This paper shows how using the Drilling Gptimization Simulator (DROPS) has been applied in the planning phase of two North Sea wells. Both the 12.25" and the 8.5" sections were optimized on Well #1 and the 12.25" section was optimized on Well #2. Geological Drilling Logs (GDLs) were generated from offset drilling data in the same field for both the two wells. Both wells with the different hole sections were simulated with the available bit types and designs. The optimum bit selection and the drilling parameters every meter for the hole-sections were optimized. The hydraulic limitations of the pump and the planned mud weight program were used to optimize the bit hydraulics in conjunction with the bit operating parameters, different pull depths and bit designs. The 12.25" sections showed savings potential of 72.4 percent on Well #1 compared to the last well drilled in the field. This included optimizing bit type, hydraulics, operating parameters and pull depths. Well #2 showed savings potential of 15 percent using oil based mud and 20 percent using water based mud compared to the two other wells drilled previously in the field with oil and water based mud respectively. It was concluded that Well #1 could save $ 1.3 million, while Well #2 was originally drilled close to optimum and only showed a potential savings of $ 0.3 million when using optimum drilling parameters.

The optimization of the 8.5" section was more complex because of several coring intervals. The five full hole sections between the coring intervals were optimized. The five subsections were drilled through formations of different length and lithology. The bit designs, pull depths, number of bits, hydraulics and operating conditions were optimized for each section. In addition to optimization of the drilling parameters, simulations for reuse of bits were conducted to further cut the drilling costs. The cost savings on the 8.5" section for well#1 showed a maximum potential for saving varying from 23.4 to 78.8 percent for the different sections.

From the simulations it can be concluded that the optimum drilling scenario of the 12.25" and 8.5" fitll hole sections for well #1 would reduce the drilling cost with more than $ 4.5 million.

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