Determinacion de La Porosidad en Pozos Horizontales

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SPWLA 39th Annual Logging Symposium, May 26-29,199s

POROSITY DETERMINATION IN HORIZONTAL WELLSS. Calvert*, M. Lovell*, P. Harvey*, J. R. Samworth+ & J. Hook+ABSTRACT

Experience demonstrates that there is a needto assess whether or not logging tools areproviding acceptable porosity values inhorizontal wells. The economic viability of afield crucially depends on accurate poros itydetermination. Porosity can be derived froma number of different wireline and LWDtools; neutron, density, sonic, NMR andresistivity. Porosity estimates together withcore measurements that provide importantconstraints for the range of porosityestimations.There are a number of unusual effects thathave been seen in horizontal well porositylog data when compared with vertical wellsthrough the same formation, typicallyresulting in increased porosity values fromsome of the porosity logs (notably density).A number of reasons can be proposed, suchas: permeability aniztropy leading toirregular invasion variable watersaturation above and below the borehole,differential stress, micro-fractures anddisturbed too l placement. Often the porosityvalues derived from the well data areapplied field wide, this is regardless ofwhether the well location represents areasonable sample of the reservoirparameters or not. The well data are the bestinformation available that can shed light onthese quantities. Hence, there is a need toassess which logs provide acceptableporosity estimates. Horizontal wells allow agreater volume of the field for investigationthan vertical wells and therefore represent astatistically better sampled population ofthe field parameters.In the case study examined, examples ofvertical well and horizontal side track datafrom the North Sea demonstratedinconsistencies in porosity values. Thevertical well wireline derived porosityvalues and LWD neutron are less than thecore po rosity.

* Department of Geology, Leicester University Wireline Technologies Ltd Enterprise Oil Plc

But, in the horizontal well, the LWDmaximum density derived porosity andneutron porosity values are lower thanexpected from the vertical well values. Thissuggests that through the horizontal sectioneither the formation porosity is lower;increased gas effects are observed orborehole conditions are degrading thequality of the log values.For the dataset examined, the LWDmaximum density derived porosity providedthe best porosity estimator in the horizontalwell and the borehole conditions are themost likely cause of the reduced porosityestimate.

The values have been validated, calibratedand compared to assert the fundamentalcauses of the inconsistencies. The integrateddata sets have then been used to formulatealgorithms and approaches to interpretationby using a range of numerical methods toconstrain the derived porosity values.INTRODUCTION

The Southern North Sea is still an activearea of hydrocarbon exploration and a richsource of gas for north-western Europe. AsBritain turns increasingly to gas firedgenerators to help meet the proposedreduction in carbon dioxide emissions, thereis an increase in demand for natural gas. Asa result, the Southern North Sea has had anew lease of life for gas production. Theexploitation of previously uneconomicreserves and exploration for new reservoirshas stimulated the use of more elaboratemethods of extraction to extend the life offields.One of these methods has been the use ofhorizontal wells. Drilling horizontal wellsoffshore is expensive and must normally bejustified as the most cost effective mannerof overcoming a specific production problemor simply the most cost efficient way todrain the reservoir. The production problemsthat may be encountered are:. Tight formations. Horizontal wells canopen up more migration paths or


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SPWLA 39th Annual Logging Symposium, May 26-2991998

possibly be used for future use as aninjector well to induce fractures into theformation.l Fractured formations. Drillingperpendicu lar to the formation fractureorientation means as many fractures aspossible are intersected. This often

