1-1995 AAPG Treatise Handbooks 1 Source 18 Chapter13 in-situ Evaluation Using Wireline Logs

7/28/2019 1-1995 AAPG Treatise Handbooks 1 Source 18 Chapter13 in-situ Evaluation Using Wireline Logs

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Chapter 13In Situ Evaluation of Potential Source Rocks by

Wireline LogsSusan L. Herron

Schlumberger-Doll ResearchRidgefield, Connecticut, U.S.A.

INTRODUCTIONNumerous studies published in recent years haveillustrated the poten tial value of wireline logs for sourcerock evaluation. The work done to date has generallyfocused on the qual i tat ive ident i f icat ion of organic-r ichformations or the quantification of organic matter. Theadv an t a ges ove r a m o re tr ad i t i o na l app r oac h ofana l yz i ng cu t t i ngs i nc l ude con t i nuous s am p l i ng ,greatly improved depth control, and enhanced verticalresolut ion. Alth oug h the quantificat ion of organicmatter is neither a s accurate nor a s precise as the analytical techniques used on core, i t does el iminate thesampling bias and contaminat ion that can be introduced by cuttings analyses. To date, there are only afew examples of wirel ine interpretat ion of organicmatter maturity and n one of type, but there are indicat i ons t ha t t he i n t eg ra t i on o f ex i s t i ng t echn i quescombined with some additional log data could lead toquanti tat ive logs of total organic carbon as well asestimates of maturity and inferences of depositionalenvironment.

The feasibility of interpreting organic matter fromwireline mea surements stems from its physical pro perties, which differ co nsiderably from those of the mineralcomponents of its host rock: lower density, slower sonicvelocity or higher sonic transit time, frequently higheru ran i um con t en t , h i ghe r r e s i s t i v i t y , and h i ghe rhydrog en an d carbon concentrations. Consequently, thelogs used for source rock evaluation most commonlyinclude density, sonic, gam ma ra y, an d resistivity. Thelimitations inherent in the interpretation are primarilydue to the fact that several of these properties are quitesimilar to those of pore fluids, and therefore sol idorganic ma tter in source rock s is som etimes difficult todifferentiate from either water- or hydrocarbon-filledporosity. Some of these limitations can be elimina tedby u s i ng pu l s ed neu t ron geochem i ca l l ogs wh i ch

provide me asures of the carbon/oxy gen ratio as well asconcent ra t ions of the major inorganic e lements toestimate the total carbon, inorganic carbon, and organiccarbon in the formation.

This chapter briefly reviews the "logg ing" p ropertiesof organic matter and presents a variety of wirelineapproaches that have been taken to evaluate potentialsource rocks. The advantages of the various techniquesare presented along with some suggested directions forfuture applications.

RESPONSE OF WIRELINE LO GSTO O RGAN IC MATTERThe qualitative response of wireline logs to organicmatter (OM) present in the formation is presented inTable 1. A variety of examples that show log responsesto volumes, types, and maturi t ies of organic matterdeposited in different environments are presented byMeyer an d Nederlof (1984). A single exam ple of a wellin which most of the logs respond in an almost idealway is taken from the organic-rich Kimmeridge shale inthe North Sea and is presented h ere as Figure 1. Theresponses of the individual logs shown in Figure 1 willbe explained in terms of organic matter content, andsome of the techniques that have used these logs toevaluate source rocks will be reviewed.

Neutron and D ensity Logs and OrganicMatterThe neutron and density logs both display significant deflections in the organic-rich Kimmeridge shale(Figure 1). The neutron log, which reads about 20porosity units (pu) in the overlying Upper Cretaceousform at ion , incre ases to as mu ch as 45 pu in th eKimm eridge. This increase is due to the high hydrogenconcentration in the organic matter. For the pur pos e of

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128 HerronTable 1 . Log responses to organic matter.Log/Property

Response/Value forOrganic Matter (OM)High~1 g/cm3HighHigh transit timeHighHigh C/O ratio

CommentsHigh GR caused by U; can be linear with OM ;U not always present.Similiar to pore fluidsDue to H in OMEstimates vary from 150 to >200 /isec/ftMight not affect log response unless generatedHCs occupy poresMost direct measurement of C;needs inorganicC correction

Gamma ray (GR) oruranium (U)Density (p)NeutronSonic (At)Resistivity (R)Pulsed neutron

log interpretation, the neutron response is sometimesexplained in terms of the hydrogen index (HI), which isdefined as the ratio of the num ber of hyd roge n atom s ina cubic centimeter of sample to the number of hydrogenatoms in a cubic centimeter of water; thus, water has anHI of 1. T he rang e of hydroge n concentrations (- 3-10wt. %) reported for typical kerogens by Tissot andWelte (1984) would correspond to HI values of 0.3-0.9,with a typical type II kerogen hav ing a value nea r 0.7.

