Study on Performance of A New Oil Base Mud Lost Circulation Material

Fractures are usually highly developed in shale formations,making the shale easily swelling and breaking.Mud loss is another problem frequently encountered in shale drilling.To ensure hole stability,oil base drilling fluids are usually used and the losses of these expensive drilling fluids mean severe economic loss.To prevent the loss of oil base drilling fluids,an organophilic high molecular weight resin lost circulation material,YDLJ-1,has been developed.It has been proved that the YDLJ-1 has good stiffness and deformability,making it easy for the YDLJ-1 to fill the fractures through which the mud is lost.The capability of the YDLJ-1 to absorb oil makes it expandable,and in 5 h the volume of the YDLJ-1 that has absorbed oil is 5 times of its original volume.After ageing at 150℃ for 30 days,YDLJ-1 still retains certain compressive strength and deformability.The compressive strength of YDLJ-1 is 20 times that of the other similar products.Breakthrough pressure in forward direction against the surface of YDLJ-1 is greater than 15 MPa,and in backward direction against the surface of YDLJ-1 0.9 MPa,satisfying the needs for mud loss control.YDLJ-1 has been used in drilling the lower part of the Shiqianfeng formation penetrated by the Well Yunyeping-1 in Yanchang oilfield.2 ton of YDLJ-1 was used and the volume of mud loss was 30 m³ less than the offset well,time spent controlling the mud loss was shortened by 2 days,proving the efficiency of YDLJ-1 in mud loss control.