A novel hyper-cross-linked polymer for high-efficient fluid-loss control in oil-based drilling fluids

In order to control filtrate at high-temperature and high-pressure condition in oil-based drilling fluid for drilling process of oil and gas wells, an amine cross-linked polymeric fluid-loss-control material (ACP) was designed and synthesized. This material was synthesized through cross-linking poly (maleic anhydride-alt-1-octadecene) (PMAO) with amine. The structure of hyper-cross-linked copolymer enables the ACP polymers to withstand higher aging temperatures and less affect the rheology of oil-based drilling fluid. The structures of ACP polymers we synthesized were confirmed by FT-IR spectra and elemental analysis. TGA results showed that the decomposition temperature of ACP polymers exceeds 400 degrees C. And the amphiphilic nature of ACP polymers makes them enhance the stability of water-in-oil emulsion of oil-based drilling fluid. In addition, combining the viscoelasticity data of amine cross-linked PMAO suspensions and the fluid-loss control performance of ACP in oil-based drilling fluid, it was found that the increase of amino number in the cross-linker can effectively reduce the filtrate permeating, which is because the aggregation of hydrophilic amino makes ACP polymer form a dense structure to prevent oil from passing through. After screening of ACP polymers, the preferred one (ACP-5) can reduced filtrate volume of oil-based drilling fluid by over 90% with small dosage (3 g in 400 mL drilling fluid) after hot rolling for 16 h at 232 degrees C.