Drill Core Orientation Tool

Overview

A drill core orientation tool records which way a piece of recovered rock core was pointing while it was still in the ground. Diamond coring brings up a cylinder of rock, but once that cylinder leaves the hole it has no record of its rotation, so a geologist cannot tell a fault dipping north from one dipping south. The orientation tool solves this by measuring the direction of the borehole and the rotation of the inner core barrel at the instant a coring run finishes, then transferring that reference onto the core so structures can be measured in real three-dimensional space. The result is a reference line drawn down the core that points to the bottom of the hole, from which the geologist computes the alpha and beta angles of every vein, fracture, and contact.

The tool rides inside the inner barrel above the core stub. Its Orientation Sensor Pack reads the gravity and rotation field, the Logging Electronics decide when the bit has stopped and log the reading, the Battery and Power keeps it running, and the Marking System system transfers the answer to the rock. The Pressure Housing keeps borehole fluid out, the Core Barrel Coupling fixes the tool angle to the core, and the Surface Readout reader shows the result at the rig.

How it senses orientation

The job of the Orientation Sensor Pack is to find two things: which way the hole is leaning and how the tool is rotated about its own axis. Three MEMS Accelerometer accelerometers sense the gravity vector, which gives both the hole inclination and the toolface, the angle from the high side of the hole to a fixed mark on the tool. In a hole that is close to vertical the gravity vector gives little toolface information, so three MEMS Gyro rate gyros track rotation continuously and three Fluxgate Magnetometer magnetometers add azimuth where the rock is non-magnetic. A Temperature Sensor sensor lets the firmware correct each reading for downhole temperature, because MEMS sensor bias drifts with heat. The combination is what lets the tool work in steep holes and through magnetic ground that would defeat a magnetometer alone.

Logging and timing

The key trick is taking the reading at the right moment. While the drill string is rotating, the sensors see only spin and vibration, so the Logging Electronics use a Vibration Detector detector to tell drilling from rest. When the bit stops at the end of a run and the string sits still for a set number of seconds, the Microcontroller captures a clean orientation reading and writes it to Flash Memory flash with a time stamp from the Real-Time Clock clock. Because every reading is time-stamped, the surface crew can match it to the depth recorded in the rig log. Continuous logging through the run also lets the geologist see whether the tool was disturbed before the core broke, which is the usual cause of a bad orientation.

Power and housing

The Battery and Power pack carries several Lithium Cell lithium cells sized to run a full coring shift, a Voltage Regulator that holds a steady rail as the cells drain, and a sealed Charge Port for charging and configuration at surface. All of this lives inside the Pressure Housing, a thick Housing Barrel of 316L stainless closed by two End Cap caps and sealed with an O-Ring Set against borehole pressure that can reach several hundred bar at depth. A Shock Mount isolates the sensor pack from the hammering and vibration of drilling, which would otherwise wreck the MEMS sensors. The housing has to survive both pressure and shock, so it is built heavier than the electronics alone would require.

Transferring orientation to the core

Reading the orientation is only useful if it ends up on the rock. The Core Barrel Coupling fixes the tool at a known angle to the core stub: a Stop Ring keys the tool rotation to the inner barrel, a Landing Ring seats it, and a Spearhead Adapter lets the overshot pull the whole assembly up the rods. At surface the geologist uses the Marking System system to draw the reference. Some tools light a Toolface LED Ring that shows the bottom-of-hole position so the geologist marks the core by hand with a Core Marker against the Orientation Line; others cut a physical groove with a Reference Scribe. Either way the mark points to the low side of the hole.

Reading and using the data

At the rig the Surface Readout system closes the loop. A rugged Handheld Reader handheld pulls the log over a Data Link wireless or contact connection and shows the toolface on an LCD Panel, then computes the orientation the geologist needs. Once the reference line is drawn, structural features are measured as alpha and beta angles, the dip and the rotation of each plane relative to the core axis, and converted into true dip and dip direction in the deposit. This is what turns a stack of unmarked rock cylinders into a three-dimensional structural model that guides where the next hole is drilled and how the orebody is interpreted.

Use and variants

Orientation tools are standard on mineral exploration programs where structure controls the ore, and they come in versions for every wireline core size from slim BQ to large PQ. Older designs used a clay or pin imprint of the core stub to record the bottom-of-hole position mechanically; modern electronic tools like this one are faster, work in any hole angle, and keep a continuous log that exposes bad runs. The tool pairs with the same coring string used by a Diamond Core Drill Rig, and its output feeds directly into the geological interpretation that justifies further drilling.