Since the sequence of geological formations penetrated whilst drilling have different pore and fracture pressures as well as characteristics, the well cannot be drilled in one section to total depth. The conventional well design consists of different hole sections and multiple sized casing strings used mainly to isolate each section and protect it from hazards in subsequent formations to reach the target safely.

Depending on the conditions encountered whilst drilling, three, four or more casing strings might be required. The cost of the casing strings represent approximately 20-40% of the total well cost. Additionally, running and cementing the casing consume rig time adding additional costs to the well.

The Reelwell Drilling Method (RDM) is a new method developed and tested that is based on the use of a Dual Drill String (DDS) where the drilling fluid flows to the bit via the drill string annulus, and the return flow carrying cuttings to the surface is through an inner pipe as the annulus is sealed off using a Rotating Control Device (RCD) atop the Blow Out Preventer (BOP). With this unique flow arrangement, nothing is flowing in the annulus.

The following is a proposal of how the RDM can be used to drill a vertical well in one hole section to the target. This includes stacking different drilling fluids possessing different weight and properties against each section, the procedures to do that safely without problems and the recommended practices. It is found feasible that the well can be drilled in one-hole section saving the cost of extra casing strings and rig time consumed.

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