Drilling fluid technology for horizontal wells in Luojiazhai structure.

According to the geological characteristics of Luojiazhai structure and technical difficulties in drilling horizontal wells, drilling principle in this area is described as “drilling upper formation for deeper section, drilling vertical hole for deviation interval and mainly solve drilling fluid difficulty in large angle deviation section”. 1) in the vertical hole, potassium/calcium based polyalcohol-organosilicon polymer drilling fluid was used. In this fluid, drilling fluid additives such as polyalcohol and organosilicon were added in to stop hole sloughing and cuttings dispersing; 2) in the large angle deviation interval, potassium/calcium based polyalcohol-MMH drilling fluid was employed. In this fluid, collide protecting agent, lubricator, surfactants and diesel oil were combined to prevent cuttings-bed form forming, and improve anti-contamination property. 3) in the horizontal section, modified potassium/calcium based polyalcohol-MMH drilling fluid was applied. In this fluid, polyalcohol was used to protect the productive formation, and maintain excessive hydrogen sulfide scavenger. On-site application of this fluid verified that this fluid worked well in alleviating cuttings-bed building and preventing cuttings from dispersing, lost circulation was stopped, frictional drag during tripping was reduced, and formation was protected effectively.