In HPHT environments it has been common to drill very hard and abrasive formations with impregnated bits and turbines, because of the low resistance that the elastomers of Positive Displacement Motors (PDM) have at high temperature. Compared to PDM the efficiency of turbines is smaller and the sensitivity with regards to erosion in the power section is greater, but these disadvantages are compensated by the lack of elastomer, resulting in a wider operating temperature range and reduced reactivity towards chemical additives in the mud. However, the necessity of using turbines introduces a limitation in the bit selection. In fact, the choice of drilling bits is limited to impregnated and TSP (Thermally Stable Polycrystalline), resulting in a drilling performance (i.e. ROP) that offers margins of improvement. Latest high speed motors proved to be reliable in the HT/HP wells of the Villafortuna/Trecate Field. Providing up to twice the horse power than turbines at the same differential pressure, those high speed motors achieve faster penetration rates while maintaining full control over the drilling process and steerability along the entire well path. Furthermore, the use of motors permits to remove the above mentioned limitation on the bit selection and therefore PDC bits can be run, wherever there are conditions to achieve better ROP. The paper details the features and describes the introduction of a latest generation of downhole motors in the HT/HP wells of the Villafortuna Trecate field.

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