A low density micro-foam workover fluid for deep and ultra-deep wells with low-pressure coefficient and high inorganic salt

The leakage of workover fluid often occurs in the workover operation of low-pressure oil wells due to the pressure coefficient is generally less than 1.0, which leads to the slow recovery of oil well productivity or even failure to recover. The performance of workover fluid will directly affect the degree of damage and production of oil and gas wells. In this paper, SBX (Water+0.5% sodium dodecyl sulfate SDS+0.5% dodecyl dimethyl betaine BS-12 +0.7% polyurethane thickener XH-ZC-5) has been found to be a very effective temperature-resistant and salt-resistant low-density micro-foam workover fluid. Warning Blender experimental results showed that the half-life and foaming volume of SBX were 3084 min and 360 mL, respectively. Microscopic experiments demonstrated that the particle size of the foam gradually became smaller and the foam became denser with the increase of foam stabilizer XH-ZC-5 concentration. The foam stabilizing mechanism of XH-ZC-5 was mainly to keep the foam in a lower surface energy state by reducing the surface tension, and to increase the liquid viscosity of the foam to maintain the strength and elasticity of the liquid film. Besides, the tolerance of SBX to NaCl and CaCl2 was 20% and 15%, respectively. The half-life and foaming volume of SBX after thermal aging at 150 degrees C for 16 h were 2562 min and 430 mL, respectively. At the same time, the anti-oil pollution experiment indicated that SBX had good anti-pollution ability to crude oil when the crude oil concentration was less than 15%. The static suspended sand experiment showed that the settling time of carbonate sand particles with sizes of 2.1 cm and 1.7 cm in SBX foam was 550 times and 1160 times that in tap water, respectively. What's more, the density and filtration loss of SBX at 150 degrees C were 0.64 g/cm3 and 9.6 mL, respectively. SBX was a non-Newtonian fluid at 150 degrees C, and the power-law model of the foam system was tau = 2.187r ' 0.419. SBX is of great significance to the workover operation of deep and ultra-deep wells with low-pressure coefficient and high inorganic salt.