A Polymer Water Based Drilling Fluid for 220 ℃ Bottomhole Temperature

The efficient development of the abundant deep oil and gas boasted by China is of great significance for ensuring the national energy security. The regular polymer drilling fluids presently used generally have temperature resistance of less than 220 ℃. Salts, which are commonly used in formulating water-based drilling fluids, greatly damage the performance of the fluids. Deterioration of the properties of a drilling fluid during drilling causes downhole accidents and economic losses to the development of deep oil and gas. To deal with the deterioration of the properties of drilling fluid at high temperatures and high salinities, a high temperature zwitterionic polymer and a high temperature anionic polymer are synthesized. The two polymers have synergistic effect, and control and adjust mud rheology through high-strength network structures. To improve the plugging performance and filtration control property of a drilling fluid, an ultrahigh temperature high efficiency plugging agent is developed to plug pores in the formation, thereby stopping the transmission of pressure across the borehole wall. A water-based polymer drilling fluid is formulated with these three core additives to work in ultra-high temperature (220 ℃) environment. Laboratory evaluation of the performance of this drilling fluid shows that it has good rheology, filtration property, suspending capacity, plugging capacity and lubricity; the high-temperature high-pressure (HTHP) filtration rate is only 9.6 mL. The viscosity and gel strengths of the drilling fluid remains stable at HTHP, and the settling factor of the drilling fluid after being aged for 72 hours is only 0.5113 in testing with the test cell in an upright position. In sand-bed test the depth at which the drilling fluid invades into the sand-bed is only 6 mm. The friction coefficient of the drilling fluid after being aged and the mud cake frictional coefficient are 0.1224 and 0.0875, respectively. This drilling fluid has good high temperature resistance and stability, and is of great importance to the development of deep oil and gas development.