Although the increase in the neutron log responsehas been obse rved in m an y organic-rich form ations, it isgenerally not used as anything other than a qualitativeindicator. The reason for this is the m ultiple sources ofhydrog en in the formation. The other large contributors to hydrogen in the formation would be the clayminerals, which have HI values of 0.12 for illite, 0.36 forkaolinite, and 0.13 for montmorillonite with no inter-layer water (Juhasz, 1981). For a montmorillonite withtwo layers of interlayer water, the HI would increase toabo ut 0.6. Clearly, the similar HI values of organicmatter and the coexisting clays complicate the interpretation of the neutron log for the purpose of source rockevaluation.

A significant decrease occurs in the bulk density ofthe format ion in the Kimmeridge format ion , wi thdensity dropping from about 2.45 to about 2.3 g/cm 3 .This decrease can be attributed to the presence of theorganics, which have a low densi ty, about 1 g/cm 3 ,relat ive to that of their host minerals (~2.65-2.70g/cm

3). If one is willing to ma ke the assumption thatthere is no water-filled porosity or that the porosity is

constant throughout the formation, the density log canbe used to est imate the organic content . Schmoker(1979) and Schmoker and Hester (1983) successfullyimplemented this concept for Devonian shales. Theyfirst compensated for the presence of a high-densitymineral, pyrite, by assuming that it is proportional tothe amou nt of organic carbon in the formation. Theythen so lved for the volume of organic mat ter andconve rted to total organic carbon (TOC), with the resultbeing the following eq uation:

154 497TOC = -57 .2 61Pb (1)

wh ere pb is the bulk densi ty of the formation. Thetechnique worked fairly well (to within a few weightpercent) in these formations where the TOC valuesaverage about 12 wt. %. At lower TOC values, belowabout 2-3 wt . %, the assumpt ion that there i s noporosity or that porosity is constant, combined with theimplicit assumption that the only variations in matrixdensity are due to pyrite, would introduce such largerelat ive errors that i t would be impract ical to applysuch a technique.

Gamma Ray Logs and O rganic M atterThe gamma ray log displayed in Figure 1 shows anincre ase f rom ab out 60 to >200 API un i t s in the

Kimm eridge formation. The elevated gamma ray isattributed predominan tly to the presence of uranium inthe organic-rich sediments. This would be seen directlyin data from a spectral gamma ray tool which separatesthe total gamma ray into i ts thorium, uranium, andpo t a s s i um com p one n t s . The occu r ren ce o f h i ghuranium in such sediments is due to the reduction ofU+6 which is extracted from seawater and precipitatedas U+4 . The redu cing condition s respo nsible for theprecipi tat ion of uranium are also conducive to thepreservation of organic matter, and hence correlationshave f r equen t l y been no t ed be t ween TOC anduran ium. The practical application of using ura niummeasured from a natural gamma ray logging tool topredict TOC was proposed by Supernaw et al . (1978) ina U.S. patent . I t should be noted, however, that theconstant of proportionality between TOC and uran iumcan change considerably (see examples in Mendelsonand Toksoz, 1985). Among the factors controlling thisrelationship are the rate of sedimentation, the concentrations of uranium and organic matter in the seaw ater,the type of organic matter, the uranium content of thes u r r o u n d i n g m i n e r a l s , a n d t h e n a t u r e o f t h esedime nt-water interface. Therefore, to use uran ium ortotal gamma ray to predict TOC, the relationship must


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130 Herronand Nederlof (1984), the resistivity increases from tensto thousands of ohm meters in mature, oil-generatingsource beds . The res i s t iv i ty log has been used inconjunction with other logs to indicate the presence oforganic-rich deposits, but it is actually a better indicatorof organic maturity than organic richness, and in somecases it has been used to predict organic maturity.

