Preparation of amphoteric starch-based flocculants by reactive extrusion for removing useless solids from water-based drilling fluids

In drilling operations, the removal of drill cuttings from recirculating drilling fluids is one of the most important procedures. The high cost and low efficiency of present solid control technologies are two crucial problems that need to be solved urgently. In this work, a series of amphoteric starch-based flocculants (CS-g-DC) were developed to remove useless solids from drilling fluids. These flocculants were synthesized by grafting diallyldimethylammonium chloride (DADMAC) onto carboxymethyl starch (CMS) with different grafting frequencies through reactive extrusion. The physicochemical property of the CS-g-DC products was measured by Fouriertrans-form infrared (FT-IR) spectroscopy, proton nuclear magnetic resonance (H-1 NMR) spectroscopy, and zeta potential analysis. It has been found that DMDAAC had been successfully grafted onto the starch backbone and the isoelectric points (IEP) of different CS-g-DC samples increased with grafting degree of DMDAAC (G(DMDAAC)). Three types of clay suspensions (kaolinite, smectite and illite) were used to study the flocculation performance and mechanism of CS-g-DC by turbidity and particle size distribution. The results of these analyses showed that CS-g-DC samples with a G(DMDAAC) higher than 98% flocculated well all three clay suspensions depending on charge attraction and bridging mechanism. The flocculation performance of CS-g-DC was also evaluated in drilling fluids from a drilling site by mineral content analysis. The results showed that these CS-g-DC samples with appropriate G(DMDAAC) could remove useless solids from the drilling fluids effectively, indicating it could be used as flocculants for drilling fluids reuse or recirculation during drilling operation.