Petrophysics Related to Enhanced Oil Recovery

8/8/2019 Petrophysics Related to Enhanced Oil Recovery

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Petrophysics Related to EORLithology, Porosity, water saturation, and wettability

7/18/20lOGraduation Project, Mining Engineering DepartmentMourad Hosni


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Contents:IntroductionPorosityFactors Governing Sandstone PorosityClassification of PoresEngineering Porosity Classification

Absolute Porosity Effective Porosity

Geological Porosity Classification Primary Secondary

Direct determination of porosity (laboratory) Bulk Volume Measurements

Indirect determination of Porosity Density Log One detector formation density tool Dual-spacing density logging tool Electron Density and Bulk Density

Typical Reservoir Porosity ValuesWater SaturationResistivity Log Types of resistivity log Principal of electrical logs Types of electrode logs Normallog device Lateral log device Focused logs Laterolog

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Formation Resistivity factor Archie's Formula

Lithology of the Formation

Properties of gamma rays Theory Lithology Index

Volume of ShalePorosity CorrectionWater Saturation CorrectionWettability and interfacial phenomena

Wettability Surface tension Interfacial tension

Surfactant and its use in EOR Mechanism of surfactant in decreasing the interfacial tension

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IntroductionAlmost all oil and gas produced today comes from accumulations in the porespaces of reservoir rocks -usually sandstones, limestones, or dolomites. Theamount of oil or gas contained in a unit volume of the reservoir is the product ofits porosity by the hydrocarbon saturation. In addition to the porosity and thehydrocarbon saturation, the volume of the formation containing hydrocarbons isneeded in order to estimate total reserves and to determine if the accumulation iscommercial. Knowledge of the thickness and the area of the reservoir needed forcomputation of its volume.To evaluate the producibility of a reservoir, it is necessary to know how easily fluidcan flow through the pore system. This property of the formation rock, whichdepends on the manner in which the pores are interconnected, is its permeability.The main petrophysical parameters needed to evaluate a reservoir, then, are its

1- Porosity2- Hydrocarbon saturation3- wettability4- Thickness5- Permeability6- Area7- Reservoir geometry8- Formation temperature and pressure, and lithology

Our goal is to discuss the three italic bolded petrophysical parameters ...

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PorosityVoid spaces within the rock neededfor storage capacity.Sand grains and particles of carbonate materials that make up sandstone andlimestone reservoirs usually never fit together perfectly due to the high degree ofirregularity in shape. The void space created throughout the beds between grains,called pore space or interstice, is occupied by fluids (liquids and/or gases).The porosity of a reservoir rock is defined as that fraction of the bulk volume of thereservoir that is not occupied by the solid framework of the reservoir. This can beexpressed in mathematical form as:'

where:

4 1 = p(Jt(l!\'ii~ry, fractien.Vb = = bulkvotume ,ofm e reservelr rock.V~r: ~ g:rn.~r' ! 'Vo[~m(;.Vp =pore volume.

Pore v olum ePercentage Porosity x 100b"uU:volumeBulk Volume =the total volume of the rock

IClhl !Ml ,1

1 Solved example. [Petrophysics, 2nd Ed. Theory and Practice of Measuring Reservoir Rock and FluidTransport Propert ies. Pg.89

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Classification of Pores:1- Interconnected Pores: This type of pore has more than one throat

connected with other pores and extraction of hydrocarbon is relatively easyfrom such pore, as shown

2- Connected or dead end: This type of pore has one throat connected withother pores. It may yield some of the hydrocarbon by expansion as reservoirpressure drops

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3- Closed or isolated (blind) pore: This type of pore is closed. It does not havethroat and cannot connect with other pore. It is unable to yieldhydrocarbons in normal process as shown

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Engineering Porosity Classification:1- Total [absolute] porosity: it's the ratio of total void space in the sample to

the bulk volume of that sample, regardless of whether or not those voidspaces are interconnected.

2- Effective porosity: is the ratio of effective void spaces in the sample to thebulk volume of that sample, it's affected by many factors, such as: Type, content, and hydration of the clays present in the rock. Heterogeneity of grain sizes. Packing, and cementation of the grains Weathering, and leaching.

Total Porosity = effective porosity + ineffective porosity

Note: Interconnected and connected pores constitute effective porosity becausehydrocarbons can move out from them. In the case of interconnected porosity, oiland gas flowing through the pore space can be flushed out by a natural or artificialwater drive. Connected porosity is unaffected by flushing but may yield some oil orgas by expansion, as reservoir pressure drops. Reservoirs with isolated porosity areunable to yield hydrocarbons. Any oil or gas contained entered the pore spacesbefore they'd been closed by compaction or cementation.

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Geological Porosity ClassificationThis method of classification depends on whether pore spaces in which oil and gasare found originated when the beds were laid down [primary or matrix porosity],or if they were formed during a subsequent processes [secondary or inducedporosity].

1- Primary porosity Intercrystalline: voids between cleavage planes of crystals, voidsbetween individual crystals, and voids in crystal lattices.

Intergranular or interparticle: voids between grains, i.e., interstitialvoids of all kinds in all types of rocks.

Bedding planes: voids of many varieties are concentrated parallel tobedding planes.

