Project Mohole Preliminary Report on Drilling to 35,000 Ft. From Varied Ocean Depths Compared to 18,000 Ft. depth

摘要

Drilling to 35,000 feet from the respective water depth of 10,000, 12,000, 14,000 and 16,000 feet, compared to drilling in an 18,000 foot water depth, presents more disadvantages than advantages. As illustrated in Sections 2 and 3, the cost and drilling time increase in approximately a straight line ratio as the water depths are decreased. The riser casing system, riser buoyancy, and re-entry are simplified and reduced in cost, but the disadvantages and extra cost for the drill pipe and the extra cost of drilling tools offset these gains. The cost and time for daily operating expense increases steadily with the greater drilling depth at the rate of $14,314 per day. The vessel positioning accuracy for 10,000 feet of water will suffice for depths up to 18,000 feet. Drilling from shallow water depths and consequently greater rock depths will possibly increase the bottom-hole temperature. A consideration difficult to evaluate quantitatively, but which is of great importance, is that added drilling footage and time increases the chance of a catastrophic failure and loss of the hole. (Author)