In this paper the designing process and the development work involved in the optimization of the drilling and completion fluids and their subsequent successful application in a highly deviated gas well recently completed in the South of Italy is reported. The most suitable fluid for drilling and underreaming operations was identified by an extensive laboratory study on the basis of the reservoir characteristics: temperature, estimated pore pressure gradient, effective permeability and sand control completion type. Two nondamaging fluid formulations were proposed: an environmental friendly formate-CaCO3 system and a conventional calcium chloride-CaCO3 formulation. For both these fluids the most suitable viscosifier, effective fluid loss reducer and appropriate particle size distribution of the bridging solids had been investigated and identified in the laboratory. Coreflooding tests showed similar fluid loss properties and return permeability results for both the formulations, but different trends had been observed during backflow as far as the removal of the filtercake and the lift-off pressure are concerned. Other considerations regarding the use of the expensive heavy formate-based brine in high permeable sands where massive fluid loss can be experienced led the selection of the CaCl2-formulation, even for drilling and completion.
In the field, all drilling and completion phases proceeded as planned and no fluid losses were recorded while drilling, underreaming and gravel packing, confirming the good work carried out in the laboratory. No matrix stimulation treatments were performed for clean up and expected gas rate was soon overcame by the well.