A Bit-Based Data-Acquisition System for Hard-Rock PDC Bits
Authors: Bybee Karen 
Published: February 2015

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 105017, "Development and Utilization of a Bit-Based Data- Acquisition System in Hard-Rock PDC Applications," by Paul Pastusek, SPE, Eric Sullivan, and Tommy Harris, SPE, Hughes Christensen Co., prepared for the 2007 SPE/IADC Drilling Conference, Amsterdam, 20–22 February.
The full-length paper describes the development and use of a bit-based module designed to monitor accelerometer and magnetometer sensors and to record selected data. The authors also describe the effort to infer dynamic dysfunctions from the data in the fast-growing hard-rock polycrystalline-diamond-compact (PDC) -bit application and to mitigate them by modifications to drilling parameters and bit designs.

Introduction
Drill bits are developed iteratively for specific applications to meet performance objectives such as aggressiveness, durability, stability, and steerability. The transition from one iteration to the next occurs when dull bits are examined, run data are analyzed, and the inferences are implemented as revisions to the bit design and/or the operating parameters. Experience has shown that the efficiency of the process depends strongly upon the appropriateness and significance of the data collected. If, for example, a dominant cutter-failure mechanism is characterized incorrectly as abrasive wear and is, in fact, impact wear, then both the proposed solution and the development time will be affected significantly.
One method for improving the significance of the data collected is to implement a special-purpose data-acquisition system within the bit. Such a device has at least three significant advantages over available subassembly-based data-acquisition systems:Its bit-based sensors will detect bit-based events more accurately,it can be deployed economically over many bits, andit is relatively transparent to the user.

Objective
The objective of the project was to develop an inexpensive battery-powered programmable data-acquisition system sized to fit within a bit and sufficiently robust to function under typical downhole-service conditions to monitor and record data for post-well analysis. The device is intended to support bit design, drilling-parameter development, and validation of laboratory simulation software and tests.
A device has been designed, manufactured, and tested that is an integrated battery-powered dynamic-behavior sensor and data-acquisition module. The module typically is implanted within the pin portion of a downhole tool, (e.g., within the shank portion of a bit). Modules are being run currently in bits in selected applications.
Form. The sensor/data-acquisition module is sized and constructed so that it can be implanted within an annular recess machined between the inside diameter (ID) and outside diameter of the end of a rock-bit shank. The electronics are implemented with rigid/flex circuit boards to minimize the number of failure-prone wire interconnects. The board, a temperature-measuring device, three orthogonal (x, y, z) accelerometers, three orthogonal (x, y, z) magnetometers, and the batteries are attached to a rigid "backbone" to form the integrated (standalone) module. An end cap with O-ring seals and backup rings forms the ID and bottom of the sealed-module cavity when installed and protects the device from moisture and hydrostatic pressures.