P u l s e d N e u t r o n o r G e o c h e m i c a l L o g sa n d O r g a n i c M a t t e rIn addition to the wireline logs presented in Figure 1and jus t descr ibed , there are a number of nuclearlogging devices that can be grouped as geochemicallogs. Included amon g these are the gamm a ray andnatural gamma ray spect roscopy logs that provideconcentrations of thorium, uranium , and potassium. Inaddition, there are the pulsed neutron devices that canprovide measurements of the carbon to oxygen (C/O)ratio in the formation, which can be used to indicateorganic -rich depo sits (Lawrence et al., 1984). Pulse dneutron logs can also be operated in conjunction with anatural gamm a ray spectroscopy tool and an alum inumactivation tool, as is done in the Geochemical LoggingTool (GLT*) service, to determ ine elemental concentrations of some of the inorganic elements (Al, Si, Ca, Fe,K, S, Ti , Gd, and sometimes Mg) in the formations(Hertzog et al . , 1989). Wh en these capabil i t ies arecombined , i t i s poss ib le to use the C/O ra t io todetermine the total carbon in the formation and theother inorganic elements to predict the mineral carbon,thus making i t possible to predict the TOC contentquantitatively (H erron, 1986; He rron and Herro n, 1990;Herron and Le Tendre, 1990). The techniques for doingthis will be described later.

MULTILOG APPROACHES TOPREDICTING ORGANICRICHNESSCombinations of Gamma Ray,Resistivity, Sonic, and Density Logs

Using data from gamma ray, resistivity, sonic, anddens ity logs from 15 wells in nine different coun tries,Meyer and Nederlof (1984) took a statistical approachto develop techniques to separate source rocks fromnonso urce rocks. For a cutoff betw een the two, theyselected an organic con tent of 1.5 wt. % TOC. Theyus ed va r i ous com bi na t i ons o f l ogs (gam m aray/sonic/resist ivi ty, gamma ray/densi ty/resist ivi ty,sonic/resist ivi ty, and densi ty/resist ivi ty) to developfamilies of discriminant functions that could be appliedto log data to identify source rocks in formations thatare composed of either shales or other lithologies. Toapply the technique, one converts the resistivity log

data to 75F (24C), and then computes the appropriatediscriminant scores, or D values, from the publishedequation s. For example, the functions for shales are asfollows:D = -8.094 + 0.739 log GR + 3.121 logio At

+ 0.399 logioR75-FD = 0.817 + 0.856 logio GR - 7.524 logio A>

+ 0.292 logioRys-FD = -6.906 + 3.186 logio At + 0.487 logio RZS-FD = 2.278 - 7.324 log10 pb + 0.387 logio R75-F (2)

A posi t ive value of the discriminant score D wouldindicate a source rock, and a negative value of D wou ldindicate a nonso urce rock. The major advan tage ofsuch a techn ique is that it is a general function th at do esnot require cal ibrat ion on a well-by -well basis . I tpermits the user to examine a num ber of log combinations so that one log will not unduly influence the interpretation. The corresponding disadvantages are that itis not qua ntitative, and for a given location, it might n otprovide the o ptimum disaiiriinators (Abrahao, 1989).What is accomplished stat is t ical ly by Meyer andNederlof (1984) might also be performed manuallyusing a series of crossplot techniques. An example isthe work of Dellenbach et al. (1983) wh o prop ose d aseries of three crossplots: resistivity and gamma ray,resistivity and sonic transit time, and sonic transit timeand gamma ray, which are first used to establish thegamma ray and transi t t ime signatures of a barren

formation with out any organic matter. Those valuesare then used to compute the param eterl x = ( C j K l o g _ ( - "^ b a rr e n shale X ^ l o g A t b a r T e n s h a l e ) (3)

and it is suggested that when performed on an individual basis, this parameter could be linearly calibratedto total organic matter. The similarity betwee n the techniques of Dellenbach et al . (1983) and Meyer andNederlof (1984) is illuminated in a study that appliesthe two techniques to a num ber of wells and concludesthat, in general, the same organic-rich zones are identified (Autric and Dum esnil, 1985).A slightly different approach to the interpretation ofTOC from log data was also taken by Mendelson andToksoz (1985), wh o approa ched the problem in tw oway s . The fi rs t appro ach wa s to t reat the organicmatter as a rock constituent with know n properties andto predic t TOC theoret ical ly f rom log responses .Although they observed good qual i tat ive agreementbetween log responses and organic r i chness , theyimplied that , in general , the physical propert ies oforganic matter are too poorly characterized and the

Trademark of Schiumberger.


