Study on Correction of Safe Mud Weight Window (SMWW) for Horizontal Well

摘要

In drilling operation, to determine the safe mud weight window rationally is very important for borehole stability. Conventional safe mud weight window is based on fracture pressure and caving pressure. However, drilling practice experience has shown, although the mud weight meets the standard of SMWW, there are some borehole problem such as lost circulation and cave-in in the process of tripping because of swabbing and surging. Compared with the vertical well, the soakage time of drilling fluid in horizontal well is longer, the lost circulation and cave-in are more likely to happen. Therefore, SMWW of horizontal well should be calculated more precisely. This paper starts with an analysis of mud rheological property, combined with flow rate equations of different operating conditions, through math deduction for fluctuation pressure distribution model; a method of corrected SMWW calculating was established.