Abstract

The passive-Vibration Assisted Rotary Drilling (p-VARD) technology was developed to enhance the drilling Rate of Penetration (ROP) for using Poly-crystalline Diamond Compact (PDC) drill bits by modulating the rock-bit interactions. A labscale p-VARD prototype was tested by drilling rock analogue fine-grained concrete samples with an Unconfined Compressive Strength (UCS) ~50 MPa. Results showed that within the operational range of the tool, defined by the range of WOB applied during drilling, ROP was consistently 50% or more greater as compared to conventional drilling without the p-VARD tool, as other drilling conditions being the same. A field-scale p-VARD prototype was developed and tested during field trials in September 2014. Evaluation of data from the field trials is ongoing; however, representative drilling results for drilling a red shale formation (with mechanical properties similar to the laboratory concrete material) showed similar results with ROP increased 50% to 100% when WOB was in the operational range of the tool.

1. INTRODUCTION

By studying Vibration Assisted Rotary Drilling (VARD), the Advance Drilling Laboratories (ADL) of Memorial University of Newfoundland aims to introduce technologies that provide higher penetration rates and greater economic values in the process of drilling. Vibrations are mostly considered undesirable in the field of drilling and efforts are done to mitigate them. Vibrations are linked to whirl, stick-slip and nonuniform dynamic loading, which cause damage to bits and down-hole equipment. The Institute of Technical Mechanics, Ukraine tested devices that work on the principle of cavitation. A two to three times increase in ROP was reported [1]. Another study was done on an Axial Oscillation Generator tool (AGT) and it was found that the AGT improves weight transfer to the bit and reduces torque on bit. Also it was found that it significantly reduces stick-slip [2]. National Oil-well Varco Down-hole Ltd. (NOV) developed a small scale vibration test-rig, to simulate stick-slip and study stickslip mitigation methods. Axial friction reduction and axial load transfer can be achieved by introducing axial excitations in the oil-well, which results in an improvement in ROP and better Mechanical Specific Energy (MSE) [3]. Heng Li et al reported that the combined effect of vibrations and rotation increases the rate of penetration for a coring bit [4]; also ROP improvement was reported as a function of amplitude of vibrations. Babatunde et al studied the effect of vibration frequency on penetration rates using natural diamond drag bits. Here again VARD improved the penetration rates [5]. Both Heng Li et al and Babatunde et al used a shaker table under the sample as a source of vibrations. To further study the effect of vibrations on drilling performance, a prototype in-line tool (lab scale p-VARD tool) was designed and tested. Initial results were promising and significant increase in ROP using concrete specimens of medium strength was observed.

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