Natural polymer materials are increasingly utilized in drilling fluid additives. Starch has come to be applied extensively due to its low cost and favorable fluid loss reduction properties. However, its poor temperature resistance and high viscosity limit its application in high-temperature wells. This study innovatively introduces for the first time diatomite as an inorganic material in the modification process of starch-based fluid loss additives. Through synergistic modification with acrylamide and acrylic acid, we successfully resolved the longstanding challenge of balancing temperature resistance with viscosity control in existing modification methods. The newly developed fluid loss additive demonstrates remarkable performance: It remains effective at 160 °C when used independently. When added to a 4% sodium bentonite base mud, it achieves an 80% fluid loss reduction rate—significantly higher than the 18.95% observed in conventional starch-based products. The resultant filter cake exhibits thin and compact characteristics. Moreover, this additive shows superior contamination resistance, tolerating 30% NaCl and 0.6% calcium contamination, outperforming other starch-based treatments. With starch content exceeding 75%, the product not only demonstrates enhanced performance but also achieves significant cost reduction compared to conventional starch products (typically containing < 50% starch content).
The copolymer (PAAN-SiO 2 ) of acrylamide (AM), 2-acrylamido-2-methyl-1-propane sulfonic acid (AMPS), N -vinylpyrrolidone (NVP) and modified nano-silica (M-SiO 2 ) was synthesized by free radical polymerization in a water solution. The composition, micro-morphology and thermal stability properties of PAAN-SiO 2 were characterized by Fourier transform infrared spectroscopy, thermal gravity analysis and transmission electron microscopy (TEM). The results showed that AM, AMPS and NVP were successfully grafted onto the surface of M-SiO 2 and formed a spherical core–shell structure copolymer. A significant reduction in the filtration volume was achieved after PAAN-SiO 2 added, and this phenomenon was even more pronounced after aging at the high temperature. The filtration volume of base slurry containing 2 wt% of calcium chloride after aging at 180 °C was reduced from 186 to 6 ml after adding 2 wt% of PAAN-SiO 2 , which exhibited a special property of anti-calcium contamination at high temperature. The interaction mechanism between PAAN-SiO 2 and bentonite and calcium ions was analyzed by particle size analysis, scanning electron microscopy, TEM and X-ray diffraction. Because of the stretching of polymer chain under 180 °C that more amide, sulfonic acid groups and cyclic rigid groups were exposed and the strengthening of the connection between PAAN-SiO 2 and clay prevents a large amount of ion exchange between Ca 2+ and clay layers, reducing the agglomeration of clay. Meantime, the distribution of clay particles was more extensive and some particles with a size of 1–10 μm plugged the micro-nano-pores on the filter cake, and eventually the thin and compact filter cake was formed.
Using common corn stalks as raw materials, a functional dense-structured carbon microsphere with good elastic deformation and certain rigid support was modified from biomass through a step-by-step hydrothermal method. The composition, thermal stability, fluid-loss reduction performance, and reservoir protection performance of the modified carbon microspheres were studied. Research indicates that after hydrothermal treatment, under the multi-level structural action of a small amount of proteins in corn stalks, the naturally occurring cellulose, polysaccharide organic compounds, and part of the ash in the stalks are adsorbed and encapsulated within the long-chain network structure formed by proteins and cellulose. By attaching silicate nanoparticles with certain rigidity from the ash to the relatively stable chair-type structure in cellulose, functional dense-structured carbon microspheres were ultimately prepared. These carbon microspheres could still effectively reduce fluid loss at 200 °C. The permeability recovery value of the cores treated with modified biomass carbon microspheres during flowback reached as high as 88%, which was much higher than that of the biomass itself. With the dense network-like chain structure supplemented by small-molecule aldehydes and silicate ash, the subsequent invasion of drilling fluid was successfully prevented, and a good sealing effect was maintained even under high-temperature and high-pressure conditions. Moreover, since this functional dense-structured carbon microsphere achieved sealing through a physical mechanism, it did not cause damage to the formation, showing a promising application prospect.
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