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13 . In Situ Evaluation of Potential Source Rocks by Wireline Logs 13 1physical properties of the rock matrix are too critical tos o l ve t he p rob l em quan t i t a t i ve l y . The i r s econdapp roach was t o pe r fo rm m u l t i va r i a t e r eg res s i onanalysis on five wells with mean TOC values rangingfrom a pproxima tely 3 to 10 wt . % us ing mea suredvalues of TOC along with sonic, neutron, density, andgam m a ray logs . F o r each i nd i v i d ua l we l l , t h eyachieved reasonably good predictions of TOC, but theyfound that none of the regressions could be appliedsuccessfully to the other we lls. The adva ntage of such atreatment of the data is that it provides an optimizedsolution to the problem of quantifying TOC, bu t it doesso at the expense of fairly detailed core (or cuttings)calibration, and the extent of its applicability remainsunknown.

Quantitative Predictions of TOC fromSonic and R esistivity LogsMore recent interpretation schemes have returned to

the petrophysical approaches of t rying to interpretorganic matter in terms of its theoretical log response(Carpentier et al., 1989; Stocks and Lawrence, 1990;Passey et al., 1989, 1990). Carpentier et al. have introduced a technique to interpret TOC from sonic andres i s t i v i t y l ogs . The p r i nc i p l e under l y i n g t he i rapproach states that an increase in sonic transit timeaccompanied by a decrease in resistivity is attributed toan increase in c lay content or water , whereas anincrease in t ransi t t ime coupled with an increase inresistivity indicates an increase in organic matter. Theirtechnique uses the Wyll ie t ime average and Archieresistivity relationships to set up the response equationfor sonic and resistivity logs in a formation composedof organic matter, water, clay minerals, and nonclayrock matrix . It then use s core or cuttings TOC datafrom a key we ll (or formation) as a calibration for determ i n i ng t he A t va l ue for o rgan i c m a t t e r . Ha v i ngoptimized the solution, the authors apply the techniquein the calibration zone to get a continuous TOC log thatis in very good agreement with the core and cuttingsdata. They also provide examples of extending thesolution to other wells in a given basin after havingperformed the calibration on one or two key wells, andagain their predic tions of TOC are reasonably good. Inthe analysis of these data, the authors reveal two of theshortcomings of relying on cuttings which can translateinto two significant advantages of using wireline data.The first is the improved vertical resolution obtainedwh en using wireline logs comp ared to cuttings. Thesecond is the inaccuracy of cuttings data due to contamination from other zones, which they illustrate quitedramatically in a comparison of TOC values obtainedfrom cuttings, sidewall cores, and cores.

Another interpretation of organic carbon content thatrelies on the sa me principles of sonic and resistivity logshas been p resen ted by P assey et al. (1989, 1990). The

in terpreta t ion technique cons i s t s of over lay ing , orbasel ining, the sonic and resist ivi ty logs in "clean"nonreservoir zones and using separations between thetwo curves to indicate the presence of organic matter.This is actually identical to a technique used in conventional log interpretation for qualitatively identifyinghydrocarbon-bearing reservoir units. The major innovat ion of this work is the incorporat ion of organicmaturity as an input to the interpretation, which m akesit possible to interpret the separation between the twocurves (Alog R) in terms of TOC content and level oforganic metam orphism (LOM). The key to the interpretation is the set of calibration curves originally derivedfrom core data and dup l ica ted in F igure 2 . Theequations required for this interpretation are

Alog R = log RV ^base l ine J + 0 .02 (At -At b a s e l i n e ) ,TOC = (Alog R )l0 2.297-0.1688 LOM + 0.8. (4)

Since the in terpreta t ion impl ic i t ly assumes noorganic matter in the baselined portions of the log, avalue of 0.8 wt. % TOC is taken as a background levelof organic carbon and adde d to the compu ted result, asindicated in equation (4). An exam ple of this interpretation implemented in the North Sea is presented inF igure 3 , wh ere TOC value s of about 3 wt . % arepredicted quite well by the log data.The techniques of both Carpentier et al. (1989) andPassey et al. (1989,1990) offer the adv antag es of continuous logs of organic richness with bet ter resolut ion

than can be obtained by cuttings. At best, these techniques offer a good quantitative value of TOC, and atworst, they provide excellent qualitative information onTOC. The appro ach of Carpen tier et al. (1989) doesrequires calibration with TOC in a key geological unit,and i t presumes that a geological s imilari ty existsbetween the calibrated formation and the formationsthat are to be interpreted. How ever, the technique ofPassey et al . has a predefined calibration am ong Alog R,TOC, and LOM , and it requires LOM as an input.A Geochemical Approach to PredictingTotal Organic Carbon

