Single Cutter Testing - A Key For PDC Bit Development

Abstract

Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere is usually granted upon request provided proper credit is made. Abstract A 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 PDC bit performance in various shales. Introduction Since the introduction of a cutting element provided with a polycrystalline diamond layer in 1973, considerable effort has been put into the application of this element for drilling of sedimentary rock. The efforts resulted in a new generation of Polycrystalline Diamond Compact (PDC) bits that proved to have great potential for oil- and gas-drilling. In the interim various bit manufacturers have developed a wide range of PDC bit designs the vast majority of which is based on the 13.3 mm diameter disk-shaped cutter and its derivatives. Full-scale laboratory testing and field testing provided the main guidelines for development of the PDC bit concept. The development of cutters mainly concerned improvement of the wear resistance. So far insights into the cutting process of a PDC in sedimentary rock under simulated downhole conditions have had a minimum impact on cutter development.