Main challenge in drilling through unconsolidated sand zones in shallow sections, and time-dependent unstable shale zones in deeper sections is inability to secure them without significant rig time delay. Loss circulation zones exist around these problematic zones. When severe to complete loss of circulation is experienced, the complexity of securing the problematic zones increases. The level-I casing-while-drilling (CwD) technology was utilized successfully to hard ream and permanently isolate the problematic zones without nonproductive time.
Drilling or tripping through shallow and relatively deep unstable zones with severe loss of circulation may result in, for example, hard backreaming, severe tight spots, and stalling tendencies. Same applies for casing string when being run to permanently isolate unstable zones. Significant nonproductive time (NPT) is added when the casing string has to be pulled out to run a reaming bottomhole assembly (BHA), or when it is cemented off-bottom to clear and inhibited remaining rathole. CwD with reamer shoe and drill shoe were successfully utilized to ream the 18-⅝-in, 13-⅜-in, and 9-⅝-in casing strings, and eliminated NPT related additional operations.
In offset wells, some broken casing centralizers were left inside wellbore when 13⅜-in casing string was pulled out to clear wellbore with subsequent reaming trip. Additional two trips where necessary to mill broken centralizers left in wellbore, and to clean cuttings accumulated fill left on bottom before the casing string was run again. In addition, an additional cleanout trip was necessary to inhibited and clean the accumulated cuttings in the +/-400 - 1000-ft ratholes left below casing string when the wellbore bridged off completely around the 13-⅜-in and 9-⅝-in casing strings. A solution was necessary to reduce or to eliminate these additional trips.
CwD were successfully utilized to hard ream the casing strings to target depth to case-off the severely unstable zones experienced in the offsets. The additional NPT trips were eliminated completely. In addition, the 9-5/8-in casing string hard reaming was performed while incorporating a multistage differential valve (DV) and cemented in two stages. During the job execution, the reaming parameters are constantly monitored to not exceed casing strings limitations, especially the accumulated fatigue on the string as they are rotated. As a result, the troubles experienced in offset wells were successfully managed.
Complexity in drilling wells is increasing. Therefore, introducing innovative solutions that enable reducing the number of extra trips, is essential to reducing NPT. The offset wells drilling troubles related to securing unstable formations were studies thoroughly. Level-I Cwd technology was successfully utilized to eliminate those identified troubles without adding additional time-delaying trips. The unstable zones were secured in a record time compared to the offsets.
