Treatment Technology of Brine Contamination and Barite Settlement for the High Temperature and High Density OBM for Ultra-Deep Well Drilling in Western China

Due to the existence of extremely high temperature, high pressure thick evaporite bed and brine layer, Kuqa piedmont structure has been identified as one of the most complicated drilling regions in the world which locates in Tarim Basin of China. In Keshen Block the occurrence rate of high pressure brine invasion during the drilling progress is high up to 56%, and barite in OBM mud is easy to settle under high temperature and longtime static conditions. Therefore, brine invasion and barite settlement are serious challenges for ultra-deep wells drilling in Western China. Increasing the density of mud is one method to deal with brine invasion during drilling, but lost circulation is easy to be caused. Another method is discharge the brine in batches to reduce the high pressure of brine layer, which requests the higher brine capacity of OBM. In this instance, a new emulsifier used in OBM was compounded to enhance the emulsifying efficiency through the increase the number of hydrophilic group on single emulsifier molecular structure. The experiment results indicated that the ability of OBM tolerance to brine contamination is higher than 60%. The instrument for evaluating the sedimentation rate of OBM at high temperature (200°C) and high pressure (20MPa) has been developed. The experiment results indicated that increasing RM6 value could improve the stability of settlement. Well KS1101 encountered lost circulation and high pressure brine layer in the same horizon, the safety density window of the drilling fluid is almost zero. Thus, the method of brine discharge in batches was used to reduce the brine layer pressure to ensure the drilling safety. A total of 1129.98m3 brine was discharged by 64 times of drainage and avoided the lost circulation. The rheology of OBM is stable, and the brine water capacity of the drilling fluid system is more than 45%. Throughout the drilling process, there was no downhole complex occurred. This OBM system has been wildly used in Keshen Block.