ANALYTICAL AND EXPERIMENTAL STUDY ON PDC DRILL BITS QUALITY
Under geological extreme conditions, polycrystalline diamond compact bits (PDC) are a relevant choice because of their interesting drilling performances. In this way, the quality of innovating PDC bits materials has to be determined with accuracy by measuring cutting efficiency and wear rate, both related to the overall mechanical properties. A lathe-type test device was used to proceed to the first experiments. During these tests, cutters have been worn over an abrasion length greater than 15 km, with a mean normal load range from 3000 to 5000 N, a cutting speed about 1:8 m/ s and a penetration depth close to 2 mm. Analyses are based on models establishing coupled relations between cutting and friction stresses related to the drag bits excavation mechanism. In this work, models are implemented in order to evaluate cutting efficiency and to estimate the life time of the diamond insert. A variety of cutters was characterized by wear rates ranged from 9.4•10^(-15) to 1.1•10^(-13) mm^3/(Nm) (Archard’s model) and cutting efficiencies at 10 km evaluated between 31 and 55%. From here, an original approach is developed to describe the overall cutter quality by defining a ratio between efficiency and wear. The reference samples during preliminary tests clearly revealed various mechanical behaviors due to changes in the material composition and distinct manufacturing production methods. These changes are detected at several levels: coatings, grain sizes, surface roughness, etc.
Mathematical Modeling of PDC Bit Drilling Process Based on a Single-Cutter Mechanics
An analytical development of a new mechanistic drilling model for polycrystalline diamond compact (PDC) bits is presented. The derivation accounts for static balance of forces acting on a single PDC cutter and is based on assumed similarity between bit and cutter. The model is fully explicit with physical meanings given to all constants and functions. Three equations constitute the mathematical model: torque, drilling rate, and bit life. The equations comprise cutter’s geometry, rock properties drilling parameters, and four empirical constants. The constants are used to match the model to a PDC drilling process. Also presented are qualitative and predictive verifications of the model. Qualitative verification shows that the model’s response to drilling process variables is similar to the behavior of full-size PDC bits. However, accuracy of the model’s predictions of PDC bit performance is limited primarily by imprecision of bit-dull evaluation. The verification study is based upon the reported laboratory drilling and field drilling tests as well as field data collected by the authors.
Status of polycrystalline-diamond-compact bits: Part 2 - Applications
Part 1 discussed the characteristics, development, and outlook for polycrystalline diamond compact (PDC) bits. This second part treats applications of PDC bits, including suitable locations, types of hole, and uses.