Miscellaneous sedimentary voids: ( 1 ) voids resulting from theaccumulation of detrital fragments of fossils, (2 ) voids resulting from thepacking of oolites, (3) vuggy and cavernous voids of irregular andvariable sizes for at the time of deposition, and (4) voids created byliving organisms at the time of deposition.

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2- Secondary porosity Solution porosity: channels due to the solution of rocks by circulatingwarm or hot solutions; openings caused by weathering, such as enlargedjoints and solution caverns; and voids caused by organisms and laterenlarged by solution.

Fracture porosity: openings created by structural failure of the reservoirrocks under tension caused by tectonic activities such as folding andfaulting. These openings include joints, fissures, and fractures. In somereservoir rocks, fracture porosity is important.

Miscellaneous secondary voids: (1 ) saddle reefs, which are openings atthe crests of closely folded narrow anticlines; (2 ) pitches and flats, whichare openings formed by the parting of beds under gentle slumping; and(3) voids caused by submarine slide breccias and conglomeratesresulting from gravity movement of seafloor material after partiallithification

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Mai [1 type (Time offormation) OriginPr~nrlary or D epositional Inrergranu lar, Of

I nte rp ar tic l eItragranular, O F 'intn.iJl]]rut]d~e

Sed imen ra tion

I nte re ry sta l t in eFenestral

Secondary 0[Post-depositional

VuggyModicFracture

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SolutionTectonics"Compaetion,Dehydration,D ia ge nes is"


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Factors Governing the Magnitude of Sandstone Porosity1- Uniformity of grain size: is the gradation of grains, it depends on on at least

four major factors: Size range of material Type of deposition Current characteristics Duration of sedimentation processe.g. if small particles of clay are mixed with larger grains of sand; theeffective porosity will be reduced, [they are called dirty, or shaly reservoirs]

B

A

2- Degree of cementation or consolidation: it's filling the void spaces withmineral materials. It occurs while alteration or lithification, by groundwater. The highly cemented sandstones have low porosities, and vice versa.

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3- Amount of compaction during and after deposition: compaction tends tolose voids and squeeze fluid out to bring the mineral particles closetogether, especially the fine-grained sedimentary rocks

4- Method of packing: with increasing overburden pressure, poorly angularsand grains show a progressive change from random packing to a closerpacking, some crushing and plastic deformation of the sand particles occur. Cubic packing has a porosity of 47.6% Hexagonal packing has a porosity of 39.5% Rhombohedral has a porosity of 25.9%

o ~ M'Viii0;)V;~;tD~f6el]'~(1-1


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Determination of absolute and effective porosityThree basic parameters are to determine porosity:

1- Bulk volume [Vb]2- Pore volume [Vp]3- Solid volume (rock matrix) [Vs]

For example: the mass (M) of a sample of rock with a bulk volume (Vb) of 1 5 crnj is30.3 grams; it was found to contain an absolute grain volume(V,) of 11.25 crrrj, an interconnected pore volume (Vp) of j.o cmj, an unconnected(isolated) pore space (VI) of 0.75 crrrj, and an irreducible water saturation (Si,)equal to 6%.Absolute Porosity:To determine absolute porosity, the density of the solid portion of the rock (itsgrain density) should be determined.Density of the solid portion:

The rock sample should be crushed using an impact crusher. An appropriate size pycnometer", whose volume is known, is dried and

weighed, and then the volume and mass of a portion of the sand grainsis determined using the pycnometer.

1- Fill the pycnometer with a liquid (water or hydrocarbon), and obtain itsmass (Mpyc+Md

2- Empty and dry the pycnometer3- Place a sample of crushed rock in the pycnometer (about one-half the

volume of the pycnometer) and determine the mass (Mpyc+ Mgrains)4 - Fill the pycnometer (containing the sand grains), then with the liquid usedin (1 ) above, and determine the mass (Mpyc+ Mgmins+ Mj).5- The sand grain density is calculated from the data as follows:

2 Specific gravity bottle.16


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Vry,dkmowmdume)~ 10.0cm~~i l ' o 1 lfiirc (m.eilslwed) ,= 1~,;" gMp)! , t"+M I ( m ea sure d}:= 26 . ' SS g

MI= I, (MIJ),~+M~)I-Mp~T] ' : : : ; ; : : ~ 6 .58 - 16.57=U}.Ol g ,

P r u =,{M!/Vp),d= W"Ollir~ij.O=OAng/cl]]j5Mpyc- +Mgr.:liiliS (tIrilea~!!I!I',cd)=20.59' g

Mpy,~+Mg, rnh1~ +M] (..du~ed)=' 29'"17', gMg~;)inS :={Mpyt: +M ~liH~ ) - M pyc g:; 20,59 -t6 "51=< i A J 2

M JI{:added] =1 MIIJrt:+MiWr.~in! '>+M l,'~ddled)1-(M lIJl fC +M~ln~ )=29'.115 - 20.'5'9~$. '585

v:u(added)=(MI (added)/PI) =8.51/ 'C'- V~(ad!dled}~ =l(tO~ 8,.,0 = m,',o gIP'gmurl l~;;:::;(M !l~jlt,~./V ~r.jj i 'ILd;;;;:4.0 2/ ~ .5 0=2 .6 8 g!em!!

Empty and Full Pycnometers

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Grain and Bulk VolumesThis step is concerned with determination of grain and bulk volumes of a rocksample (core)

1- The core is dried and its mass is determined (Mcore)2- The core is then saturated with liquid by first evacuating the core to remove

air and then admitting the liquid into the vacuum flask containing the coreto fill the pores with the liquid.

