Abstract: In order to reduce the dependence on oil-based drilling fluid in the operation of extended reach well(ERW), and to meet the requirements of offshore environmental protection, a kind of specific drilling fluid should be used in the operation of ERW in East China Sea. Based on the comparison and evaluation of several types of drilling fluid systems such as PEM, Balance-Water Drilling Fluid and DHS in the anti-collapse, plugging performance, rheological property and anti-contamination, the authors believe the DHS, with better comprehensive performance, can meet the requirements of drilling fluid system for ERW in inhibition ability, sealing ability, carrying ability, and lubrication ability, and can be selected as the drilling fluid of the Well T13.