Drilling hole with shallow gas risk has always been a challenge. Conventional Diverter system doesn't qualify for a well control device but a device that is expected to reduce safety risk. Unfortunately, Diverter system has numerous failures when engaged for diverting gas flow. This paper provides a successful case history of a feasible and sustainable solution to drill shallow holes with safer control of gas at surface and superior operational liberty.
Diverter system coupled with autonomous Ram-BOP was deployed successfully in development well for drilling of a surface hole section with better control and safety. This Modified Diverter system allows independent control for Ram-BOP and Diverter operations with back-up flow path in case of diverter failure. This also creates ability to drill surface hole deeper by providing operational liberty to control or divert well flow.
This system was designed to support two well control scenarios, on drilled depth basis, and prepared accordingly:
Conventional diverter system, keeping alternate flow diversion path as backup to diverter failure Modified well control method, that approach well control with Kill Mud cap and provides option for close-system flow check
Surface hole section was planned to drill till 1300 meters BKB, with the application of this modified diverter system that allowed safe control of well/gas diversion in contrast to the conventional diverter system. For this purpose, Conductor pipe was set to 80m BKB rig less. And surface hole drilling was split in two sections with respect to application modes of modified diverter system. For initial 600 meters conventional diverter system was in-place with complete hole volume Kill Mud available at surface. This system also allowed alternate gas diversion in case of diverter failure during gas flow. For next 700 meters of drilling surface hole, same volume of Kill Mud was available to use as a mud cap and system allowed spotting mud cap and perform flow check in close-system environment, without exposing safety risk.
This systematic approach allowed drilling of surface hole section deeper in a safer environment that was previously required to drill in two hole sections. This returned 400k USD direct saving in one well.