3- The bulk volume ( Vb ) of the core may be determined accurately using abeam balance. Tie the core to a fine wire, attach it to the beam balance, andthen immerse the core in a beaker with the same liquid used for themeasurements above. The core should be immersed until it is just below thesurface of the liquid, and it should not touch the sides or the bottom.Obtain the mass of immersed core (Mim).4- Remove the beaker of liquid, carefully wipe the excess liquid from thesurface of the core, and obtain the mass of the saturated core (Mcorc-sat)

5a!mpLeCI l tu : ladM!Moore: = = 3:9.522 gM~m: : : = 24.393 g .

M(lC!~~;:n = 43 . ,fiJi S .V.R.f3i[lJ~=M:t.:t)fdp~t~iilS ~ 39522:!2~.6S=14.74i'(;m~

Vb = [ fM c .o f C -- 's f l ~ - fr~!l1)/p~1= (43./97 - 24.39 '3) /1 .01 = 19..2;U ,ern 'Po'ro! i ity ' ( iI ] )~( ) ] l1 i t .oe) " ' " U- V8f'lilil~./VI;i) .:;:;:;.~- 04.747) /1 9.2W Z ~ O.i~2

Effective PorosityThe effective porosity is the ratio of the interconnected pore space in the rock tothe bulk volume minus the irreducible saturation.

!Effective [ por,e vo il lU lme of core(V p, ) = [ fM ( jO i. t= ~ t ~ M"uirJI p~i' iJI~ H3.797 - ~~;t522)!lJll= 4.23.3cl11'

Eff~ci[: i".e P().[ 'Q5ruty(Vp/V IIl - i~W) = = 4.i33/19.:;r~l - 0'.06= O.~.6

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SummaryAb iSO~~U~ 'P()f f i~ruty = IJiI-Vl[!r.lli!ll~IVb=0.232-

Po re Vo l l: !!me' = = (M ""m M ;Jt ~ M O O M ' l / p l . " ' " 4.2 :2 5 cmr3 'Bl'ective Poros~fy =Vpo re /, VI 'b ~ Siw=0.],60 or 16%

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Indirect determination of porosity:Porosity can be determined using well logs.Well logs: the continuous recording of a geophysical parameter along a borehole.The value of the measurement is plotted continuously against depth in the well.

Porosity can be determined using one of three logs:1- Sonic log2- Density log3- Neutron log

We are concerned with density log here.

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Density logTheoryA radioactive source, applied to the borehole wall in a rays Shielded sidewall skid,emits medium-energy gamma rays into the formations. These gamma rays may bethought of as high-velocity particles that collide with the electrons in theformation. At each collision a gamma ray loses some, but not all, of its energy tothe electron, and then continues with diminished energy. This type of interactionis known as Compton scattering. The scattered gamma rays reaching the detector,at a fixed distance from the source, are counted as an indication of formationdensity.The number of Compton-scattering collisions is related directly to the number ofelectrons in the formation. Consequently, the response of the density tool isdetermined essentially by the electron density (number of electrons per cubiccentimeter) of the formation. Electron density is related to the true bulk density,Pb , which, in turn, depends on the density of the rock matrix material, theformation porosity, and the density of the fluids filling the pores.

Gamma ray sources:The most widely used are:

6Cobalt which emits photons at energies OfI.17 and 1.33 MeV. 137Cesiumthat emits photons of energy 0.66 MeV

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One detector formation density tool:

I rays

Schematic of the one detector formation density tool.

The first tools used only one detector. Although pushed against the borehole wallby a spring, the measurement suffered from the effects of mud-cake, its type,thickness and density.

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In the Dual-Spacing Formation Density Logging Device, compensated formationdensity tool, two detectors of differing spacing and depth of investigation are usedto eliminate the muudcake effect.

Schematic of dual-spacing density logging tool

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Log information is presented as shown:

I~ IGDlMI~C!I_!I!in"~ B!UUIDEHlsm,t.....""",..... i. d i , t l o l- .- It

~ ' U ! I N RiI!o_I~1I!.

l~ '~_'!!!!I! : ! I ! ' : ! O - - - - ! I ! ! ~ ~ - _I Q O I R R O T I O H

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Starting from left to right: Track 1 : shows the gamma ray log, which measures the natural gammaradiation of the formation. Radioactive elements such as uranium,potassium, and thorium tend to occur more in shales than in sands. As aresult, the gamma ray log is a lithology log that identifies shales from sands.

The Caliper: it's the dotted line in the same track that measures theborehole diameter

Track 2: Porosity, plotted on a scale ranges from 0 to 30% Trackj: Bulk density plotted on a scale ranges from 2.0 to 3.0 gm/cc A correction shows how much density compensation has been applied to

correct for mudcake and borehole rugosity. The correction scaled from -0.5to +0.5

But if the correction was z O.ls gm/cc, the data in the main curve will not be veryreliable.

