The Effect of Additives on Impregnated Diamond Bit Performance
Authors: Selim A.A. , Schultz C.W. , Strebig K.C. 
Published: December 2007

The effect of some organic additives in diamond drilling of quartzite was investigated in the laboratory. The drill was designed to measure the rate of penetration, the trust, and the torque and to record penetration, the trust, and the torque and to record each as a function of the distance drilled. A statistical plan was followed throughout the investigation and an equation representing the bit performance was derived from the mathematical performance was derived from the mathematical theory to reliability. The drilling torque was found to increase with the use of additives while the sliding coefficient of friction and the wear coefficient decreased. The energy per unit volume consumed was found to increase with the use of additives. A hypothesis explaining the effects achieved with the additives is given.

Introduction

For some time researchers have attempted to increase drilling efficiency by adding certain agents to the flushing medium. Much of this interest is the result of the observations of Rehbinder, Shreiner and Zhigach. The postulate that "...in processes for the mechanical destruction of solids, a region of increased crack formation is created in the deformed layers adjoining the surface of destruction, forming the predestruction zone. The surrounding medium (for example, a liquid which wets a given solid will penetrate the embryo micro cracks of the predestruction penetrate the embryo micro cracks of the predestruction zone. Increasing the molecular affinity of this liquid for the surface of the solid considerably facilitates the deformation and destruction by softening the solid in the zone of increased crack formation. In this manner, the hardness or strength of the deformed body is decreased by the influence of the penetration of the liquid into the predestruction zone." This is known as the "Rehbinder effect". Rehbinder's work has prompted many investigators to examine the effect of additives on the mechanical destruction of rocks. Engelmann, Terichow and Selim reported that the maximum penetration of the rock by a diamond point in a solution environment was at the isoelectric point of the solution. Robinson reported that his point of the solution. Robinson reported that his results did not appear to support the theory of Rehbinder. Joris and McLaren suggested that additives with surface tension lower than water will be more efficient in cooling the diamonds. Their effectiveness in removing the fine cuttings from the face of the bit will also improve the efficiency of the system. They reported an improvement in impregnated bit life and penetration rates with the use of soluble oil additives. In contrast, Long and Agnew, drilling with surface set bits, reported that lubricating agents increase bit temperature and wear. A significant change was reported in the mechanical properties of rock with polar additives. It properties of rock with polar additives. It was concluded that this change in the mechanical properties of the rock in the presence of the additive properties of the rock in the presence of the additive is due to the rock hydrophilic properties. Ethylene glycol, glycerine and anionic detergent were selected for this investigation because their surface tension is lower than that of water. The surface tension of these additives for the concentrations studied was 42 to 75 percent of the surface tension of water. A low surface tension additive would wet the surface of the diamonds more easily and hence would be more effective in cooling the diamonds. Another characteristic of these low surface tension additives is their effectiveness in removing the cuttings and preventing the flocculation of the formed particles in the drilling process. This article summarizes the results of an investigation performed at the laboratories of USBM, Twin performed at the laboratories of USBM, Twin Cities Mining Research Center. The objective of the investigation was to study the over-all effects of some organic additives on the performance of diamond impregnated bits in atmospheric drilling conditions only and not in downhole pressured conditions.