A completely different approach to the quantification of organic matter is to use the C/ O ratio measuredby pulsed neut ron logging devices to compute thecarbon content of the formation directly, according tothe relationship

lo j x Oformation formation (5)where the oxygen in the formation is an est imated


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13 2 Herron

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LOG GEOCHEM DIAGRAM2018161 41 2

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Figure 2. Diagram relating Dlog R to TOC and level of organic m etamorphism (LOM). (From Passey et al., 1989,1990.)

value that depends on the porosity of the formation(Herron, 1986, 1987; Herron and Herron, 1990; Herronand Le Tendre , 1990). The key to the interpretation isthe estimation of formation oxygen which is accomplishe d in an iterative fashion. The formation is firstpartitioned using a density log into two components: amineral matrix with 50 wt. % oxygen and a p ore spacefilled with wa ter that has 89 wt. % oxygen. The totalcarbon (TC) based on this solution is then treated askerogen with an oxygen content of about 6 wt. %, and anew TC is comp uted. The calcium and m agnesiumlogs, which can also be obtained from pulsed neutronmeasurem ents (Hertzog et al , 1989), are then used todetermine the amounts of calcite and dolomite in theformation, and the corresponding value of inorganiccarbon is subtracted from the TC to produc e TOC. Themajor advantages of such an approach are that i t isfairly sensitive to low amounts of organic carbon and itdoes not require calibration to core data. The precisionon the measured C/O rat io is poor at conventionallogging speeds, so higher qual i ty logging data areacquired from stat ionary measurements or s low (ormul t ip le) cont inuo us passe s . An exam ple of th i stechnique applied to a short interval of the Toarcianshale in the Paris basin is prese nted in Figure 4. Thefirst two graphs show the TC and TOC determined

from stationary log measurem ents and from core slabstaken over identical vertical intervals. The third gra phdisplays the TOC log computed in the same mannerbut this time using log data taken from a single continuo us pass a t a logg ing speed of 600 f t / hr . Theagreem ent betwe en the core and log data is excellent forthe stationary data, and it is still quite good for thecontinuous pass. While the organic contents are quitehigh in this example, the same degree of accuracy hasbeen demons t ra ted us ing s ta t ionary C/O measureme nts for TOC value s at the 1 wt. % level (Herron an dHerr on, 1990).

PREDICTING ORGANICMATURITY FROM RESISTIVITYLOGSAttempts to interpret organic maturi ty from logshave focused on deep resistivity measurem ents, and ingeneral, researchers have credited Meissner (1978) fordemonstrating the relationship between oil generationand sh ale resistivity. A good exam ple of this relationsh ip i s provided by Smagala e t a l . (1984) in theCretaceous Niobara Formation in the Denver basin. Inthat study, the authors first used vitrinite reflectance


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13 . In Situ Evaluation of Potential Source Rocks by Wireline Logs 13 3

3700-

3800-

3870

Figure 3. North Sea example from Passey et al. (1989,1990) of the prediction of TC from sonic and resistivitylogs for a formation with a m aturity of LOM 9-10. Thecore data (+) are from closely spaced measurementsmade ona conventional core.

data to determine the log-linear relationship betweenvitrinite reflectance and depth and consequently to picka representative vitrinite reflectance value for a givenzone in the well. They then empirically correlated thevitrinite reflectance to the formation resistivity usingdata from 23 wells in the basin, as shown in Figure 5.The correlation was found to be good enough to applyto resistivity logs from o ther we lls, and it enabled themto map maturity patterns throughout the Denver basin.Schmoker and Hester (1990) also used resistivity logs asan indicator of oil genera tion in the Bakken Shale wherethey found that a formation resistivity of 35 ohm meffect ively discriminated between thermally maturean d imm ature shales. They also offered the interestingobservation that in the two organic rich members of theBakken Shale, the 35 ohm m resistivity contour thatrepresents o i l generat ion corresponds to d i f feren tvalues of thermal maturity, and they attributed this todifferent kero gen comp ositions in the two shales.

