Synthesis and Plugging Performance of Nano-Micron Polymeric Gel Microsphere Plugging Agents for Oil-Based Drilling Fluids

Abstract

As shale gas recovery progresses to deep layers, the wellbore instability during drilling in applications of oil-based drilling fluids (OBFs) becomes increasingly severe. This research developed a plugging agent of nano-micron polymeric microspheres based on inverse emulsion polymerization. Through the single-factor analysis with respect to the permeability plugging apparatus (PPA) fluid loss of drilling fluids, the optimal synthesis conditions of polymeric microspheres (AMN) were determined. Specifically, the optimal synthesis conditions are as follows: the monomer ratio of 2-acrylamido-2-methylpropanesulfonic acid (AMPS): Acrylamide (AM): N-vinylpyrrolidone (NVP) were 2:3:5; the total monomer concentration was 30%; the concentrations and HLB values of emulsifier (Span 80: Tween 60) were 10% and 5.1, respectively; the oil–water ratio of the reaction system was 1:1; the cross-linker concentration was 0.4%. The polymeric microsphere (AMN) produced via the optimal synthesis formula had the corresponding functional groups and good thermal stability. The size distribution of AMN ranged mainly from 0.5 to 10 μm. The introduction of AMND in OBFs can increase the viscosity and yield point of oil-based drilling fluids and slightly decrease the demulsification voltage but significantly reduce high temperature and high pressure (HTHP) fluid loss and permeability plugging apparatus (PPA) fluid loss. The OBFs with 3% polymeric microsphere dispersion (AMND) reduced the HTHP and PPA fluid loss by 42% and 50% at 130 °C, respectively. In addition, The AMND maintained good plugging performance at 180 °C. The AMN particles can block leakoff channels of artificial cores, effectively prevent the invasion of oil-based drilling fluids into formations and suppress pressure transfer. OBFs with 3% AMND enabled the corresponding equilibrium pressure to decrease by 69%, compared with that of the OBFs. The polymeric microspheres had a wide particle size distribution. Thus, they can well match leakage channels at various scales and form plugging layers via compression–deformation and packed accumulation, so as to prevent oil-based drilling fluid from invading formations and improve wellbore stability.

Development and Characterization of the Shale Stratum Well Wall Stabilized with Nanosomal Sealing Agent

“…The permeability of shale is extremely low (10 −6 –10 −12 μm 2 ); therefore, Darcy’s law is not applicable. However, pressure transfer methods can be used for detection [ 36 , 37 ]. Shale pressure transfer technology provides a scientific and effective experimental means for optimizing and evaluating the performance of anti-collapse drilling fluid systems and is one of the principal indicators of the important progress in the mud shale wellbore stability research in recent years [ 38 ].…”

Development of Multiple Crosslinked Polymers and Its Application in Synthetic-Based Drilling Fluids

“…With the introduction of HEAA and nano-SiO 2 , the initial decomposition temperature and maximum decomposition temperature increased to 367.9 • C and 427.2 • C, and the addition of crosslinked monomers and nanoparticles significantly improved the heat resistance of the polymer. In addition, the final mass loss of MBAH/ nano-SiO 2 was 94.87%, indicating that the doping of nanoparticles enabled the polymer to maximally maintain its structural rigidity at high temperatures, which is also favorable for the potential application of the material under extreme HTHP conditions [18].…”