Evaluation of the Xanthan Gum, Gum Acacia, and Their Graft Copolymers with Acrylamide as Low-Dosage Hydrate Inhibitors for Their Application in the Drilling of Gas Hydrate Reservoirs

Abstract

Hydrate formation is a significant issue while drilling into deep-water reservoirs containing gas hydrates. They may form in the drilling fluid flowlines, wellbore annulus, and ram cavities of blowout preventers. The natural gums, i.e., xanthan gum (XG) and gum acacia (GA), and their two graft copolymers with acrylamide (AAm), i.e., XG-g-PAAm and GA-g-PAAm, have been synthesized and tested as low-dosage hydrate inhibitors using THF hydrate systems via temperature-augmented visual method. XG-g-PAAm and GA-g-PAAm have shown better inhibition efficiencies and higher induction times than XG and GA. All of these inhibitors are then tested as drilling fluid additives to the formulated water-based drilling fluid systems (WBDFs). The formulated WBDFs contained 0.4 w/v % of each carboxymethyl cellulose (CMC), polyanionic cellulose (PAC), and 5 w/v % of potassium chloride (KCl). The rheology of the formulated WBDFs has been tested at an ambient temperature (293 K) and low temperature (275 K). The rheological parameters of WBDFs obtained from the experiments are within permissible limits with an inhibitor concentration of 0.5 w/v %. The rheological data are then fitted to the Bingham–Plastic (B–P) model and Herschel–Bulkley (H–B) model. The coefficient of determination’s (R 2) upper and lower limits for the B–P model is 0.9715–0.9969 for 0.5 w/v % GA- and 0.5 w/v % XG-g-PAAm-containing WBDF systems. Again, for the H–B model, the range for R 2 is from 0.9891 to 0.9980 for 0.5 w/v % GA- and 0.5 w/v % XG-containing WBDFs. Hence, the R 2 showed a better agreement with the H–B model than with the B–P model. These observations suggest that XG, GA, XG-g-PAAm, and GA-g-PAAm may be used as hydrate inhibitors in the formulated WBDFs while drilling into gas hydrate reservoirs.

Comparing the Kinetic Hydrate Inhibition Performance of Linear versus Branched Polymers

“…They all have very poor KHI performance when tested alone and under typical field conditions. They may be affecting the gas mass transport by increasing the viscosity, which will slow the rate of hydrate formation. − Even grafting acrylamide or other purely hydrophilic monomers does not improve the performance significantly for gas hydrate systems because you need amphiphilic groups such as those found in VCap or NIPMAm to be added . Branched polycitramides were shown to give good KHI performance but only when suitably large (C3–C6) alkyl groups were attached to the amide groups …”

“… 40 − 43 Even grafting acrylamide or other purely hydrophilic monomers does not improve the performance significantly for gas hydrate systems because you need amphiphilic groups such as those found in VCap or NIPMAm to be added. 44 Branched polycitramides were shown to give good KHI performance but only when suitably large (C3–C6) alkyl groups were attached to the amide groups. 45 …”