Results from Pilot Tests Prove the Potential of ... - Saudi Aramco

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one lithology and a wireline density neutron log suggestinganother — but some uncertainty in the interpretation, nofirm conclusion can be drawn. We had an illustrative caselike that on an appraisal well, where the initial geologicaldescription suggested an almost 100% dolomite lithologywith seemingly little doubt. The well site XRD system,however, showed a roughly 50/50 dolomite/anhydritemixture, Fig. 7, and only subsequent reexamination revealedthe formation to consist of anhydrite grains fully coveredwith a thin layer of dolomite.Fig. 9. A good match between cuttings and wireline derived grain densities.Comparison between AML and Wireline NMRThe newly developed NMR system on its very first field testalready showed clear trends in determining formation porosityin line with porosity from the wireline NMR, even when theactual porosity values were biased, confirming that some moredevelopment work is to be done in this area.AML Hydrocarbon Composition Matches PVT ResultsFig. 7. Seemingly 100% dolomite turns out to be 50/50 anhydrite/dolomite on XRD.Correlation of XRF Trace Elements and Mud Gas ReadingsThe quality and potential value of the XRF measurements isnicely illustrated in Fig. 8, showing a correlation betweentrace elements detected by XRF known to be associated withhydrocarbon resources, detected by XRF, and the mud gasreadings.Close Match between AML and Wireline Derived GrainDensitiesA comparison of grain densities derived from the directcuttings measurements and those determined after elaboratemulti-mineral analysis using a full wireline logging set, includingelemental spectral logs, shows encouraging results, Fig. 9.All the efforts put into fine–tuning the whole acquisition andprocessing chain for the compositional analysis of the mud gasstream came to fruition when the composition, determined inreal time and continuously obtained from this system, appearedto match perfectly with results from a full PVT analysison wireline fluid samples obtained subsequently, Fig. 10.This perfect match was one of the results obtained in amore elaborate test of two distinctly different AML systemsfrom two different companies conducted on a specialtechnology test well. As mentioned before, having several(advanced) mud logging units operating in parallel whiledrilling is about the only realistic way in which mud gasanalysis systems really can be properly compared. If twosystems were tested on two different wells, and the match withthe PVT results on one were not perfect, the question wouldremain whether or not the other unit would have done better.The results of the other system employed, while very goodon any absolute scale one may use and significantly betterFig. 8. Correlation of XRF trace elements and mud gas readings.Fig. 10. AML gives real time, continuous equivalent of PVT analysis of wirelinefluid sample.SAUDI ARAMCO JOURNAL OF TECHNOLOGY FALL 2011 23
than many would have expected only a few years ago, were alittle less in terms of a perfect match than the results of thesystem presented in Fig. 10.The potential business value of compositional informationas precise and reliable as this, provided in real time andcontinuously, is obviously enormous. The first benefit is anoptimization of the subsequent formation fluid samplingprogram whether wireline or logging while drilling (LWD).For example, taking more subsequent samples in a case whereunexpected variations in fluid composition are encounteredacross a reservoir section would assist in the delineation ofseparate reservoirs; alternatively, one could economize onfurther sampling activities when the information alreadyobtained is adequate.Reservoir Correlation and Geosteering with AML Fluid FaciesGiven the quality of the fluid characterization previouslymentioned, it becomes possible to do reservoir correlation andeven geosteering based on AML fluid facies. As shown in Fig.11, two distinct reservoirs, labeled “A” and “B,” had differentfluid types. Having penetrated reservoir/zone A, the well siteoperators easily established the reservoir from normallyavailable data and confirmed it with a few samples of thedetermined fluid facies. When the new well penetrated zone“X,” even with conventional electric logs, it was not clearwhether or not this zone X was in reservoir B or whetherreservoir B lay still deeper. The fluid facies analysis, however,clearly indicated that zone X did not belong to reservoir B, orthat reservoir B was split into distinct units/blocks withdifferent fluids, type B and type X.GETTING LARGE CHUNKS FROM PDC ANDCONVENTIONAL DIAMOND BITSHowever successful conventional diamond and PDC bits havebeen for drilling, the major drawback is that rather thancuttings of several millimeters, these bits produce only powder.Making a “dream bit,” which combines the advantages ofdrilling performance with the production of (very) large piecesof rock, also described as “microcores,” can be done byleaving out the center of the bit, as if it were a very smallFig. 12. Typical chunks recovered from a “dream bit.”diameter core bit. The microcores that are drilled are brokenoff, ejected into the annulus and then transported with thecuttings to the surface.In several tests done in Saudi Aramco, the potential of thesedream bits has been confirmed, with nice large chunks of rockbeing recovered amid the otherwise near powder formation,Fig. 12.While these chunks are not as nicely shaped as, and smallerthan, a conventional core plug, clearly they are large enough formany a measurement normally done on core plugs.Even though some more testing and further development ofthis technology might be required, the problem of PDC bitsproducing only powder has been resolved in principle, andtherefore moved from a research area to a development andapplication area.CONCLUSIONSGiven the still early stages of AML development, severalchallenges remain to be tackled: A further reduction in thetotal well site footprint, including the number of staff requiredfor the unit’s full operation; a further refinement of samplingand sample cleaning procedures; and an improvement in theaccuracy and precision of some of the measurements oncuttings. Therefore, further R&D AML efforts will berequired to achieve the ultimate goals.Yet, based on the foregoing, we may conclude the following.Cuttings Size from PDC Bits Is No Real ProblemReservoir/Zone A infieldand fluid facies in newwell.Zone “X” in new well.Uncertain from conventionallogs whether Reservoir B hasalready been penetrated.Reservoir/Zone Binfield.Fig. 11. Zonation, correlation and possible geosteering with AML fluid facies.It can no longer be said that PDC and other diamond bitsproduce cuttings that are too small. When desired, a dream bitshould produce chunks large enough even for many conventionalcore plug measurement techniques.AML Is EstablishedWe have developed an Advanced Mud Logging system,including instruments and processes that serves: (1) In aidof formation evaluation, as a complete “first aid,” and(2) To assist, optimize and improve drilling operations.Measurements that previously were limited to large24 FALL 2011 SAUDI ARAMCO JOURNAL OF TECHNOLOGY
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Results from Pilot Tests Prove the Potential of ... - Saudi Aramco

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