To increase productivity and profitability from Mumbai High field drilling of ERD wells had to be implemented. Using ERD techniques, new infill wells had to be drilled, which were otherwise not cost effective. Uses of Hi-tech tools were considered necessary to drain oil from distant subsurface locations, thus eliminating prerequisite of constructing new platforms for such wells. Further, these types of wells were presumed to serve significantly to achieve new enhanced production from the reservoir.

Experience of drilling an ERD well in 1995 with the available drilling tools and conventional mud system conveyed that these wells could not be drilled to longer departures of 2 Kms from platform to L-III reservoir level owing to onset of complications like formation collapse and stuck pipes before reaching the target. Even casing could not reach bottom due to the swelling in shales which were exposed for a prolonged duration. Feasible departures from platform were of the order of 1500 to 1600m only. However to enhance production in limited time, the need was to drill wells from an existing wellhead platform to reach a substantially far subsurface location in the reservoir. A tool was needed which can drill a well up to 2 Kms departure at landing point so that oil can be drained from a subsurface location as far as 3.5 Kms, keeping 1.5 Kms as drain hole. To overcome previous constraints in drilling, Rotary Steerable System (RSS) was adopted in the year 2003 and its use has reduced the drilling time of extended reach (ERD) wells noticeably as compared to previous wells. Targets from platform to entry point at producing reservoir L-III has been increased to 2.2 Km and total well length to 3.5 km. 12 ¼" section of 1597m inclined at 75° was drilled successfully in one week with the Rotary Steerable System and Glycol mud as drilling fluid. Drilling time has been additionally reduced by 3.25 days with oil Base mud used with Rotary Steerable System. The average number of drilling days, which were 95.87 in 95–96, has been reduced to 45 days today. The system have been found indispensable

for drilling ERD horizontal wells of lower layers of L-III in Mumbai High and it's adoption in 8½" hole size have opened the possibility of drilling a well with a departure of more than 5 Kms.

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