1.Determine the operational characteristics of the hammer drill. The hammer drill will be thoroughly tested on land before it is deployed at sea; however, it is difficult to simulate the shipboard deployment environment. We will deploy the hammer by itself for evaluation prior to using the entire hammer drill-in casing system.
2.Determine the viability of the hammer drill-in casing system. Once the shipboard operational characteristics of the hammer drill are established, we will deploy the complete hammer drill-in casing system for evaluation. Three boreholes in increasingly difficult environments are planned to completely test the equipment.
3.Determine the maximum allowable slope for hammer drill operations. If information on seafloor slope is available from a planned survey cruise that will occur before Leg 179, then we will drill multiple shallow (1-3 m) holes on progressively steeper slopes to determine maximum operational grade for the system.
A supplementary objective for Leg 179 is to recover cores from a cased reentry hole established by the hammer drill-in casing system. We would like to recover at least two cores from each reentry site. Two cores (19 m penetration) will ensure that we penetrate through the cement bond pinning the casing to the formation. Recovering rock from below the casing string provides final proof of the viability of the system and allows us to identify with certainty the lithologies where the casing has been emplaced. Given the recent success on Leg 176, these cores will also help establish the lateral heterogeneity in lithologies exposed in the vicinity of Site 735.
To 179 Part I: Drilling Plan
To 179 Table of Contents