Experimental optimization of drilling, rock strength and backfilling for mining by drilling applications

Quan, Weizhou (2021) Experimental optimization of drilling, rock strength and backfilling for mining by drilling applications. Masters thesis, Memorial University of Newfoundland.

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Abstract

A comprehensive study has been conducted to study rock characterizations, drilling performance through drill-off-test (DOT), optimization of cemented tailings backfill (CTB), and investigation of anti-washout property for CTB. The mechanical strengths and ultrasonic velocity of granite, representing high strength of natural isotropic rock, and rock like material (RLM), representing high strength synthetic isotropic rock, were determined in the laboratory. Empirical equations have been developed between these parameters. A novel strength testing method named mono UCS-PLI test was proposed to reduce limitations and strictness of the conventional standard strength tests. Then, the drilling rate of penetration (ROP) as main function of drilling performance was evaluated through two different drill bit types, including roller cone (RC) bit and polycrystalline diamond compact (PDC) bit. Sandstone was used as the testing rock, representing a tight and low permeability isotropic formation. A fully instrumented laboratory scale drilling simulator was used for drilling experiments. Weight on bit (WOB), rotary speed (rpm) and water flow rate (FR) were monitored and recorded. The drilling performance was evaluated based on drilling parameters and drill bit type. Besides, investigations of the use of lower binder proportions and optimization of backfill strength development were conducted because of the relatively high cost of Portland cement. The optimization work studied the effects of lower binder proportions (2 wt.% and 4 wt.% by solids mass) and internal vibration on the designed CTB density and mechanical strength development. An extra 10.9% tailings can be placed into extracted wellbore when the CTB is fully vibrated. This behaviour allows more tailings to be securely placed underground and further reduces the surface tailings impoundment requirements and the costs of tailings disposal for the mining industry. The first design of cemented tailings backfill preparation system is a batch system based on many technical experiences from those successful operations. Finally, an anti-washout admixture was found to achieve the anti-washout property of the designed CTB, which can prevent the CTB from being affected by the water during placement.

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