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Electron Density and Bulk Density:The density log responds to the electron density of the formations.For a substance consisting of a single element, the electron density index, pe, isrelated to the bulk density, Pb :

( 2 Z JP.,""A. A',Where:pe is the electron density indexPb is the bulk densityZ is the atomic number of the elementA is the atomic weight of the elementFor a molecular substance, the electron density index is related to the bulk density:

/ ' " J_. 2~Zip , , - P b l M, ,,'Where:M is the molecular weightLZ is the sum of the atomic numbers of the atoms making up the molecule, whichis equal to the number of electrons per molecule

pe is the electron density indexPb is the bulk density

The log tool reads apparent density (pa) which is practically identical to actualbulk density (Pb)But for some substances such as: sylvite, rock salt, gypsum, anhydrite, coal, andgas-bearing formations, a correction is needed to obtain bulk density values fromthe density log reading (apparent density) as shown in the coming 3rd figure

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Atomic Properties of common elements in the formation

: E l i t ! m @ " n ,A 2, ( 2 ~)iH 1 , , O O S ], 1.'984

1C 12.'0~. 1 6 0.9991

1 1 ,0 H5.00 ,s 1.000

0 0! M , ~ 2 2 : . ' 9 ' g . 1 1 O . ,~ , S f . 5 ,

'9Mg ,~~,.3,2 1: 2 0..9868 ;

A il ,2,6.'98 1:3 O . ' ~ 6 37

S i 2,9 ..0'9 14 0.9915,8

S ,32.0i 16 , 0,'9978 :

C : l ,35.,46 1. , 0.9,S8,8

K ,39. ]0 19 0.'97 1'9

C i l i . '~IO.j),B :20 0.998,0

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Densities of Rock Formations and Fluids

C~mIHI~nd C~ln~Osi~iQ'n At!I8J1 l7)A En~t'hr~ Ap'I~~:r!)'ntBl!~k EI~CI~(Jo'~1 Bult

[Ieo!Oity. De:ncSHy. Dmsity,p~ ~. Pl .QUll r tZ :S iO~ 2.654 0_9985 2..650 2_f!4S

Caldrre CaCO~ 2.710 0_9991 2 ..708 2_7H)D.olo~l1' i te CaOD, , , MgO)1. 2,87(} 0-9977 U163 :2 ,876AL~hydr i t e C n : SO~ 2 , 9 6 0 0 00.9990 2 , . 9 5 7 2.977

Syh?ute KCL 1.984 0_9657 L916 U)('i3Halite NaO 2.165 O_9:S81 2JH4 2 _ > 0 . 1 2G~lIm a~SO.l!.2H~O 2,120 1 .0222 2,372 2.351

Amima t : i t e (ImlJ!) .1.400 .~,{BO ~.441 1.355A~thr~it~ (hi!;l,h) I ,SOO ~ A ' O J . O U:~2 1.796Coo l (B i l .u lm i r !( ! ! l~$ ) 1,200 ~ , { D 6 0 11.272 U73

C> i ] i I I i l 1 . : : : : 0 0 0 ~,i (~60 l590 U~ArmeWafer H2O 1 . 0 0 0 0 1 .1 [{II l J 10 l . i j O QSa l t Watf r 200,000 I~pm N . a C l .1 ,146 1 . 0 7 9 7 L.237 U.35

O il {O:ll}" 4 185 0 1 _ 1 4 0 7 00_970 0 _ . & 5 0Melihatlie Clo l4 p m L247 U47p." 1 _ 3 3 5 p m : -

O . ~ 8 8Gas eLi Hc f\ ~.238 1.2J8,ps I 325pg-o . r s s

1! 'Q,FIM.' : ':T iONi l lENlSIT' l ' ILOG"'J"!SA ILT . .~O~ II:E:C T IC N IS

1< : I--+~......jf--+--I.-----I.NI--~)_ IIJ OO ~Q R FI:~ CT !! i;I~ Q OOIJIN lA ~l-f." :llnVI'1i1! ;: t.~c .. l= itO PI 'M T(I 'OB,AI~ 'l'FilIiliE. ".1: (: :~IKCb~ ,fjiUbl!; I)ENiS~1r'f. Pb

4Q!r---,_---t~~b.=~~~~--t---~--~--~~'~--~~+~i' t . I I , I I I~N!SI1J4 J\LIUMLMI,IMI--. " " ' 4 ~ ' "

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Porosity determination from density logs:For usual pore fluids and-for common reservoir matrix minerals, the differencebetween the apparent density pa read by the density log, and the bulk density Ph isso trivial that it is disregarded

' "" P'm,-PbPm - Pr

< l > is the porositypmis matrix densityPh is bulk densityPf is fluid density

The density porosity is usually calculated assuming pf = 1gm/ cc.

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Typical Reservoir Porosity Values:Sandstones have porosities that typically range from 8% to 38%, with an average of18%. About 95% of sandstone porosity is effective porosity.Carbonates have porosities that typically range from 3% to 15%,with an average ofabout 8%. About 90% of carbonate porosity is effective porosity.

Less than lO%: poor, productivity doubtful10- 15%: fair15- 25%: good, the most common range in productive reservoirsOver 25%: excellent, but rare.

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Water saturation:Is the percentage of the pore volume of the reservoir rock that is filled with water.It is generally assumed, unless otherwise known that the pore volume not filledwith water is filled with hydrocarbons.Determining water and hydrocarbon saturation is one of the basic objectives ofwell logging.Water saturation can be measures by resistivity log.

Resistivity Log:Resistivity is the degree to which a substance "resists" or impedes the flow ofelectrical current. It is a physical property of the material, independent of size andshape.

