CopvrIght -7, Society of '-Iroleum Ingl_ _This paper was prepered lor presentation at Offshore Europe 87, Aberdeen, 8-" september, 1987 Permission to copy is restricted to an abstract of not more than 300 words. lIIustretions may not be copied. The abstract shouldcontain conspicuous acknowledgement of where and by whom the papar was~ted. Publication elsew1'er8 is usuelly granted upon request provided proper credit is made. ABSTRACTA description is given of a single-cutter tester for studying ,the cutting process of PDCs in rock under simulated downhole conditions. The use of the tester is illustrated by a study of the effect of downhole pressures on the cutting process in shales. Prior to the tests the Pierre shale and Mancos shale outcrop samples used for the study were conditioned to enable proper downhole pressures to be simulated during the tests.The total bottomhole pressure only was found to govern the cutting process in Mancos shale, whereas both the pore pressure and the total bottomhole pressure govern the cutting process in Pierre shale. The dilatancy characteristics of the rocks are shown to be responsible for this behaviour. In addition the tests unveiled the balling mechanism of the outcrop shales in water-based and oil-based mud environments.On the basis of the insight gained from single-cutter tests, the paper discusses drilling characteristics of PDC bits in shales and bit and cutter design aspects that facilitate mechanical bit cleaning as a means of improving POC bit performance in various shales.

right 19S4 Sodety of Petroleum Engineers of AIME .-, -------~~.wh,,k hdri in !+u.qml. Texas, September 16-19, 19~:The material is aur~e w~~i~~~~~~~ufv0T~~~s~ounsloTs~~'~le%r?~xTQeef~b%'~cy~;;ot-;ire thin 3G0 words. Write SPE, 6200 NOrtn Lalirai =xpiSSS$*j, rer s4706, Dallae, Texas 75206 USA. Telex 7~89 SpEDAL. 1 TRACT Analysie of laboratory teste on full-scale fieldn PolYcrYstalline diamond compact (PDC) bits showed , frictional heat at the rocktbit interface to be 'gely generated St the diamond cutting edges of the :s. Inspection of the observed wear of the pDCS ;ether with the analysis revealed that the d~a~ond ,er attacks the formation at a large negative rake ;le and that rock flour accumlatee under the Lting edge during drilling, fo~ng a stable buildup A therelalmodel has been developed on the basis these results to predict the tentperature Stribution in the PDCS under quasi-static drilling Uditions. The tUSXimum 'emperatu~r~a~yn~n~p~d~;t the PDC'S cutting edge and ie PDC position under normal rotary drilling ,nditiona. At elevated 'ota~'p~$r~~~~&t~the Lximum cutting edge temperature tuge of the bit. TIIiS temperature can exceed thẽ iling point of water-baeed drilling fluids, >sult~ng in higher cutting edge temperatures and weal te8 of the PINs which may lead to prewture failure E the bit. Under normal rofary drilling conditions he maximum cutting edge temperature increases with he penetration rate. For the higher speed positive isp~aee~siitCIGtO~~r illintzapplicatio~however% bit! --------an be designed to give a '%rtua~~~ec~~~~~~q=b~~am utting edge temperature over a WLUC L-..*----penetration rates. This is achieved by selecting the ,Ptimum number of cutters whilet~king use 'f 'he ---..~...-F ehe hildup edge unde, hermal insulating C&pU.A.J .. ----:he PDC. In addition a further reduction in thẽ axi=m cutting edge temperature can be achieved at :hese aueeds by reducing the diamond layer thickness ...--. f the relevant PDCS. The results also showed that for effective cooling of the PDCe fluid velocities of at least 50 rnlsare required along the diamond eurfaces when drilling with oil-based fluids. with water-based drilling fluids, higher velocities should be used to prevent bit balling or boiling of the drilling fluid at the diamond surface of the pDCS. References and illustrations at end of paper. rrRoDUCTlON The wear profile of field-worn PDC bits of ã rticular design depends on the operating and field nditions. Analysis Of Wear PrOfiles 'f 'ield-wOrn OC bits has showu that the wear rate of PDCS ncreasee with temperature (Ref. 1), with an upper tm.itof 750°C above which the diamond layer rapidly eterioratea. Hence the temperature in PDCS under ield drilling conditions should be a key parameter or the distribution of the wear of p~e on a bit.In this paper a theoretical model is developed tõ redict the temperature distribution in PDCe mounted ,n a~trix-type bit under field drilling conditions. ;he model may be helpful in determining the impact of ;he temperature in a PDC on wear rate. Furthe~ore> :he effect o...

A magnetic survey correction method (MSCM) has been developed and used to process MWD surveys. The local magnetic field strength and dip angle required for the method were obtained from a commercially available computer model of the Earth's magnetic field. The method corrects for both radial and axial magnetic drillstring interference and has led to improved quality control for magnetic surveys. The only nonmagnetic tubular incorporated in the drillstring is the MWD's own nonmagnetic housing. Comparison of the MWD results with north-seeking gyro surveys confirmed that the theoretically predicted accuracy of the MWD surveys processed with the correction method is generally better than conventional surveys taken in a full length of nonmagnetic drillcollars. No additional rig time was incurred and operational benefits include reduced rental, inspection and risk of lost-in-hole costs. Magnetic survey accuracy can be enhanced by using locally measured geomagnetic parameters for the correction method. Field examples of enhanced magnetic surveying with electronic magnetic multishot tools are given. The achievable accuracy of magnetic surveying onshore in the Netherlands is comparable to the accuracy of current north-seeking gyro tools and a reduction in the number of gyro surveys is therefore planned.

This paper describes a novel polycrystalline-diamond-compact (PDC) -bit concept based on insights into PDC-bit cutting mechanism and rock behavior during drilling. The design comprises a hydraulic layout that optimizes bit cleaning and cuttings removal in soft and sticky formations. Significant improvements in performance have been achieved in Cretaceous and Triassic formations drilled with water-based muds.

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