AMC COREWELL™ delivers 91% core recovery in South Africa

Complete core using AMC COREWELL™ in South Africa

AMC COREWELL™ along with AMC’s experienced technical expertise overcame challenging geological conditions, such as poor core recovery and severe bore-hole instability, facilitating the early completion of a hole in Northern Cape, South Africa.

AMC COREWELL™ achieved:

  • improved core recovery rates averaging 91%
  • improved hole stability
  • improved rate of penetration up to 3.0m per hour
  • improved fluid management and processes
  • maintained consistent low rotational torque

Trial Overview

Date11 - 12 March 2015
LocationNorthern Cape Iron Fields, Postmasburg, South Africa
Drill hole information40.9 m HQ Triple Tube cored over a 2 day period from surface on a 90° degree angle
Bore information1 x BLY44
Mud informationPreviously using AMC CAP 21™ / AMC EZEE MIX combination. AMC COREWELL™ system prepared at a rate of 1.5kg / m3 producing a funnel viscosity of 48 seconds which eventually yielded a 52 - 54 second viscosity over a few circulations
WaterpH of 7.5 with a total hardness above 450mg / L
Geology0 - 5m competent outcrop quartzite 5 - 15m broken hard quartz with inter bedded saprollite and laterite clays leading into a black mudstone with multiple sub vertical layers of broken BIF and quartz Note: Clay was present in 90% of the strata
MineralIron ore and manganese
Activity2 diamond core drill rigs


Earth Resources had two active rigs exploring for manganese on the PMG Mining project in the Northern Cape Iron Fields. From the beginning, the crew experienced multiple problems down-hole including severe core loss. The lease holder, PMG Mining gave its the three drilling contractors on site an incentive; the company that achieved the highest, most consistent core recovery rate and overall performance would be awarded all future drilling at the site.

After losing a barrel and battling to control bore-hole stability, Earth Resources was keen to improve productivity, core sample quality and quantity. AMC was contacted to recommend a superior fluid solution and provide on-site technical support to boost Earth Resource’s chances of being awarded the project.

Arriving at site, AMC quickly tested water quality, analysed fluid properties and viewed the core to better understand hole conditions; water quality was a 7.5 pH and total hardness of 450mg / L. Coring commenced from surface or diamond tailed from pre-collars. The geology started off in competent quartzite which normally continued down to 5.0m depending and the inclination of the bore. From 5.0 m conditions changed rapidly to broken, hard quartzite with interbedded saprollite and laterite clays for approximately 10.0m. Geology then entered into a black mudstone, with multiple sub vertical layers of broken BIF and Quartz, where recovery raes were historically poor. The mudstone formation continued to a depth of 150.0m before hitting basement BIF. From AMC’s observations, the most prevalent problem was exceptionally poor recovery which instigated the recommendation of AMC COREWELL™.

Enhancing Mud Systems

Initially the client persevered using a PHPA system comprising of AMC CAP 21™ / AMC EZEE MIX. It was obvious from AMC’s interviews and observations the system was unable to provide the necessary fluid properties to support the clay rich environment. In early discussion, Earth Resources wanted to convert to a Bentonite Polymer system however after much debate and reference to previous positive experiences, they were convinced to trial AMC COREWELL™. For the trial AMC was assigned a HQ T3 hole from surface, drilled at an angle of 90 degrees.

AMC’s reasoning for not using a Bentonite system included the limited access to surface equipment; no hydration tanks or quality mixing equipment were available. Undulating hilly conditions called for earthen plastic lined sumps, this combined with the lack of shear and hydration would have caused much wastage and negated any advantage of using a Gel system. AMC provided a PVC mixer to promote best mixing conditions. AMC COREWELL™ system was prepared at a rate of 1.5 kg / m3 producing a funnel viscosity of 48 seconds that eventually yielded 52 - 54 seconds as the system was circulated. SODA ASH was used to condition the base water, the PVC mixer proved most effective creating faster yield with zero “fish eyes” or lumps.

Improved Rate of Penetration

A high Rate of Penetration (ROP) is vital to achieve an efficient operation. Prior to AMC arriving on site, penetration rates were as low as 0.40m per hour using the AMC CAP 21™ / AMC EZEE MIX system. After AMC COREWELL™ was circulating through the hole, ROP to reached a high of 3.0m per hour. Then improvement in ROP saw the hole being completed ahead of schedule, bolstering Earth Resources chances of being awarded future drilling.

On-Site Support Improved Fluid Management Processes

AMC’s mud engineers focused on the entire fluid process to ensure the project’s success. AMC’s on-site support included a full evaluation of the mud program, advice on mixing techniques and training for optimal use of equipment. Poor mixing practices and equipment had previously contributed to a fluid that underperformed and could not complete the job. AMC’s engineers introduced the PVC MUD MIXER, which ensured the fluid system remained in optimal condition. The client was very impressed with the versatility and ease of mixing with the AMC PVC MUD MIXER. The site supervisor noted that less product was being wasted while producing a better yield, zero “fish eyes” or lumps for the completion of the project.

Crucial Hole Stability Achieved

Earth Resources’ drill crew found it difficult to keep the borehole stabilised when encountering the weathered clay rich ground and the mudstone. AMC COREWELL™’s fluid properties are uniquely formulated to aid hole stability by forming a protective layer to prevent dispersion and collapse. The use of AMC COREWELL™ stabilised the borehole, resulting in gauge holes and reduced breakdown of formation into the system.

Reduced Wear and Tear on Drill Components

Previously, core recovery rates were around 10 – 50% when coring through the clay bearing formations and mudstones, with up to 100% sample loss in the wash-out zones. AMC COREWELL™ provided an immediate improvement, with an overall average of 91% being achieved.

The AMC COREWELL™ system provided:

  • Consistent low rotational torque
  • Reduced blocking of the waterways in the drill bit
  • Reduced core lifter cage from getting stuck
  • Eliminated the core from wedging up into the inner tube
  • Dramatically reduced clay build up in the annulus and on the outside of the rods
  • Prevented down-hole tool loss
  • Eliminated core being dropped down-hole
  • Clay samples were no longer getting stuck in the splits of the tube
  • Dramatically improve drilling conditions
  • Dramatically improve core integrity and quantity retrieved
  • Due to no overtime, wear to core lifters, lifter cages, reamers and inner tubes was reduced.

Project Outcome

AMC COREWELL™ improved core recovery to an average of 91% compared to previous result of 0 - 50%, proving highly successful in the trial. AMC COREWELL™ delivered high productivity and operational success to the contractor, leading to reduced operational costs and the completion of the project ahead of schedule.

Experienced AMC mud engineers worked with the Earth Resources drill crew, providing fluid management training and recommendations, helping to deliver improved core recovery, Rate of Penetration (ROP), stabilising the borehole and reducing wear and tear on drilling components. The AMC COREWELL™ system enabled the bore-hole to progress quicker and more efficiently than it had previously. A substantial increase in core recovery was critical to the success of the project, core sample recovery reached a peak of 100% and settled to an average of 91% which helped to improve the drill crew’s confidence, and deliver comprehensive, complete samples to the client.

For more details on this successful project, contact [email protected]