requires horizontal drilling.l Channel sands. Drilling horizontally tointersect as many channels as possible.l Water and/or gas coning problems.Horizontal wells can delay thewater/gas break through.. Permeability barriers. Horizontal wellscan drain otherwise inaccessible parts ofthe formation.It has been noted that horizontal wellporosity data from the Southern North Sea inany given reservoir tends to be greater thanthe corresponding vertical well datasuggests, A number of previous authors haveinvestigated this problem (Bigelow andCleneay, 1992; Cuddy et. al., 1994;Cunningham et. al., 1990; Day and Petler,1990; Holenka et. al., 1995; Prilliman et. al.,1995; Schroeder et. al., 1991; Went andFisher. 1997; Wolcott et. al., 1995;Woodhouse et. al., 1991), but the matter stillremains unresolved. The likely cause ofthese inconsistencies will probably be aculmination of effects ranging from toolresponses to environmental effects.In the North Sea, new vertical wells areoften logged with LWD and wireline tools,but horizontal wells are generally onlylogged with LWD tools. The LWD derivedporosity values from horizontal well areoften found to read higher values thanthrough equivalent formations in the verticalwells. This behaviour suggests that thedifferences between the porosity values inthe wells are not just due to natural lateralvariations in reservoir porosity, but as aresult of the change in tool response due tothe change in tool orientation and loggingenvironment.

BACKGROUND GEOLOGYThe Southern North Sea has been an area ofactive hydrocarbon exploration andproduction since the early 1960s. This areacovers what is known as the SouthernPermian basin that stretches from the midNorth Sea high and the north-east England in

the west of the basin to the Polish-Russianboarder in the east. The hydrocarbon fieldsof the offshore UK sector of the SouthernNorth Sea are predominantly gas producing.The North Sea basins (North and South)were formed as a result of tensional stressesin the Hercynian foreland during the lateCarboniferous and early Permian (Walkerand Cooper 1986). Towar,ds the end of theHercynian orogeny, there was a period ofuplift that affected the North Sea basins.This uplift lead to a period of erosionaccompanied by volcanism during the lateCarboniferous and the early Permian.The Sole Pit sub-basin formed during theearly Permian and lies off ,the North coast ofEast Anglia, England (Figure 1). The SolePit basin gas was derived from devolatilitiedcoal from the underlying Carboniferous coalmeasures (Walker and Cooper 1986). Thereservoir rocks are predominantly Permian,Rotliegendes aeolian/fluvial sands.Generally, the aeolian sand members havegreater porosity than the fluvial mem bers.The cap rock is forme,d by the basalPermian, Zechstein mudstone(Kuperschiefer) and the overlying evaporitesequences. The basin has suffered twoperiods of inversion. The first during the LateJurassic/Early Cretaceous that stripped awaymost of the Upper Jurassic sediments andanother in the mid-Tertiary as a result of theAlpine orogeny.Rotliegendes aeoliamfluvial sands wereformed on the Southern North sea basinmargins and are known as the Leman sands.The primary sediment source was fromerosion of the Carboniferous coal measures(Westphalian) from the nearby London-Brabant massif that lay to the south of theSole Pit basin (Ziegler 1975 and Glennie1990). The sediment was carried byephemeral fluvial channels into the basin.Here, on the flood plain, rhe sediment wasacted on by the strong trade winds from theNorth to North-east to form aeolian deposits.Immediately overlying the Rotliegendes isthe basal mudstone of the Zechstein. Aninitial rapid marine transgression (Jenyonand Cresswell 1986) lead to an increase inmoisture allowing a covering of vegetationto form that later provided the basalmudstone of the Zechstein. Later, the basin

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became extremely dry with intermittentrecharging of the basin that provided thesource for the deposition of evaporities.There are five cycles of evaporities known,indicating at least five marine transgressionsduring the Zechstein. Owing to the thicknessof the evaporities (ignoring later thickeningdue to halokinesis), the basin must havebeen regularly recharged with saline water.This conclusion is further supported by localinterbedded thin evaporities (Taylor 1990).Although, some gas is found in the dolomiticmembers of the Zechstein. The mostimportant reservoir rock is the aeoliansandstones of the Rotliegendes. The aeoliansandstones are generally better sorted andcleaner than the fluvial members thatcontain more siltaceous material.

COMPARISONFirstly, it must be established that thevertical well data is of good quality andprovides consistent reservoir porosity valueswith wireline, core and LWD derivedporosity data. Once acceptable reservoirporosity values have been estimated, atransform is formulated to calculateacceptable reservoir porosity values from theLWD measurements, normally a linear shift.The transformed LWD values provideestimates of porosity from the LWDmeasurements in the horizontal well.The reservoir is assumed to be homogeneousand laterally continuous with low dip (Wentand Fisher 1997). Then if the LWD tools a reworking in the same manner in a horizontalwell as in the vertical well, the porositytransform should provide the best estimatereservoir porosity values at the equivalenttrue vertical depth.

