Wells in the Midland Basin have a high potential to encounter whole mud losses while drilling through the mechanically weak sandstones in the Sprayberry formation. The efforts to keep mud weights lower than the fracture gradient while drilling through the extremely fragile Sprayberry formation can be challenging with narrow pore pressure/frac gradient windows.
While setting 8 5/8–in. casing across the San Andres formation, the operator was targeting the Lower Sprayberry, using an 8.3 lb/gal oil-based mud (OBM). The operator encountered seepage losses and pumped a conventional lost circulation material (LCM) pill. The pill failed and losses increased. While pumping the second pill, with a larger concentration of lost circulation material, the losses climbed and eventually total lost circulation was encountered.
After several attempts to stop downhole losses failed, the use of conventional LCM seemed to increase the mud losses. STAR SHIELD 3000 was pumped in sweeps and spotted in the open hole. The mud losses stopped and full circulation was re-established once the sweep reached the thief zone. STAR SHIELD 3000 was maintained at 8 lb/bbl in the OBM circulating system until the operator reached total depth (TD).
Low concentrations of STAR SHIELD 3000 proved more effective than high concentrations of conventional LCM’s. The operator drilled the lateral interval to TD at 18,348-ft. through the highly depleted Sprayberry formation without encountering any additional mud losses or influxes. Successfully ran casing to bottom and cemented with full returns.