Complex deep well drilling fluid technology for Well Wugu-4

Well Wugu-4 is a key exploration well with total depth of 5750m. During drilling the 2nd interval open hole, thick mudstone was penetrated. Polysulfonate drilling fluid was taken to solve the serious mud-making and wellbore stability issues. For the 3rd interval, multiple pressure system and faults were encountered, and plaster, plaster mudstone, huge basalt, tuff, and blacks were penetrated, which makes it prone to collapse, leaking and wellbore instability. Organic salt drilling fluid was taken to slove the issues of reaming down, bit bouncing, bit sticking, etc. The low permeability additive, temporary blocking agent, and sealing agents were added to improve wellbore pressure bearing ability. The risk of bit sticking from pressure difference during the 3rd interval drilling was solved and drilling safety was ensured. The completion logging was successful with only one run, and the drilling cycle was decreased significantly.