11) .,. 1heSlshvlty'" . . .ConductivityThe resistivity unit used in well logging is ohm-metert/meter, which is usuallyshortened to ohm-meter.Electrical conductivity is expressed in mhos per meter. In order to avoid decimalfractions, in electrical logging, it is expressed in millimhos per meter.

Theory:In reservoir rocks, the sedimentary minerals that make up the formation matrixare non-conductors. Also, hydrocarbons such as gas and oil are non-conductors.Therefore, current flow in sedimentary rocks is associated with the water in thepore space.Most of the waters encountered in well logging contain some sodium chloride(NaCl) in solution. The current then is carried by the ions of the salt, which isdissolved in the water. Therefore, conductivity is proportional to the saltconcentration (salinity) of the water.

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The amount of water contained in the formation is directly related to the porosityand, also, affects the formation resistivity. As the volume of water increases, thecapacity for ions increases and the conductivity increases. Thus, the formationresistivity is affected by:

Salt concentration in the water (salinity) Reservoir temperature Water volume (porosity) Hydrocarbon content.

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Types of Resistivity Logs1- Induction Electric Log (measures conductivity)2- Electrode Log (measures resistivity)

Principle of Electrical Logs:Currents were passed through the formation by means of current electrodes, andvoltages were measured between measure electrodes. These measured voltagesprovided the resistivity determinations for each device.Types of Electrode Log:

1- Normal Logs2- Lateral Logs3- Laterolog

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Normal Log Device:In the normal device, a current of constant intensity is passed between twoelectrodes, A and B. The resultant potential difference is measured between twoother electrodes, M and N. Electrodes A and M are on the sonde. Band N are,theoretically, located an infinite distance away. In practice, B is the cable armor,and N is an electrode on the bridle (the insulation-covered lower end of the cable)far removed from A and M. The distance AM is called the spacing (l&in. spacingfor the short normal, &in. spacing for the long normal), and the point ofinscription for the measurement is at 0,midway between A and M.

N

Normal Device, basic arrangement

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Lateral Log Device:In the basic lateral device, a constant current is passed between A and B, and thepotential difference between M and N, located on two concentric sphericaleqoipotential surfaces centered on A, is measured. Thus, the voltage measured isproportional to the potential gradient between M-and N. The point of inscriptionis at 0,midway between M and N. The spacing Ao is 18ft 8 in. The sonde used inpractice differs from that shown in Fig. 7-2 in that the positions of the current andmeasuring electrodes are interchanged; this reciprocal sonde records the sameresistivity values as the basic sonde described above. Also, all electrodes are in theborehole, with N located 50 ft 10 in. above M.

i

:1

-~ 'l-~~apacilig. 1

... .....-!'~I'_JI_J .... ; ........ ~I'I!!II"W'"""",,-Ol

Lateral Device, basic arrangement

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Focused Logs:Focused logs replaced Normal and Lateral logs since 1950The responses of conventional electrical logging systems can be greatly affected bythe borehole and adjacent formations. These influences are minimized by a familyof resistivity tools that uses focusing currents to control the path taken by themeasure current. These currents are emitted from special electrodes on thesondes.The focused log used to obtain our data is: Laterolog

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Laterolog:The laterolog is a direct current (DC) tool based on Ohm's Law. The tools havebeen designed to produce reliable resistivity measurements in boreholescontaining highly saline drilling fluids and/or when surrounded by highly resistiverocks. The logging current is prevented from flowing up and down within thedrilling fluid by placing focusing electrodes (AI and A2) on both sides of a centralmeasure electrode Ao. The focusing electrodes force measure current to flow onlyin the lateral direction, perpendicular to the axis of the logging device.The laterolog electrode arrangement consists of a center current electrode placedsymmetrically between three short-circuited pairs of electrodes. A controlledcurrent is emitted from the short-circuited outer pair of electrodes in such amanner that the voltage difference between the two inner short-circuited pairs ofelectrodes is essentially zero. These electrode arrangements focus the formationcurrent into a thin disc, which flows perpendicularly to the borehole.

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Formation Resistivity Factor:It has been established experimentally that the resistivity of a clean, water-bearingformation (i.e., one containing no appreciable amount of clay and nohydrocarbons) is proportional to the resistivity of the brine with which it is fullysaturated. The constant of proportionality is called the formation resistivity factor,F. Thus, if R, is the resistivity of a non -shaly formation rock 100% saturated withbrine of resistivity Rw then

~,' ~F 'R ' 'F" = : - " ' . ' _ ' ','illl"l."=_", .', ' , ' ,~~O[ , ,~

F: Formation resistivity factorR w : the resistivity of the formation waterRo: the resistivity of the formation saturated 100%by the formation water ofresistivity Rw

c[;'r

a is an empirical constantmis a cementation factor that varies from 1.3for unconsolidated sands to 2.5 forconsolidated sandstones.< l > is the porosity

F= 0.81/


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Archie's FormulaArchie determined experimentally that the water saturation of a clean formationcan be expressed in terms of its true resistivity as:

Where:Swis water saturationn: Is water saturation exponentRt: the true resistivity of the formation partially saturated with water of resistivityRw and hydrocarbon.F: Formation resistivity factorRw : the resistivity of the formation waterRo: the resistivity of the formation saturated 100%by the formation water ofresistivity Rw