EXAMPLEThe example used for the study is a gasreservoir in the Rotliegendes Leman sands.The Leman sands are underlain by theWestphalian coal measures (the sourcerock) and overlain by a thin -2ft (< lm)mudstone and dolomitic limestone - lft(-0.5m) (Figure 2 ). Above the dolomiticlimestone is -40ft (-13m) of anhydrite withsome thin dolomite interbeds. The anhydrite

is capped by a minor gas reservoir consistingof -30ft (- 10m) of dolomite. Above thedolomite, -8ft (-2m) of anhydrite followedby a substantial thickness ofhalite/polyhalite.The datasets consist of measured valuesfrom a vertical well and its horizontal side-track (Figures 3 and 4). Both wells weredrilled using 8.5 bits with barite free oilbased mud (70% oil, 30% water) with amud weight of -10.5 lbm/gal (1.26 g/cm3).The vertical well is deviated at -57through the reservoir and has both wirelineand LWD datasets with accompanying core.The wireline tools include gamma ray, bulkdensity, caliper, neutron porosity, acoustictravel time, induction and formation tester.The LWD tools run were gamma ray,density (average density, maximum density,maximum densiiy correction, densityderived caliper), neutron porosity, amplitudeand phase resistivity. The core data includehorizontal helium porosity, vertical andhorizontal permeability and grain density(Figure 5).The horizontal side-track k icks off in thehalite and is horizontal (-88O) in the Lemansands. The horizontal dataset consists ofLWD average density, maximum density,maximum density correction, densityderived caliper and neutron porosity data(Figure 4).VERTICAL WELLIn the vertical well, the wireline densityderived porosity (matrix density = 2.65g/cm3, fluid density = 0.9 g/cm3) providesthe best estimate of the core porosity, whichis used as a reference for the reservoirporosity. All the other porosity estimatesappear only to require a linear shift to be ingood agreement with the core porosityvalues (Table 1).The borehole condition appears to very goodfor the vertical well with both wireline andLWD caliper values indicating the hole isin-gauge and smooth. The respective densitycorrections are also small showing that thereis minimal mudcake thickness.

BThe core permeability values and theformation tester responses agree well

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indicating that the interval (x138 ft to x222fi) is porous and permeable. Above thisinterval the core and chippings show thatanhydrite cement (most probably derivedfrom the overlying anhydrite bed) isaffecting the reservoir quality. The base ofthe interval is the PermianKarboniferousunconformity, below which mudstones withminor sands are encountered.The high porosity/permeability interval isthe target for the horizontal side-track. Theinterval can be identified from the LWDlogs from expected porosity values of - 16%(LWD average and maximum densityporosity) and -13% (LWD neutron porosity)with accompanying high permeabilityindicated by low LWD amplitude and phaseresistivity values of -3 0hm.m (Table 2).Also, it should be noted that the acousticderived porosity (matrix acoustic velocity =55 psec/ft, fluid acoustic velocity = 220psec/ft) is within good agreement (+lstandard deviation) with core derivedporosity over this interval. However, this isnot the case above x138fi, where theanhydrite cement may be adverselyaffecting the measured acoustic travel time.This high porosity and permeability intervalis considered throughout the vertical tohorizontal well comparison.HORIZONTAL WELLSince, the log responses are similar, it isexpected that the LWD data in thehorizontal side-track will be very similar tothe vertical well da ta. The high porosity andpermeability zone can be easily picked out(x905 ft - x1655 ft Figure 4.), butimmediately it can seen that the measuredvalues are not those expected from thevertical well (Figures 3 and 5). Also, thereis a periodic signature with a wavelength of-8fi.The periodic waveform can be smoothed bya moving point filter or a Wiener filter,which preserves more of the features withinthe data. The periodic behaviour hints thatthe borehole had a corkscrew shape (Cuddyet. al. 1994) or that tool is being physicallylifted by the drilling process . The LWD tool(and the drill string) may then be liftedrepeatedly from the borehole floor or in factbe oscillating completely within the mud

