RHEOLOGICAL PROPERTIES OF POLYMER DRILLING FLUID DEVELOPED FOR PERMAFROST NATURAL GAS HYDRATE DRILLING

The rheological properties of water-based drilling fluids are heavily influenced by low temperatures and are some of the most important issues for permafrost natural gas hydrate drilling. In this work, we developed a polymer drilling fluid formula and studied its rheological properties at low temperatures. The rheological properties of four different drilling fluids including macro-polymers, amphoteric polymers, sulfonated polymers, and biopolymers were tested. The corresponding rheological-property/temperature response curves were drawn. The response characteristics of the rheological properties with temperature were analyzed. Based on these, a novel research idea was developed to adapt to permafrost drilling a poly-sulfonate drilling fluid system in which sulfonated lignite (SMC) and sulfonated phenolic resin (SMP) were used as the main agents while xanthan gum (XC) served as a flow-pattern modifier. According to orthogonal test results, the optimized drilling fluid formula was base mud + NaCl (20 wt. %) + NaOH (0.1) + SMP (3) + SMC (4) + XC (0.3). Moreover, the rheological-property/temperature response mechanism was analyzed using Fourier transform infrared (FT-IR) spectroscopic tests of the treating agents and scanning electron microscopic (SEM) tests of the mud cakes.