Where n in mostly all cases = 2R, can't be measured, so it's substituted by FRwR, is extracted from the resistivity logF is calculated as mentioned before

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Different resistivities and salinities of water (fresh & saline)

To'tcal,sal~inity TypeUlpm}

R I .~ ~ !i !i !'~l1mm2lmS ea w ~nefLagu:n~]] IM,tVeM,t~llalW~lbin,e~~E. Telt lSBU. ,am.Kuwa i tS im psom 001 ."O'kia l1oma

0.11

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Lithology of the Formation:The GR3log is a measurement of the natural radioactivity of the formations. Insedimentary formations the log normally reflects the shale content of theformations. This is because the radioactive elements tend to concentrate in claysand shales. Clean formations" usually have a very low level of radioactivity, unlessradioactive contaminant such as volcanic ash or granite wash is present or theformation waters contain dissolved radioactive salts.

Properties of Gamma Rays:Gamma rays are bursts of high-energy electromagnetic waves that are emittedspontaneously by some radioactive elements. Nearly all the gamma radiationencountered in the earth is emitted by the radioactive potassium isotope of atomicweight 40 (1(44 and by the radioactive elements of the uranium and thorium series.Each of these elements emits gamma rays; the number and energies of which aredistinctive of each element.The coming figure shows the energies of the emitted gamma rays: potassium (1(40)emits gamma rays of a single energy at 1.46MeV, whereas the uranium andthorium series emit gamma rays of various energies.

:2.~2

~IU I l l l l l l , I

1.76II I l .I I , I n i1.5 :22:5 3

3 Gamma Ray4 Formations without shale

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Theory:In passing through matter, gamma rays experience successive Compton-scatteringcollisions with atoms of the formation material, losing energy with each collision.After the gamma ray has lost enough energy, it is absorbed, by means of thephotoelectric effect, by an atom of the formation. Thus, natural gamma rays aregradually absorbed and their energies degraded (reduced) as they pass through theformation. The rate of absorption varies with formation density. Two formationshaving the same amount of radioactive material per unit volume, but havingdifferent densities, will show different radioactivity levels; the less denseformations will appear to be slightly more radioactive.

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So the lithology of the reservoir must be determined to know the volume of shale(Vsh) , because it affects the resistivity and porosity calculationsIt produces more porosity readings, and low resistivity ones.

To calculate Vsh , first we must obtain the gamma ray index (IGR)Schlumberger formula to calculate IGR:

IGR: Gamma ray indexGRlog : Gamma ray log (GRmin : Gamma ray minimum (clean sand)GR m ax: Gamma ray maximum (shale zone)

Calculating Vsh using Dresser-Atlas formula: For consolidated rockVsh = 0.33 [2(2xIGR) - 1.0]

After calculating Vsh , it's needed to correct the previously calculated porosity andwater saturation

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Porosity correction:For porosity calculated using density log, we apply Dresser-Atlas formula:

V vo l um e of .~ h~ rulc-~ h'rpbcrn de nsity I log derived po rosity ('OIT{!Cled fo r shalePrna m atrix dc-n sity of forrnarin nPh ~ belk density of format ionPr nuid density I{ ] ,, 0 ~hrfresh m ud and ~ ". 1 fo r s~lh

mud)Pt:h bulk density of adjau~mt[ 'shule

Water saturation Correction:For water saturation calculated using resistivity log we apply Schlumbergerformula

S . . . . . , , _ wate r sa turutio n l'J lnm n va dcdzone c o r r e c t e d f o rvo luUTI IC o f shale

R w - - 'k ) rmath ~nwater rcsisti vityat fortnatjo ntem IPcru tu rc

R . tru e to rm a tio n re sis tiv ity( / > porosity corrected for volume of shaleV:-.h \to lume of shaleRSI~ resisti ' I l ly of adj.a~e[u shale

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Calculating IGR using data obtained from well (A):GR max=120.79 at depth-Bjox ftGR min=2S.632 at depth=8437.S ftGR [og=64.496 at depth= 8277.S ft

64,496,-,25.6,32IGR= 120,79-25.6,32 = 0.387

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Interfacial Phenomena and WettabilityIntroductionThe pore space in a petroleum reservoir rock is usually occupied by more than onefluid. In an oil reservoir, water and oil occupy the pore space. In some oilreservoirs, at some stage of depletion, water, oil and gas may occupy the porespace.

When more than one fluid occupies the pore space of a porous medium, new set ofproblems arise. Interfacial forces (surface forces) between the immiscible fluidsand between the fluids and the rock surface come into play. Further, the rocksurface can show a marked affinity for one of the fluids. Such an affinity ischaracterized by the concept ofwettability.

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Surface and Interfacial TensionsSurface TensionSurface tension is the contractile force that exists at the interface of a liquid and itsvapor (or air). Surface tension makes the surface of a liquid drop act like amembrane. The force is caused by unequal molecular attractions of the fluidparticles at the surface as shown in figure. The force per unit length (o =Force/Length) tending to contract the surface of a liquid is a measure of thesurface tension of the liquid. It is a property of the liquid and is usually expressedin units of dynes/ern.

M ' E N r s c u s

Factors that affect the surface tension of a liquid include pressure, temperatureand solute concentration.The effect of solute concentration on the surface tension of a liquid depends onthe liquid and the nature of the solute.Liquids having fairly close values of surface tension. Generally, the surface tensionof the mixture varies approximately linearly with the composition.Liquids having widely different values of surface tension.In general, the surface tension of a liquid is reduced substantially by addition of aliquid of lower surface tension, but is only slightly increased by addition of a liquidof higher surface tension.

