Proactive measures for the borehole

Geodrilling International asks Cory Mackay, of Imdex, about AMC Drilling Fluids & Products’ recently launched borehole optimisation system, the AMC BOS™.
What was the original idea behind the AMC BOS™?
AMC, which forms part of Imdex, identified a number of clients that had been experiencing fluid losses, high torque and borehole instability issues, causing reduced penetration rates, increased rod trips, increased downtime and/or grouting/cementing the borehole. AMC develops and manufactures a number of additives, which can address these issues as they occur. We identified the need to develop a solution that could be used as a proactive measure, not just reactive. The focus was then on developing a proactive method that was faster and more effective than the current torque control and grouting/cementing methods.

What does the system consist of and how do these parts work together?
The AMC BOS™ comprises the AMC BOS UNIT™, an in-hole lubricating and casing-while-drilling tool, and AMC BOS FIX™, a rapid-fill lubricating grout. The AMC BOS is a proactive solution combating fluid losses, borehole instability and torque, by delivering a measured amount of AMC BOS FIX™ at regular intervals to the bottom of the drill string and up the annulus. The fluid reacts instantly with borehole fluids, permeating and sealing fractures, providing a thin but robust lubristic membrane to the borehole wall.

How does the AMC BOS™ complement your other drilling optimisation products?
The following AMC products can be introduced into the mud system to provide further beneficial properties to the solution,
  • AMC PLUG™ assists in sealing zones of fluid loss or lost circulation. This granular polymer absorbs up to 500 times its original volume in water.
  • AMC COREWELL™ assists in core recovery and further borehole stabilisation; a multifunctional single-sack system created especially for diamond coring and slim-hole drilling.
  • AMC EZEE TROL™ increases core recovery and hole stability. This dispersive, versatile blend of polymers forms a high-viscosity fluid suitable in all types of drilling applications.
  • AMC EZEE PAC R™ increases core recovery. This dispersive polyanionic cellulose polymer also aids viscosity and water loss control in most water- based drilling fluid systems.
When used in conjunction with AMC’s solids removal units (SRUs), the AMC BOS™ can improve a drill site’s environmental impact. The SRU™’s closed-loop system eliminates the need to dig earth sumps, which are both costly to construct and to rehabilitate, and which create a large disturbance on the surrounding environment. It also provides a solution to enable drilling to occur in environmentally sensitive areas or privately owned land, minimising impact on the area. The mud system is contained in the on-board tanks of the SRU™, and piped directly to and from the drill collar, minimising the risk of fluid leaking into the surrounding environment or waterways.

What are the disadvantages of the traditional, reactive methods used for borehole stabilisation?
When encountering borehole instability, high torque or fluid- loss zones, traditionally a driller will use the following methods or avoid the situation. If the driller continues to drill through unstable, high-torque or fluid-loss zones without treatment, there is an increased risk of rod trips, prematurely worn-out bits, borehole collapse and stuck drill pipe. The driller will also experience increased water, grease and drilling fluid consumption, as well as increased risk of injury.

To manage and reduce borehole torque, a drilling contractor has two options. The first option is to manually apply rod grease to the drill string at regular intervals. This method requires the drill string to be tripped out of the borehole, causing time loss and increasing manual handling.

The second option is to introduce a liquid rod grease to the mud programme. This method is easier to manage (as it avoids the need to trip the drill string in and out of the borehole); however, is less effective at controlling borehole torque and more expensive than rod grease.

Cementing/grouting commonly takes 48 hours or more. The process can be very costly, introduces significant risk of injury due to increased rod tripping, and it quite often has only a 50% success rate.

In fluid loss scenarios, lost circulation materials (LCMs) are usually applied as the first measure to avoid or delay cementing/grouting. Using LCMs can compromise the borehole annulus, causing in-hole tooling to become stuck and resulting in unwanted rod tripping. It can also potentially increase borehole torque. Depending on the circumstances, the effectiveness of LCM materials may vary. Using LCMs also requires added mixing and management time.

In what ground conditions is the system most efficient/beneficial?
AMC BOS™ works well in a range of conditions. It is highly effective in broken or fractured ground, high-friction environments or boreholes that experience voids or washouts. The solution is also effective in aiding boreholes with swelling, loose or unconsolidated ground, caving or sloughing.

What makes it particularly easy to use?
The AMC BOS UNIT™ is designed for easy use on site. The unit takes less than five minutes to set up. Set-up or refilling can be done at any time during the drill shift, prior to injection, without interrupting drilling time.
AMC BOS FIX™ is applied neat into the tool, not requiring time to mix drilling fluids and combine multi-part grouts. For preventative action against borehole instability or fluid loss, the AMC BOS UNIT™ should be refilled at least once a shift. For torque control, it should be applied once every two shifts.

Source: GeoDrilling International Magazine June/August 2017

Geodrilling International asks Cory Mackay, of Imdex, about AMC Drilling Fluids & Products’ recently launched borehole optimisation system, the AMC BOS.