column by pivoting about the bit andpossibly the LWD tool stabilisers. However,filtering will only remove the periodicperturbation from the log curves, but it doesnot remove other anomalies.The horizontal well LWD caliper andphotoelectric factor are both significantlygreater than the equivalent log responses inthe vertical well. The LWD caliper hasincreased on average by -0.5 and thephotoelectric factor by -1.9 B/e (Table 1).The LWD caliper is derived from differentialrotational density (derived from the shortspaced detector count rate variance) and thedifference between the matrix density andthe effective mud density (Best et. al. 1990).The matrix density used to record the logwas limestone, so correcting for thelithology (sandstone) will increase the LWDcaliper by -0.02 and will not make thecaliper measurement signifcantly worse.However, the greater than expectedphotoelectric response indicates that amaterial with a high Z material is present.The oil based mud used to drill both wellswas low density and barite free. This wouldsuggest that with the increased stand-off of-0.5 (- depth of investigation of thephotoelectric factor measurement), thephotoelectric factor should be measuring thephotoelectric factor of the mud, -0.2 B/e.Therefore, the photoelectric factor valuesshould decrease to approximately equal tothe mud photoelectric value. The LWDdensity values (maximum and average) donot indicate large increase in density. Also,in an overlying anhydrite bed, thephotoelectric factor measured in the verticalwell was -6 B/e and close in value for bothwireline and LWD tool. However, theequivalent anhydrite bed measured ~12 B/ein the horizontal well (wel:! deviation >70)by the LWD tool. The photoelectric factormeasurement is responding to lithologychanges, the values are far greater thanexpected. Therefore, the photoelectricmeasurement in the horizontal well issuspect. The photoelectrlc measurementproblem suggests that there may be morequality issues with the LWD densitymeasurements than is evident from the data.Without the detector count rates it is

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difficult to come any satisfactory conclusionas to the cause of the perturbations.The average density and maximum densityare calculated on the basis o f the count ratedistribution recorded during rotation (Best et.al. 1990). The average density is calculatedfrom the mean count rate and the maximumdensity is calculated from the minimumcount rate. Note, the tool is run with a threefinned stabiliser providing a 1 stand-off.Windows in the fins of the stabiliser providelow absorption passages for the gamma-rays.The actual mean and standard deviation ofthe count rate distribution are compared withthe expected count rate and standarddeviation of an in-gauge hole. The differencebetween the two (actual and expected) isthe basis of the derived calipermeasurement. Therefore, the calipermeasurement is not independent of thedensity measurement and any unusualvalues in the density measurement will bereflected directly in the caliper values andthus it is very difficult to identify the sourceof the measured density perturbation. It isnot clear whether the perturbation is causedby the borehole condition or a toolmeasurement problem.The density corrections (traditionalcorrection is a function of the long spacedminus the short spaced density androtational correction is a function of thevariance density) are applied to themaximum density measurement. In ahorizontal well, the maximum densitymeasurement could be expected to measurethe density of the low side of the borehole,although from the data there is no way ofknowing where around the circumference ofthe borehole the maximum densitymeasurement is sampled. It is possible toenvisage situations in which the maximumdensity would not read the density along thelower side of the borehole. However, it isaccepted that in a low density mud, themaximum density measurement shouldprovide the best estimate of the formationdensity.The traditional wireline density toolcorrection is applied to the LWD densitymeasurements co rrects for parallel stand-offof up to -1 and the rotational densitycorrection should correct for the tool


