Abstract: To solve the sand carrying problem of highly deviated well and horizontal well and avoid the pollution and damage for reservoirs better,China National Offshore Oilfield Service Company Limited researched and applied the PRD drilling-in fluid system and matching technology.By forming weak gel structure rapidly to obtain the special rheological property,the requirements of suspended sand carrying ability and borehole cleaning for horizontal well are met.Then the erosion of drilling fluid to the sidewall is reduced.Meanwhile,solid-liquid intruding into reservoirs is stopped effectively.Therefore,the role of stabilizing sidewall and protecting reservoirs are played.The PRD drilling-in fluid system and matching technology are applied successfully and widely in the development of marine and terrestrial oil and gas field.The application of PRD bentonite free and water based drilling-in fluid system for horizontal well in different area achieves downhole safety and meets the optimal and fast operation need.As a result,all the commissioning productivity reaches or exceeds the ODP distribution requirements,and the project operation time shortens 15%-20%.The field application proves that the PRD drilling-in fluid is an excellent drilling-in fluid for highly deviated well and horizontal well.