The success of these two studies can be attributedpart ial ly to the fact that the formations being interp re t ed have no t und erg one s i gn i f ican t po ros i t y

reduction due to compaction, and consequently, theincrease in resistivity is dominated by oil generation.S igni f icant poros i ty var ia t ions would in t roduce acomplicating factor to the interpre tation.

FUTURE INTEGRATION OFWIRELINE MEASUREMENTS INSOURCE ROCK EVALUATIONTo da t e , w i re l i ne i n t e rp re t a t i o n has focus edprimarily on the quantification of TOC and secondarilyon the es t im at ion of orga nic ma tur i ty . W i th theexception of the geochemical logging approach, thequantitative techniques rely on calibrations that eitherare made on a local basis (e.g., Mendelson and Toksoz,1985; Carpenter e t al., 1989) or are implicit in the mo delitself (Passey et al., 1989). The logs being used for mostof these interpretat ions are fairly insensi t ive to the

differences between kerogen, hydrocarbon, and water,and therefore the techniques are fairly insensitive tosmall volum es of organic matter. The geochemicall ogg i ng app ro ach o f fer s a m o re d i r ec t and m oreaccurate measurement of organic carbon content ,particularly at low levels of organic carbon, but thesetypes of logging data are not yet routinely obtained.Organic maturity has been estimated from resistivitylogs, but it has required calibration with substantialamounts of core data (Smagala et al., 1984; Schmokerand Hester, 1990). Passey et al. (1989,1990) hav e establ ished a broad-based empirical relat ionship betweenorganic matu rity, resistivity, and TO C. It seems clear

that i f a TOC log can be obtained independently ofresistivity, the relationship described by Passey and coworke r s cou l d be exp l o i t ed t o s o l ve fo r o rgan i cmaturity.Interpretations have not been developed for determining the type of organic matter. Passey et al. (1990)have sugges ted that in some ins tances i t might beposs ib le to infer the depos i t ional envi ronment oforganic mat ter and then fur ther infer the type oforganic matter, and they provide an example of someth in ly bed ded coals and del ta ic sed iments . Alongsimilar lines, Meyer and Nederlof (1984) and Abrahao(1989) both present examples of logs i l lustrat ing acyclical depositional sequence commonly observed inlacustrine enviro nm ents. High-re solut ion boreholeimaging tools would also provide the abi l i ty to seesmall-scale depositional pattern s.Future enhancements to a l l aspect s of wi re l ines ou rce rock eva l ua t i on can be env i s i oned by t heinclusion of nuclear geochemical logs in the interpretation. Ou tpu ts from nuclear devices such as the GLTst r ing include not only TOC but a l so a number ofinorganic elemental concentrations that can be interpreted to characterize different depositional fades and


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134 Herron

1725 -

I 1735

17450 15 0 15 0 15C (%) TOC (%) TOC (%)

Figure 4. Paris basin examp le of TC estimated from stationary C/O m easurem ents (circles conn ected by solid lines) andTO C estimated from stationary C/O measuremen ts and a single pass at 600 ft/hr continuo us C/O measu rements. Coredata (solid dots) are provided from com parison . Note the large difference between TC and TO C due to the relatively highconcentration of carbonate minerals in the formation . (From Herron and Le Tendre, 1 990.)

to begin in terpreting the depos i t ional envi ronme nt(Pr imm er e t a l . , 1990). For exa mp le , Berner andRaiswell (1984) demonstrated a technique for distinguishing freshwater from marine sedimentary rocksusing the rat io of organic carbon to pyri te or totalsulfur. In a later wor k, they further dem onstra ted ho wthis ratio changes with maturation and might actuallybe used to predict thermal maturation (Raiswell andBerner, 1987). T he elem ental conce ntration logs alsoin t roduce the capabi l i ty of determining format ionmineralogy on a continuous in situ basis (Herron andHer ro n , 1990 ). Th i s p rov i des t he opp o r t un i t y t oexamine the relationship between clay mineralogy anddeposi tonal environment as well as the relat ionshipbetwee n clay diagenesis and organic maturi ty. Therealization of these techniques will require additionalresearch, but w ill undou btedly enhance wireline interpretation of potential source rocks in the future.

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Figure 5. Relationship betwee n vrtrinite reflectance andresistivity determined from 23 wells in the Denver basin.(From Smagaia et al., 1984.)

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1-1995 AAPG Treatise Handbooks 1 Source 18 Chapter13 in-situ Evaluation Using Wireline Logs