curvature to borehole curvature, as well asperturbation of the borehole shape i.e. notcircular (affects the total amount of mudaround the tool). However, the traditionalwireline density correction will only correctfor the parallel stand off along a strip fromthe source to the detectors. The rotationaldensity correction applies a correction basedon a circumferential variance from theaverage density count rate, which wouldhave no or very little effect on the maximumdensity measurement if the tool is in contactwith the borehole floor. Although, thecorrection corrects for the mismatching tooland borehole curvature. Thus, the rotationaldensity correction will over correct themaximum density measurement and therebyreduce the derived porosity values. However,the maximum density measurement providesa relatively good estimate of expected coreporosity (from the vertical well) in thehorizontal well.It is also interesting to note that the averageLWD density correction in the vertical was-0.011g/cm3, but +0.026g/cm3 in thehorizontal well (Table 1). Although, it iseasy to understand a positive densitycorrection with a low density mud, anegative correction is difficult to explainunless the borehole/LWD tool axes are notaligned.The average density measurement is reading-0.14 g /cm lower (-8 pu. greater) than themaximum density measurement in thehorizontal well. The tool response is quitedifferent from that seen in the vertical well.Either the borehole condition is significantlymore rugose and/or the borehole is non-circular, in which case a single set ofestimated caliper values withcircumferential data is useful only as anindicator of poor borehole condition, Theincreased caliper value could be explainedby poor tool detector/formation contact.Although, the maximum density derivedporosity values are in good agreement withthe expected porosity values from thevertical well core porosity values. Thiswould indicate that at least for some of thetool rotation the stabiliser fins are pointinginto the formation with little mud to perturbthe measurements.The LWD average density values average2.28gkm3. The LWD maximum density

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Bigelow, E. L. and Cleneay, C. A., 1992, Anew frontier: Log interpretation in horizontalwells, SPWLA 33d Annual LoggingSymposium transactions.Brooks, J. and Glennie, K. W. (Eds.), 1986,Petroleum Geology of North West Europe,Proceedings of the 3rd Conference onPetroleum Geology o f North West Europe,Graham & Trotman, London, pp. 263-305.Cuddy, S., Day, S., Page, G. and Fletcher,J., 1994, The observed effects of highdeviation wells on porosity measurements,16 European Formation EvaluationSymposium.Cunningham, A. B., Bullion, D. and Opstad,E. A., 1990, Use of MWD formationevaluation in the Endicott reservoir northslope, Alaska, USA, 131h EuropeanFormation Evaluation SymposiumTransactions.Day, S. N. J. and Petler, J. S., 1990, Toolmotion and borehole environment effects onMWD neutron porosity measurements, 131bEuropean Formation Evaluation SymposiumTransactions.Glennie, K. W., 1990, Upper Permian -Rotliegend, in Giennie, K. W. (Ed.), 1990,Introduction to the Petroleum Geology of theNorth Sea, Blackwell ScientificPublications, London, pp. 120- 152.Holenka, J., Best, D., Evans, M., Kurkoski,P. and Sloan, W., 1995, Azimuthal porositywhile drilling, SPWLA 36 Annual LoggingSymposium transactions.Jenyon and Cresswell, 1986, The SouthernZechstein salt basin of the British NorthSea, as observed in regional seismictraverses, in Brooks, J and Glennie, K W.(Eds.), 1986, Petroleum Geology of NorthWest Europe, Proceedings of the 3rdConference on Petroleum Geology of NorthWest Europe, Graham & Trotman, London,pp. 277-292.Prilliman, J. D., Allen, D. F. and Lehtonen,L. R., 1995, Horizontal well petrophysicalevaluation using LWD, SPE AnnualTechnical Conference and Exhibition 1995,SPE Paper No. 30549.

