A New Comparative Evaluation for the Rheological and Filtration Properties of Water-Based Drilling Fluids Utilizing Sodium Salt of Linear and Cross-Linked Acrylate Polymer Hydrogels

Abstract

Currently, polymers were applied as the most functional additives for optimizing the rheological behavior and filtrate volume control of water-based drilling fluids. To affirm this concept, the present work aims to prepare sodium salt of linear polyacrylic acid (NaLPAA), polyacrylamide (NaLPAM) and their cross-linked polymer hydrogels (NaCPAA and NaCPAM), in different ratios using N,N′-methylenebis(acrylamide), as a cross-linker, potassium persulfate and ascorbic acid as initiators. FTIR characteristic spectra, 1H NMR analysis, SEM micrographs and elemental analysis for the formed gels were employed to emphasize their consistence. TGA and TGA-DTG thermo-grams displayed that NaCPAA polymer hydrogel offered the highest thermal stability behavior. The swelling behavior of the prepared hydrogels was examined and demonstrated that CPAM showed the best behavior at pH = 4 (acidic medium). The rheological properties of the investigated water-based mud samples were studied at various temperatures. For sample containing 0.57% (2 g) of NaCPAA at ambient temperature, it showed the highest rheological behavior in which AV achieved the highest value at 118 cP, PV was recorded at 69 cP, and YP was detected at 99 lbf/100 ft2. At LTLP conditions, sample containing 0.57% of XC-polymer and 2.86% bentonite in its composition offered the most enhanced mud cake thickness at 4.2 mm. At HTHP conditions, the filtrate volume of sample containing 0.29% NaLPAA was detected at 35 mL and for sample containing 0.57% was calculated at 22 mL. In addition, the modified mud samples with the same recipe of NaLPAA and NaCPAA at different applied temperatures showed moderate rheological properties compared to the commercial XC-Polymer. Furthermore, NaCPAA manifested a reduction in the swelling properties of water-based mud system containing high amount of API bentonite (2.85%, 10 g) in which AV and PV were calculated at 30 and 17 cP, respectively. In addition, YP was recorded at 22 lbf/100ft2. So, it could be used as a thinner for water-based bentonite mud systems.