Drilling Fluid Techniques for Borehole Stability in Shahejie Formation of Qingdong Block in Shengli Oilfield

Qingdong Block is located in northern faulted zone,Qingdong sag in Jiyang Depression.The geologic structures are complex in Shahejie Formation,faults are well developed locally,and ground stress is clear below the faults.The mudstones in Sha-3Member are hard and crisp,and lamination is clear.The borehole was very instable during well drilling,and complex accidents occurred frequently.Repeating dummy trips occurred frequently,and stick was severe case,which slow down the exploration progress in the study area severely.By using aluminum-amino inhibitive,sealing and anti-caving drilling fluid,many measures were taken,such as suitable density supporting,multi-variate synergism inhibition,compelling formation sealing,and reasonable rheological behavior controlling.In addition,corresponding onsite maintenance technology was taken,which guaranteed the borehole stability of Well Qingdonggu-1 in Shahejie Formation.Well Qingdonggu-1 was completed in advance,and borehole was stable in Shahejie formation.In addition,the drilling period was shorten by 20%.