Using Conventional and Unique Methods to Drill a Technically Demanding Shallow Flow Zone

Deepwater drilling operations require a great deal of planning and logistical support, even under the most ideal situations. When shallow water flow hazards are a concern, the importance of the planning and logistical support increases tremendously. The Green Canyon 288 Intruder Project utilized both conventional and unique methods to control the shallow water flow zones that are prevalent in the Green Canyon area of the Gulf of Mexico. These included the use of sophisticated hydraulics software to maintain the equivalent circulating density (ECD) required to inhibit the flow and prevent losses while drilling to casing point. The operational and logistical considerations and pre-planning that combined for the successful drilling of a prospect on Green Canyon Block 288 with an upgraded semi-submersible drilling rig will be examined in detail. Introduction Drilling riserless in deepwater with the possibility of encountering a shallow water flow zone presents a number of challenges. The severity of problems associated with a shallow flow zone can ultimately prevent deepwater wells from reaching projected casing points and even total well depths.' The technical challenges commonly encountered when drilling riserless intervals are: ○ Logistics - being able to supply enough weighted fluid at the wellsite to drill the interval ○ Preventing bit balling and hole pack-off with cuttings ○ Maintaining adequate hole cleaning in a large sized hole with acceptable rate of penetration ○ Maintaining control of the well and avoiding shallow water flow problems by monitoring ECD at the suspected flow zone as well as at the bit while drilling ahead. In order to drill this interval with a minimum of problems, it was decided to use the weighted mud for the entire section thereby avoiding the risk of encountering a shallow water flow zone with an underbalance of hydrostatic pressure that could result in an uncontrolled well flow. This method, commonly referred to as the Pump and Dump Method, utilizes drilling mud rather than seawater and high viscosity sweeps. Like the seawater/sweep method, the pump and dump method has the mud returns taken at the sea floor. Drilling riserless with weighted mud has been done quite successfully in recent deepwater operations. However, most of these recent operations have been accomplished with the newer, fifth generation drillships that have enormous mud storage capacities relative to older semi-submersible rigs.