Control Mud Losses in Well Shunbei-5-9 with ZYSD High Fluid Loss Solidifying Slurry

The Well Shunbei-5-9 is an appraisal well drilled in the potential area of the low uplift Shuntuoguole north margin. The Silurian system penetrated by this well has low pressure bearing capacity and plenty of induced fractures which are easy to widen and extend when pressure surge is applied, and mud losses are thus occurring. When using bridging lost circulation materials (LCM) to control mud losses, it is difficult to have suitable particle size distribution of the LCMs, and the LCMs deposited on the surface of the wellbore has pressure bearing capacity that is not sufficient to resist mud losses again. Furthermore, there are high pressure saltwater zones developed in the Silurian system, making the mud loss control more difficult. Several wells drilled nearby experienced severe mud losses, borehole wall collapse and even well abandonment. To overcome the difficulties encountered in controlling mud losses in the Silurian system, a ZYSD high fluid loss LCM was used. ZYSD is able to seal off the mud loss channels in 30 s, and the formation plugged with ZYSD has pressure bearing capacity of at least 18 MPa. This technique has been used 7 times in field operation and were all successful. Time spent dealing with mud losses was reduced by 81%. Mud loss zones treated with ZYSD had pressure bearing capacity of 8.5 MPa. Equivalent circulation density of mud when drilled into the Silurian system was 1.51 g/cm³. The application of the ZYSD technique successfully solved mud losses and water kick problems encountered in drilling the Well Shunbei-5-9.