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Report 8

FIGURĘ 13: Drilling performance of several selected Olkaria wells against the planned Schedule using a rotary table rig

5.10.2 Overall drilling time for several wells, case study in Kenya and Iceland

In Figurę 13 the drilling performance for several geothermal wells in Kenya is compared. It shows the number of days it took to complete the well. The counting began from the time of spud-in until the time of rig release after the well completion tests. In Kenya it takes between 48-68 days to complete a well with an average depth of 2,600-3,000 m. There are several factors which determine the time it takes to complete a well but the main ones are formation hardness, bit life, ratę of penetration, and problems encountered during drilling like the BHA getting stuck, unrecoverable loss of circulation, and a longer cementing time due several backfills.

In the Icelandic case, as shown in Figurę 14, the first section of the hole 0-90 m was drilled using a smali portable rig. This saved the bigger rig time, and cost to the Client. It took an average of 45 days to drill a directional well to a total depth of 2,500-3,000 m. As can be seen it reąuired two bit changes at the 8‘/i" section. This proves the efficiency of the top drive system in terms of bit life management.

FIGURĘ 14: Top drive drilling progress by Iceland Drilling Company (Iceland Drilling Company, 2009)