Control Lost Circulation in Well S25 of Block Y

Mud losses were frequently encountered when drilling the Pabdeh, a low strength dolomite formation in the south edge of the HOS, Block Y in a country. Many mud loss zones are present and irregularly distributed, with lost circulation continually lasting for a long time. Rates of mud losses are sensitive to mud weight. To control the mud losses which had been difficult to stop during drilling operation, a bridge LCM formulation was developed through experiment on a DL-A HTHP LCM tester. This LCM formulation is suitable for controlling mud losses into 2 mm wide fractures. By analyzing the mud loss behavior in whole well drilling operation, it is recommended that when drilling the top formation, more attention should be paid to mud loss prevention, and use LCM mud to stop them if mud losses do occur. In the upper middle section of the well, low density should be used to drill through the thief zones. In the lower middle and lower section of the well, a combination of "control mud losses while drilling" and "control mud losses under pressure" techniques can be applied to stop mud losses or mitigate the negative effect of mud losses on drilling operation. These practices have been proved successful in the drilling operation of the Well S25.