Flocculating fine cuttings particles suspended within partially hydrolysed polyacrylamide (PHPA) solutions used as drilling fluids in mineral exploration

Abstract

Aqueous solutions of high molecular weight partially hydrolysed polyacrylamide (PHPA) are used in mineral exploration drilling to increase fluid viscosity and thereby help maintain the suspension of fine cuttings being brought to the surface. However, clarifying such suspensions prior to drilling fluid recycling can be problematic, leading to recirculating particle loads that can impact on drilling performance. Total particle encapsulation by adsorbed polymer is assumed to stabilize suspensions, thereby preventing subsequent flocculation. Batch testing with aggregation monitored in real-time by focused beam reflectance measurement (FBRM) confirmed anionic flocculants were ineffective, but significant aggregation was achieved with a nonionic product. Field trials dosing a nonionic flocculant in advance of a decanter centrifuge required higher dosages, but still consistently reduced centrate solids by ∼ 50 %. This indicates cuttings particle surfaces may in fact be accessible for flocculant absorption and particle bridging, but the charged tails of adsorbed PHPA prevent any such access by similar anionic flocculants.