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Solutions of colloidal (long chain) electrolytes.In general, the surface tension decreases with solute concentration but is followedby a region over which the surface tension is virtually unchanged by soluteconcentration. For example, the surface tension of water at 25 Cwill be reducedby addition of sodium lauryl sulfate from 72dynes/em to 40 dynes/em at aconcentration of 0.01moles per liter of solution. The surface tension remainsconstant above this concentration.

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Interfacial TensionInterfacial tension is the contractile force per unit length that exists at theinterface of two immiscible fluids such as oil and water. The forces acting on thesurface molecules are similar to those in the liquid-vapor system, but the mutualattraction of unlike molecules across the interface becomes important.Chemicals that adsorb at interfaces are usually referred to as surface active agentsor surfactants. Such chemicals form a monolayer at the interface. The monolayeris in a state of compression which reduces the contractile tendency of theinterface, thereby reducing the interfacial tension. The presence of the adsorbedmolecules creates a surface or spreading pressure which reduces the interfacialtension. In fact,

Where a is the reduced interfacial intension, adls the original interfacial tensionand IT is the spreading pressure. Surfactants are often used to reduce theinterfacial tension between oil and water in order to improve oil recovery.The interfacial tensions between reservoir water and crude oils have beenmeasured for a number of reservoirs and found to range from 15 to 35 dynes/em at70 of, 8 to 25 dynes/em at 100 of, and 8 to 19 dynes/em at 130 of.

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Measurement of Surface and Interfacial TensionsRing MethodThe ring method of determining surface or interfacial tension depends onmeasuring the force required to pull the ring free of the interface as shown inFigure. Theoretically, the surface or interfacial tension is given by

f1! 'Jf=~- .2l

Where o is the surface or interfacial tension, F is the force required to pull the ringfree of the interface and L is the circumference of the ring. The factor of 2 accountsfor the fact that there are two surfaces around the ring. In practice, corrections areneeded to account for the mass of liquid lifted by the ring in breaking through theinterface as shown in Figure. Such corrections are made available with theinstrument. Figure shows a typical instrument, known as the du Nouytensiometer, which employs the ring method for surface or interfacial tensiondetermination.

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Experiment A: (applying the RingMethod by using DodecylbenzeneSulfonic Acid)Molecular Formula: C S H30 03 STypical Properties: Density (g/rnl, 20C) 1.08Standard Applications: DDBSA is suitable for use in the manufacturing ofliquiddetergents over a wide range of concentrations and viscosities. Used in themanufacturing of soapless detergent powders and pastes.

F 2LConc. (dyne) (em) lml [d lyne/cm)0 904-32 12.56 72

0.003 904-32 12.56 720.03 542.592 12.56 43.203 542.592 12.56 43.23 542.592 12.56 43.2

DDBSA8070

~60~ 50. . . . . . . .

~ 40>~ 30b20100

0 0.1 0.2 0.3Cone.

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Experiment B: (applying the Ring Method by using Sodium Lauryl Sulfate)STANDARDAPPLICATIONS: SLSis a concentrated, high purity surfactantdeveloped for systems requiring high activity. SLSis an exceptional foamer,dispersant and wetting agent and finds use in oral care products and powdereddetergents of all types.

F 2LConc. (dyne) (em) lml[dyne/crn)0 904-32 12.56 72

0.003 904-32 12.56 720.03 542.592 12.56 43.203 542.592 12.56 43.23 542.592 12.56 43.2

SLS8070

~60~ 50. . . . . . . .

~ 40>~ 30b20100

0 0.1 0.2 0.3Cone.

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WettabilityWettability is defined as the tendency of one fluid to spread on or adhere to a solidsurface (rock) in the presence of other immiscible fluids.

50% of all sandstone reservoirs are oil-wet.Strongly water-wet reservoirs are quite rare.Rock wettability can affect its relative permeability to water and oil and thusinfluence fluid injection rates, flow patterns of fluids within the reservoir, and oildisplacement efficiency.Alteration of rock wettability by adsorption of polar materials, e.g. surfactants andcorrosion inhibitors, or by the deposition of polar crude oil components, canstrongly alter the behavior of the rock.When water is injected into a water-wet reservoir, oil is displaced ahead of theinjected fluid. Injection water preferentially invades the small- and medium sizedflow channels or pores. As the water front passes, unrecovered oil is left in theform of spherical, unconnected droplets in the center of pores or globules of oilextending through interconnected rock pores. In both cases, the oil is completelysurrounded by water and is immobile. There is little oil production after injectionwater breakthrough at the production well.In an oil-wet rock, water resides in the larger pores, oil exists in the smaller poresor as a film on flow channel surfaces. Injected water preferentially flows throughthe larger pores and only slowly invades the smaller flow channels resulting in ahigher produced water/oil ratio and a lower oil production rate than in the water-wet case.

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Contact angles

(a) The surface is preferentially oil wet(b) The surface is of neutral wettability(c) The surface is water wet(d) The surface is totally water wet

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Oil

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Surfactants and its use in EORDefinition: they're surface active agents in which their molecules are composed oftwo portions called lipophilic and lipophopic.

