Mud Loss Control Technology in Qiongdongnan Basin under High Temperature and High Pressure Bearing Conditions

The well XX23-1-1 is a key exploratory well drilled in the Qiongdongnan basin (a basin located in the southeast of Hainan Province). Mud losses were encountered when drilling to 4,186.22 m. A new HTHP pressure bearing lost circulation control technique was presented to deal with the mud losses based on the rate of mud losses and the high temperature high pressure encountered in the mud loss zone. The lost circulation control slurry was formulated with particles, flakes and fibers. Based on the mud loss control mechanisms of “particles to bridge + wedge in to provide pressure bearing capacity + strengthen the borehole wall with mud cakes”, a tight plugging zone with stable structure was formed under squeeze pressure. The channels through which the mud was lost were plugged with the slurry and the loss zone was strengthened. With this technique, the mud losses were successfully stopped. Laboratory evaluation was performed on the particle size distribution, the ability of high temperature resistance and success rate of the slurry. The experimental results show that this slurry has a wide particle size distribution and is able to effectively control mud losses through induced fractures. The HTHP lost circulation materials used in the slurry has low weight losses after aging at 180 ℃ for 16 hours, showing an excellent high temperature durability. Plugging of a 5-3 mm seamed plate with the slurry can stand a pressure of more than 20 MPa. This HTHP pressure bearing mud loss control technique was used in controlling mud losses encountered in the well XX23-1-1, the final pressure bearing capacity of the plugged zone reached 3 MPa and was stabilized at this level for 30 min, with no pressure drop, and the ECD on the bottom of the hole was 1.90 g/cm³, meeting the expected requirements.