Synthesis of a Novel Modified Polysiloxane Filtrate Reducer and its Application in Water-Based Drilling Fluids

Deep and ultra-deep oil and gas resources have considerable potential and are now the primary resources to be explored and developed. However, the formation conditions get more harsh and challenging as the drilling depth increases. At 150 degrees C, the majority of natural polymers start to degrade thermally, whereas synthetic polymers perform exceptionally well under even higher temperatures. Based on the excellent thermal stability of polysiloxane in other research areas, a modified siloxane monomer (F-PDMS) was synthesized and copolymerized with acrylamide (AM), 2-acrylamido-2-methylpropane sulfonic acid (AMPS) and N-vinyl caprolactam (NVCL) to prepare a novel modified polysiloxane filtrate reducer (F-LS) with high-temperature resistance. The structure of products was characterized by Fourier transform infrared spectroscopy and the proton nuclear magnetic resonance, and their thermal stability was investigated using thermogravimetry. Furthermore, the rheological properties, filtration reduction, and inhibition performance of F-LS in base mud were evaluated. The results showed that after rolling at 220 degrees C for 16 h, the API (American Petroleum Institute) filtrate loss (ambient temperature, 0.69 MPa) of 1% F-LS was only 8.8 mL, and the high-temperature (220 degrees C) and high-pressure (3.5 MPa) filtration was 26.8 mL, and the linear swelling rate of API filtrate liquid was dropped from 12.57% to 9.74%. Compared to Driscald and Polydrill, the effectiveness of filtrate loss reduction of F-LS was superior. The filtration control mechanism of F-LS was revealed based on the scanning electron microscopy analysis, particle size analysis, and Zeta potential test. F-LS could absorb on the clay surface and cover the pores on the surface of filter cake, and make the latter more condensed. Particularly, F-LS increased the absolute value of Zeta potential of clay particles, thus increasing their double-layer repulsion, and hydration film thickness, maintaining the proportion of submicron particles, thereby improving the stability of rheology and filtration of drilling fluids under harsh conditions.