We will complete two primary sites in the Brazos-Trinity Basin (proposed Sites BT4-2A and BT4-4A) and three primary sites at Ursa (proposed Sites URS-1B, URS-2C, and URS-3C) (Table T1). The overall strategy is to complete continuous coring, wireline logging, in situ measurements, and measurement-while-drilling (MWD) operations at each primary site (Tables T2, T3, T4). Operations will begin with advanced piston corer (APC) coring and in situ measurements at Site BT4-4A followed by APC coring and in situ measurement at Site BT4-2A. We will then complete MWD operations at Sites BT4-2A, BT4-4A, URS-3C, URS-2C, and URS-1B, respectively. MWD operations at the Ursa sites will include pressure while drilling (PWD) to determine the annulus pressure in the boreholes. Drilling operations will be completed with APC coring and in situ measurements at Sites URS-1B, URS-2C, and URS-3C, respectively. Upon completion of operations, all holes will be filled with heavy mud prior to abandonment. When moving between the proposed BT4 sites, the ship will move in dynamic positioning (DP) mode. DP mode will also be used to move between the proposed URS sites. Detailed operational times are provided in Table T5.
We expect problems with hole stability at Brazos-Trinity Basin #4, where we are drilling interbedded turbidite sands and hemipelagic mudstone. In these locations it is critical to have a full logging suite, and we will run both MWD and wireline logs. Hole stability may also be a problem at Ursa when drilling overpressured levee channel sands (interbedded sands and shales above the Blue Unit). To minimize risks of flow into the borehole, heavy mud will be used to drill and core portions of Sites URS-1B and URS-2C. The heavy mud will maintain the borehole pressure. The operational plan will include decision points and contingency plans detailing procedures to be followed in the event that unexpected hole conditions are encountered.
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