A Temperature Sensitive Polymer Flow Pattern Modifier for Water Base Drilling Fluids for Deep Water Drilling

A flow pattern modifier PNAAM was developed to satisfy the needs of rheology control of water base drilling fluids at low temperatures in deep water drilling. PNAAM was synthesized with N-isopropyl acrylamide (NIPAM) and acrylamide monomers based on the fact that temperature sensitive polymers, when responding to the changes of temperature, show remarkable changes in their hydrodynamic volumes and molecular conformation. In laboratory study, the functional groups of the product of the synthesis reaction were characterized using FT-IR, and thermogravimetric analysis showed that the initial thermal decomposition temperature of the synthesis product was 300 ℃. Turbidity analysis of the synthesis product showed that the molar ratio of the monomers and salt concentration affect the LCST of the synthesis product by affecting the strength of the hydrogen bonds between the hydrophilic groups in the molecules of the synthesis product and the water molecules. The ratios of rheological parameters of PNAAM at 4 ℃, 25 ℃ and 65 ℃ in drilling fluids were: AV_{4 ℃}∶AV_{25 ℃}∶AV_{65 ℃}= 1.75∶1.22∶1, PV_{4 ℃}∶PV_{25 ℃}∶PV_{65 ℃}= 1.8∶1.4∶1 and YP_{4 ℃}∶YP_{25 ℃}∶YP_{65 ℃}= 1.8∶1∶1.09. Analysis of the mechanisms shows that before the LCST is reached, the hydrophilic amide groups in the molecular chains of PNAAM are dominating the solution and PNAAM is soluble in water, hence there is no measurable hydrodynamic radius for PNAAM. When the environment temperature is greater than LCST, the hydrophobic groups in the molecular chains of PNAAM are dominating the solution and the hydrophobic associating action among the molecular chains of PNAAM is becoming stronger, thereby forming a 3-D network structure in the solution, which increases the viscosity of the solution and the particle sizes of the polymers, and makes the bentonite particles in the mud cakes more dense and more orderly arranged.