The Research and Application of New Low Density Nitrogen Micro Bubble Workover Fluid

Abstract

Aiming at the need of coiled tubing sand washing operation for the low-pressure and leaking gas pool in Qinghai gas reservoir, we developed a kind of low density nitrogen micro bubble workover fluid technology, which is composed of a new type of composite foaming agent, temporary plugging agent, composite stabilizing foam agent and the nitrogen. Observing by a microscope, we can find that the micro bubble structure is composed of a core of gas, two membranes, three layers, which has high stability (higher stability than ordinary foam stability). The performance evaluation results show that, the temperature resistance of nitrogen micro bubble workover fluid is up to 120 ℃. Compression resistance can reach 20 Mpa. API filter loss is only 11.3 ml. The high temperature and high pressure filtration is only 16.6 ml. Anti-salt can reach 10%. Anti-calcium can reach 3% and the resistance to oil pollution is more than 15%. The recovery rate of core permeability is up to 89%. The system can not only reduce the fluid column pressure and reduce the pressure difference, but the formation of micro bubble in the leakage areas on the surface of formation is widespread, and has a certain strength and toughness, and also has a certain deformability matching leakage channel of formation, which can achieve the purpose of anti-leaking. This technology was applied in Qinghai gas field for 2 wells, with an efficiency of 100%. The sand washing operation was successfully completed, with no leakage. Key words : Low density nitrogen micro bubble workover fluid; Micro bubble; Qinghai gas field