Schroeder, T. S., Zoeller, W. A., Hammons,L. R. B. and Kane, P . J. P., 1991, Integrationof measurement-while-drilling and wirelineformation evaluation data, 14 EuropeanFormation Evaluation SymposiumTransactions.Taylor, J. C. M., 1990, Upper Permian -Zechstein, in Glennie, K. W. (Ed.), 1990,Introduction to the Petroleum Geology of theNorth Sea, Blackwell ScientificPublications, London, pp. 153-190.Walker, I. M. and Cooper, W. G., 1986, Thestructural and stratigraphic evolution of thenortheast margin of the Sole Pit Basin, inBrooks, J and Glennie, K. W. (EL&.), 1986.Petroleum Geology of North West Europe,Proceedings of the 3rd Conference onPetroleum Geology of North Wes t Europe,Graham & Trotman, London, pp. 263-275.Went, D. J. and Fisher, W. C., 1997,Integration of horizontal well geologicaldata into reservoir descriptions:Rotliegendes sandstone, Lancelot area,Southern North Sea, AAPG Bulletin. V.81No.1, pp. 135-154.Wolco tt, D. S., Shafer, D. and Vittachi, A.,1995, Characterization of a heterogeneousformation using azimuthal logging-while-drilling measurements, SPWLA 36h AnnualLogging Symposium transactions.Woodhouse, R., Opstad, E. A. andCunningham, A. B., 1991, Vertical migrationof invaded fluids in horizontal wells,SPWLA 32d Annual Logging Symposiumtransactions.Ziegler, W. H., 1975, Outline of theGeological History of the North Sea, inWoodland A . FFT Ed.), 1975, Petroleum andthe Continental shelf of North-West Europe,Elsevier Applied Science Publishers,Barking, pp. 165- 189.

ACKNOWLEDGEMENTSOne of the authors (SC) thanks the LondonPetrophysical Society and LeicesterUniversity for funding the research andSPWLA for a grant to enable the author toattend the conference. The oil companiesare thanked for supplying the data.

SPWLA 39th Annual Lugging Symposium, May 26-29,1998

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ABOUT THE AUTHORSStefan Calvert is presently studyingpetrophysics for a PhD at LeicesterUniversity, UK. He is sponsored by theLondon Petrophysical Society and LeicesterUniversity. He joined Leicester UniversityBorehole Research after completing anM.Sc. in Geophysics at Durham University,UK in 1996 and also holds a B.Sc. inPhysics from the University of Birmingham,UK.Mike Love11 is Reader in Petrophysics at theUniversity of Leicester. He obtained a B.Sc.in Geological Geophysics from theUniversity of Reading in 1977, and gainedan M.Sc. in Marine Geotechnics in 1979. Hewas awarded a PhD for research in to thephysical properties of sediments from theUniversity of Wales in 1984. In 1992-93 hewas Visiting Professor in BoreholeGeophysics at the Universidade Federal doPara in Belem, Brazil.Peter Harvey a BSc. in Geology from theBristol University in 1964 and a PhD in thesame university in 1967. From 1967 to 1989he was a lecturer/senior lecturer in Geologyat the University of Nottingham, with aninterval 197 1172 at the Geological Survey ofKansas. He transferred to the University ofLeicester in 1989 where his research isconcerned with nuclear and electricallogging, and computer modelling.Roger Samworth is Research Director withWireline Technologies Ltd. (formerly BPB).He graduated from Manchester University in1968 with an Honours Physics degree andjoined BPB in 1972. At WirelineTechnologies, he has been mainlyconcerned with improving the Companysborehole logging techniques and indeveloping new tools and methods. He haspublished papers at previous SPWLA andSPE symposia.Jeff Hook is a Senior Staff Petrophysicistwith Enterprise Oil plc. He holds a B.Sc. inPhysics from Imperial College, University ofLondon and a Ph.D. from Durham University.He has previously worked in core analysiswith Corex Labs Ltd and as a petrophysicistwith Britoil plc and Mobil North Sea Ltd. Heis currently President of the LondonPetrophysical Society.

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Vertical well. hiph oorositv and Dermeability zoneVariable

/ Photoelectric Factor (B /e)Horizontal well. hieh oorositv and Dermeabilitv zone

Table 1. Log value statistics for the high permeability and porosity zone.


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Vertical well. high porosity and Derrneability zoneVariable Minimum

LWDMaximum

Average Density Porosity (%)Maximum Density Porosity (%)Neutron Porosity (limestone p.u.)CoreHorizontal Helium Porosity (%)Horizontal Permeability (mD)WirelineAcoustic Porosity (%)Density Porosity (%)Neutron Porosity (limestone p.u.)

