Practice of fuzzy-ball drilling fluid technology in Well Ji X coal bed methane

In the second open hole between 530 m and 616 m in depth in Well Ji-X, there is an aqueous layer with high pressure, and between 780 m and 860 m in depth, there is a gravel layer. The formation pressure coefficient of Shanxi target interval formation is between 0.55 and 1.0 while the formation pressure coefficient of Taiyuan target interval formation is between 0.67 and 1.03, and different pressure coefficients exist in a same open hole. Bentonite-based and polymer-based drilling fluids were applied in the penetration of high pressure water layer. However, polymer drilling fluids with density of 1.2~ 1.5 g/cm3 and high viscosity can not maintain the hole stability and cutting carrying capacity in the gravel layer in drilling process. There was still 70 m can not reach over the open hole bottom while the well was only 925 m in depth. Then Fuzzy-ball drilling fluid technology was applied, which was weighted by mixing barites, and the density was increased to 1.03 g/cm3; the funnel viscosity reached to 90 s; and the 70 m gravel was removed in 12 hours circulation. The drilling reached to 1278 m in depth smoothly with fuzzy- ball drilling fluid, in which the fluid density was 1.07 g/cm3 while the funnel viscosity was decreased to 70 s. The processes of running casing and cementing go well subsequently. Loading bearing capacity of low-pressure target layer is greatly improved and the engineering problem of different coefficients exist in a certain open hole section is solved by application of drilling fluid with fuzzy-ball technology, which provides a new drilling fluid technology for the low-pressure coal bed methane exploration.