeability measurement by the gas permeameter and permeability measurement liquid permeameter. This rock property is determined mathematically by the following relationship:

k= µQ LA ∆ P

The measurement of rock solubility in acid is necessary for the data will be needed to determine the concentration of acid that needs to be injected into the reservoir while doing a production well stimulation. In this observation, we use HCL 5N without HF

because the rock does not contain clay. The reaction is:

CaCO3 + 2HCl CaCl2 + H2O + CO2

Result1. Effective Porosity measurement with

weighing methodDry core weight (W1) = 21,65 grSubmerged core weight(W2) = 9,5 grSaturated core weight (W3) = 24,048 grDensity of kerosene = 0,8gr/cc

Bulk Volume (Vb) =W 3−W 2

densityofkerosen

=24,048−9,5

0,8

=18,17 cc

Grain Volume (Vg) =W 1−W 2

densityofkerosen

=21,65−9,5

0,8

=15,18 cc

Pore Volume (Vp) =W 3−W 1

densityofkerosen

=24,048−21,65

0,8

=2,99 cc

Porosity (Ф) =VpVb

x100%

=2,99

18,17x100%

=16,44%

2. Measurement of saturationDry Core weight (W1) = 16,84 gramsSaturated Core weight (W2) = 21,28

gramsPore volume = 5,55 ccWater volume obtained = 2,5 ccWater weight (W3) = 2,5

gramsOil weight = W2-

W1-W3= 21,28-

16,84-2,5= 1,94

gramsOil volume =

1,94/0,8= 2,425

cc

Sg + Sw + So = 1

So=V o

V p

=2,4255,55

× 100 %

= 43,36%

Sw=V w

V p

= 2,55,55

× 100 %=45,04 %

Sg=1−S w−So=100 %−45,04 %−43,36 %=11,6 %

3. Permeability Measurement With Gas Permeametera) Flow reading =5,7

cm

Core length( L ) =2,5cm

Core sectional area (A) =4cm2

Gas viscosity( μg ) =0,0183cpPressure gap =0,25atmFlow speed(Qg ) = 4,1cm³/secSelector Valve = Medium

K1 =μ .Q .LA . ∆ P

= 0,0183 x4,1 x 2,5

4 x 0,25= 0,1824

Darcy

b) Flow reading = 8,2cm

Core length( L ) = 2,5cm

Core sectional area (A) = 4cm2

Gas viscosity( μg ) =0,0183cpPressure gap = 0,5atmFlow speed( Qg ) = 6,8cm³/secSelector Valve = Medium

K2 =μ .Q .LA . ∆ P

= 0,0183 x6,8 x2,5

4 x 0,5= 0,1513

Darcy

c) Flow reading = 13,5cm

Core length( L ) = 2,5cm

Core sectional area (A) = 4cm2

Gas viscosity( μg ) =0,0183cpPressure gap = 1atmFlow speed( Qg ) = 13cm³/secSelector Valve = Medium

K3 =μ .Q .LA . ∆ P

= 0,0183 x13 x2,5

4 x 1=

0,144625 Darcy

value of absolute permeability (K abs) can be known with plotting the value of permeability and the value of 1/Pm ( Pm = P mean ). Where, the formula

of Pm = (Ptrial+Pinlet )+Poutlet

Pinlet+Poutlet

P inlet and P outlet = 1

1. P1 ( 0,25 atm ) =0,25+1+1

2= 1,125

Maka 1

Pm 1=

11,125

= 0,89

2. P2 ( 0,5 atm ) =0,5+1+1

2= 1,25

Maka 1

Pm 2=

11,25

= 0,8

3. P3 ( 1 atm ) =1+1+1

2= 1,5

Maka 1

Pm 3=

11,5

= 0,67

∆P =0,25+0,5+1

3

=1,75

3= 0,583 atm

From the graphic (attached), we get theequation of the lineis y = 0,163x + 0,031. If, 1/ Pm (x) = 0 , and then from the equation above we get:

b= tan αKab

=0.1630,031

=5,258

K abs= K absolute from the graphicK actual= Kabs(from graphic)x(1+(b/p))

= 0,031 x (1 + (5,258/0,583))= 0,31058 Darcy

4. Permeability Measurement With liquid Permeametera ) Core length( L ) =2,5

cmCore sectional area (A) =4 cm2

Liquid viscosity(μg ) =0,895 cp

Pressure gap = 0,25atmFlow time =1337 secQl=0,0373cm³/secVolume liquid = 50 mlKabs =

μ .Q .LA . ∆ P

= 0,895 x0,0373 x2

4 x 0,25

=0,06676 Darcy

5. Measurement of Acid SolubilityCore type =LimestoneAcid type =HCl 0,15NWeight before (W1) =22,37 grWeight after (W2) =21,65 grWeight reacted (W3) =0,72 gr

Acid Solubility =W 3W 1

x100%

=0,72

22,37x

100%=3,22 %

DiscussionPorosity measurement in this research is done by weighing method. The porosity of the core sample obtained is 16,44%. Furthermore from the saturation measurement, the water saturation obtained is 0,45 and oil saturation obtained is 0,43 while gas saturation is 0,116. On the field, porosity is needed to determine the hydrocarbon reserves which are contained in a reservoir. Porosity and Saturation will be used in the calculation of OOIP and OGIP which are determined mathematically by the following relationship:

OOIP=7758× V b ×ϕeff ×(1−Swi)

Boi

Absis( 1 / Pm )

Ordinate( K )

0,89 0,18240,8 0,15130,67 0,144625

OGIP=43560 ×V b × ϕeff ×(1−Swi)

Bgi

The permeability measurement used two methods, which are permeability measurement by the gas permeameter and permeability measurement liquid permeameter. Permeability of the rock obtained from measurement by liquid permeameter is 0,06676 Darcy. And permeability of the rock obtained from measurement by gas permeameter is 0,31058 Darcy. In the field, permeability is needed to calculate the reservoir production capability (productivity index) and production rate of hydrocarbon.

PI=0,007082h

ln( re

rw) [ K o

μo Bo

+K w

μw Bw]

Q=1,127 KAμ

dpdx

The rock solubility acid is 3,22%. This data will be usedin the field to determine the amount of acid that should be injected at acidizing process for dissolving sludge or scale that reducepermeability and effectiveporosity of the rock. It is expected that permeability and effective porosity can be repaired so that hydrocarbon production can be increased than before

Conclutionaccording to this research, we conclude that:

1. Effective porosity of the rock sample is 16,44%

2. Water saturation is 0,453. Oil saturation is 0,0,434. Gas saturation is 0,1165. Permeability using gas permeameter is

0,31058 Darcy6. Permeability using liquid

permeameteris 0,06676 Darcy

7. Rock solubility in acid is 3,22%