10.700 18.3000.670 90.0007.584 17.2689.657 18.9146.945 14.410

Horizontal well. high oorositv and permeabilitv zone

Table 2. Derived porosity value statistics for the high permeability and porosity zone.


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Rate of PenetrationGamma Ray (AP b5) Resistivity (0hm.m) Density (g/cc) Density Correction (g/cc)0 50 loo 150 200 1 10 100 1000 10000 2.15 2.32 2.48 2.650.10 -0.05 0.00 0.05 0.10Caliper (inches) Core Horizontal Core and Neutron Porosit Y (%) Acoustic Travel Time (usec/ft)Helium Porosity (mD) Photoe lctric Factor (6 e).6 7 8 9 10001 01 1 10 1I I I I Ill11ll I I I,,,,, I I,,,,,, I I uI- _.

x If I \ Wirehe

W---CCJEHorizontalPermeability

RepissityX

0 120 100 80 60 4ll~l~l.~I~.IIlrIII~Il:_. .--.XT..--.

, ---.,, r:--:-.I

i-, --. Wirelinc. . -...; *.-- oustI

\: ._ G..-., ..--., --...-(._*-.-:..:..-I. *._-- ;--_-. -:.._ .--. ;:.-af::. -2:- ,-LWO ::.:. :.:Density --:.; 1:.Conectlon -a-; c--1: : -::a. :.-..-

.:.:..-.-:). \ l -- :-. .- Wireline:: .* m---L._. --,-__. --,. .-:_ .:a..~ ... ,-*-... . . , .a

-: 1

: . . .I.- __...--c...._ 2. . a--..

Figure 3. Vertical well, LWD and wireline log curves with core porosity and permeabilities.Note, wireline density porosity best matches core porosity. Caliper values in guageand density corrections are in the opposite sense for wireline and LWD. Low resistivitycorrelates with high permeability.


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6Xi: 30.-

Xi! 50,:

x1;70.x

&.cIi0

Xl! Pm

X210.:

x230,

SPWLA 39th Annual Logging Symposium, May 26-29,199sRate of Penetration (5)Gamma Ray (API) Resistivity (0hm.m) Density (g/cc) Density Correction (g/cc)0 54 100 150 2031 10 100 10032.15 2.32 2.48 2.65 -0.10 -0.05 0.00 0.05 0.10Caliper (inches)

-l--u-

GammaRay

) I

I(

C&per iiLWD

!I

i i,Wireline

Rate of GlliitPenetration ,I

i.;\ If

Core HorizontalHelium Porosity (mD)I,,,,,,II,,,

LWDbnplitude

A X. .WirelineMediuminduction

ICoreHotizontaPermeabilitX

X

X

X

XX

XXX

X

XLWDPhase X3esistivtty

\ .: . .. -*

f

:. *.

:.I; :

LWD :. ..Density . . .G3rrection~, . . *.:*

f/WirelintAcoustLQuality

Figure 5. Vertical well, high porosity and permeability zone, LWD and wireline log curves with coreporosity and permeabilities. Note, wireline density porosity best matches core porosity.Caliper values in guage and density corrections are in the opposite sense for wireline and LWD.Low resistivity correlates with high permeability.


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Density (g/cc)200 2.15 2.32 2.46 2.65

Rate of Penetration (5)0 $mma@y (ATljoCaliper (inches)

Xl10

E580

x1x

Xl%

:. .,

:,

:

:_-:-

:._:...-.

I.-.: :I

,::. . .

._,_.

: . .

,:._

-1.

,:: I :.,

_ : I :.

Resistivity (0hm.m) Core and Neutron Porosity (%) Density Correction (g/cc)

\ LWDAmplitudebsistivity

iWDPhaseResistivity

M30 Photozectric Fapr (B!e) o .lO -0.05 0.00 0.05 0.1>>--

z

Figure 6. Horizontal well, high porosity and permeability zone, LWD log curves.Note, low LWD average density and LWD neutron porosity values, the LWD maximum density valuesare greater than expected. The LWD caliper is out of guage and the LWD density correction is positive.

Determinacion de La Porosidad en Pozos Horizontales

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