King, Lauren (2009-05). A Study To Determine Necessity of Pilot Holes When Drilling Shallow Gas Zones Using Top Hole Dual Gradient Drilling Technology. Master's Thesis.
When drilling offshore, shallow gas hazards are a major concern because of their
potential to cause a major blowout. This is a special concern when drilling in shallower
water, where the gas influx reaches the rig sooner. A common practice used to avoid the
potential dangers of shallow gas is to drill a pilot hole through the shallow gas zone with
the hope that the smaller diameter hole will prevent such a large influx. The use of dual-gradient
top hole drilling technology would allow for a larger hole to be drilled and the
possible gas influx to be killed dynamically, which I have simulated with the use of a
top hole dual-gradient simulator.