The hydration and swelling of shale formations are serious problems for well drilling. The use of an efficient shale inhibitor is one of the most important methods for overcoming the wellbore instability issue. In this work, poly-L-arginine (PArg) was synthesized and used as an efficient and biodegradable shale inhibitor. This inhibitor was systematically evaluated through measuring the swelling degree of the bentonite (Bent) pellet, the rheological behavior of the Bent suspensions, and the recovery percentage of shale cuttings. The results demonstrated that 2.0 wt % PArg could reduce the swelling degree of Bent to 70.53%, improve the shale recovery percentage to 71.40% at 180 °C, and inhibit 12.0 wt % Bent mud-making. The PArg displayed a highly inhibitive performance and excellent high-temperature resistance property, better than common inorganic KCl and organic polyether diamine. The underlying inhibition mechanism was also proposed based on measuring the variation of the interlayer spacing of the Bent, observing the exterior morphologies of Bent particles, and assessing the particle size distribution and electrokinetic potential. The results indicated that the PArg displayed its inhibitive effect mainly by adsorbing onto the Bent, encapsulating the Bent particles efficiently, and decreasing the interlayer spacing in a certain degree with 0.9 Å. This study can contribute to designing highly inhibitive water-based drilling fluids containing PArg.

With increasing intensified environmental pressure and a complex drilling environment, developing high-performance fluid loss additives with environmental acceptability is becoming a research focus. Through chemical cross-linking between starch, polyphenols, and lignosulfonate, a polymer SPL was facilely synthesized and it showed good filtration performance in bentonite–water-based drilling fluids (BT-WBDFs). The BT-WBDFs containing 2.0 wt % SPL polymer had a filtration volume of 7.0 mL/30 min at 150 °C. Moreover, SPL can resist the effect of 0.75 wt % CaCl2 and 7.5 wt % NaCl at 150 °C. The polymer SPL contributed to stable bentonite dispersion and kept enough viscosity of BT-WBDFs at high temperatures. The well-dispersed bentonite and SPL formed a thin and compact filter cake, providing effective plugging and shielding effects during the filtration process. Furthermore, a WBDF based on SPL as the main fluid loss additive was prepared and it displayed excellent high-temperature resistance, rheological property, inhibition, and environmentally friendly performance. This set WBDF has promising guidance on the design of high-performance drilling fluids with excellent environmental protection property.

BACKGROUND Contaminants with either negative or positive surface charges in wastewater generated from oilfields are normally very difficult to remove by traditional flocculants owing to their strong pH‐dependence and high health risks. Natural polymer flocculants, especially chitosan‐based flocculants, have attracted much interest for their environmental friendliness, excellent flocculation efficiencies and cost‐effectiveness. RESULTS A series of amphoteric chitosan‐based grafting flocculants (CM‐chi)‐g‐PDMDAAC (denoted as CgPD) were successfully synthesized by grafting diallyl dimethyl ammonium chloride (DMDAAC) onto carboxymethyl chitosan (CM‐chi) with different grafting ratios. By carboxymethyl and grafting modification, dramatically increased water solubility of chitosan was obtained. The physicochemical structure of CgPD products was characterized by 1H NMR and elemental analysis proving that DMDAACC was grafted onto CM‐chi appropriately. Flocculation effects of CgPD were studied in kaolin and hematite suspensions having opposite surface charges. These CgPD flocculants demonstrated an excellent performance in respect of flocculation window, optimal dosage and pH sensitivity. In addition, CgPD was proven to be applicable as a flocculant in water treatment of oilfield sites. CONCLUSION The biodegradability flocculants, CgPD, can effectively remove contaminants with opposite surface charges from oilfield wastewater with low optimal dosage, wide flocculation window, low pH sensitivity and less environmental impacts than traditional flocculants. © 2017 Society of Chemical Industry