Research and Application of Solid Free Drilling Fluid Technology for Gas Storage in the Qinghai Tibet Plateau

Mabei Gas Storage is the first gas storage in the Qinghai Tibet Plateau. It is located in the Mahai Dahonggou uplift area—Mabei uplift zone of the northern margin fault zone of the Qaidam Basin. It is the “headquarters” of natural gas supply in Gansu, Qinghai and Xizang. The E31 formation of the Ganchaigou Formation below the target layer is severely depleted, with drilling fluid leakage and damage, as well as prominent reservoir protection issues, severely restricting the safety and economy of drilling operations. To solve these problems, a solid free drilling fluid system with excellent reservoir protection performance suitable for safe drilling of Mabei gas storage was ultimately formed through screening and optimization of reservoir protectants, inhibitors, weighting agents, etc. The research results show that: ① Adding acid soluble temporary plugging material BYD-2, with a sand bed filtration vector of 0 and an invasion depth of ≤6 cm, can effectively reduce the invasion of filtrate into the formation; ② Selecting weighting materials such as organic salt weight2, inorganic salt KCl, NaCl, etc. to improve drilling fluid inhibition performance, minimize solid phase invasion, and achieve a reservoir permeability recovery value of about 82% Completed on-site tests on 6 wells, and the application effect of drilling fluid was significant. There were no complex occurrences during horizontal drilling, electrical testing was conducted once to the end, and casing was smoothly inserted. The medium pressure water loss was maintained within 5 mL, and the density difference between the upper and lower parts of the drilling fluid was ≤0.01. The successful application of the solid free drilling fluid system has played a crucial role in achieving reservoir drilling for the horizontal well of the Mabei gas storage, effectively ensuring the construction and completion of the Mabei gas storage.