Lipophilic group has sufficient solubility in the solvent and always tends to bringthe entire molecule into solution, whereas the lipophopic group is rejected by thesolvent, because it has less affinity for the solvent molecules and tends to expelentire molecules from the solution.Composition:

Mechanism of the surfactant in the EOR processThe surfactant is used to lower the interfacial tension between the flooding waterand the oil in the reservoir to increase the flooding recovery efficiency.This is done since the polar group is soluble in the flooding water where the nonpolar group is soluble in oil which leads to the decrease of the interfacial tensionbetween the two fluids increasing the flooding efficiency

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EFFECT OF SURFACE ACTIVE AGENTS ON ELECTROKINETIC ANDWETTABILITY CHANGES OF RESERVOIR ROCKSWhen a solid particle is in tangential motion relative to a liquid phase, an electricfield is induced. As a result of the tangential motion along the slip plane, theequilibrium of charges within the interface is disturbed and this disturbance iscounteracted by a flow of charges attempting to restore the electrical balanceacross the whole interface. The overall phenomenon of interfacial flow and the

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associated charge redistribution is known as the electrokinetic effect. The chargegradient at the slip plane in solution is known as the electrokinetic potential.Zeta potential is the difference between the potential at the slip plane and thepotential in the bulk solution, the latter being taken as the reference and equal tozero. Whenever mobile charges are present, the interfaces become charged; theexceptions are those specific conditions, which lead to a mutual compensation ofcharges, resulting in a point of zero charge. Zeta potential is the most easilyaccessible parameter to experimentally determine the sign and magnitude of thepotential at the solid-liquid interface.Surface charge is an important property of a solid in contact with fluid since it candetermine what can adsorb, penetrate or adhere from the liquid phase. Indeed,processes such as adsorption, particularly of surfactants or macromolcules, canalter the interfacial behavior of the solids markedly. Surface charge of a solidparticle contacted with liquid phase is determined by the concentration of the"potential determining ions" in solution; the potential determining ions in the caseof sand (quartz) are H+and OH-. Other inorganic species, surfactants as well aspolymeric reagents can also affect the interfacial charge, this can in turn beimportant in controlling transport of ions through the surface layers, but thesesecondary effects are controlled by the potential determining ions.The adsorption of surface active agents at the interface of a solid and a liquidphase is a fundamentally important phenomenon. The adsorption is controlled bythe chemical nature of the species being adsorbed, including the nature of thehead group (anionic, cationic or nonionic) and that of the hydrophobiccharacteristics, also the nature of the solid surface onto which the surfactant isbeing adsorbed. Increasing the negativity in Zeta potential of silica is reported tooccur as a result of the adsorption of anionic surfactants.This work is devoted therefore, to the evaluation of the effect of some surfaceactive agents on the electrokinetic and wettability changes, obtained as the resultof contact between sandstone and fluid. Surface charge measurements wereperformed using an electrophoresis technique; wetability measurementswere carried out by the contact angle method. Elecrtrokinetic measurements withother possible interfacial techniques will assist in understanding surface behaviorand explaining different mechanisms of surfactant adsorption.EXPERIMENTALELECTROPHORETIC MEASUREMENTS

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The Zeta potential of sand particles exposed to various chemical environments wasmeasured using the Zeta Meter. The Zeta potential was measured afterconditioning the minerals in water in the absence and presence of inorganic andorganic surfactants at varying concentrations. pH was adjusted using diluted HCIand/or NaOH. Zeta potential measurements were made on a Zeta Meter modelZM3-83. The sample is loaded in a cell that contains an anode and a cathode atopposite ends. A narrow tube, which connects the two, allows the sample to flowbetween the electrodes. The cell is placed under a microscope, which is focused onthe stationary layer inside the tube. When an electrical field is applied through theelectrodes, the charged particles flow to either the anode or the cathodedepending on the polarity. The velocity of a particle can be measured bymonitoring the time required to traverse one interval on the micrometer. For eachsample, ten particles were tracked.CONTACT ANGLE MEASUREMENTSContact Angle measurement is considered one of the most usual methods ofevaluating wettability. The oil droplet was placed on the bottom of a highlysmoothed surface of a Sandstone sample immersed in an aqueous solution. Theequilibrium contact angle was then measured from the photographs. Allmeasurements were carried out at 25C. The contact angle measured in the waterphase was determined by making a tangent to both sides of the oil droplet.Contact angle ofless than 90, measured through the water phase, indicatespreferentially water-wet condition; whereas a contact angle greater than 90indicate preferentially oil-wet condition. A contact angle of 90 would indicate thatthe rock surface has equal performance for water and oil.

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References used: Schlumberger - Log Interpretation Principles &Applications Ekwere]. Peters, Petrophysics, , University of Texas. George Asquith, Basic well Log Analysis for Geologists. M. Naser Khan, Introduction To Wireline Log Interpretation Alkhatha'ami Mohammed, Permeability, Porosity, and Skin Factor. ErIe C. Donaldson, Petrophysics, Second Edition Theory and Practice ofMeasuring Reservoir Rock and Fluid Transport Properties

Experimental Reservoir Engineering Laboratory Workbook, NorwegianUniversity Of Science and Technology.

Fundamental of Well-Log Interpretation I, the acquisition ofloggingdata

Petrophysics Related to Enhanced Oil Recovery

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