Conglomerate Layer Drillability Test And PDC Bit Drilling Performance Research

When using PDC bit to drill conglomerate layers, strong impact loads and pre-failurewill occur because of the severe anisotropy of the conglomerate. At present, the conglomeratelayer drilling is always finished by using cone bits. As the properties of conglomerate layerformation is hard to grasped, there is certain blindness when selecting the bits, resulting inoccurrences of tooth wear, even tooth fracture when using the cone bits to drill the layers ofsand-shale or conglomerate. So it is necessary to have a reasonable evaluation ofconglomerates drillability to provide a reference for the selection of the cone bits. In thispaper, the factors that have influence on the conglomerate layer drillability will be discussedbased on the analysis of physical nature of the conglomerate layer and rock samplescontaining gravels of different size and continent will be made according the analysis. Afterthat, Micro-drilling experiments will be performed on the rock samples and there will be ananalysis of the relationship between drillability value of conglomerate rock samples and therock characteristic parameters such as the size and content of the gravels. Eventually, afunction formula is derived to calculate the conglomerate layer drillability with the rockcharacteristic parameters such as the size and content of gravels.In addition, for the drilling of the conglomerate layer, on the site the PDC bits are alsorepeatedly used and improved, so as to accelerate the PDC bits drilling rate in the case ofensuring a relatively long life span when drilling conglomerate layers. In order to conductfurther studies on the PDC bit in conglomerate layers drilling effect, and to provide areference to expand the application of PDC bits in the conglomerate layer drilling, an indoordrilling experiments is designed. The cement rock samples are drilled by bits of various kinds of back rack angles and a torque sensor is used to record the drilling pressure, torsion anddrilling footage of the bit when drilling in kinds of rock samples under different WOB androtation speed. Through analyzing the data recorded by the torque sensor, the effects on thebehaviors of the PDC bit caused by the conglomerate nature character, the back rack angle ofthe cutting teeth, and the drilling parameters will be discussed when the PDC bit is drilling inthe conglomerate layer, in order to provide a reference for the application of PDC bits in theconglomerate layer drilling process.